Taxonomic position of Bulimus demerarensis

In the Guianas two species of Leiostracus occur, L. demerarensis (Pfeiffer, 1861) and L. ruthveni (H.B. Baker, 1926). Recently Muratov & Gargominy (2011) have studied both species and proposed a new taxonomic placement.

In their paper, Muratov & Gargominy have studied the type material of both taxa, respectively in the London and Philadelphia museums. Moreover, they have studied the anatomy of a single specimen from French Giuana; unfortunately the specimen was dried in and had to be re-hydrated. 
The protoconch sculpture, an important characteristic in the orthalicoids, consists of fine spiral lines. The authors state this sculpture has only been observed in three genera: Discoleus Breure, 1978, Bostryx Troschel, 1847, and Leiostracus Albers, 1850. There is, however, a fourth genus with a similar protoconch scultpture, viz. Lopesianus Weyrauch, 1958, represented with a single species from Brazil. Discoleus seems improbable, as it only occurs in southern Argentina, so the choice is between Bostryx and Leiostracus.

Study of the genitalia reveals that the spermoviduct is simple. In the known Leiostracus species this duct is swollen in its distal part, becoming very slender towards the spermatheca after a sudden transition. Bostryx species have a slender spermathecal duct throughout and a distal penis sheath. “Unfortunately we were unable to observe the penial sheath clearly on our re-hydrated specimen but we strongly suspect its presence since it was quite difficult to trace the vas deferens on the surface of the distal part of the penis”. The shell morphology is quite similar to some species of Leiostracus in having a peripheral angle on the body whorl, but “does not resemble any known species of Bostryx” (o.c.: 613-614). From the genitalia they notwithstanding concluded that the species belongs to Bostryx.

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From the rehydrated specimen also the radula and mandibula could be extracted; only the mandibula was illustrated . The radula is said to be “with monocuspid central, bicuspid lateral and weakly tricuspid marginal teeth”.  The radula formula for Bostryx is C/1 + LM/2, or C/1 + L/1 + M/2; for Leiostracus C/1 + L/2 + M/3 (Breure 1978 Zool. Verhand. 164: 239-240). This points more to the latter than to the former genus. Unfortunately, the radula has not been illustrated by Muratov & Gargominy.

In conclusion, Muratov & Gargominy re-classified Bulimus demerarensis Pfeiffer, 1861 with Bostryx, at the same time considering Drymaeus (Leiostracus) ruthveni H.B. Baker 1926 as a junior subjective synonym of Pfeiffer’s taxon. 
Although I can agree with the synonymization, I find the evidence presented for the generic transfer insufficient. The more so since Leiostracus is grouped in a different family (Simpulopsidae). In my humble opinion more evidence, e.g. also molecular, is needed for such a re-classification. 
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Reference:
Muratov, I.M. & Gargominy, O., 2011. Taxonomic position of the land snail Bulimus demerarensis L. Pfeiffer 1861 (Gastropoda, Pulmonata, Bulimulidae). – Journal of Conchology 40: 611-615.

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