Ptychids

Part of speech: noun

Definitions

1. Members of an extinct order of articulate brachiopods characterized by hinged shells ; fossilized marine invertebrates within that taxonomic group ; organisms recognized by their bivalve-like shells in paleontological records
2. A group of prehistoric brachiopod animals with articulated shells found as fossils ; marine creatures belonging to an ancient taxonomic order distinguished by their shell structure ; extinct sea invertebrates with paired valves identified in geological strata
3. Extinct marine organisms classified under a specific order of brachiopods, known for their jointed shells ; ancient shelled creatures observed primarily in the fossil record ; fossil brachiopods with distinct symmetrical hinged shells

Etymology: Greek "ptyx", meaning a fold or plait, as in folded cloth, is the root behind this name. Zoologists built "ptychid" from that root and the "-id" ending used for members of a biological family, so the name is a modern scientific coinage rather than an ancient one. Ancient Greeks had no word for these creatures. The fold in the name likely refers to a folded or plaited feature of the fossil shells, which is the sort of visible detail that naming systems often pick up. The exact feature the name was meant to describe is not something I can confirm here, so treat that link as a plausible guess rather than settled fact.