Their small genome, small cell number and (usually) short life-cycle make them an attractive model system for developmental biologists (Dehal et al., 2001 Nishida and Sawada 2001). 2010).ĭuring the past two decades enormous progress has been achieved in the fields of development, evolution, immunology, natural products and ecology of ascidians. Several solitary species are cultured for food in Japan, Korea, France and Chile (Lambert, 2005) or extracted straight from rocky shores for human consumption or bait (Branch et al. The net pores range from 0.1 to 1 µm, allowing ascidians to filter even very small particulate matter, primarily in the range of 0.5 to 10 µm diameter (Bak et al., 1998 Bone et al., 2003). Particles suspended in the current are trapped along the wall of the branchial sac in a mucus net produced by the endostyle. Ascidians filter their food from the water-column via an oral siphon that brings water into the branchial sac where food items such as microalgae are filtered onto a mucus net water, feces and gametes are expelled through an excurrent siphon. Various proteins and blood cells occur in the tunic, and spicules in a few species (Monniot et al., 1991 Hirose 2009). The name "tunicate" (sub-phylum Tunicata) comes from the polysaccharide-containing tunic that envelops the animal and forms a somewhat flexible skeleton (Swalla and Cameron, 2010). Following settlement, the lecithotrophic larvae undergo metamorphosis during which they lose all of these characteristics except for the endostyle and the gill slit rudiments in the pharynx (Millar, 1971), which become functional and multiply to form the branchial sac. Another important character is the presence of the endostyle in the pharynx that will evolve as the thyroid gland in vertebrates. Adult ascidians bear little resemblance to typical chordates, though their short-lived non-feeding tadpole larvae clearly exhibit the four fundamental characteristics of the phylum: a dorsal tubular nerve cord, notochord, rudimentary pharyngeal gill slits and a post-anal tail. Recent phylogenomic studies suggest that they are actually the sister group to the vertebrates (Bourlat et al., 2006), although this conflicts with rRNA and mitochondrial data (Swalla and Smith, 2008). There are no freshwater species, and most cannot tolerate salinities below about 20‰. They comprise approximately 3000 described species found in all marine habitats from shallow water to the deep sea.
Scientific name BackgroundĪscidians (Phylum: Chordata, Class: Ascidiacea), or sea squirts, are the largest and most diverse class of the sub-phylum Tunicata (also known as Urochordata). Ascidiacea World Database By Noa Shenkar, Arjan Gittenberger, Gretchen Lambert, Marc Rius, Rosana Moreira da Rocha, Billie J Swalla, Xavier Turon Quick search
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