Belgrandia gibba (Drapanaud, 1805)

Known distribution: in perennial springs of Gard, Hérault, Aude and Pyrénées-Orientales.
Crenobiont. Original taxon: Cyclostoma gibbum. The animal is black. Above, a specimen from Cabrier karst spring, upstream Saint-Guilhem-le-Désert, Hérault. 2,2mm. Altitude ≈ 80m.

Same spot. 2mm. Deep suture, bumpy last whorl, aperture subcircular.
The species is endangered by pollution, urbanization and groundwater over-abstraction.

Same spot. Large subfossil adult from the sediments. 2,5mm. Notice how the beginning of the last whorl expands, here, centrifugally. Notice also the shallower suture. This may be a shell of what Bourguignat named moitessieri, after a population from a karst spring near Montpellier.

Same spot. Growth series from juvenile (0,7mm) to a subadult (1,7mm) of “moitessieri”.

Hydrobia moitessieri in Bourguignat: « This species is distinguished from the true gibba, with which it has hitherto been confused, by its less slender, less conical, stockier and more obese shape; by its imperforate test; by its more obtuse, less slender spire; by its faster-growing, less pot-bellied whorls, which are less distinctly separated (thanks to the suture, which is rather shallow), than those of the gibba; by its penultimate whorl, much more developed; by its peristomal edge, slightly flared, and never, as in the gibba, provided externally with a hump, etc., etc. » – J.-R. Bourguignat: Mollusques nouveaux, litigieux ou peu connus Tome I fasc. 5, Paris 1866, p.192. – Above and below: subadult specimens collected in sediments, at the emergence of the “Source du Bout du Monde”, which supplies the Verdus creek, Cirque de l’Infernet, Saint-Guilhem-le-Désert, Hérault, S. France. 1,5-1,6-1,75mm. Altitude ≈ 140m.

Same spot. Variation of shape and convexity in this population. Sometimes appears a feature that is described in “moitessieri”, sometimes appears the gibba. 1,7-1,85mm.

Specimens collected in the pond of the Buèges river spring, Pégairolles-de-Buèges, Hérault.
Altitude ≈ 170m. 2,25mm.

Same spot. 2,15-2,4mm.

A dwarf and slender population inhabits the wash-house at the foot of the fortress of Salses-le-Château, Pyrénées-Orientales. Altitude ≈ 15m. Sizes: 1,65-1,85mm.