Question

What feature is used to define the anterior-posterior orientation of an echinoid test?​

Answer 1

Answer:

An echinoderm is any member of the phylum Echinodermata  (from Ancient Greek "hedgehog" . The adults are recognizable by their (usually five-point) radial symmetry, and include starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Adult echinoderms are found on the sea bed at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are the largest phylum that has no freshwater or terrestrial members.

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