Snail for identification

Ignacio Agudo sent me some photos for identification. Even with the best photos, it always is tricky to give an identification based on pictures only. Especially if parts are obscured (in this case by the withdrawn animal obscuring the inside of the aperture).

Locality: Itaiópolis Municipal District (26º20’11” S ; 49º54’23W), Santa Catarina State/ SC, Southern Brazil.
Date photos: November 18 2013.
Author photos: Germano Woehl Jr.
Environment: Preserved forest of “Araucaria angustifolia”, in slopes area of the Upper Itajaí River Basin Valley, 925 m.s.n.m.

My first impression the shell being subadult, making the ID process somewhat more difficult. There was no species that quickly came to mind. According to Ignacio Agudo this is none of the local taxa of Megalobulimus; he thinks it is a species of Plekocheilus.
Carefully inspecting the photographs, the following observations may be made:
(1) the protoconch sculpture is worn away; this is not uncommon in larger shells and may be due to environmental factors (a relatively low pH?) and this species is probably a ground-dweller, so also degradant products from fallen leaves may play a role;
(2) the shell is thin, as may be seen by the piece broken off in the last photo on the left;
(3) the sculpture of the teleoconch is made up by incrassate growth striae on the upper whorls (photo 2 and 4), crossed by spiral impressions and forming in part puckered bands (especially on the last whorl, photo 1);
(4) the pattern superficially seen in the shell, especially the last whorl, seems to be mainly produced by the still living animal; photos 1, 2 and 4 make the impression of a shell colour pattern, but this is probably caused by the palleal organs shining through the thin shell (the broken off part in the last photo suggests the periostracum colour to be olive-green to brownish, potentially with some yellowish marks);
(5) the colour of the animal (i.e. the foot) is purplish-brown (photo5), but may be covered with yellowish tints as well (photo 3).

Let’s assume the specimen found is indeed a Plekocheilus. What species could it be? As far as I know none has been reported from Santa Catarina. Geographically closest is possibly P. (Eurytus) floccosus (Spix, 1827), but this specimen does not belong to that species. Other suggestions which I have seen (P. (E.) coloratus (Nyst, 1845) and P. (E.) lamarckianus (Pfeiffer, 1848)), are too distinct in shell shape and occur in northern Venezuela resp. Colombia; their types have been located in the Brussels resp. London museums (Breure 2011: fig. 3A-B; Breure & Ablett 2011: fig. 18A-C; see also Borrero & Breure 2011).

So, if we know what’s not, what else could it be? Frankly, the only species it vaguely reminds me is P. (E.) rhodocheilus (Reeve, 1849). This taxon has been described from “Brazil”, without further specified location and has never been recognized since. The type specimen is present in the London museum (Breure & Ablett 2011: fig. 21E-H). This taxon has been classified as Dryptus rhodocheilus by Simone (2006: 147). However, Dryptus is different by its shell shape and all species that I have seen have more solid shells; moreover, it also occurs only in northern South America.

If this find would really be P. (E.) rhodocheilus (Reeve, 1849), it would be a rare, endemic relict species, and this could possibly explain why this species has not been re-found since its description. Nevertheless, these photographs are not convincing evidence. Anatomical data, preferably of an full-grown specimen, and molecular research are needed to bring this species home.

Update:

The collector, Germano Woehl jr., has posted interesting observations about this snail on his blog. The observations were made at night and the specimen was found in litter. The fracture of the shell was caused by a predator (presumably a mammal), not long before. The snail secreted an orange mucus – which might be a defensive mechanism. But more interestingly is that this snail makes noise when being approached (http://www.ra-bugio.org.br/audio/_1767a.wav); to my knowledge this is the first time this phenomenon has been recorded. Is this something special to this species or more general? Curious minds always want to know more…

References:
Borrero, F.J. & Breure, A.S.H. (2011). The Amphibulimidae (Mollusca: Gastropoda: Orthalicoidea) from Colombia and adjacent areas. — Zootaxa 3054: 1-59.
Breure, A.S.H. (2011). Annotated type catalogue of the Orthalicoidea (Mollusca, Gastropoda) in the Royal Belgian Institute of Sciences, Brussels, with description of two new species. — ZooKeys 101: 1-50.
Breure, A.S.H. & Ablett, J.D. (2011). Annotated type catalogue of the Amphibulimidae (Mollusca, Gastropoda, Orthalicoidea) in the Natural History Museum, London. — ZooKeys 138: 1-52.
Simone, L.R.L. (2006). Land and freshwater molluscs of Brazil. EGB/Fapesp, Sao Paulo, 390 pp.

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