Biology Topics related to disease and health provide critical insights into human physiology and medicine.
General Characteristics and Classification of Echinodermata
Phylum Echinodermata (Gr., echinos – spiny or hedgehog; derma – skin; spiny skinned animals)
1. Simple animals may be star-like, spherical, or elongated.
2. Body triploblastic, coelomate, unsegmented (nonmetameric), and radially symmetrical (larva bilaterally symmetrical), i.e., pentamerous symmetry in adults.
3. Body lacks a head, but has oral and aboral surfaces. The oral surface of the body has five radial areas called ambulacra.
4. Body wall is covered with spiny hard calcareous (calcium carbonate) plates (ossicles) that form a rigid or flexible endoskeleton.
5. Body cavity is modified into a unique water vascular system that moves respiratory and locomotory organs, the tube feet or podia.
6. Digestive system is usually complete. Anus is absent in ophiuroids.
7. Excretory organs absent.
8. Reproduction sexual, asexual, or by regeneration. Sexes are separate.
9. Exclusively marine, free-living and gregarious (live in groups) animals.
Phylum Echinodermata includes the following five classes:
Class 1. Crinoidea – The oral surface is directed upward.
Example: Antedon (feather star)
Class 2. Holothuroidea – Worm-like body without arms and spines, Mouth surrounded by tentacles.
Examples: Holothuria, Cucumaria (sea cucumber)
Class 3. Echinoidea – Spherical or discoidal body lacking arms, Body enclosed in an endoskeletal shell or test of closely fitted calcareous plates covered with movable spines.
Examples: Echinus (sea urchin)
Class 4. Asteroidea – Flattened, pentagonal or star-shaped body with a flexible endoskeleton.
Examples: Pentaceros (sea pentagon), Asterias (starfish or sea star).
Class 5. Ophiuroidea – Asteroid-like body is flat and composed of long arms and a central disc.
Examples: Ophioderma (brittle star), Ophiura (brittle star).