Tunicate
Marine chordates with a tunic and tadpole-like larvae.
DataBase Center for Life Science (DBCLS) · CC BY 4.0
Tunicates are marine invertebrates belonging to the subphylum Tunicata, part of the phylum Chordata, which also includes vertebrates. Despite their simple adult appearance, their close relationship to vertebrates is certain because during their mobile larval stage they possess a notochord, hollow dorsal nerve cord, pharyngeal slits, post-anal tail, and endostyle, resembling a tadpole. They are the only chordates that have lost myomeric segmentation, except possibly in the seriation of gill slits, though doliolids still display segmentation of muscle bands.
- subphylum
- Tunicata
- number_of_species
- about 3,000
- habitat
- marine, mostly shallow water
- key_feature
- tunic (exoskeleton of proteins and carbohydrates)
- larval_stage
- mobile, tadpole-like, with chordate features
- adult_form
- sessile or pelagic filter feeders with siphons
Lore & Background
The subphylum was at one time called Urochordata, a valid synonym for Tunicata, but Tunicata has precedence and is now almost invariably used in modern scientific works.
Reader's Guide
Tunicates are significant as the closest invertebrate relatives of vertebrates, providing insight into the evolution of chordates. Their larval stage exhibits all key chordate features, while adults often lose these traits, making them a model for studying developmental and evolutionary transitions. The subphylum includes about 3,000 species, with ascidians being the most numerous. Tunicates are the only chordates that have lost myomeric segmentation, though doliolids retain muscle band segmentation. Their tunic, containing cellulose (tunicin), is unique among invertebrate exoskeletons in that it grows with the animal. Tunicates are also notable for their colonial forms, where zooids can integrate into complex structures, and for their filter-feeding lifestyle using siphons.
Did You Know?
- Tunicates are the only chordates that have lost myomeric segmentation, except possibly in the seriation of gill slits.
- The tunic of tunicates is unique among invertebrate exoskeletons because it can grow as the animal enlarges and does not need to be shed.
- Some tunicates, such as sea squirts, are named for their habit of contracting their bodies sharply and squirting out water when disturbed.
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