rostellum

noun

1. A small beak-like process or extension; a small rostrum.

   the rostellum of the stigma of violets, or of the operculum of many mosses

2. A projecting part of the column in the flower of an orchid that separates the male stamen from the female gynoecium.

   The rostellum has an outer firm pouch, inside which is the viscid substance to which are firmly attached the caudicles of the pollinia. An insect entering the fl. probes the spur of the labellum and its back comes into contact with the rostellum and depresses the pouch, causing the viscid substance to adhere to the insect.

   1922, John Christopher Willis, "Orchidacea", entry in A Manual and Dictionary of the Flowering Plants and Ferns, page 471,

3. A retractable protruding part at the anterior end of a soft-bodied tapeworm; the scolex from which it protrudes is often armed with hooks which serve to keep it in place attached to the host.

   The morphology of the scolex, particularly the rostellum, is also useful in diagnosis; T.^([Taenia]) saginata has no rostellum and its scolex bears no hooks, making it easily distinguishable from T. solium, which has an armed rostellum.

Where it comes from

From Latin, diminutive of rostrum (“beak”).

Adapted from the Wiktionary entry rostellum (CC BY-SA 4.0).

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