The thornback guitarfish (Platyrhinoidis triseriata), a species of ray in the north-eastern Pacific Ocean. / The thornback ray or thornback skate (Raja clavata), a species of ray in the Atlantic Oc...

(zoology) Any of the genus Fissurella of marine gastropod mollusks.

(preceded by definite article) A medieval instrument of torture consisting of an iron frame that encased the leg and was then heated.

acetylated at all sites of a molecule