[Cephalopoda] Elongate, fourth circumoral appendages of cuttlefishes and squids used to capture prey; divided into a proximal stalk and a distal club; clubs generally expanded with arrangement of suckers (or hooks); stalks commonly devoid of suckers; tentacles can retract into pockets on the head of cuttlefishes, or merely contract, as in squids.

[Siphonophora] A hollow, highly contractile organ with sensory, feeding and occasionally anchoring functions.

[Hydromedusae] A hollow or solid, highly contractile organ; differentiation between marginal tentacles and oral tentacles.
Marginal tentacles occur in almost all species around the perimeter of the bell, and always well armed with nematocysts, either regular or in clysters. Generally marginal tentacles are entire, but in a few species tyhey are bifurcated or branched.
Oral tentacles are situated around the mouth in some species. They are either simple and undivided, or dichotomously branched. Oral tentacles terminate in a cluster of nematocysts.

[Gastropoda] Before the eyes in heteropods, usually the tentacles are finger-shaped outgrows of the body; the eyes in pteropods are placed on the dorsal or nuchal tentacles in the neck region, these are very flat structures and only well visible in Thecosomata; the term tentacle is also used for the two tubercles found on top of the hood covering the head, these are the anterior tentacles.

Alternative form for tentacle : tentacles.