BASTERIA, 65:1-15, 2001 Pyrenees 1. Topographical and Geological
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BASTERIA, 65:1-15, 2001 A remarkably rich prosobranch fauna endemic to the French Pyrenees Hans+D. Boeters Karneidstrasse 8, D 81545 Miinchen, Germany & Alain Bertrand Laboratoire Souterrain, F 09200 Moulis, France This article describes a remarkably rich fauna of freshwater prosobranchs endemic to the French which three viz. Moitessieria Pyrenees, comprises new (sub)species, nezi spec. nov., bessoni nov. and (?)P. nanum and Alzoniella Palaospeum rebenacqensis subspec. spec. nov., junqua Boeters, 2000. These four endemic species can be found sympatric with two species of Bythinella which have a larger distribution in the Pyrenees. Key words: Gastropoda, Prosobranchia, Moitessieriidae, Moitessieria, Palaospeum, Hydrobiidae, Alzoniella,Bythinella, France, Pyrenees, taxonomy, biogeography. I. SPECIATION AND ITS TOPOGRAPHICAL AND GEOLOGICAL ASPECTS 1. Topographical and geological aspects In the Pyrenees-Atlantiques, the Gave d'Ossau rises in the area of the Pic du Midi d'Ossau, flows past Gabas, Laruns and Arudy, and finally into the Gave d'Oleron at Oleron about km southwest of Pau. At Gave 5 Arudy, the d'Ossau butts against a mora- nic wall (Delfaud et al., 1980: figs 7-13) deposited on a layer of the Early Cretaceous peri- od which overlaid the (cretace inferieur) is in south by a layer of the Later Cretaceous period (cretace superieur) (Delfaud, 1980: fig. 0-8). Where it butts against the moranic wall about above the Gave d'Ossau 390 m sea level, loops westwards from its original south-north direction. To the south of this wall, the small river Nez has cut its bed into the Later Cretaceous and flows south-northdirection layer in a towards Pau, joining the Gave at de Pau opposite Pau. The main source of the Nez is L'Oeil du Nez, a karstic 315 above level km distant from large spring m sea only 4 the loop of the Gave d'Ossau at Arudy. L'Oeil du Nez is used for the water supply of Pau. L'Oeil du Nez is about lower than the of Gave d'Ossau 75 m loop the at Arudy. The large karstic spring is supplied by water trickling away from the Gave and making its way through the karst (Bauer et al., 1992). L'Oeil du Nez is the main source ofthe Nez, but it is associated with a number ofsmal- ler springs. An examination of three of these smaller springs has revealed that karstic of waters the Vallee du Nez are inhabitedby the following six prosobranchs, the first four of which characteristic of this and be are valley can regarded as endemic: Moitessierianezi 2 BASTERIA, Vol. 65, No. 1-3, 2001 bessoni spec, nov.;Palaospeum rebenacqensis subspec. nov.; (?) Palaospeum nanum spec, nov.; Alzoniellajunqua Boeters, 2000; Bythinella servainiana (Paladilhe, 1870); Bythinella cf. utri- culus (Paladilhe, 1874). The four representatives of Moitessieria, Palaospeum and Alzoniella are stygobionts. The number of six taxa of the Moitessieriidae and Hydrobiidae is remarkable in view of the fact that the waters of the best-known karstic spring in France, the Source du Lez north of Montpellier, are not inhabited by more than seven species of these two families: Moitessieria rolandianaBourguignat, 1863; Paladilhiapleurotoma Bourguignat, 1865; P. conica Paladilhe, 1867; Arganiella exilis (Paladilhe, 1867); Bythiospeum bourguignati (Paladilhe, 1866); Belgrandia gibba (Draparnaud, 1805); Bythinella eutrepha (Paladilhe, 1867). 2. Speciation Gorthner & Meier-Brook (1985) stressed the following three factors as being essential for endemism freshwater molluscs Lake Ochrid: speciation resulting in in in (1) a great age (Lake Ochrid is dated as Late Pliocene); (2) low temporary fluctuationof abiotic fac- the of niches. tors; (3) presence various ecological In 1991 Boeters & Miiller discussed whether these factors couldalso explain the origin of the rich subterranean prosobranch fauna of the Rhone basin if this basin is roughly understood as a lake-like subterraneanarea. They came to the conclusion that factors (1) and (2) do not apply to the Rhonebasin and that the subterranean prosobranchs ofthe Rhonebasin might have invaded the valley from the neighbouring karst. As regards the subterranean prosobranchs of the Nez, the following can be concluded. Factor (1). In view of the fact that the waters of the Nez originate from karst of the Cretaceous has period in a region which not been covered by marine waters any more it (Delfaud, 1980), can be assumed that this aquatic habitat exists for a very long time already. Factor (2). Even under the assumption that the area ofthe loop of the Gave d'Ossau at covered of be excluded that the kar- Arudy was by ice during periods glaciation, it cannot stic labyrinth ofthe Nez was not constantly, entirely frozen and remained at least partly inhabitablefor freshwater Reference is made organisms. to Bythiospeum spec, living at a temperature of 4.5°C (in May) at the cave Angerloch (Upper Bavaria) supplied at least during the cold season by melted snow (Boeters, 1984: 144). Factor (3). For Lake Ochrid Gorthner & Meier-Brook (1985) described ecological niches for of G. for limestone two species Gyraulus. lychnidicus lives, example, on rocky bottoms ofthe littoral zone at a depth of not more than 1 m, whereas G. trapezoides lives soft bottoms covered Chara beds of 6 15 on by at a depth to m. As regards subterranean prosobranchs, we are not yet in a position to characterize their ecological niches adequately. In such a situation it seems logical to refer to obser- vations published for subterranean animals other than molluscs. Bou (1968: 469) exam- ined the subterranean fauna of water bodies and reported differences between popula- tions of springs emerging from the water bodies and of artificial pipe wells bored into these water bodies: nous "Si considerons les stations les plus riches ... nous remarquons que les especes sont Les Salentinella, Microcharon, et inegalement reparties. genres Stenasellus, Bathynella sont abondants dans la nappe des puits tubes alors que Niphargus gineti et Asellus albigen- sis essentiellement dans les la des se rencontrent sources, sur peripheric nappes." Notenboom (1986: 81) foundHaploginglymus and Pseudoniphargus species together in habitats in the lower of river but added: "In the of some hyporheic course a river system Boeters & Bertrand: A freshwater prosobranch fauna inS. France 3 1. Fig. Map ofsouthwestern France (top), with an enlarged detail. 4 BASTERIA, Vol. 65, No. 1-3, 2001 the Rio Deva (Picos de Europa) which was investigated at several localities, Haploginglymus shows a preference for the upper courses, while Pseudoniphargus prefers the lower courses." These observations show least that subterranean at indirectly even waters may offer different niches for speciation. II. MOITESSIERIIDAE AND HYDROBIIDAE IN THE VALLÉE DU NEZ As far as the Vallee du Nez has been examined, the valley is inhabitedby three repre- sentatives of the Moitessieriidaeand three of Moitessieria species Hydrobiidae: nezi spec, bessoni nov., Palaospeum rebenacqensis subspec. nov., (?) Palaospeum nanum spec, nov., AlzoniellaBythinellajunqua Boeters, 2000, Bythinella servainiana (Paladilhe, 1870), and cf. utriculus (Paladilhe, 1874). Details of these species are given below. Abbreviations used for collections: BOE, colln H.D. Boeters, München; MNHN, Museum national d'Histoire naturelle, Paris; RMNH, Nationaal Natuurhistorisch Museum (formerly Rijksmuseum van Natuurlijke Historie), Leiden. Moitessieria nezi spec. nov. (fig. 34) Material. — France, Pyrenees-Atlantiques, spring below the farms Hiqueres and Junqua, 1.35 km WSW. ofthe center of Rebdnacq [UTM YN18]; Boeters leg. 20.ix.2000 (MNHN holotype ex BOE 1483, shell; BOE 1483/2, shells) and 3/4.vi.l998 (BOE 1446/1, shell). Shell. — Shell with cylindro-conical. Spire 6.25 convex whorls, separated by a deep The first whorls suture. three of about the same size; the to the following ones, up aper- Rows of form ture, gradually increasing in size. pits a spiral sculpture (21 rows above the of the The last whorl edge aperture). ascends very slightly on the shell wall. The apertu- is ral lip very slightly thickened, indicating that shell growth has been completed. The lip makes merely point contact with the shell wall and does not close the umbilicus. ovoid and Viewed from the the of the Aperture slightly oblique. side, edge aperture is curved like a question mark. Height and width of shell 2.35 and 0.8 mm, height and width of 0.6 and aperture 0.5 mm (holotype). Anatomy. — Unknown. features. —Moitessieria close Moitessierialesche- Differentiating nezi spec. nov. occurs to rae Boeters, 1981, in the west, and Moitessieriasimoniana (Saint-Simon, 1848) in the east. The shell ofM. lescherae differs by a partially scalaroid last whorl and closely arranged spi- ral ridges. (Closely arranged spiral ridges are also shown by two samples of Moitessieria spec, from the Pyrenees-Atlantiques, both collected by Bertrand, at Tardets in deposits ofthe Saison and at Alcay). As regards M. simoniana, Bodon & Giusti (1991) have publis- hed biometric of shells of this from Garonne a analysis six species deposits of the at Toulouse and found the ratios 3.3-3.6 for 'total height:width ofsecond to last whorl' and 1.4-1.5 for 'height oflast whorhwidth of second to last whorl'. For the holotype ofM. nezi spec. nov. these ratios are 3.3 and 1.5. The data for M. nezi spec. nov. show that the size of the whorls scarcely increases before the fourth whorl. Further, according to photo- graphs offour of the shells examinedby Bodon & Giusti (1991: 3, fig. 1A-D), the height ofthe shell in M. simonianais only 1.55-1.85 mm and never reaches 2.35 mm. These fin- Boeters &Bertrand: A freshwater prosobranch fauna inS. France 5 dings agree with a shell height of 1.65 mm of another specimen from deposits of the Garonne Toulouse which be ofM. at might a syntype simoniana (Boeters, 1988: pi. 1 fig. SMF 1; 307268, ex colln Charpentier, Lausanne).