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Ascidiacea World Database
Noa Shenkar, Arjan Gittenberger, Gretchen Lambert, Marc Rius, Rosana Moreira Da Rocha, Billie J Swalla, Xavier Turon (2012). World Ascidiacea Database. Available online at http://www.marinespecies.org/ascidiacea. Consulted on yyyy-mm-dd
Availability: This dataset is licensed under a Creative Commons Attribution 4.0 International License.
A world checklist of Ascidiacea, compiled by taxonomic experts and based on peer-reviewed literature. more
Ascidians (Phylum: Chordata, Class: Ascidiacea), or sea squirts, are the largest and most diverse class of the sub-phylum Tunicata (also known as Urochordata). They comprise approximately 3000 described species found in all marine habitats from shallow water to the deep sea. There are no freshwater species, and most cannot tolerate salinities below about 20.
Recent phylogenomic studies suggest that they are actually the sister group to the vertebrates, although this conflicts with rRNA and mitochondrial data. 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. Another important character is the presence of the endostyle in the pharynx that will evolve as the thyroid gland in vertebrates. 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, which become functional and multiply to form the branchial sac.
The name "tunicate" (sub-phylum Tunicata) comes from the polysaccharide-containing tunic that envelops the animal and forms a somewhat flexible skeleton. Various proteins and blood cells occur in the tunic, and spicules in a few species. 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. Particles suspended in the current are trapped along the wall of the branchial sac in a mucus net produced by the endostyle. 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. Several solitary species are cultured for food in Japan, Korea, France and Chile or extracted straight from rocky shores for human consumption or bait.
During the past two decades enormous progress has been achieved in the fields of development, evolution, immunology, natural products and ecology of ascidians. Their small genome, small cell number and (usually) short life-cycle make them an attractive model system for developmental biologists. Investigating the phylogenetic position of the subphylum Tunicata in relation to the other subphyla in the phylum Chordata is crucial to the understanding of possible mechanisms of chordate evolution. The study of self/non-self recognition in ascidians provides important information regarding the evolutionary origin of the vertebrate immune system. In addition, ascidians provide a fertile ground for studies in the field of natural products, and play an important role in marine bioinvasions across the globe.
Biology, Biology > Ecology - biodiversity, Biology > Invertebrates
Marine, Classification, Marine invertebrates, Species, Taxonomy, World Waters, Ascidiacea
World Waters [Marine Regions]
From 1758 on [In Progress]
Vlaams Instituut voor de Zee (VLIZ), more, database developer
WoRMS: World Register of Marine Species, more
Dataset status: In Progress
Data type: Data
Data origin: Literature research
Metadatarecord created: 2007-12-06
Information last updated: 2013-04-23