LIME-TWIG GLANDS - A UNIQUE INVENTION OF AN ANTARCTIC ENTOPROCT

Specialized glands that release formed secretions of a complex structu re are known from several invertebrate phyla. A novel type of such an extrusive organ has been detected in the newly described Antarctic ent oproct Loxosomella brochobola Emschermann, 1993 and is reported here. The specialized extrusive organs known from other invertebrates are ge nerally unicellular, but these entoproctan glands are multicellular or gans. The structured secretion of these glands is an extracellular pro duct homologous to the body cuticle and is discharged in long sticky, hollow threads. In evolutionary convergence to the glutinant spirocyst s of the Anthozoa, these threads are assumed-like set out single lime- twigs-to trap larger prey organisms inaccessible to the ciliary feedin g current of the entoproct. Specialized glands of this kind have not b een known previously in Entoprocta. This ''invention'' by a nanoplankt on feeder must be seen as a specific adaptation to life in an environm ent that is poor in nanoplankton. L. brochobola was found exclusively on the inner, abfrontal surface of the tube-shaped, calcareous colonie s of the bryozoon Porella malouinensis and shares this microhabitat on ly with some smaller predators, such as the hydrozoan Halecium sp.; no other ciliary feeders are present.