echinoderm n.

Australian egg-laying hedgehog-like mammal, 1810, said to have been named by Cuvier, usually explained as from Greek ekhidna "snake, viper" (also used metaphorically of a treacherous wife or friend), from ekhis "snake," from PIE *angwhi- "snake, eel" (source also of Norwegian igle, Old High German egala, German Egel "leech," Latin anguis "serpent, snake").

But this sense is difficult to reconcile with this animal (unless it is a reference to the ant-eating tongue). The name perhaps belongs to Latin echinus, Greek ekhinos "sea-urchin," originally "hedgehog" (in Greek also "sharp points"), which Watkins explains as "snake-eater," from ekhis "snake." The 1810 Encyclopaedia Britannica gives as the animal's alternative name "porcupine ant-eater." Or, more likely, the name refers to Echidna as the name of a serpent-nymph in Greek mythology, "a beautiful woman in the upper part of her body; but instead of legs and feet, she had from the waist downward, the form of a serpent," in which case the animal was so named for its mixed characteristics (early naturalists doubted whether it was mammal or amphibian).

Proto-Indo-European root meaning "to split, flay, peel," with derivatives referring to skin and leather.

It forms all or part of: derm; -derm; derma; dermal; dermato-; dermatology; echinoderm; epidermis; hypodermic; pachyderm; scleroderma; taxidermy; tart (adj.) "having a sharp taste;" tear (v.1) "pull apart;" tetter; turd.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit drnati "cleaves, bursts;" Greek derein "to flay;" Armenian terem "I flay;" Old Church Slavonic dera "to burst asunder;" Breton darn "piece;" Old English teran "to tear, lacerate."