Cochlostoma gigas Gofas and Backeljau,1994

Gofas, Serge, 2001, The systematics of Pyrenean and Cantabrian Cochlostoma (Gastropoda, Cyclophoroidea) revisited, Journal of Natural History 35 (9), pp. 1277-1369 : 1307-1309

Cochlostoma gigas Gofas and Backeljau,1994

(®gures 22±23) Cochlostoma (Obscurella) gigas Gofas and Backeljau, 1994: 45 ±54. Type locality: near Ceresa,

42 ss 30,1 ¾ N, 3 ss 52,3 ¾ E, UTM BH-70-10 (province of Huesca , Spain). HOLOTYPE and ten

PARATYPES in MNHN, four PARATYPES IRSNB Bruxelles , RMNH Leiden, SMF Frankfurt,

MNCN Madrid, MZB Barcelona, UPV Bilbao.

Description

Shell up to 18 Ö 7.5 mm with eight to nine quite rounded whorls. Early whorls with a peripheral angle which may be concealed by the suture or slightly apparent next to it; body whorl slightly constricted in males, more so in females, with a very slight peripheral angle in prolongation of the suture. Apex usually decollated on adults. Sculpture very weak, wrinkled, on the ®rst embryonic half whorl, then with crowded (20±25 ribs/mm) ribs on the second whorl. Spire whorls with rather ®ne sculpture (9±11 ribs/mm) on third to ®fth whorls, then with ribs becoming gradually more crowded (up to 12 ribs/mm) on the penultimate whorl, more spaced and less acute on the last part of the body whorl; ribs hardly or not at all thickened at their termination along the suture.

Aperture thickened and expanded into a somewhat distorted collar, with a distinct rim inside the outer lip. Peristome distinctly auriculated, abruptly narrowing at the columellar insertion, slightly auriculated at the parietal insertion.

Shell colour with a tan to greyish brown background, with one subsutural and one suprasutural series of brown blotches, and a third blurred brown band on the peri-umbilical area of the body whorl; blotches may be conūent to form axial ¯ames. Peristome white.

Female genitalia as in general description, but with a rather small ovary occupying only one and one half whorl in the apical part of the spire. Male genitalia with a tapering penis of rather rounded section, and with the testis tending to invade the space along the columella, otherwise like in general description.

Remarks

The populations of C. gigas (AnÄisclo, Ceresa) in the valleys of Cinca and tributaries and the nearest population of C. martorelli (Campo) in the valley of Esera diOEer at ®ve loci (LAP, PEP, IDH, MEN, PGM) out of 16 by alternative ®xed alleles. Two of these (PEP G and IDH C) are exclusively found in the populations of Ceresa and AnÄisclo. There is a gap of 20 km between Ceresa and Campo, along which limestone outcrops seem to be an appropriate habitat but where specimens of Cochlostoma could not be found despite a careful search in the summer of 1990. Conversely, the populations of Ceresa and AnÄisclo which are indistinguishable on any ground, are 15 km away from each other and physically separate d by the alluvial part of the valley where the species is absent. The morphological and allozymic diOEerentiation over a distance in the same order of magnitude, between Ceresa and Campo, was the reason for holding the populations as not conspeci®c.

The a nities of C. gigas are nevertheless demonstrated to be with C. martorelli . The populations which most resemble C. gigas are found further east, around OrganÄa canyon and Sierra de OdeÂn. Specimens there are nearly as large (16 mm for large females) and share a PGM allele with C. gigas . They diOEer in a less cyrtoconoid spire and a less distorted outer lip. Cochlostoma gigas diOEers from all C. martorelli in the sculpture of the ®rst spire whorls, which maintain a homogeneous spacing of ribs whereas juvenile C. martorelli have loose, faint ribs on the ®rst whorl, which become more distinct and more crowded on the second one, then very loose on the third one. The colour pattern of C. gigas , of brown ¯ames on the shell, is not seen in any population of C. martorelli ; there the patterns result rather from interruptions in the whitish tracts of the ribs.

Habitat

In Ceresa and AnÄisclo, C. gigas was found on shaded rock surfaces, often on an overhanging part of large limestone blocks. In Bielsa, it was found among large rock mounds on a slope exposed to direct sunlight, whereas the sympatric C. crassilabrum were found in more shaded sites.

Distribution

Endemic to the valleys of Rio Cinca and tributaries; the most important populations are in the AnÄisclo canyon, within the Ordesa national park.