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Polyceridae Family

Family Polyceridae

Polycerids have an elongate and high body shape. There is a much reduced mantle skirt with a remnant being the rounded frontal veil the margin of which often possesses branched or papillate processes (velar processes). In some species there is a further remnant, a narrow ridge along the lateral sides of the body bearing a few papillae and tapering to the tail. In some the tail has also taken on a paddle-like form allowing those to swim using this tail and by vigorous flexions of the whole body.
The Triophinae (a subgroup including Kaloplocamus, Plocamopherus, Kalinga, Thecacera & Crimora) have pronounced tubercles arising from this lateral ridge. In Plocamopherus some or all of these tubercles finish in a globular-shaped structure. In some species the oral tentacles are well-developed into wide lappets. The rhinophores are lamellate and retractile into pockets that sometimes have a sheath. In most, the gills are non-retractile however the Triophinae can retract the gills but none possess a gill pocket. Some gills are simply bipinnate or tripinnate and limited in number and arranged on the dorsum as a circle, an arc, or a row. In others (genera Nembrotha, Roboastra, and Tambja) the gills are carried as a high, prominent cluster midway down the dorsum. Some polycerids, such as the genus Polycera, bear a few, large papillae near the gills. In the genus Thecacera these extrabranchial processes can be quite considerable in size. Many polycerids feed upon bryozoans and their lifecycle is governed by the short life span of those bryozoans.
Members of the genus Nembrotha feed on ascidians. The genus Roboastra feeds rapaciously on other polycerids.
Worth particular mention is the ability of several members of the Triophinae to produce light, bioluminescence, from their lateral globular processes, possibly for defensive purposes. This bioluminescence is intrinsic meaning it is produced by the animal’s own biochemistry and is not dependant upon symbiotic bacteria.