HUTCHINSON, J.M.C., REISE, H. & SCHLITT, B: 2020. Mating behaviour and genital anatomy of Deroceras cecconii (Pollonera, 1896), a widespread but overlooked slug from Italy, now introduced to eastern Germany. Archiv für Molluskenkunde 149: 221–236.

Click on picture below to start/stop video (6 MB download)

This three-minute video shows the copulation phase of the mating of the terrestrial slug Deroceras cecconii. The species is widely distributed in Italy, but this pair are from an introduced population in Ostritz, Germany. The slugs have already been courting for many minutes; the pointed structure emerging behind the head is the sarcobelum, with which they paint each other with a secretion. Prior to the copulation the sarcobelum is raised vertically and the animals twist their heads back towards each other. Contact between the bases of each sarcobelum may be the trigger for the simultaneous eversions of both partners' penes. The small caecum pushes the sperm mass onto the partner's penis within 0.5 s. At the same time, the trunk of the penial glands everts; each trunk is then raised to point vertically by the eversion of a third pocket, the balloon-like lobe. While this is everted the mantles start to oscillate. After the lobes have retracted, the penial glands themselves evert over the body of the partner, depositing a secretion. Once the glands are retracted, the mantle oscillation continues for a while but then the slugs crawl apart. It is the same copulation as illustrated with labelling in Figure 7M–S in the above article.
Other videos of copulations of this species are downloadable from
Compare with the copulations of some other related Deroceras.

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