CLASSIFICATION OF ASCIDIA

PHYLUM :- CHORDATA (Notochord, dorsal tubular nerve cord present and gill slits present)

Group :- ACRANIATA (No head, cranium or brain)

Sub-phylum :- UROCHORDATA (Marine. Body covered by a thick test. Notochord present only in larval tail)

Class :- ASCIDIACEA (Test with scattered muscles. Many pharyngeal gill-slits. Bottom-dwelling).

Order :- ENTEROGONA  (Neural gland ventral to nerve ganglion. Gonad one).

Genus :  Ascidia

GEOGRAPHICAL DISTRIBUTION

  • It is commonly found in cold temperate regions.

HABIT AND HABITAT

  • Solitary, marine and sedentary urochordate inhabiting shallow water but some occur deep upto 5500 metres.
ASCIDIA

GENERAL CHARACTERSTICS OF ASCIDIA

  • Commonly called as sea squirts.
  • Shape of body short and cylindrical with a broad base attached to rocky substratum.
  • Test translucent, wrinkled and brownish in colour. Below test is mantle.
  • Anteriorly body contains eight-lobed terminal branchial siphon and six-lobed sub-terminal atrial siphon having mouth and anus, respectively. Mouth is surrounded by 50-100 tentacles.
  • Branchial siphon leads into pharynx which is perforated by stigmata. Pharynx contains endostyle.
  • Dorsal tubercle separated from the nerve ganglion neural gland and membranous dorsal lamina.
  • Alimentary canal consists of mouth pharynx, stomach, intestine, rectum and anus.
  • Gonads, gonoduct and gonopore distinct.
  • Monoecious. Ovary, testes in the same animal. Reproduction sexual. Oviparous. Metamorphosis retrogressive.
ASCIDIA TUNICATES LOWER CHORDATA

SPECIAL FEATURES

  • There are some compound ascidians in which individuals are buried in a common test. The development includes tailed larva exhibiting typical chordate characters having notochord, nerve cord, etc. Kowalewsky (1886) carefully studied the development of larval ascidians and brilliantly demonstrated true position of the group among chordates. The tunicates are best understood by studying first free-living larva of an ascidian, than the adult. The larva shows chordate characters but same are absent in adult and others are modified to sessile mode of life. Compound ascidians reproduce asexually by gemmation and also produce eggs and sperms for sexual reproduction.

IDENTIFICATION

  • The animal contains lobed siphons and all above features, hence it is Ascidia.
ASCIDIA TUNICATES LOWER CHORDATA
ASCIDIA TUNICATES LOWER CHORDATA

REFERENCES

  • https://en.wikipedia.org/wiki/Ascidia
  • Book of Practical Zoology VERTEBRATE by S.S.LAL – Rastogi Publications.
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