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Classification Of Urochordata

#classificationofurochordata The characters and examples of these classes are given here: A. Class — Ascidiacea: ADVERTISEMENTS: General characters: 1. Comprises mostly brightly coloured marine animals. 2. Some species are solitary, others are colo­nial. 3. Adults are sessile, but larvae are plank tonic and do not feed. 4. Adults having sac-like body, covered by tunic. 5. Most of the chordate characters that were present during larval period disappear during metamorphosis into adult. 6. In adult, nervous system transforms into a nerve ganglion. Examples: Ascidia , Ciona , Herdmania B. Class — Thaliacea: General Characters: 1. These are free-living pelagic urochor­dates. 2. The tunic is transparent and thin. 3. They possess encircling circumferential bands of muscles within the walls of the test. 4. Incurrent and ex-current siphons are pre­sent at opposite end of the body. 5. A few pharyngeal gill slits are present. 6. In the life-cycle polymorphism and clear alternation of generations are evident. Examples: Salpa...Doliolum . . . .. ...... C. Class — Larvacea/Appendicularia: General characters: 1. These are tiny marine planktonic uro­chordates found worldwide. 2. Larvacea received their name because the adults retain larval characteristics similar in some way to the ascidian tad­pole with its tail and trunk. The general resemblance of adult larvaceans to asci­dian tadpoles suggests that larvaceans may be neotenous form. 3. They produce a remarkable feeding apparatus (house) that consists of three components: screens, filters and expan­ded gelatinous matrix. Disturbed or actively feeding larvaceans abandon their old house and builds a new one. 4. The trunk holds major body organs. 5. The tail is thin and flat. 6. Muscle bands act on notochord to pro­duce movement. 7. A tubular nerve cord is present. 8. All species, except one, are monoecious, and most of these are protandrous. Examples: Oikopleura .....Appendicularia