24 August 2007

Slug yin yang

lusitanicus mating1

These are a couple of Arion vulgaris mating. I photographed them in Antwerp, Belgium last July during the World Malacological Congress. A group of us came upon these slugs and hundreds of others around midnight one night as we were walking back from a pub to our dorms thru a wooded path. It was almost pitch black, so I turned on my flashlight. Suddenly, we realized that there were slugs everywhere. You have to be with people who study these animals to appreciate the excitement such a moment can bring: Look at all these slugs! Here is a mating pair!

The slugs in the genus Arion, although they are hermaphrodites, do not have penises. The mating processes of A. hortensis and A. subfuscus, related species, were described by H. E. Quick2. During mating each slug everts its lower (distal) genitalia, including the atrium1, the epiphallus and the oviduct. The everted organs apparently intertwine and exchange spermatophores. The white organs visible between the 2 slugs in the picture below are probably their everted atria.

lusitanicus mating2

During the week I was in Antwerp the identifications, or rather, the names of these slugs, which were quite common on the Campus Groenenborger of the University of Antwerp where we were staying, changed 3 times. First, I thought they were Arion rufus, then I was told that they were A. lusitanicus, and finally, the name was corrected to A. vulgaris3.

1The common tube into which the epiphallus and the oviduct open and which forms the entrance, or the exit, to the outside.
2Quick, H.E. 1946. The mating process in Arion hortensis and in Arion subfuscus. J. Conchol. 22:178-182.
3Appreciations to Ira Richling for the final name.


Snail said...

What a terrific find and great photos. A. vulgaris indeed! They're not that vulgar!

xoggoth said...

Resemblance to yin/yang uncanny.

Durch Arion look much like British one, Arion ater, Great Black Slug. Finally got a new camera and just bunged a pic of GBS on my site.

PS But I would never post slug porn on my site as you do. Rude.


>I would never post slug porn on my site as you do. Rude.

You ain't seen nothing yet. Soon I will post pictures of Limax maximus mating.

Schnäggli said...

Nice captures! There's an open debate over the taxonomy of Arion species. Arion ater and Arion rufus are believed to be morphs of the same species. As for the highly invasive Arion vulgaris, until very recent time it was wrongly known as Arion lusitanicus and as such mentioned in many authoritative texts. However, it turned up that the proper Arion lusitanicus is a different, unrelated species endemic (as the name suggests) to Portugal and that hasn't spread to the rest of Europe. Now there's an ongoing debate whether Arion rufus and Arion vulgaris are actually the same species (it's been suggested to rename Arion vulgaris as Arion rufus var. vulgaris). They are indeed physically indistinguishable to the naked eye - unless you dissect them, as according to some sources they feature differences in their reproductive systems (I do not know the details of these differences, though). An authority on Arion slugs is Dr Ted von Proschwitz (Sweden).