6 天之前 · Echinoderm, any of a variety of invertebrate marine animals belonging to the phylum Echinodermata, characterized by a hard, spiny covering or skin. Living species include sea lilies, sea urchins, sea cucumbers, starfishes, basket stars, …

2017年7月30日 · Echinoderm Definition. An echinoderm is a member of the phylum Echinodermata which contains a number of marine organisms recognized by their pentamerous radial symmetry, calcareous endoskeleton, and a water vascular system which helps operate their small podia.Podia are small extensions of flesh which are operated by water pressure and muscles, and controlled by the nervous system of the ...