Bythinella navacellensis, Prié & Bichain, 2009

Prié, Vincent & Bichain, Jean-Michel, 2009, Phylogenetic relationships and description of a new stygobite species of Bythinella (Mollusca, Gastropoda, Caenogastropoda, Amnicolidae) from southern France, Zoosystema 31 (4), pp. 987-1000 : 995-997

Bythinella navacellensis n. sp.

Bythinella sp. – Bichain et al. 2007a: figs 2, 3, clade F + G (and Bythinella sp. 2 on the figure 5).

Bythinella sp. – Prié 2008: fig. 1H.

HOLOTYPE. — France, Folatière cave , VII.2003, V. Prié collector, 1 specimen ( MNHN-9315 ; Fig. 5A ).

PARATYPES. — Same data as holotype, 19 specimens ( MNHN- 9316).

TYPE LOCALITY. — France, Grotte de la Folatière (Folatière cave), town of Rogues, Gard département, 3.5264E, 43.8636N.

ETYMOLOGY. — The specific epithet refers to the grandiose Cirque de Navacelles located near the Folatière cave.

VERNACULAR NAMES. — Bythinelle de Navacelles (French), Navacelles’ cave snail (English).

OTHER MATERIAL EXAMINED. — See Table 1.

DISTRIBUTION. — The species is present in the subterranean aquifers of the Blandas and southern Larzac plateaus, France, Gard and Hérault departments. Sample sites details are given in Table 1 and inferred distribution is shown in Figure 1.

DESCRIPTION

Shell

Teleoconch conical and variably elongate, spire formed by c. 4 well convex whorls, gradually increasing, separated by deep sutures ( Figs 4 ; 5 ). The shell width is c. ⅔ of the shell length and the last whorl is more than ⅔ of the shell length. Shell is transparent, with marked growth lines in the form of collabral grooves but no visible spiral micro-sculpture.Aperture holostome,oval; external margin of peristome slightly fluted. Umbilicus is widely open. Aperture could be rejected on the side, giving the shell a distinct globular shape. Operculum is thin, pliable, transparent and oval. Protoconch of 1¼ whorls, almost smooth, but exhibits thin spiral micro-sculptures in the form of shallow grooves. Basic statistics of 11 shell parameters from 35 shells are given in Table 2.

Anatomy

The entire body is unpigmented. Eyes are invisible externally; however, a lens may be present but pigmented retinal cells were not observed( Fig.5C ).Snout is about as long as wide, approximately parallel-sided or slightly tapered, with a weak but noticeable distal lobation. Tentacles are longer than the snout, more than 10 times as long as they are wide with the distal end slightly expanded. Under an optical microscope no ciliation is visible on the tentacles ( Fig. 5B ).

On dissection, the anatomy of the male genitalia shows the typical organization found in Bythinella : penis bi-armed, the left arm (the penis proper) cylindrical and the right arm (usually referred to as the flagellum) short, blunt and thinner. The intestine makes a loop visible through the translucent shell. Content of stomach and intestine consists of clay and sand particles.

Ecology

The only known living population comes from the Folatière cave. Living animals were found in shallow water, in streams and puddle in the active hydro-geological karstic network. In the Folatière cave, about 67% of the individuals were found by sight trapped in puddle and 33% were collected on the submerged gallery walls, from the surface to about the depth of one meter. Only empty shells were collected by divers in deep water, i.e. more than one meter below the water surface. Since this species, which exhibits troglomorphic features, has only been sampled alive in hypogean habitats, we consider B. navacellensis n. sp. as a strictly stygobite species.

Figures

FIG. 5. — Hypogean and epigean species of the Bythinella Moquin-Tandon, 1856 genus:A, holotype of B. navacellensis n. sp. (MNHN 9315) from the Folatière cave;B, live specimen of B. navacellensis n. sp. in situ from the type locality,with scattered fecal pellets visible on the ground and a drawn Buxus sempervirens L. leaf; C, histological section of the eye of a specimen from the Folatière cave; D, shell of Bythinella eurystoma (Paladilhe, 1870); E, syntype of Bythinella padiraci Locard, 1903 (MNHN); F, holotype of Bythinella bouloti Girardi, Bichain & Wienin, 2002 (MNHN); G, holotype of Bythinella galerae Girardi, Bichain & Wienin, 2002 (MNHN). Abbreviations: L, lens; R, retina without pigmented layer. Scale bar: 1 mm.

FIG. 1. — Study area and sampling sites: A, view of the Folatière cave entrance; B, view inside the Folatière cave (type locality of Bythinella navacellensis n. sp.) showing the typical erosion resulting from the active network; C, location of sampling sites (station code and details on localities are given in Table 1); Thick lines, main rivers;○, sampling sites (sites with occurrence of B. navacellensis n. sp. are numbered, data from rivers alluvium are not shown); ▲, sampling sites of B. eurystoma (Paladilhe, 1870). The geographical range of B. navacellensis n. sp., inferred from hydro-geological data (see text), is darkened.

FIG. 4. — Intra- and inter-specific shell variability of Bythinella eurystoma (Paladilhe, 1870) and B. navacellensis n. sp.: A-H, individuals sampled in the Folatière cave and attributed subsequently to B. navacellensis n. sp.(from clade B) after COI sequencing;I-P, individuals sampled in the Folatière cave and attributed subsequently to B.navacellensis n. sp.(from clade A) after COI sequencing;Q-V, individuals of an epigean population (Saint-Julien-de-la-Nef, Hérault, France) of B. eurystoma. Scale bar: 1 mm.