Monday, June 15, 2015

Introduced Species: Snails - Cepaea spp.

So I've noticed one thing about Montreal's fauna that's quite different from the upper Gatineau: extremely abundant relatively large snails. They are Cepaea hortensis (white-lipped snail) and Cepaea nemoralis (grove snail).

Cepaea hortensis - notice that the shell margin at the lip of the shell is pale
Both species are native to Europe and have been introduced in North America. I have found their abundance here in Montreal quite striking, as until coming here I had never seen snails of this size anywhere I had been in Quebec or Ontario.

Cepaea hortensis
Like most gastropods, this species are both hermaphrodites (but still have to mate with others to produce viable eggs). They are also among the species which produce a "love dart" -- essentially a sperm-filled spike that is shot into the body of another snail during mating. This dart actually does pierce the body of the other snail. Violent! ... Reproduction can be a very strange process indeed.

Distinguishing the two closely-related species without dissecting them is not 100% accurate -- while generally Cepaea hortensis has a white or yellow lip to its shell and Cepaea nemoralis has a brown lip, this isn't a perfect correspondence, so it is possible (but unlikely) that these individuals are misidentified.

Cepeaea nemoralis - notice that the shell margin at the lip (opening) is brown
Aside from the lip colour difference, both species show quite a lot of shell pattern polymorphism, varying in base shade from a pale creamy colour to a richer yellow, and having a variable number of brown stripes.

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