Select the search type
  • Site
  • Web

Student Project

Aplidium sp. (Savigny 1816)

Chloe Jayakody 2016


Aplidium is one of the largest Ascidian genus within the family of Polyclinidae.  Commonly known as sea squirts, these marine invertebrates are considered to be the closest invertebrate relatives to vertebrate animals (Evolution and Systematics) . Preserved Aplidium speciemen are difficult to identify due to post-mortem changes. They are often obscured by sand or endure colour oxidisation or loss. Species identification is further complicated due to their plasticity in appearance, a result of their ability to accommodate diverse substrates and surfaces (Kott 1992). They are characterised by their 3 body sections; thorax, abdomen and post-abdomen and longitudinally lobed stomachs.  Aplidium sp. was collected by the University of Queensland on Heron Island (Figure 1). It is a small, stalked, ovoviviparous ascidian with a colonial lifestyle. Physically, they lack defensive capability, however Ascidian tunics hold bioactive chemicals with predatory deterrents and anti-fouling abilities (Defence and Competition) .

Due to observational limitations and diversity of the genus, the specimen has not been identified on a species level. Physical Description was based on personal observations, while Anatomy and Physiology is a reflection of the general Aplidium body structures and functions. 

Figure 1

Physical Description

The Aplidium sp. colony is situated atop a 1-2cm hard, thin, sand encrusted stalk (Figure 2).  The entire colony is approximately 3cm in length with individual zooids measuring roughly 4mm in length.  Zooids are bright orange, rectangular shaped and circularly arranged at the top of the stalk with a hollow centre. The tunic surrounding the zooids collectively, is gelatinous and translucent with small amounts of sand grains embedded. Dark orange pigment marks are found surrounding the branchial siphon (Figure 3). Each colony supports approximately 9 zooids and consist of a single head. 

Aplidium sp. zooids consist of three body parts; the thorax, abdomen and post-abdomen. The unrelaxed zooids thorax measures approximately 1mm in length.  Its branchial (incurrent) siphon is lobed and has a denticulate margin.  The atrial (excurrent) siphon is not apical, small, lobed and is located mid-thorax with outgoing matter guided into a cloaca system by the atrial languet (Kott 1992). The reduced atrial siphon indicates the presence of a communal cloacal system in the colony and is a defining characteristic of the family Polyclinidae (Kott 1992). The pharynx has 7-8 rows of stigmata indicative of prolific replication (Kott 1992).  The endostyle runs longitudinal along the entire thorax with musculature along the body wall tracking parallel to the endostyle (Moreno and Rocha 2008).

The abdomen and post abdomen are continuously joined without constriction.  The oesophagus is curved and joins a large stomach.  The outer stomach appears smooth and round but viewed from a cross section appears to have inner undulations. Directly posterior of the stomach is a digestive gland followed by a long vertical, U-shaped gut loop and a post-stomach on the proximal end of the ascending loop.  One observed zooid contained a large embryo positioned in the atrial cavity close to the atrial siphon (Figure 4).  The embryo measured roughly 0.5mm.  The heart is believed to be situated in the posterior abdomen, a characteristic of the family Polyclinidae. However, it was difficult to observe.

Figure 2
Figure 3
Figure 4


Ascidians are marine invertebrates found in diverse natural and artificial substrates such as coral reefs (Figure 5), sea grass beds, inter-tidal rocky areas, muddy sediments and in fouling communities (Ali and Tamilselvi 2016). They are able to live in polluted habitats and are often found in harbors with the help of their high tolerance to accumulative heavy metals (Lambert 2005; Papadopoulou and Kanias 1977; Philp et al. 2003). Some ascidian species have immune responses to these environmental stressors and have capabilities of acting as bioremediators (Lambert 2005; Monniot et al. 1986).  It has there been suggested the potential to use ascidians in water quality control in polluted marine environments. However, it is accompanied with the caution of introducing potential invasive species with high intra- and inter-specific competition to already vulnerable ecosystems (Stabili et al. 2015).

Despite numerous ascidian species being considered invasive species due to biofouling and successful colonizing abilities (Ali and Tamilselvi 2016), some ascidian species have been seen as ecosystem engineers, due to their ability to provide microhabitats, extended surface areas for settlement and improving environmental conditions for other organisms (Monteiro et al. 2002). 

Adults are sessile therefore dispersal stage occurs only during larvae stage (Lambert 2005). Studies have indicated the significance of environmental cues from either light or chemical signals and their impact on ascidian larvae and development (Degnan 2001; Svane et al. 1987; Svane and Young 1989; Davis et al. 1991; Wieczorek and Todd 1997). However, the understanding of the molecular mechanisms that are fundamental to the processes of settlement induction and inhibition factors is limited (Degnan 2001). 
Figure 5

Life History and Behaviour


Adult ascidians are predominantly sessile and have therefore adapted to a sedentary lifestyle. Ascidians are able to filter 24 to 540 ml of water per hour, per gram of wet weight of the individual, making them highly efficient filter feeders (Kott 1989; Goodbody 1974). Volume of food ingested is dependent on food availability, time spent filtering and the filtering capacity of the individual animal (Kott 1989). Ascidians are able to control their food consumption by halting the secretion of mucus by the endostyle, seizing ciliary beating, closing the branchial siphon or by expelling unwanted particles from the atrial siphon (Ruppert et al. 2004; Young 1989; Hetch 1918;McGinitie 1939).

Colonial ascidians mainly feed on phytoplankton and organic matter, however various species also consume zooplankton (Young 1989, Ruppert et al. 2004). Some species have been observed having the capability of retaining particles as small as 0.0005mm through their mucous sheet (Kott 1989; Flood and Fiala-Medioni 1979; 1981). 


Colonial ascidians are hermaphrodites which reproduce sexually and asexually. Sexual reproduction is ovoviviparous whereby eggs are internally fertilized and embryogenesis occurs in the atrium in a brood pouch (Satoh 1994). Asexual reproduction in colonial ascidians occurs through budding strobilation. Strobilation is the most common asexual reproductive method in the family Polyclinidae, however reproductive methods can vary between species within genera (Satoh 1994).

Aplidium have gonoducal openings directly into the communal cloaca system where sperm is released to the exterior or the cloacal cavity. This suggests that Aplidium are not self-fertilising. Fertilization in Aplidium, generally occurs in the atrial cavity or top section of the oviduct (Kott 1992).

Colonial species typically have larger eggs rich in vitellum and undergo lecithotrophic development (Satoh 1994; Ruppert et al. 2004; Núñez-Pons 2012). Colonial species have short ranges of larval dispersal due to limitation in egg abundance (Núñez-Pons 2012). The lecithotrophic larvae are brooded internally until it is released as a tadpole (Núñez-Pons 2012; Lambert 2005; Brusca and Brusca 2003). Reproduction typically coincides with food availability. Maximum phytoplankton productivity has been suggested to correlate with ascidian reproductive seasons with studies finding ascidian tadpoles able to delay settlement if cues do not occur (Lambert 2005; Svane and Young 1989; Havenhand 1991).


Ascidian larvae contain all key chordate traits; notochord, endostyle, dorsal tubular nerve chord, pharyngeal slits and a postanal tail (Ruppert et al. 2004).  Larval complexity is higher in colonial ascidians due to modes of adultation and caudalization (Figure 6) (Satoh 1994).  Precocious development allows a developed tail, cerebral vesicle, adhesive organs and partially developed but non-functional branchial and atrial apertures, branchial sac and gut loop (Kott 1992; Ruppert et al. 2004). In caudalization, where muscles cells are added to the tadpole tail, has been suggested to it increase the swimming ability of the larva (Satoh 1994), and therefore may allow greater dispersal range or predation avoidance. Egg size is roughly correlated to caudalization and therefore it has been suggested that mode of development is maternally controlled (Satoh 1994).

Aplidium larvae are generally small with a trunk measuring often less than 0.8mm. They differ from other genera in Polyclinidae due to the presence of ectodermal vesicles being directly separate from larval ectoderm around the anterior end of trunk. They have a cerebral vesicle which contains a well developed ocellus and otolith. Three anteriorly located adhesive papillae allow larvae to settle and attach itself to the substrate (Kott 1992). This then triggers radical metamorphosis where the tail is retracted and causes the loss of the dorsal tubular nerve chord, notochord and tail musculature (Ruppert et al. 2004)

Figure 6

Defence and Competition

Intra and inter-specific competition for space and food is a common occurrence with ascidians. Occupying spaces in order to out-compete neighbours and other species with similar niches is an example of interspecific and intraspecific competition between colonial ascidians (Lambert 2005; Lambert 2000; G. Lambert 2001).  Generally, size of an animal or a colony will increase competitive ability, fecundity, resistance to predators and environmental fluctuations (Jackson 1986).  Aplidium sp., however, are limited in their ability for spatial competition due to their limitations in size (Digestive and Excretory System) , therefore different defence mechanisms are required.

Colonial ascidians unpalatable and toxic tunic is usually the first line of protection assumed due to their ability to accumulate heavy metals and acids (Tunic) (Núñez-Pons 2012). Colonial ascidians consisting of genetically identical but independent zooids, generally cultivate more of these inducible bioactive secondary metabolites (Núñez-Pons 2012; Jackson 1986). They also typically maintain unfouled surfaces in order to inhibit bacteriofilms, infections, epibiosis and biofouling. These mechanisms are indicative of anti-fouling properties, often seen with animals that do not self-fertilise (Reproduction) (Núñez-Pons 2012; Wahl 1989).

These secondary metabolites are mostly nitrogen-bearing such as peptides, alkaloids and amino acid derived products. Types of metabolites change among species, and despite little knowledge of their ecological function, some of these are known to be predator deterrents and antifoulants. High concentrations of vanadium found in vanadoctyes (Hemal System) and sulfuric acid within bladder cells play a crucial role in predatory defence, particularly considering the lack of physical defence ability in ascidians (Stoecker 1980).  

The genus Aplidium is known for its diversity in alkaloids and variability of metabolites (Núñez-Pons et al. 2010; Zubía et al. 2005; Arabshahi and Schmitz 1988). Locality of these metabolites is generally expected to be within the tunic. However, and particularly with colonial ascidians, tunics often have little nutritional value and therefore it is suggested to be unappealing to predators.  Furthermore, taking into consideration the importance of larval defence on species survival, it is hypothesised that metabolites may be found within the gonads or visceral mass where protein and lipid content is higher (Núñez-Pons et al. 2010; McClintock et al. 1991; Young and Bingham 1987).

Tunic shrinkage allows relatively fast tunic regeneration and is an important defence mechanism for colonial ascidians (Hirose 1997 et al.). The selection of settlement in habitats such as rock crevices or beneath marine flora where predators have difficulty reaching prey, is another defence strategy that ascidians commonly use (Stocker and Bergquist 1987). Consequently, predators will often prey on larvae prior to settlement and tunic synthesis.  Once metamorphosis occurs, predation usually reduces significantly (Lambert 2005; Osman and Whilach 1998; Pisut and Pawlik 2002). 

Anatomy and Physiology


Tunicates (or Ascidians) gain their name from a gelatinous outer integumentary tissue called a tunic (Figure 7). Tunics are multifunctional as they harbour multiple cell types, and in some species symbionts (Núñez-Pons 2012; Hirose 2009). Due to the tunics multifunctional capabilities, it is theorized to be one of the explanations for ascidians high adaptability and tolerance to extreme and changing environmental conditions (Hirose 2009). Species lacking tunic vessels have a higher abundance of tunic cells than those with tunic vessels. Phagocyte cells, found in all ascidians, function as scavengers by engulfing remnants of discarded tunic cells. Tunic bladder cells contain sulfuric acid filled vacuoles and are believed to be associated with chemical defence, however, they are absent in Polyclinidae species (Hirose 2001, 2009). Polyclinidae have tunic contracting cells called tunic net cells.  Tunic contractility varies between species and therefore the amount and distribution of these tunic net cells is suggested to differ among species (Hirose 2001). Tunic contraction is believed to be a process of regeneration whereby the tunic is shrunk around wounds, resulting in tunic cuticle closure. Regeneration then completes with the deposition of electron-rich fibers located on the exposed wound surface.  (Hirose et al. 1997). Certain Aplidium species have been found to have 7 types of tunic cells (Hirose 2009). Tunic cell types were not identified in the Aplidium sp. However, the absence of tunic vessels suggests the species may have a high number of tunic cells (Hirose et al. 1997).  
Figure 7

Internal Anatomy

Aplidium ascidians are composed of three body regions; the thorax, abdomen and post-abdomen. Zooids are typically small and thread-like with their posterior abdomen being continuous from the abdomen (Kott 1992). The thorax is narrow with the endostyle situated along the ventral mid-line of the branchial sac (Figure 8) (Kott 1985). The 6-8 lobed branchial siphon is found anterior of the thorax while the small atrial siphon is situated mid-thorax with the small atrial lip arising from the body wall above it. The pharyngeal basket houses the pharynx and rows of stigmata. Aplidium typically have 6 or more rows of stigmata with transverse muscles fibers between them (Moreira de Rocha et al. 2012).  The anus and brooding embryos are found approximately halfway up the atrial cavity (Kott 1992). Longitudinal muscles extend from the thorax down to the posterior abdomen. The oesophagus is vertical and descends into a U-shaped vertical gut-loop. The stomach is vertical and barrelled-shaped with longitudinal folds in its wall (Figure 9) (Kott 1992). Gonads and heart are found in the posterior abdomen (Kott 1990). 
Figure 8
Figure 9

Nervous System

The structural body plan and central nervous system of ascidian larvae demonstrate a close relationship to vertebrates (Zaniolo et al. 2002; Burighel and Cloney 1997). However, during larval metamorphosis, reabsorption of the post-anal tail results in adult ascidians losing the notochord and are left with modified remnants of the neural tube developing into a modified central nervous system (CNS) and a neural gland. The CNS is composed of the cerebral ganglion, the visceral nerve, nerves of the body wall, the dorsal strand plexus and sensory structures of the siphons (Satoh 2014). The cerebral ganglion is located anteriorly between the two siphons with the neural gland posterior to it (Ruppert et al. 2004). The ganglion innervates the caudal viscera, siphons and body wall (Satoh 2014), and holds exclusively motor neurons (Zaniolo et al 2002).  
A peripheral nervous system branches posteriorly from the cerebral ganglion. It is associated with ciliated feeding mechanisms with relative autonomy from the CNS and has been observed to respond to external stimulus in deganglionated species (Zaniolo et al 2002). A ciliated duct and coiled funnel called the dorsal tubercle lie anterior to the neural gland (Figure 10). These create an incurrent flow of water entering the gland, crossing the walls and entering the branchial blood vessels (Ruppert et al. 2004) The neural gland together with the duct, dorsal tubercle function to mediate blood volume and has been theorised as being a precursor for the pituitary gland due to pituitary-like hormones found in neural gland tissue (Ruppert et al. 2004).
Despite the absence of sensory organs, sensory cells are found in abundance on internal and external surfaces of siphons, branchial tentacles and in the atrium cavity. It is suggested that these contribute to water current flow control within the pharynx (Ruppert et al. 2004). 
Figure 10

Digestive and Excretory Systems

Ascidians are mostly ciliary-mucus filter feeders that feed on plankton that have been pumped though the branchial siphon into the pharynx (Lambert 2005; Ruppert et al. 2004). Food particles enter the branchial sac, crossing ciliated gill slits and are strained through a mucous sheet secreted by the endostyle (Ali and Tamilselvi 2016; Kott 1985). The secreted food net is rolled into a thread-like cord and is slowly transported from the pharynx to the dorsal lamina and then to the oesophagus (Ruppert et al. 2004). Food is then digested extracellularly in the secretory cell lined stomach. Absorption is suggested to occur in the intestine situated on the ascending arm of the gut loop. The intestine then forms faeces that are discharged through the anus and into the atrium to be expelled by the atrial siphon (Ruppert et al. 2004).

Aplidium have large, irregular, circular cloacal systems, with each zooid having a conspicuous cloacal aperture referred to as the atrial languet (Kott 1992). Those with a single or communal cloacal system generally have a finite size and shape and are typically smaller (Kott 1992). 

Hemal system

Ascidians have well developed hemal systems with a high diversity in hemocytes. These include, vanadocytes which serve two functions; tunic synthesis through the polymerization of tunicin filaments, and the possible use of its toxicity for antifouling and predation deterrence (Ruppert et al. 2004). The hemal system includes a short curved heart located in the posterior abdomen of Aplidiums, vessels and small sinuses for blood flow. Periodic reversal blood flow found only elsewhere in certain arthropods is suggested to be the reason for organs and systems to be arranged along the blood circuit rather than parallel to it (Ruppert et al. 2004).

Biogeographic Distribution

Aplidium is the most speciose genera of the family Polyclinidae and can be found in various climatic zones such as temperate, polar and tropical waters worldwide (Figure 11).  47 species of Aplidium genera have been recorded in Australian waters (Mather et al. 1998). The Aplidium sp. in discussion was found on coral boulders collected from the reef crest off of Heron Island. 
Figure 11

Evolution and Systematics

Aplidium belong to the phylum Chordata, sub-phylum Urochordata and class Asciacea. The three sub-phyla of Chordata; Vertebrata, Urochordata and Cephalochordata, all share similarities in body plans and have provided insights into vertebrate origins (Holland 2015). Although there has been much contention over which sub-phylum is sister taxa to Vertebrates, genomic sequencing has concluded as Cephalochordates having key genome features of the last common ancestor, placing Urochordates as the sister taxa to Vertebrates (Putnam et al. 2008). Tsagkogeorga et al. (2009) found tunicates to have an evolution two-fold faster to other chordates, suggesting to be the reason of high diversity within the class.

Aplidium belong to the family Polyclinidae within the monophyletic suborder of Aplousobranchiata (Stach and Turbeville 2002). They are primarily differentiated from the other genera of Polyclinidae for their longitudinally folded stomach walls (Kott 1992) Within Polyclinidae, generas Aplidium and Synoicum are suggested to be closely related phylogenetically. They consist of very similar body plans and larvae but are differentiated by Aplidiums lobed stomach (Kott 1992)

There is much contention towards Aplousobranchiatas internal classifications as little knowledge is available on the sub-order. Turon and López-Legentil (2004) suggested Aplousobranchia’s simple branchial sac, complex Larvae and coloniality, to be secondarily derived from a theoretical solitary ancestor with simple larvae and pharyngeal vessels (much like those of Phlebobranchiata). Swalla et al. (2000) proposed that colonial adults evolved independently several times, resulting the possibility of losses or gains of a colonial lifestyle within a given clade.

Conservation and Threats

Ascidian conservation status is currently unknown. However, reduction of coral reef ascidians has been recorded after significant El Niño events. ENSO events are associated with elevated sea surface temperatures and increased UV radiation exposure (Kelmo et al. 2006).  Consequences of these ENSO events have had impacts on reef ascidian populations with UV exposure having proven to be detrimental to eggs and embryos of certain ascidian species (Lambert 2005; Bingham and Reitzel 2000).  The negative impact of rising water temperatures affects all trophic levels.  This in turn disturbs phytoplankton populations and thus affects the availability of food for larval and adult ascidians (Kelmo et al. 2006). 


Ali, H.A.J., and Tamilselvi, M., 2016, Ascidians in coastal water: A comprehensive inventory of ascidian fauna from the Indian coast, Springer Verlag, 1st edition, pp. 7-149.

Arabshahi L., Schmitz F.J., 1988, Thiazole and imidazole metabolites from the ascidian Aplidium pliciferum, Tetrahedron Letters, volume 29, pp. 1099–1102.

Berrill N.J., 1935, Studies in tunicate development. Part III. Differential retardation and acceleration. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, volume 225, no. 525, pp. 255–326.

Bingham, B.L., and Reitzel, A.M., 2000, Solar damage to the solitary ascidian, Corella inflata., Journal of Marine Biological Association, U.K., volume 80, pp. 515– 521.

Burighel P., Cloney R.A., 1997, Urochordata: ascidiacea, In: Microscopical anatomy of invertebrates. Hemichordata, Chaetognatha and the invertebrate chordates, New York, volume 15, p 221–347.

Brusca R.C., Brusca G.J., 2003, Invertebrates. 2nd. Sinauer Associates, Sunderland, MA, USA, p. 895.

Davis, A.R., Butler, A.J., Van Altena, I., 1991, Settlement behaviour of ascidian larvae: preliminary evidence for inhibition by sponge allelochemicals, Mar Ecol Prog Ser, volume 72, pp. 117-123.

Degnan, B., 2001, Settlement and metamorphosis of the tropical ascidian Herdmania curvata, In: The Biology of Ascidians, New York, Tokyo, Springer, pp. 258-263.

Flood, P. R., and Fiala-Medioni, A., 1979, Filter characteristics of ascidian food-trapping mucous films. Acta zoology I. Stockholm, volume 60, pp. 271-272. 

Flood, P. R., and Fiala-Medioni, A., 1981, Ultrastructure and histochemistry of the food-tapping mucous film in benthic filter-feeders (ascidians), Acta zoology, Stockholm, volume 62, no. 1, pp.  53-65.

Global Biodiversity Information Facility (GBIF), 2016, Georeferenced data of Aplidium global distributions.  accessed on 29/05/16 

Goodbody, I., 1963, The biology of Ascidia nigra (Savigny), II. The development and survival of young ascidians, Biological Bulletin of Marine bioIogy Lab. (Woods Hole), volume 124, pp. 31-44.

Hecht, S., 1918, The physiology of Ascidia atra Lesueur II, Sensory physiology, J. exp. Zoology, volume 25, pp. 261-299.

Hirose, E., 2001, Acid containers and cellular networks in the ascidian tunic with special remarks on ascidian phylogeny, Zoological Science, volume 18, no. 5, pp. 723-731.

Hirose E., 2009, Ascidian tunic cells: Morphology and functional diversity of free cells outside the epidermis, Invertebrate Biology, volume 12, pp 83–96. 

Holland, L.Z., 2015, Genomics, evolution and development of amphioxus and tunicates: The Goldilocks Principle: Amphioxus and tunicates, Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, volume 324, no. 4, pp. 342-352.

Jackson J.B.C., and Coates A.G., 1986, Life-cycles and evolution of clonal (modular) animals, Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences, vol. 313, no. 1159, pp.7–22.

Jeffery, W.R., 1994, A model for ascidian development and developmental modifications during evolution, Journal of the Marine Biological Association of the United Kingdom, volume 74, no. 1, pp. 35-48.

Jeffery, W. R., 2007, Chordate ancestry of the neural crest: New insights from ascidians, Seminars in Cell and Developmental Biology, volume 18, no. 4, pp. 481-491.

Kelmo, F., Attrill, M.J., and Jones, M.B., 2006, Mass mortality of coral reef ascidians following the 1997/1998 El Niño event, Hydrobiologia, volume 555, no. 1, pp. 231-240.

Kott, P., 1985, The Australian Ascidiacea I: Phlebobranchia and Stolidobranchia, Memoirs of the Queensland Museum, volume 23, no. 1, pp. 8-19.

Kott, P., 1990, The Australian Ascidiacea II: Aplousobranchia (I), Memoirs of the Queensland Museum, volume 29, no. 1, pp. 7-19.

Kott, P., 1992, The Australian Ascidiacea III: Aplousobranchia (II), Memoirs of the Queensland Museum, volume 32, no. 2, pp. 379-513.

Lambert, C.C., 2000, Germ-cell warfare in ascidians: Sperm from one species can interfere with the fertilization of a second species. Biology Bulletin (Woods Hole), volume 198, pp. 22–25.

Lambert, G., 2001, A global overview of ascidian introductions and their possible impact on the endemic fauna. In The biology of ascidians. Edited by H. Sawada, H. Yokosawa, and C.C. Lambert. Springer-Verlag, Tokyo. pp. 249–257.

Lambert, G., 2005, Ecology and natural history of the Protochordates, Canadian Journal of Zoology, volume 83, no. 1, pp. 34-34.

Mackie, G.O. & Burighel, P., 2005, The nervous system in adult tunicates: current research directions, Canadian journal of zoology, volume 83, no. 1, pp. 151-183.

Mackie, G. O., 1995, On the visceral nervous system of Ciona, Journal of the Marine Biological Association of the United Kingdom, volume 75, no. 1, pp. 141-151.

Mather, P., Wells, A., and Houston, W.W.K., 1998, Hemichordata, Tunicata, Cephalochordata, Zoological Catalogue of Australia, CSIRO publishing, Australia, volume 34, no. 8, pp .114-115.

McClintock J.B., Heine J., Slattery M., Weston J., 1991, Biochemical and energetic composition, population biology, and chemical defense of the Antarctic ascidian Cnemidocarpa verrucosa Lesson, Journal of Experimental Marine Biology and Ecology, volume 147, pp. 163–175.

McGinitie, G. E., 1939, The method of feeding of tunicates, Biology Bulletin, marine biology Lab., Woods Hole, volume 77, pp. 443-447.

Monniot, F., Giannesini, P.J., Oudot, J., and Richard, M.L., 1986, Ascidies: “salissures” marines et indicateurs biologiques (métaux, hydrocarbures), Museum of Natural History Bulletin volume 8, pp. 215–245.

Monteiro, S.M., Chapman, M.G., Underwood, A.J., 2002, Patches of the ascidian Pyura stolonifera (Heller, 1878): structure of habitat and associated intertidal assemblages, Journal of Experimental Marine Biology and Ecology, volume 270, pp. 171–189.

Moreira da Rocha, R., Zanata, T.B., Moreno, T.R., 2012, Keys for the identification of families and genera of Atlantic shallow water ascidians, Biota Neotropica, volume 12, no. 1.

Moreno, T.R., and Rocha, R.M., 2008 Phylogeny of the Aplousobranchia (Tunicata: Ascidiacea), Revista Brasileira De Zoologia, volume 25, no. 2, pp. 269-298.

Núñez-Pons, L., Forestieri, R., Nieto, R. M., et al., 2010, Chemical defenses of tunicates of the genus Aplidium from the Weddell Sea (Antarctica), Polar Biology, volume 33, no. 10, pp. 1319-1329.

Núñez-Pons, L., Carbone, M., Vázquez, J., et al., 2012, Natural products from Antarctic colonial ascidians of the genera Aplidium and Synoicum: Variability and defensive role, Marine Drugs, volume 10, no. 8, pp. 1741-1764.

Osman, R.W., and Whitlatch, R.B., 1998, Local control of recruitment in an epifaunal community and the consequences to colonization processes, Hydrobiologia, volume 375/376, pp. 113–123.

Papadopoulou, C., and Kanias, G.D., 1977, Tunicate species as marine pollution indicators, Marine Pollution Bulletin, volume 8, no. 10, pp. 229-231.

Philp, R.B., Leung, F.Y., and Bradley, C., 2003, A comparison of the metal content of some benthic species from coastal waters of the Florida panhandle using high-resolution inductively coupled plasma mass spectrometry (ICP–MS) analysis, Archives of Environmental Contamination and Toxicology, volume 44, no. 2, pp. 218-223.

Pisut, D.P., and Pawlik, J.R., 2002, Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids?,  Journal of Experimental Marine Biology and Ecology, volume 270, pp. 203–214.

Putnam, N.H., Butts, T., Ferrier, D.E.K., et al., 2008, The amphioxus genome and the evolution of the chordate karyotype, Nature, volume 453, no. 7198, pp. 1064-71.

Ruppert, E.E., Fox, R.S., and Barnes, R.D., 2004, Invertebrate zoology: A functional evolutionary approach, 7th edition, Brooks/Cole, Belmont USA, pp. 931-959.

Satoh, N., 1994, Developmental biology of ascidians: Developmental and cell biology series, University of Cambridge, New York, series 29, pp. 167-202.

Satoh, N., 2014, The larval and adult nervous systems, Hoboken, NJ, USA, John Wiley & Sons, Inc, pp. 89-105.

Stabili, L., Licciano, M., Caterina Longo, C., et al. The Mediterranean non-indigenous ascidian Polyandrocarpa Zorritensis: Microbiological accumulation capability and environmental implications, Marine Pollution Bulletin, volume 101, no. 1, pp. 146-152.

Stach, T., and Turbeville, J. M., Phylogeny of Tunicata inferred from molecular and morphological characters, Molecular Phylogenetics and Evolution, volume 25, no. 3, pp. 408-428.

Stocker, L.J., and Bergquist, P.R., 1987, Importance of algal turf, grazers, and spatial variability in the recruitment of a subtidal colonial invertebrate, Marine Ecology Progress Series, volume 39, pp. 285-291.

Stoecker, D., 1980, Chemical defenses of ascidians against predators, Ecology, volume 61, no. 6, pp. 1327-1334.

Svane I., and Young, C.M., 1989, The ecology and behaviour of ascidian larvae, Oceanography Marine Biology Annual Review, volume 27, pp. 171-181.

Svane I., Havenhand, J.N., Jorgensen, A.J., 1987, Effects of tissue extract of adults on metamorphosis in Ascidia mentula O. F. Muller and Ascidiella scabra (O.F. Muller), , Journal of Experimental Marine Biology and Ecology, volume 110, pp. 171-181.

Swalla, B.J., Cameron, C.B., Corley, L.S., et al., 2000, Urochordates are monophyletic within the deuterostomes, Systematic Biology, volume 49, no. 1, pp. 52-64.

Tsagkogeorga, G., Turon, X., Hopcroft, R.R., et al., 2009, An updated 18S rRNA phylogeny of tunicates based on mixture and secondary structure models, BMC Evolutionary Biology, volume 9, no. 1, pp. 187-187.

Turon, X., and López-Legentil, S., 2004, Ascidian molecular phylogeny inferred from mtDNA data with emphasis on the Aplousobranchiata, Molecular Phylogenetics and Evolution, volume 33, no. 2, pp. 309-320.

Wahl M., 1989, Marine epibiosis. I. Fouling and antifouling-some basic aspects, Marine Ecology Progress Series, volume 58, pp. 175–189. 

Wieczorek, S.K., Todd, C.D., 1997., Inhibition and facilitation of bryozoan and ascidian settlement by natural multi-species biofilms:effects of film age and the roles of active and passive larval attachment, Marine Biology, volume 128, pp. 463-473.

Young, C.M., 1989, Larval depletion by ascidians has little effect on settlement of epifauna, Marine Biology, volume 102, no. 4, pp. 481-489.

Young, C.M., Bingham, B.L., 1987, Chemical defense and aposematic coloration in larvae of the ascidian Ecteinascidia turbinate, Marine Biology, volume 96, pp. 539–544.

Zaniolo, G., Lane, N.J., Burighel, P., et al., 2002, Development of the motor nervous system in ascidians, The Journal of Comparative Neurology, volume 443, no. 2, pp. 124-135.

Zubía E, Ortega M.J., Salvá J., 2005, Natural products chemistry in marine ascidians of the genus Aplidium, Mini-Reviews in Organic Chemistry, volume 2, pp. 389–399.