ˌpinəˈthi(ˌ)rēz noun
Usage: capitalized
Etymology: New Latin, from Latin pinoteres, pinotheres crab living in the mantle cavity of the pen shell, from Greek pinotērēs, from pino- (from pinē pen shell) + -tērēs (from tērein to guard) — more at pain
: a genus (the type of the family Pinnotheridae) of small crabs (as the oyster crab and the pea crab) having usually a thin membranous covering and living as commensals in the mantle cavity of various bivalve mollusks or in some similar cavity in other marine animals