CLASSIFICATION OF CEPHALODISCUS
PHYLUM :- HEMICHORDATA (Notochord, dorsal tubular nerve cord present and gill slits present)
CLASS :- PTEROBRANCHIA (Small hemichordates with encased body. V-shaped intestine.)
ORDER :- CEPHALODISCIDA (Solitary or colonial, 2 gill slits, 2 gonads).
FAMILY :- CEPHALODISCIDAE
Genus :- Cephalodiscus
GEOGRAPHICAL DISTRIBUTION
Cephalodiscus is found in antarctic and sub-antarctic region and restricted to archibenthal and sub-littoral zones. It has been reported from India, Japan, Sweden, Borneo, Malayasia, Archipelago and Pacific Ocean.
HABIT AND HABITAT
It is a marine colonial animal, found at a depth of 50 to 60 meters. The animal was first discovered by Challanger (1876) at a depth of approximately 245 fathoms in Magellan Strait. Antarctic and Indian oceans have abundant number of this animal.
GENERAL CHARACTERSTICS OF CEPHALODISCUS
- Colony of Cephalodiscus is composed of several unconnected animals, or zooids, which are enclosed in a common case known as coenoecium.
- Zooids have no organic connections with each other, but they can move freely in the chambers.
- Zooids are microscopic and differentiated into protosome or cephalic shield, mesosome or collar and trunk.
- Protosome or proboscis is flexible and contains heart, buccal diverticulum and the central sinus.
- Protosome is shield-shaped and continuous with collar, which bears two groups of bilaterally arranged arms which contain tentacles.
- Trunk is divided into anterior sacciform part, containing alimentation and genital organs, and posterior slender adhesive stalk. Anus is present ventrally.
- Digestive tube is V-shaped.
- Breeding seasonal, sexes are separate.
- A sexual reproduction takes place by the budding of the stolon. New individuals detach for free existence but maintaining colonial relationship.
SPECIAL FEATURES
Zooids or individuals separate but aggregated into a common housing.
IDENTIFICATION
- The animal has coenoecium and all above features, hence it is Cephalodiscus.
REFERENCES
- https://en.wikipedia.org/wiki/Cephalodiscus
- https://slidetodoc.com/protochordata-zly-304-phylogenetic-relationship-between-echinoderms-hemichordates/
- Book of Practical Zoology VERTEBRATE by S.S.LAL – Rastogi Publications.
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