30 May 2006

North American Land snails: Discus patulus


The genus Discus is one of the land snail genera with representatives both in Europe and North America. There are several species of Discus in North America and 3 in Europe, including D. rotundatus that has been introduced to many countries, including the U.S.

The snail pictured here, D. patulus, is endemic to the U.S. This specimen, whose shell was 8.5 mm in diameter, came from Garrett Co., Maryland.

Thomas Say described this species as Helix perspectiva in 1817 in one of his first papers on snails (Journal of the Academy of Natural Sciences of Philadelphia, vol. 1, p. 18). However, unbeknown to Say, the specific name perspectiva had already been used for another species. So, the name given to it, Helix patula, by Deshayes in 1830 replaced Say's H. perspectiva.

As Say indicated in his description (above), his specimen(s) had been collected by his friend the French naturalist and painter Charles Alexandre Lesueur (1778-1846). Lesueur lived in the U.S. between 1815 and 1837. He was a member of the Academy of Natural Sciences of Philadelphia and later moved to New Harmony, Indiana with Say and others to participate in Richard Owen's short-lived experimental utopian society. Say's wife Lucy took drawing and painting classes from Lesueur in Philadelphia and New Harmony.

According to Say's biographer Stroud (Thomas Say: new world naturalist. 1992), when Lesueur first came to the U.S. he spoke little English. Say read his papers at the Academy's meetings and prepared them for publication in the Academy's journal. In return, Lesueur helped Say with his French and drew illustrations for his articles.

Previous posts about Say and some of the snails he described:
Say's creatures
Say’s snails: Helicodiscus parallelus
Cast from the past: the first American papers on American mollusks
Where were you on the night of 30 August 1820?
Cast from the past: Thomas Say’s male and female pulmonates


pascal said...

Do you have biogeographic maps of Eurasian Discus?


Kerney & Cameron give maps for part of Europe. You can create distribution maps at http://www.faunaeur.org, but their maps only have country-level resolution. So, if, for example, a species has been recorded from one corner of a country, their map will include the enire country in the range of the species.

pascal said...

I wonder if it would be possible to do mRNA analysis of both North American and Eurasian Discus to figure out which species were around longest. Since Anguispira is only in North America (I think), perhaps we could figure out which one is descendant from the other.

Perhaps I should do more cladistics...

Tim Pearce said...

And Discus ruderatus is known from easternmost Asia. There is some question about the distinction between D. ruderatus and D. whitneyi (=D. cronkhitei), but not I nor anyone else I know has addressed the question yet. Someday!

Clare said...

That is such a beautiful little snail - is there any explanation why some snails are round and flat, and others are more upright?

Myla's Bags said...

I believe I have this snail... We picked up while on vacation in Ocean City, MD...

This little (and I mean little) guy is such a wonderful pet... I guess we've treated him so well, he decided to lay eggs and now we have babies.... what now?