rostellum

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

rostellum (plural rostella or rostellums)

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. (botany) A projecting part of the column in the flower of an orchid that separates the male stamen from the female gynoecium.
   • 1922, John Christopher Willis, "Orchidacea", entry in A Manual and Dictionary of the Flowering Plants and Ferns, page 471,

     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.

   • 1993, Robert L. Dressler, Phylogeny and Classification of the Orchid Family, page 45,

     In many orchids there is a discrete "viscidium," or sticky pad, formed by the rostellum.

   • 2005, Orchids of Manitoba: A Field Guide, Native Orchid Conservation Inc., page 20,

     The third stigma is sterile and has developed into the rostellum, a sticky structure that aids in pollination by attaching the pollen to insects.

3. (biology) 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.
   • 2005, Burton Jerome Bogitsh, Clint Earl Carter, Thomas N. Oeltmann (editors), Human Parasitology, page 273,

     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.

   • 2008, Dwight D. Bowman, Charles M. Hendrix, David S. Lindsay, Stephen C. Barr, Feline Clinical Parasitology, page 216,

     The scolex exhibits a retractable rostellum with crowns of recurved thorn-like hooks and four cup-like suckers.

   • 2012, Thomas C. Cheng, General Parasitology, page 405,

     Some species also possess an anteriorly projecting rostellum, which may or may not be armed with one or more rows of hooks. The rostellum can be retracted into the rostellar sac within the scolex.

• rostellar