HUTCHINSON, J.M.C. & REISE, H. 2009. Mollusca 27:183–200.

Mating behaviour clarifies the taxonomy of slug species defined by genital anatomy: the Deroceras rodnae complex in the Sächsische Schweiz and elsewhere.

In this paper we describe the anatomy and mating behaviour of two Deroceras species from the uplands along the Elbe south of Dresden. One is the same as those populations hitherto known as D. rodnae occurring further west; we show that these populations should now be termed D. juranum . The other species we call species A, but it has most in common with D. praecox and populations of D. rodnae from further east. Please download the paper to read the details.
Here we additionally provide the video recordings of copulations, the evidence that most clearly demonstrates the significance of the differences between these species.
If you would like to examine these videos frame by frame, we recommend VirtualDub2.

Mating of Deroceras juranum viewed from below

Click on picture below to start/stop video (1.4 MB download)

This one-minute video shows the copulation, during which the penes evert, coiling round each other and exchanging the sperm. The smaller window shows the same mating viewed from above (for orientation, top is roughly the top in both views). One penial gland becomes visible both from above and below (from above it looks like a grasping hand), whereas the other gland everts under the sole of the partner: this might be the intended site of application. After this both partners vigorously apply their mouths to the intertwined penes, and then wrench themselves apart. Note the pink sperm mass. The same mating as in Fig. 5 in the article.

Click on picture below to start/stop video (1.1 MB download)

Mating of
Deroceras juranum
viewed from above

This one-minute video shows the end of courtship and a copulation (between slugs from site 15). The penes can only just be glimpsed underneath as they evert around one another, but one penial gland is visible as it reaches up around the left side of the slug at the bottom of the picture. Note also the heads pulling back anticlockwise, the sarcobela partially retracting, the vigorous “mouthing” of the penes after they intertwine, and the penes being pulled apart.

Mating of species A

Click on picture below to start/stop video (1.2 MB download)

This 41 s video shows a copulation. At the end of courtship, the bases of the sarcobela are opposed side to side, the axe-shaped sarcobelum tongues contract, and then the rest of the penes evert explosively before immediately retracting. Unlike in D. juranum the penes are clearly visible from above and they twist around each other for only one revolution. Note also the longer penial gland, usually with two branches. The same mating as in Fig. 2 in the article.

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