The seaslug, or nudibranch,  Polycera faeroensis mating.  Like all nudibranchs, Polycera faeroensis is a simultaneous hermaphrodite.

The seaslug, or nudibranch, Polycera faeroensis mating. Like all nudibranchs, Polycera faeroensis is a simultaneous hermaphrodite. Image MBI000678

Spring is in the air, the sea is getting warmer – slowly – and the birds and bees, and most things beneath the waves too. Polycera faeroensis is a very common seasulg in British waters, and although colourful is often overlooked due to its small size, large individuals are no more than 4.5 centimetrs long. Like all nudibranchs they are simultaneous hermaphrodites – possessing both male and female sex organs at the same time (sequential hermaphrodites have either only male or only female sex organs at any given time). Copulation works both ways (reciprocal copulation, as it is termed). As the sex organs always appear to be on the right side or their bodies, Polycera faeroensis nudibranchs copulate head to tail. The missionary position has not caught on in the nudibranch world. One might think this was already exciting enough for any mollusc, but some nudibranchs, (such as the related Palio dubia found around the northern Uk shores) add a touch of S & M to their sex lives. Unlike many nudibranchs, Palio dubia does not have a complete vaginal opening. Thus copulation occurs by hypodermic injection; the barbed penis (or penile cirrus as it is properly termed) simply punctures the body wall into its mating partner. Ouch!
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