الفهرس 
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Abstract
INTRODUCTION
Ascidians or sea squirts (Subphylum Urochordata or Tunicata, Class Ascidacea) are sessile marine animals ubiquitous throughout the world. It was reported that this group of fouling animals were known to Aristotle (384-322 B. C.) in ancient Greece who named them ’Thalia’, a name still in use for a Class of Tunicata (Gilbert and Raunio 1997). Georges and Schwabe (1999) mentioned that the fossil record of tunicates reaches back to the upper Cambrian period. Although Cüvier (1769-1832) is the first author who gave the name Tunicata to the group. He has misunderstood the systematic position of these animals and placed them between diploblastics and verma.
Tunicata include three major subdivisions which are ascidians, larvaceans (appendicularians) and thaliaceans (Giese and Pearse 1975; Young 1981; Adiyodi and Adiyodi 1990, Gilbert and Raunio 1997). The first author added that ascidians are with a little doubt the most primitive of the three groups of tunicates and comprise about 2,300 species. They have evolved rich patterns and modes of development in that they exhibit a life cycle with larval and adult stages. In other words, they undergo an indirect development (Berrill 1947a, b).
Concerning the habitat, ascidians are entirely fouling animals inhabiting marine habitats worldwide. They usually attach to rocks, iron objects, shells pilings and ship bottoms and some of them are found in mud and sand. They are somewhat barrel-shaped animals and the entire body is invested with a thick covering, the tunic or test from which the name Tunicata is derived (Croepler, 1992 ; Satoh 1994). Ascidians live by filtering tiny plankton and particulate nutrient material from sea water which is taken through the pharynx, one animal can jet 1-3 litres of water per hour (Khalil 1961 ; Abdel Messeih 1982 ,1994 ; and Michael et al., 2008 ; Saad, et al. 2011, Saad, 2010, 2008a).
A general survey for the fouling community including ascidians was made in the eastern harbour of Alexandria (Banoub, 1960; Megally, 1970). Along the northern sea shore of Egypt, in the region from Abu-Kir (area of study) to Arabs Bay there are 36 species of ascidians (Abdel Messeih, 1982, 1994). It was recorded that 85% of ascidians are oceanic and occupy regions up to the depth of 1000 meters. Ascidians spread only during their larval stage (Young, 1981; Hofmann, et al. 2008; Saad and Hamed, 2009) while the adult may be transported to distant areas via oysters. In India, in the vicinty of Madras harbour, erratic Pyura squmulosa were found attached to stones and molluscan shells (Seshachar and Rao, 1983). In the works of Goodbody and Fisher, 1974; Goodbody and Gibson, 1974 it was mentioned that ascidians are capable of slow-crawling. This movement involves the progressive formation of new colonies for attachment and tearing or dissolving the old ones (Carlisle, 1961). It appears that the body form in ascidians depends upon the kind of substratum to which they are available for bottom animals and they become adapted. Accordingly Hüus (1937) identified about 53 species of ascidians collected from the Red Sea, While Pérès (1958) listed 130 Mediterranean species, of which 32% occur in the temperate part of Atlantic. About 83 species in tropical American Atlantic is based on the accounts of Millar (1961, 1962). The ascidian fauna of Japan and in adjacent water is very diverse. Tokioka (1963) listed 277 species; some 74% of them occur in Southern Japanese waters while only about 18% are strictly warm-water species belonging to the warm Indo-west. Over 70 species are known from the tropical part of West Africa (Millar, 1965). Many species of ascidians are known to be invasive. As early as 1915, non-native ascidian species were identified and recorded.
Current surveys show that along the northern sea shore of Egypt, in the region of Abu- Kir to Arabs Bay there are 36 species of ascidians (Banoub, 1960 and Megally, 1970). Abdel Messeih (1982 &1994) identified, through taxonomical study, about more than 100 species colonizing the Mediterranean and Red Seas. Saad (1995& 2002) studied the morphology and anatomy of both nervous and reproductive systems and the life cycle of three ascidian species living in Alexandria waters, namely Styela plicata, Styela partita and Ciona intestinalis. Moreover, the latter author studied the embryonic development of Phallusia mammillata collected from the North Sea Germany and Ascidiella aspersa collected from the Mediterranean Sea at France. The effect of some biochemical compounds on development of the larvae of both Phallusia mammillata and Ascidiella aspersa is commented. Moreover, through experimental embryology technique some results and observations are commented. These introduction events are hypothesized to occur by anthropogenic means, either through fouled ships or ballast water introduction. Once introduced, these invasive species can persist for many years. With predicted increases of sea-surface temperature, more tropical ascidian species will likely also be introduced and established in harbors throughout the world. Prenant (1928) and Monniot (1966) found a close relationship between the distribution of ascidian species and the granulometric composition of the soft sea-bed of Brittany and France. They concluded that ascidians are good ecological indicators of the nature of the sediment. Millar (1970) concluded that the ascidians have colonized most types of marine habitat from rocky shores to the muddy sea-bed of the abyssal region, and some of them have penetrated into estuaries and harbours, where the water may be polluted and of increased salinity. Many are fixed to firm substrates such as rock, stones, shells or body of other animals and others are loosely attached to submerged sand and mud or partly embedded. Due to their sessile and filter-feeding habit, ascidians have limited distribution on soft bottoms because of the lack of substrate for attachment and the clogging effect of the suspended particles. Delicate species may be damaged by sand abrasion (Millar, 1971 and Monniot, et al. 1991). Therefore, lower diversity and abundance of ascidians is expected near soft bottoms compared with rocky substrates. Light may be an important selection force resulting in specific depth distribution, due to the tendency of ascidian larvae to attach to shadow substrates (Young and Chia, 1984; Hurlbut, 1993). Styela plicata (Lesueur, 1823) is a solitary ascidian found in shallow environments in tropical and warm-temperate oceans. Its origin is uncertain, and it has already been identified in several oceans since it shows a very broad geographical distribution (Lambert, 2001). Although S. plicata has been historically classified as a cosmopolitan species, in the past few decades, it has been considered as an introduced or invasive species in some regions of the world. The type-specimen was found attached to the hull of a ship in Philadelphia, although no other individual was detected in natural substrates in this region (Van Name, 1945). Other records of the presence of S. plicata on ship hulls have been made in the Bay of Hann, Senegal, in 1950 (Pérès, 1951) and on the USS Palos after a voyage through the Pacific, coming from either China or Japan (Tokioka, 1967). The species has been recorded in warm, temperate waters of the Atlantic Ocean and the Mediterranean Sea (Harant, 1927; Harant and Vernières, 1933). Although it has been found throughout much of the eastern coast of North America since the beginning of the 20th century (Van Name, 1912), it had been considered very rare on the west coast until the mid 1940’s (Van Name, 1945). It was considered as an introduced species in the Gulf of Mexico (Lambert et. al. 2005). The earliest record in the Pacific Ocean is in the Sydney harbour, Australia, in 1878 (Heller, 1878), but it is also considered as an introduced species in that region (Kott, 1985; Berents and Hutchings, 2002; Wyatt et al. 2005), whereas it was first reported in New Zealand in 1948 (Brewin, 1948). Styela plicata is invasive in southern Brazil (Rocha and Kremer, 2005) and southern California (Lambert and Lambert, 2003). In addition, this species thrives on brackish and polluted waters, frequently being found in estuarine environments (Kott, 1952 , 1972a ; Kott and Goodbody,1980) or in shallow waters surrounding the mainland where large flows of freshwater reduce local salinity (Sims, 1984). It is also found in disturbed areas such as in the proximity of refineries, power plants, and fishing harbours (Carballo and Naranjo, 2002). It can be considered as an indicator species in areas that have experienced intense stress (substrate transformation, water stagnation, and excessive sedimentation) for extended periods of time (Naranjo et al. 1996). It can adhere to several types of substrate, particularly artificial substrates, and is also found in epibiosis. Styela plicata occurs on the shells of bivalves and competes with them for resources (Perera et al. 1990), and can also prey on their larvae (Bingham and Walters, 1989). In some countries, of the Far East and certain parts of the Mediterranean Sea, most ascidians are eaten by man. Styela plicata And Pyura chilensis are eaten by man in South America (Van Name, 1945). Styela plicata and Polycarpa pomaria are collected and artificially reared (Harant, et al. 1951). Halocynthia rorelzi in Japan was cultured in the north of Honsy (Tokioka, 1953). Various Ascidiacea are used as food. Sea pineapple (Halocynthia roretzi) was cultivated in Japan (hoya, maboya) and Korea (meongge) and, when eaten raw, has been described by Lonely Planet as tasting like ”rubber dipped in ammonia”. The peculiar flavor is attributed to an unsaturated alcohol called cynthiaol.
”They are actually farmed in parts of Korea, and sea squirt bibimbap is a specialty of Geojae-do Island, not far from Masan, also ” Microcosmus sabatieri and several similar species from the Mediterranean Sea are eaten in France (figue de mer, violet), Italy (limone di mare, uova di mare), Greece (fouska, φούσκα). In Greece they are consumed just raw with lemon or in salads with olive oil, lemon and parsley. The piure (Pyura chilensis) is used as food in the cuisine of Chile, consumed both raw and used as ingredients in seafood stews like bouillabaisse. Pyura stolonifera is known as cunjevoi in Australia. This was once used as a food source by Aboriginal people living around Botany Bay, but is now used mainly for fishing bait. Note: the word ”cunjevoi” is also used for two species of rainforest plant, at least one of which is toxic to humans (Lukowiak, 2012).
In recent years, ascidians have gained interest as fouling organisms which cause problems for the growers in terms of costs and labour in relation to extra handling of the equipment, but potentially also with decreased bivalve production due to competition for food (Altnöder, et. al. 2007).
Ascidians are considered as an excellent model system for biogeographical studies (Monniot, 1983), given that the adult stage is sessile and natural dispersal occurs through larvae (Lambert and Brandt, 1967 and Hofmann, et al. 2008). Under natural conditions, colonial ascidian larvae usually do not disperse more than a few meters. Larvae of solitary species, on the other hand, can remain swimming freely for periods longer than 12 hr, causing a consequent broader distribution (Ayre et al, 1997; Hofmann et al, 2008 and Saad & Hamed, 2009).
Marine bio-fouling is caused by the adhesion of sessile animals. It is a worldwide problem in marine systems, costing the US Navy alone an estimated $1 billion per annum. On ships’ hulls, bio-fouling results in an increase in roughness, which in turn leads to an increase in hydrodynamic drag as the vessel moves through water. Increased fuel consumption, hull cleaning, paint removal and repainting, and associated environmental compliance measures all contribute to the costs of biofouling. Effective and environmentally compatible options are needed to control fouling. An active research was aimed to understanding how adhesives, produced by fouling organisms, interact with surfaces, so that coatings may be designed in a rational way to inhibit this process. Antifouling paints have a profound effect on the environment, and research on bio-adhesives may contribute to the development of environmentally benign fouling control. In addition, Ascidians contain a host of potentially useful chemical compounds, including Didemnins, Aplidine and Trabectedin which are effective against various types of cancer, antiviral and immunosuppressant Cragg and Newman, (2004).
Woollacott (1977) mentioned that members of the Class Ascidiacea traditionally have served biologists as a rich source of material for descriptive and experimental embryological studies. The abundance of ascidians in the nearshore environment, their year-round availability in many localities and the suitability of certain species for providing large quantities of synchronously ripe gametes makes them ideal material for investigating problems in biology. In the work of Khlalil (1961), Sedra and Khalil (1970-1971), Millar (1982), Abdel Messeih (1982), Hofmann et al. (2008), Michael et al. (2008) and Saad, et al. (2008 & 2011) it was recorded that some physical and biological factors control the distribution of ascidians. These factors are light, temperature, water current, contour texture, land masses, angle of the surface of the substratum, presence of the same species, type of algae and presence of microbial organisms and intensity of pollution. Due to their bio-fouling behavior, adult ascidians, which settle on ships, boats or iron objects are likely to become transient members of multiple marine communities. It is possible that even a single ship-borne ascidian could start a new population as ascidians are hermaphrodites and many are able to self-fertilize. Non-self sperm is typically much more effective than self sperm during fertilization, a mechanism which supports out-crossing when multiple ascidians of the same species are in a single location, but this potential for self fertilization may help establish ascidian colonies in new localities.
In some textbooks [Gilbert and Raunio (1997) and Barnes et al. (2001)], it was mentioned that there are many reasons of why ascidians are popular as research animals in many aspects in biology, as well as biomonitors to measure pollution stress in a given marine habitat. In fact, ascidians are cosmopolitan in the seas and oceans and their embryos and larvae have a small number of cells, at the beginning of gastrulation. Ascidian embryos contain only about 110 cells whereas amphibian gastrulae contain about 10 000 cells. Ascidian tadpole larva consists of a few thousand cells and only six different tissues. Ascidian larvae develop rapidly. Swimming larvae hatch after 12-18 hr after fertilization. Ascidians have small genomes that facilitate cloning genes involved in developmental process from another point of view, there are some limitations in using ascidians as an experimental system. This is due to the fact that most of them have restricted breeding seasons and living embryos can be obtained only at certain times of the year. Moreover, genetic analysis is not available as it is in Drosophila for example. However, genetic approaches have been developed in some of the compound ascidians (Rinkevich and Weissman (1987).
It is well-known that ascidians live solitary, semi-colonial or colonial. In the textbooks of Young (1981), Satoh (1994), and Gilbert and Raunio (1997), it was mentioned that the solitary forms are commonly named ’Ascidiae simplicies’ whereas those forming colonies are named ’Ascidiae compositae ’. In the work of Niermann-Kerkenberg (1985&1989) and Lübbering (1989), ascidians in general are referred to as ’mantle animals’.
Generally, the ascidian animal is sub-cylindrical in shape, its size ranged from 2-80 mm in total length and it is devoid of axial musculature, appendages and special sense organs (Deck et. al. 1966). The free end of the body bears two openings, a branchial (oral) opening while lies ventrally and a dorsal atrial opening (atriopore). Each opening is carried on a siphon. In other words the atrial siphon marks the dorsal side of the ascidian body whereas the oral siphon guides the ventral side (Millar 1970, 1971). Satoh (1994) and Westheide & Rieger (1996) mentioned that each siphon can be closed by sphincter muscles and has ocelli at its terminal end. According to Barnes (1980); Brusca and Brusca (1990); Barnes et al. (2001) the body is covered with a special covering, the tunic or ’test’. This tunic is secreted by a single layer of epidermal cells. This layer is smooth and transparent as in Ciona intestinalis (De Leo et. al. 1981) or tough and wrinkled as in Perphora viridis (Deck et. al.1966) and Styela plicata (Khalil 1961; Abdel Messieh, 1982 & 1994; Michael. et al. 2008; Saad, 2008). Hirose et al. (1990) studied the fine structure of the tunic in 25 species belonging to 9 families of ascidians. This study were carried out tusing scanning and transmission electron microscopy. They stated that the cuticular surface is ornamented with minute protrusions in some species. These minute protrusions are usually papillate in shape with different height in different species of ascidians. No protrusions are found in Cionidae while in Styelidae, only the colonial forms possess such protrusions.
Concerning the chemical composition of the tunic, Deck et al. (1966) studied the chemical structure of the tunic of Perophopra viridis and mentioned that, it contains cellulose-like polysaccharide ’tunicin’ in its substance. The glycoprotein mantle contains filaments very much like plant cellulose in morphology. They gave for the first time direct autoradiographic evidence that epidermal cells are involved in the synthesis and secretion of tunicin the tunic is studied in much detail in Phallusia mammillata by Endean (1961). He showed that the tunic in this animal consists of translucent gelatinous material bounded externally by a thin brownish layer and histological and histochemical examinations of this tunic showed the presence of blood vessels which contain blood cells, bladder cells and an apparent variety of small cells. Which were surrounded by hyaline test material. Some ultraexaminations of the tunic revealed the presence of an open meshwork of myofibrils. Through histochemical examinations the same author he clarified the share of each structure in the formation of the chemical constituents of the tunic. He proved that water constitutes 90% of the components of the tunic. The dried tunic constituents of acid mucopolysaccharide, hexamine and glucose. De Leo et al. (1981) and Storch and Welsch (1993) studied the structure of the tunic in Ciona intestinalis through light and electron microscopy and stated that the tunic consists of two layers, a thin layer exposed to the outer environment and an underlying gelatinous layer, which is the ground substance. Within both layers two components are recognized: one is a fibrous system and the other consists of certain cell types. Both layers contain protein and neutral polysaccharides. The fibrous system has been reported to contain a cellulose-like polysaccharide associated with a collagen-elastin-like protein. The cellular components are named in their morphology as ’large granule’, multivascuolar, morula, granular and fusiform cells. Previously, Brien (1948) stated that tunicin is ’une sort de chitin’. This point of view is parallel with that of Pearse (1968) who stated that tunicin is a type of chitin, This tunic wall not only encloses the animal but also out-pushes a holdfast processes for attachment (Endean,1961 and Khalil,1961).
The tunic is followed internally by the mantle which encloses the internal viscera. This mantle varies from thin and transparent as in Ciona to thick and opaque as in Styela (Van Beneden and Jullin, 1987; Khalil, 1961; Millar, 1971 and Abdel Messieh, 1982, 1994). It was reported in the available textbooks (Parker & Haswell1974; Young, 1981; Satoh, 1994; Gilbert and Raunio, 1997; Barnes, et al. 2001) that this mantle consists of the ectoderm with underlying layer of connective tissue enclosing muscle fibres. The latter are arranged in an irregular network, crossing one another in all directions, but for the most part either longitudinally or transversely. It seems that these muscles are responsible for the rhythmic action which enables the animal to expand to take in water and to shrink getting out water. It seems again that according to this phenomenon, these animals deserve their common name ’sea squirts’.
The previously mentioned two openings, consists generally of the tunic together with the mantle. The distal end of a siphon (branchial or atrial) is a taxonomic feature. The siphon in Styela either oral or atrial is terminated with 4 lobes (quadrilobed) (Khalil, 1961; Millar, 1971; Michael, et al. 2008). In Ciona intestinalis the oral siphon is terminated with 8 lobes and the atrial siphon is sub-terminal and provided with 6 lobes. (Millar, 1971).
Ascidians are often brightly coloured, the pigment being either in the tunic or the underlying body, which may appear through the tunic. The colour can change at least over a period of some days. Little is known about the origin of the pigment, but it may be derived from the blood and may lie in special cells (Young, 1981).
The different internal organs were carefully described in some studies recorded in the available literature (Khalil,1961; Sedra and Khalil, 1971; Millar,1970&1971; Mancuso,1974; Dunn,1974 ; Giese and Pearse,1975 ; Flood and Fiala-Medioni,1981; Young,1981; Pennachetti,1984; Adiyodi and Adiyodi,1990; Hirakow & Kajita,1990 ;Croepler,1992; Satoh,1994; Marchenkov & Boxshall,1995; Gilbert & Raunio,1997; Coniglio et. al. 1998).
The alimentary canal of different solitary ascidians begins with the mouth opening which lies at the base of branchial siphon and leads to an immense pharynx (branchial chamber).The entrance of this chamber is guarded by a ring of tentacles which is identical to the velum of Amphioxus (Hirakow and Kajita, 1990). This chamber or sac serves both respiration and filter feeding. This branchial basket is perforated by dorsoventral rows of numerous gill slits called stigmata (Young, 1981; Satoh, 1994). Blood vessels traverse the pharyngeal wall between the slits. Each stigma is ciliated with frontal and lateral cilia that evoke incurrent flow from the pharynx. In other expression, water passes through the gill slits to the atrium and then expelled through the atriopore. Along the ventral margin of the branchial basket is a specialized organ called endostyle. Satoh (1994) added that a median strip of endostyle cells bears long flagella and adjacent strips are ciliated and glandular.This organ contains iodine, therefore it is thought that there is an evolutioary relationship to the vertebrate thyroid gland. The endostyle secretes large quantities of mucus which is distributed as a thin sheet over the inner surface of the branchial basket by the flagella and pharyngeal cilia. Food particles become entangled in the mucus, are collected along the dorsal wall of the pharynx and are propelled by ciliary action to the oesophagus behind the pharynx.The digestive tract leads to a stomach at the bottom of the U-shaped digestive loop and an intestine terminates at the anus which opens in the atrial cavity.
Concerning the circulatory system, it is of an open type. It consists of a short tubular heart as well as numerous blood vessels. The heart lies posterioventrally in the body near the stomach and behind the pharyngeal basket. It is surrounded by a pericardial sac. The heartbeats and the direction of the blood flow reverse periodically. Blood contains several different cells or coelomic cells including haemocytes, lymphocytes, amoebocytes (Wright, 1981), vacuolated cells and pigment cells. Ascidian blood has several specialized functions such as the accumulation of vanadium, gas exchange (may occur across the body wall). Satoh (1994). Fisher (1976) observed the uptake of oxygen by Styela plicata. The blood plasma is colourless. Some of the blood cells are phagocytic while others contain orange, green or blue pigment in differnt species. Higher concentrations of ions of iron, titanium and vanadium were found in the blood cells of Pyura chilensis and Ascidia dispar (Curtin, et al. 1985; Roman, et al.1988).
There are no tubular excretory organs in ascidians. Certain blood cells called nephrocytes function in the accumulation of nitrogenous waste products. Much of the metabolic waste products lost from the internal body surface aided by the water current passing through the pharynx and atrium Satoh (1994). Young (1981) mentioned that 95% of nitrogenous waste products are excreted as ammonia and added that nephrocytes may be stored in the ascidian body in an excretory sac until the animal dies.
Concerning the reproductive system, ascidians are generally hermaphrodites. According to the position of this system in the body, ascidians can be catagorized into two groups: Pleurogona and Enterogona.In the former group, gonads are paired and located in the body wall in between the mantle and the branchial sac wall whereas in the latter type, gonads are unpaired and situated in/or below the gut loop (Berril, 1947; Khalil, 1961; Sedra and Khalil, 1971; Millar, 1971; Riedl et. al. 1983). The morphology, anatomy and histology of the gonads of the ascidians: Styela plicata (Tucker, 1941, 1942); Dendrodoa grassularia (Millar, 1954); Styela coriacea and Styela rustica (Lützen, 1960); Styela partita (Millar, 1971); Botryllus violaceus (Yamaguchi, 1975; Abdel Messieh, 1984) showed that these above mentioned ascidians belong to Pleurogona. On the other hand, the same study was done on Diplosoma listerianum (Millar, 1952) ¬¬¬¬¬¬¬ Ciona intestinalis (Millar, 1952; Khalil, 1961; Dybern, 1965; Abdel Messieh, 1982, 1994). These outhers reported that these species belong to Enterogona. In both types of ascidians, gonads are compound and appear as an elongate irregular mass extending towards the atriopore but open a short distance before it. Each compound gonad consists of an ovary and a testis, each has its own definite duct.Ascidians are usually oviparous or oviviviparous, some of them are protandrous while others deliver eggs and sperm simultaneously. In many species, however, an individual egg is not fertilized by a sperm from the same animal (self-infertility), Satoh (1994) and Gilbert and Raunio (1997).
In solitary ascidians, fertilization takes place externally in the water while in colonial forms, sperm enters the pharyngeal basket with the incurrent water where fertilization occurs. Moreover, in the latter type there is the so-called ’paternal care’ (Millar, 1971; Satoh, 1994). The size of newly hatched larva varies from one species to another. They range in length from 0.6mm (Molgula manhattensis), 0.7 mm (Ciona intestinalis), 1.5 mm (Halocynthia roseria ) , to 11 mm (Eudistoma digitatum). The length of the swimming period in oviparous species can range from only a few minutes to several hours, while in most oviviviparous species, it ranged from a few minutes to several days. The larva swims for 6hr to several days and during this swimming period, the larva prepare for the onset of metamorphosis. For instance it alters its response to light and gravity. The larva is first negative geotactic and positive phototactic. Soon immediately before settlement it avoids light and prefers to settle on dark or shaded surfaces.
Tucker (1941&1942) studied carefully the anatomy and histology of the gonads of Styela plicata and gave a monographic explanation only through light microscope for the structure of the egg and its different developmental phases. Grave (1944) studied the larval structure and life span of the ascidian Styela (Cynthia) partita. He added that this solitary ascidian is abundant in the Woods Hole region and spawns from early June to the end of September. Khalil (1961) and Sedra and Khalil (1971) reviewed the previous work and added a description for the general system of four species living in Alexandria waters. Two of them are solitary (Styela plicata and Ciona intestinalis), one semi-colonial (Symplegma viride) and one is colonial (Botryllus schlosseri). Giese and Pearse (1975) provided a review about reproduction and development as well as larval settlement in ascidians in general. De Leo et. al. (1981) were interested in the study of the fine structure of the tunic of Ciona intestinalis. They showed that the outer covering is formed of a thin outer cuticle, a subcuticle of variable width and a large single layer of ground substance. Flood (1978) illustrated the process of filter feeding of Oikopleura dioica (appendicularian), using scanning electron microscope. He clarified the extensive filter surface in the external food catching net of planktonic appendicularia. Filteration probably enables these animals to feed efficiently on particles much smaller than bacteria. Hirose et. al. (1990) studied the fine surface structure of the tunic in ascidians. They added that the cuticular surface is ornamented with numerous minute protrusions in some ascidian species but not in others. Cloney (1990 a&b) emphasizes current investigations of fertilization, cellular lineages, embryogenesis, experimental analysis of development. Comparative larval history and metamorphosis of 10 families of ascidians as well as the process of budding, vegetative reproduction and habitat in Diplosoma migrans have been investigated (Croepler, 1992).
The most attracting field of work concerning the reproduction of ascidians was that concerning their breeding. This was studied according to different aspects. The somewhat comprehensive work was that concerning the growth, maturation and seasonal variation of gonads, spawning, ecological factors affecting breeding and geological distribution of the genus or/and species. It was found that Ciona intestinalis and Styela plicata were the most favourable ascidians chosen to study one or more of the above aspects (Berrill, 1947a; Sabbadin, 1957; Dybern, 1965; Lambert, 1968 and Yamaguchi, 1970 &1975). Sabbadin (1957) studied another solitary ascidian Molgula manhattensis. Also, in another publication, Berrill (1947b) studied the metamorphosis of Ciona intestinalis, Ascidiela aspersa, Diplosoma listerianum and Botryllus schlosseri. Diehl (1957) studied the effect of the ecological factors on the reproductive cycle of Styela coriacea and provided that the temperature is the main factor affecting this cycle. The same point of view was provided in another species Styela rustica (Lützen, 1960) but with a different investigation based on histological observation.
The experimental work attracted the attention of more than one investigator to study related aspects to the reproduction. One of the pioneers in this field was Morgan. In his work published in 1942, he reviewed the results of his experiments and those of others who provided descriptions during the period from 1904-1941. He studied the percentages of abnormality of the development of the tadpole of Styela by self-fertilizing and cross-fertilizing the eggs. One species of Styela which is Styela plicata was used as an experimental animal to provide the effect of other factors on reproduction of ascidians by West & and Lambert (1975). They provided that the light is another factor controlling the spawning of this species and supported their laboratory observations by field collection data and derived statistically from the spawning curves that gamete release occurs in the afternoon, close the sun set. These authors used white light during their experiment. Previously, Lambert & Brandt (1967) used white light and monochromatic light to study their effect on spawning of Ciona intestinalis. Their results were later confirmed by Yamaguchi (1970). Ascidia nigra used in another type of experiment to study the factors affecting the development of embryos (Goodbody and Fisher , 1974 ) and those affecting the survival of the populations of the juvenile and adult ascidians (Goodbody and Gibson,1974). These co-workers provided that the eggs are available throughout the year and are always capable of successful development, artificial fertilization, rearing of the embryos and juviniles. The salinity, pH and other factors may be involved in the development and survival of Ascidia nigra. Yamaguchi (1975) added that nutritional conditions as a factor may be involved in some other ascidians.
An ultrastructural study on the testis of the ascidians Clavelina lepadifarmis, Ciona intestinalis, Ascidiella aspersa (Enterogona) and Styela clava, Dendrodoa grossilaria and Molgula manhattensis (Pleurogona) were studied by Jorgensen and Lützen (1997). The latter authors mentioned that there are non-genital cells in the testes of ascidians These authors added that elimination of waste sperm following the reproductive season was observed to be undertaken by the epithelial wall cells in some species in which these cells detach and migrate to the interior of the testis where they contiue and complete the phagocytosis of the sperm. In other species, the non-germinal epithelium plays no role in the elimination of superfluous sperm which is probably phagocytosed together with the rest of the body by wandering trophocytes.These authors concluded that within the Urochordata the effectiveness of the testis epithelium as a blood-testis barrier varies, but is not corrected to modes of reproduction as postulated for other taxa.
Concerning the female part of the gonad, it is described as a compound gonad. Consisting of units referred as to ’overules’ (egg tubes). Each one extends anteriorly as a short oviduct that opens a little distance before the atrial opening (Millar, 1970, 1971; Satoh.1994; Gilbert and Raunio, 1997). The experimental study cocerning ovulation, eggs and the environmental conditions or stimuli (light, temperature and time of the year) controlling the reproduction of ascidians were the interest of many authors. Control of spawning in the ascidian Styela plicata by variation in the natural light regime has been studied (West and Lamber,t 1976). Styela plicata spawns in the laboratory if subjected to a sufficient amount of light followed by a minimum dark period. The amount of dark adaptation affects the amount of light necessary to induce spawning suggesting a reversible photochemical reaction.
Shedding of gametes in the ascidian Botryllus primigenus have been noticed to occur in the natural environment early in the morning, about 1hr after dawn. The shedding of sperm from a testis is completed within a few seconds, all spermatozoa are released at once then ovulation begins about 10 minutes after shedding of sperm and is completed in about one minute (Mukai and Watanabe, 1977). Rosati and De Santis (1978) interested in the study of the process of fertilization in Ciona intestinalis and the so-called self-sterility and specific recognition between gametes. They predicted that only 15% of the animals are self sterile. Self-sterility and self-fertility are specific properties of ascidian gametes.Eggs from self sterile animal are not fertilized even at very high sperm concentration.
Concerning the breeding season and spawning, ascidians spawn sperm and eggs every day during the breeding season. This breeding season differs among ascidian species.Some species have breeding season restricted to the summer or winter months, whereas others breed throughout the year (West and Lambert, 1976). Spawning is triggered by changes in the photoperiod. Whittingham (1967) concluded that in some ascidian species, a short pulse of light following an extended dark period triggers spawning. In some other species, spawning is initiated by a longer light period following darkness (West and Lambert, 1976).These authors added that the former species spawn in the morning while the latter species spawns at dark moreover, sperm and eggs can be obtained for experimental purposes at any time during the breeding season. Ripe gametes can also be obtained by excision of the gonoducts (Reverberi, 1971). In the text-books so far available it was stated that larvae of sessile marine invertebrates are generally pelagic and respond to ecological factors in species-specificways by which they reach the substratum. One of the predominate ecologicasl factors involved in larval settlement is the light (Millar, 1971; Stern and Holland, 1993; Satoh, 1994; Burighel and Cloney, 1997 and Wolpert, et al. 1999).
Biotrophic parasitism is a common mode of life that has arisen independently many times in the course of evolution. Depending on the definition used, as many as half of all animals have at least one parasitic phase in their life cycles. Moreover, almost all free-living animals are host to one or more parasite taxa (Lassalle, et al. 2007; Price, 1980). Parasites evolve in response to defense mechanisms of their hosts. Examples of host defenses include the complex immune system, which can target parasites through contact with bodily fluids, and behavioral defenses. Some parasites evolve adaptations that are specific to a particular host toxin and specialize to the point where they infect only a single species. Such narrow host specificity can be costly over evolutionary time, however, if the host species becomes extinct. Thus, many parasites are capable of infecting a variety of host species that are more or less closely related with varying success.
Host defenses evolve in response to attacks by parasites. Theoretically, parasites may have an advantage in this evolutionary arms race because of their more rapid generation time. Hosts reproduce less quickly than parasites, and therefore have fewer chances to adapt than their parasites do over a given span of time. In some cases, a parasite species may coevolved with its host taxa. Long-term coevolution should lead to a relatively stable relationship tending to commensalism or mutualism, in that it is in the evolutionary interest of the parasite that its host thrives. A parasite may evolve to become less harmful for its host or a host may evolve to cope with the unavoidable presence of a parasite to the point that the parasite’s absence causes the host harm. For example, although animals infected with parasitic worms are often clearly harmed, and therefore parasitized, such infections may also reduce the prevalence and effects of autoimmune disorders in marine hosts, including ascidians (Rook, 2007). The presumption of a shared evolutionary history between parasites and hosts can sometimes elucidate how host taxa are related. Parasitism is a part of one explanation for the evolution of secondary sex characteristics and seen in breeding males throughout the animal world. According to this theory, female hosts select males for breeding based on such characteristics because they indicate resistance to parasites and other disease, (Co-speciation). In rare cases, a parasite may even undergo co-speciation with its host. A major problem for parasites is to ensure that offspring will reach a correct host. Responses to this problem include several reproductive adaptations, including increased number of gonads and offspring, synchrony of hatching with host larval hatching, facultative parthenogenesis, and mating. Parasites infect hosts that exist within their same geographical area (sympatric) more effectively. This phenomenon supports the Red Queen hypothesis which states that interactions between species (such as host and parasites) lead to constant natural selection for adaptation and counter adaptation (Lively and Dybdahl, 2000). The parasites track the locally common host phenotypes, therefore the parasites are less infective to allopathic (from different geographical region) hosts. As chemical defences, tunicate blood is particularly interesting, many sea squirts intake and maintain an extremely high concentration of the transition metal vanadium-associated proteins as well as higher than usual levels of lithium in the blood. Some tunicates can concentrate vanadium up to a level one million times that of the surrounding seawater as in Pyura chilensis and Ascidia dispar (Curtin et. al. 1985; Roman et. al. 1988). Ascidians have a very low pH of the tunic due to acids in easily-ruptured bladder cells, and / or produce secondary metabolites harmful to predators and invaders (Hirose, et al. 2001). Some of these metabolites are toxic to cells and are of potential use in pharmaceuticals. Natural chemicals produced by marine algae could act as control against ectoparasite infections of ascidians.
Parasites inhabit living organisms and therefore face problems that free-living organisms do not. Hosts, the only habitats in which parasites can survive, actively try to avoid, repel, and destroy parasites. Parasites employ numerous strategies for getting from one host to another, a process sometimes referred to as parasite transmission or colonization (Harbison, et al. 2008). Some endoparasites infect their host by penetrating its external surface, while others must be ingested. Once inside the host, adult endoparasites need to shed offspring into the external environment in order to infect other hosts (Dranzoa, et al. 1999). Many adult endoparasites reside in the host’s gastrointestinal tract, where offspring can be shed along with host excreta. Adult stages of tapeworms, thorny-headed worms and most flukes use this method. Larval stages of endoparasites often infect sites in the host other than the blood or gastrointestinal tract. In many such cases, larval endoparasites require their host to be consumed by the next host in the parasite’s life cycle in order to survive and reproduce. Alternatively, larval endoparasites may shed free-living transmission stages that migrate through the host’s tissue into the external environment, where they actively search for or await ingestion by other hosts. Some ectoparasites, rely on direct contact between hosts. Some aquatic parasites locate hosts by sensing movement and only attach when certain temperature and chemical cues are present. Some parasites modify host behavior to make transmission to other hosts more likely. For example, in California salt marshes the fluke reduces the ability of its host to avoid predators (Lafferty and Morris, 1996).This parasite matures in egrets which are more likely to feed on infected than on uninfected host, a change which may increase transmission to final hosts. (Berdoy, et al. 2000).
Ascidians parasites can be either generalists (infecting many host species) or host-specific (infect only one or a few closely related host species). Ascidians may obtain parasites from their food, or are directly infected by free-living parasite stages in the sea (Ciancio, et al. 2001). Parasites may have complex life-cycles, involving up to 3 or more different host species (including marine invertebrates), or direct life-cycles, involving a single host species. The parasites pass eggs in the host’s faeces, and the eggs are ingested by a crustacean. The trematodes have a complex life cycle.
Ascidians are probably infected when they ingest infected crustaceans. Some of the most common parasites include skin crawlers (copepods), Milne Edwards (1840), tongue biters (isopods), Latreille (1817) , ectoparasitic flukes (monogeneans), Carus (1863), endoparasitic flukes (digeneans), Carus (1863), round worms (nematodes), Diesing (1861), tapeworms (cestodes), Rudolphi (1808) spiny headed worms (acanthocephalans), Koelreuther (1771), and protozoa. Integrated parasite management strategies will be identified to aid the adaptive capacity of industry to climate-induced parasite outbreaks in the tropics. Climate change, higher water temperatures and extreme salinity fluctuation is expected to exacerbate the frequency and intensity of parasite epizootics in aquaculture by enabling parasites to complete their life-cycles faster. Parasites can spread easily and cost effective. Biological information for many parasites is unknown as for example species determination, epidemiology, fecundity, time to reach sexual maturity, adult longevity and effect of water temperature and salinity (Hutson et al. 2007). In colonial ascidians predation often results in fragmentation of a colony into subcolonies. Subsequent zooid replication can lead to coalescence and circulatory fusion of the subcolonies. Closely related colonies which are proximate to each other may also fuse if they coalesce and if they are histocompatible. Ascidians were among the first animals to be able to immunologically recognize self from non-self as a mechanism to prevent unrelated colonies from fusing to them and parasitizing them.
Gregarines are a diverse group of Apicomplexan parasites that inhabit the intestines, body cavities and reproductive vesicles of marine invertebrates. Approximately 250 genera and 1650 species have been so far by Clopton 2000; Hausmann et al. 2003 and Levine, 1976, 1977, 1988 described. Some ancestral characteristics found in gregarines (e.g. Extracellular feeding stages and a monoxenous life-cycle) have given the group a reputation of being “primitive” (Leander, 2008). Most of the species are known to be host specific e.g. Lankesteria sp. infects the intestines of ascidians; Genus: Lankesteria ascidiae. The gregarine Lankesteria ascidiae (Lankester, 1872) is a parasite within specimens of the ascidian Ciona intestinalis collected from the Bay of Naples (Ciancio et al. 2001). The trophozoites inserted in the host’s stomach epithelium or found free in the lumen. The gregarine induced a hypertrophic reaction in the host’s epithelium cells, and free trophozoites in the stomach were surrounded by cilia of gastric cells (Ciancio et al. 2001). The hosts infected cells appeared laterally compressed and a niche formed as an invagination of the gastric wall covering the trophozoite. Studies by transmission electron microscopy of C. intestinalis gastric epithelium showed mononucleotide trophozoites with large mitochondria frequently arranged in peripheral clusters. Maturing trophozoites showed a mucron filled by a dense fibre matrix; these fibres extended in a root-like formation through the whole trophozoite cell up to its periphery and appeared to occupy a separate cytoplasmic compartment enclosed in a membrane (Ciancio, et al. 2001).
Nephromyces had been found in the renal sac lumen of five tunicate Molgula species (M. manhattensis, M. arenata, M. complanata, M. citrina, M. occidentalis) and one species of the molgulid genus Bostrichobran chus (B. pilularis). This is the first report (using modern taxonomic schemes) of Nephromyces from a molgulid genus other than Molgula (Saffo, 1982). Like many structures, the renal sac of molgulid tunicates was named before critical demonstration of its function. Although it has often been hypothesized (or assumed) that the renal sac is an excretory organ but the biological role of this organ remains uncertain (Saffo, 1978). Recent work has focused on the morphological and chemical peculiarities of the renal sac. Most unexpectedly for an excretory organ, the renal sac has no openings at any stage in its development (Saffo, 1978; Saffo and Davis, 1982). Consequently, it has been assumed that renal sac waste product are not excreted from the renal sac, but accumulated in the organ for the life of the tunicate (Das, 1948). The renal sac lumen contains a large volume of concretions, which are chiefly uric acid and calcium oxalate in Molgula manhattensis (Lowenstam and Saffo, 1978) and a possible metabolic origin that resemble human kidney stones (Nolfi, 1970). Unlike kidney stones, however, these concretions show no evidence of being pathological deposits, but seem to be normal metabolic products. The chief organic component of the renal sac fluid in M. manhattensis has been identified as homarine (Gasteiger, et al. 1960). Early papers (de Lacaze-Duthiers, 1874) assert that fungus-like microbial cells known as Nephromyces (Giard, 1888) are present in the renal sac. Despite their potential significance in the activities and biological role of the renal sac, these cells received little attention. In all adults of molgulid examined species (Molgula manhattensis, M. citrina, M. complanata, M. arenata, M. occidentalis and Bostrichobranchus pilularis) these cells are present in the renal sac lumen. These cells differ markedly in morphology from tunicate cells, and at least broadly resemble the Nephromyces described by earlier authors. In contrast to Giard (1888) and Harant (1931), there is no qualitative difference in cell-type distribution with season, at least in adult M. manhattensis (the only species sampled at all times of year).
The trophozoites of almost all the isolated Acanthamoeba species had broad hyaline zone from which several to many slender, tapering, flexible characteristic projection called acanthopodia are produced, which many appear rounded or pointed at tip; outline oval, elongate, or irregular (Abu Kabsha, 2013).
Perkinsus marinus are protozoa, and in particular belong to a group called the alveolates. The individual cells have two flagella, and have a partial polar ring used to attach to their hosts at the anterior. This is similar to structures found among the Apicomplexa, and Perkinsus was previously classified with them. However, genetic studies show that P. marinus is probably closer to the dinoflagellates, which also appear to have modified polar rings. If Perkinsus is a dinoflagellate, it is a basal one (Hackett et al. 2004).
Perkinsus marinus is a prevalent pathogen of oysters, causing massive mortality in oyster populations. The disease it causes is known as ”Dermo” (or, more recently, as ”Perkinsosis”) Susan, 2009 and is characterized by proteolytic degradation of oyster tissues.
P. marinus may start out in an immature trophozoite stage (also referred to as a meront, merozoite, or aplanospore stage depending on the authors’ taxonomic preferences), at 2-3 µm in diameter. A mature trophozoite stage (also known as mature-meront, mature-merozoite, or mature-aplanospore stage) then forms with an appearance of a ”signet-ring” 3-10 µm in diameter each containing a large eccentric vacuole with the nucleus dislocated to the periphery of the cell. The tomont stage (a.k.a. sporangia or schizonts), may form ”rosettes”, 4-15 µm in diameter, and containing 2, 4, 8, 16 or 32 developing immature trophozoites (Susan, 2009). Under certain conditions there may also be an additional stage known as a biflagellate zoospore (Mears, 2008). P. marinus primarily infects hemocytes of Crassostrea virginica or Eastern oysters.
Many scientists believed that there are still hundreds of marine flatworms species still undiscovered (Newman and Cannon, 2005). The marine flatworms Polycladids are the largest group of the flatworms sometimes reaching lengths of 15 centimeters. They are greatly flattened and more or less oval shape, with a pair of anterior marginal tentacles and brightly coloured. Intestine elongate and centrally located with many highly branched diverticula. Polycladids get their name from their highly branched digestive cavity. These individuals were photographed on a reef near the island of Guam, (Alessandrello, et al. 1988). Most common polyclads are active carnivorous predators and scavengers and can be found feeding on various sessile invertebrates including ascidians. Some species are herbivores and have specialized green algae or benthic diatoms. In a few flatworm species of the order Acoela (an old taxonomic order which is distinct from the order Polycladida), ingested microalgae are not degraded but become endosymbionts (Zoochlorella). Khalili et al. (2009) mentioned that the order polycladida flatworm is divided into two group, A cotylea which lack a ventral sucker, and a cotylea, the pseudocerotidae contain many conspicuous and colourful species.
Many species of the Family Pseudocerotidae are thought to prefer colonial and solitary ascidians, sponges, and bryozoans showing no regular specificity in their diet (Coles, 2002). For feeding, the highly ruffled pharynx which when not in use is retracted in a pocket, protrudes and can be expanded into the individual zooids of colonial ascidians, while discharging photolytic secretions by accessory glands, the muscular pharynx is used like a pestle to macerate the prey’s tissue. Partially digested tissue is then drawn into the intestine which acts as a reservoir while further digestion takes place in the highly branched gut. The gastrovascular cavity also transports food particles to all parts of the body. In Pseudobiceros species (Holligan and Gooday, 1977) suggest that prey can also be engulfed by the muscular pharynx which can expand to the same size as the whole animal. A digestion is then started outside of the body allowing the pharyngeal muscles to break up the prey which is then sucked as a whole into the intestine. Polyclad that preys upon ascidians (Barnes, 1982) yet another technique has been observed for Eurylepta leoparda. This species penetrates the mantle of the solitary ascidian Corella willmeriana and by using these drill holes, they suck its complete content within several hours (Holligan and Gooday, 1977). Juveniles even can be found inside tunicates. After that they have eaten the entire contents, and then crawl across the rocks to another tunicate. When occurring in masses flatworms can have disastrous impact on human aquaculture. Tropical polyclads are known as pests of oysters and giant clams Stylochus matatasi. After further enzymatic degradation of food particles in the gastro vascular cavity nutrients are transported into the intestinal branches resembling a highly absorptive surface. Most food particles are engulfed by phagocytosis of the gastro dermal cell layer and further enzymatic breakdown occurs intracellular. Undigested material is egested through the pharynx, the same opening through which food enters, because flatworms have a blind digestive system. In some species it has been observed, that after complete digestion the gut was cleaned by flushing it with water (Holligan and Gooday, 1977).
The little blue-spotted flatworm Pseudoceros indicus is often seen on many of our Northern shores. On rocky shores, on boulders and under stones. They are 2-3cm long with body plain white and closely-set dark blue spots along the margin. The body margins are slightly ruffled when the worm is in water. It has a pair of erect pseudotentacles at the front made up of folded edges of the body. The worms have been observed enveloping spherical objects. They eat the yellow clustered bead ascidians Eudistoma sp. (Newman and Lester, 2003).
The flatworm Cycloporus sp. lives on the colony and inside the digestive system of the compound ascidian Botryllus schlosseri present on the base of a rock just south of the Lihou Island causeway (Carver and Gurr, 2006). They mentioned that the Botryllus schlosseri colony had been excavated and several deposits of very small eggs of the worm were deposited in the depression. (Newman and Cannon, 2002) of all the polyclad flatworms, the pseudocerotids (Platyhelminthes, Polycladida) are thought to be the most conspicuous and diverse throughout tropical and subtropical waters (Newman & Cannon, 1994a, b, 1995a, 1997, 1998; Newman & Anderson, 1997; Newman et al., 1994).
According to Faubel (1984) and Prudhoe (1985) there are only six known species of Cycloporus known worldwide. Prudhoe (1985) described the Cycloporus sp. that has elliptical body with rounded ends and colored body. He mentioned that they are found A mong seaweeds, sponges, and compound ascidians.
Boomker and Junker, (2007) demonstrated the diagnostic criteria of previously described species of the genus Tetrameres from Africa and other parts of the world.
Solitary ascidians are stable microhabitats potentially favourable for feeding, shelter and reproduction for amphipods. Occurrence of the amphipod Leucothoe spinicarpa in the ascidian Phallusia nigra (Urochordata, Ascidiacea) in Southeastern Brazil was reported by Cantor, et al. (2009). They mentioned that the occurrence and size range of Leucothoe spinicarpa, the symbiotic species of the solitary ascidian Phallusia nigra was evaluated at Praia da Enseada, Ubatuba, Northern coast of Sao Paulo State. The amphipods collected from the ascidians pharyngeal basket or atrium were measured and sexed and the ascidians were weighed. Juveniles, males and females were separated by differences in the excavations on the palm margin of gnathopods. The number of amphipods in each ascidian varied and there were few adults in opposition to a high number of juveniles. Males and females did not show difference in body size, but sexual dimorphism based on excavation of gnathopod and dactylus proportion was presented. Also, the ascidian weight was related with the number of associated adult amphipods but not with the juveniles. The high number and size range distribution of juveniles, the low number of oviparous females, and even the presence of single adult in the ascidians, suggest the possibility of extended parental care. Associations of different degrees of complexity established by crustaceans with hosts have been related to the need for shelter, foraging and breeding. The black solitary ascidian, Phallusia nigra is very abundant in the rocky shores of the coast of Sao Paulo State (Rodrigues et al. 1998) and may provide potentially favourable and stable microhabitats for both breeding individuals and recruiting juveniles of amphipods. The gammarid amphipod Leucothoe spinicarpa, whose genus was recently revised by Serejo (1998), has been described as an endobiont of some species of ascidians (Ortiz, 1975). This interaction provides not only food, but refuge for the juvenile amphipods, that can grow nearby the adults of the same species (Thiel, 1999, 2000). Furthermore, within this microhabitat, parental care may occur in amphipods both in embryonic and post embryonic stages (Dick et al. 2002). Once the adults are dead, juveniles may even ‘inherit’ the ascidian in which they were born (Thiel, 1999). The aim of the last author was to observe the occurrence, abundance and variation in size of the commensal gammarid amphipod Leucothoe spinicarpa in all stages of its life cycle. Also, his study intended to relate these observations to the biomass of the solitary ascidian Phallusia nigra.
Some Anamixis sp. are also another gammarid that inquilines on corals, sponges, ascidians and some often sessile invertebrates (Barnard & Karaman, 1991).
Thomas and Krapp-Schickel (2011) mentioned that the Leucothoid amphipods are of interest for their unusual ecology as commensal inhabitants of sessile invertebrates. They added that obligate commensal species have evolved highly characteristic and unusual morphologies and feeding strategies as a consequence of their way of life, including eusocial structure, a condition once thought limited to insects and naked mole rats. Duffy (1996, 2003) first documented eusocial behaviour in marine sponges-inhabiting snapping shrimp. Thomas (1983, 1997) documented eusociality and communal living in highly derived tropical leucothoids in the genus Anamixis. Thiel (1999) reported on nest guarding in Leucothoe spinicarpa from Florida, USA. Because of their cryptic lifestyle and need for specialized collecting methods, Leucothoid diversity has been vastly underrepresented in museum collection.
The Anamixidae have been assumed in the past to be piercing and sucking inquilines and are usually found in warm shallow waters on sessile invertebrates, particularly sponges, tunicates, corals and perhaps hydroids. However, Thomas and Taylor (1981) have found that male Anamixis are filter feeders. Thomas and Barnard (1983) also find that leucothoids are filter feeders, often inside ascidians and tunicates.
Parasitic isopods are among the dominant groups of crustacean ectoparasites (Moller and Anders 1986) with a short free-living planktonic phase. Sexual dimorphism is the rule among the members of the Cymothoidae. Males are of a similar size and shape to females at the aegathoid stage, which makes it is difficult to separate males from immature females; however, females are relatively larger and their bodies asymmetrically proportioned in all other stages. Females brood their eggs in a marsupium under the thorax. The male phase continues through several additional moults until a second individual attaches itself to the same host. The presence of mature females inhibits further development of males in their vicinity. After that the larger of isopods is transformed into a functional female and begins to produce eggs (Sindermann 1990, Grabda 1991, Trilles 1994).
Mothocya sp. Costa 1851 and Anilocra prionuri (Isopoda: Flabellifera: Cymothoidae) are hermaphrodite and parasitize mainly the branchial cavities, as well as the buccal cavity of Styela plicata and Ciona intestinalis (Fig. 51). Mothocya sp. is found in the various parts of the Mediterranean Sea (Bello, et al. 1997). In all cases, Mothocya sp. was attached with its claw-like pereopods to the anterorventral portion of the host’s branchial cavities. The effects of the cymothoid infection vary according to the combination of the host-parasite status, behavioral changes; tissue damage; decrease in mean weight, size and growth; and in some cases, death (Brusca 1978, 1981, Romestand and Trilles 1979, Kabata 1984). These are pullus primus, pullus secundus and adult stage (Trilles, 1968). They distribute in Mediterranean, Black Sea, Adriatic and Atlantic (Trilles et al., 1989 and Trilles, 1991).
Wetzer, 1990 mentioned that members of the family Aegidae are typically predators/parasites on marine fishes. He added that isopod species have been reported as commensals or parasites in ascidians. Species of isopod Aega (Rhamphion), was isolated from the cloaca of an ascidian from Galapagos Island. Aega (Rhamphion) francoisae, a new species of Aegidae, is reported from a depth of 316 m in Galapagos Island (Wetzer. 1990). All of specimens of the series were found in the cloaca of a single ascidian Halocynthia hispida. This is the first species of aegid isopod to be reported inhibiting an ascidian (Wetzer, 1990). A single deep-water specimen of the stolidobranchiata ascidian Halocynthia hispida (Herdman, 1881) was collected. The ascidian had 10 specimens of described aegid isopod in its cloacal chamber. Members of the family Aegidea are peridators/parasites on marine fishes and no aegid or any other isopod have been reported as commensals or parasites on ascidians.
The variable neon slug Nembrotha nigerrima feeds on ascidians (Debelius, 2001) and has been observed in the at Verde Island, the Philippines feeding on the green-ringed ascidian Sigillina signifera (Cervera et al. 2008). Nembrotha nigerrima eating Oxycorynia fascicularis tunicates. In fact, Nembrotha nigerrima uses the toxins in its prey ascidians to protect itself from predators. It stores the ascidian’s toxins in its tissues and then releases them in slimy defensive mucus when alarmed. In the course of preparing a new Fact Sheet for N. nigerimma I was reading Pola, Cervera et al. (2008) on synonymising Nembrotha kubaryana and N. nigerrima and was puzzled by their argument that Yonow had no grounds for discarding N. nigerrima as the senior synonym. My understanding was that as both names were published simultaneously. Neither was senior to the other. On reflection I think we should continue to use N. kubaryana. All known nudibranchs are carnivorous. Some feed on sponges, others on hydroids,(e.g. Cuthona) Folino, 1997 others on bryozoans (phanerobranchs such as Tambja, Limacia, Plocamopherus and Triopha) Domínguez et al. 2008 and some eat other sea slugs or their eggs (e.g. Favorinus) Rudman,1999 or, on some occasions, are cannibals and prey on members of their own species. Other groups feed on tunicates (e.g. Tambja, Nembrotha, Polycera, Thecacera), Valdés, 2004 other nudibranchs (Roboastra, which are descended from tunicate-feeding species), Valdés, 2004 barnacles (e.g. Onchidoris), Barnes and Powell, 1954 and anemones (e.g. the Aeolidiidae and other Cladobranchia). Domínguez et al. 2008. Its synonyms include Nembrotha kubaryana (Cervera and Gosliner, 2008).