In this article we will discuss about the structure of Sea Urchin (Echinus) with the help of a diagram.
1. It is commonly known as “sea urchin” and is formed in shallow water in both rocky and sandy place in sea.
2. Body is Sub-globular and convex or dome-shaped above and flattened below. The aboral and oral surfaces are distinct.
3. Central dise and arms are completely wanting and body is covered over with long, strong, sharp, solid and movable spines bone on protuberance and groups of dermal brabchiae.
4. Exoskeleton is made up of closely fitted calcareous plates, which form a corona enclosing the soft body organs.
5. Pedicillariae are present and are having three jaws instead of two.
6. Mouth lies in the centre of oral surface and is bound by a membranous rim the peristome.
7. Anus is eccentric and lies on the aboral surface bordered by a papillated rim – the periproct. Madreporite and genital pore are also present on aboral surface near anus.
8. The whole oral and aboral surface, leaving the periproct, are traversed by 5 ambulacral areas and 5 inter ambulacral areas made up of definite plates.
9. The ambulacral areas, in addition to spines and branchiae, bear 5 double rows of tube feets.
10. Sexes are separate. Development includes Echinopluteus larva.
11. Aristotle’s lantern is well developed and its teeth can be seen projecting out of mouth.
Note:
Echinus differs from Arbasia in size and colour, the former is blackish and of larger size and later is of orange 11 3 colour and of smaller size.