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In this article we will discuss about the structure of Sand Dollar (Echinarachinus) with the help of a diagram.
1. It is commonly known as “sand dollar” and is a marine echinoderm found buried in sand at the bottom of sea.
2. Body flattened and somewhat round but without any central disc or arms.
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3. Whole body surface is covered over with small and delicate papillate spines.
4. It has a distinct oral and an aboral surface.
5. The oral surface bears a central mouth and five radial ambulacral grooves which near the periphery, get branched.
6. Lateral margins of ambulacral grooves are having rows of small tube-feets.
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7. The aboral surface bears a centrally located madreporic plate and five pairs of convergent adradial rows of plates forming a definite petaloid pattern.
8. Pedicillariae are present and are having 3 jaws.
9. A well-formed Aristotle’s lantern is also present.
10. Anus is eccentric and is situated on oral surface.
11. Tube feet’s also work as respiratory organs.
12. Sexes are separate and development includes an Echinopluteus larva.
