The plural of ecardine; a group of mollusks or shells lacking cardinal teeth or structures in their hinges.
From ecardine + -s (regular English plural). The root is Latin e- (without) + cardinalis. This term names a taxonomic or morphological category of mollusks.
Naturalists grouped weird shellfish without fancy hinges and basically called them 'the no-cardinal-teeth crew'—nothing fancy, but the name stuck for 200 years!
Complete word intelligence in one call. Free tier — 50 lookups/day.