The story
From cteno- + cyst, in which the first component can be understood as a clipping of ctenophore or of the taxonomic name Ctenophora.
Etymology from Wiktionary, CC BY-SA 4.0.
ctenocyst
Today it means: A sensory organ of the ctenophores (comb jellies). It is a black speck in the depression on the aboral side of the body. Full definition →