BAsrERIA, 65: 1-15, 2001 A remarkably rich prosobranch fauna endemic to the French Pyrenees Hans D. BOETERS Karneidslrasse 8, D 81545 Munchen, Germany & Alain BERTRAND Laboratoire SOlllerrain. F 09200 Moulis, France This article describes a remarkably rich fauna of freshwater prosobranchs endemic to the French Pyrenees, which comprises three new (sub)species. viz. Aloilmieria 1UV. spec. nov., Pnlaosptll7n bmolli rebmocqensis subspec. novo and (fJP. /la/lilT/! spec. noy., and Ahj)lliella jllllqUO Boeters, 2000. These four endemic species can be found sympalric with two species of BJlhinella which have a larger distribution in the Pyrenees. Key words: Gastropoda. Prosobranchia. Moitessieriidae, JUoilwieria, Po/aospeum, Hydrobiidae, Ahfmiella, B)'lhillella, France, Pyrenees, taxonomy, biogeography. I. SPEClATlON AND ITS TOPOGRAPHICAL AND GEOLOGICAL ASPECTS I. 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 5 km southwest of Pau. At Arudy, the Gave d'Ossau butts against a mora­ nic wall (Delfalld et aI., )980: figs 7-13) deposited on a layer of the Early Cretaceolls peri­ od (cretace inferieur) which is overlaid in the south by a layer of the Later Cretaceous period (cretace sllperiellr) (DeIfalld, 1980: fig. 0-8). Where it blllls against the moranic wall about 390 m above sea level, the Gave d'Ossau 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 layer and flows in a south-north direction towards Pau, joining the Gave de Pau atJuranc;on opposite Pau. The main source of the Nez is L:Oeil du Nez, a large karstic spring 315 m above sea level only 4 km distant from the loop of the Gave d'Ossan at Arlldy. [;Oeil dll Nez is lIsed for the water sllpply of Pall. [;Oeil dll Nez is about?5 m lower than the loop ofthe Gave d'Ossau at Arudy. The large karstic spring is supplied by water trickling away from the Gave and making its way through the karst (Baller et aI., )992). LOeH 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 waters ofthe ValIee du Nez are inhabited by the following six prosobranchs, the first four of which are characteristic ofthis valley and can be regarded as endemic: Moitessieria nezi 2 BASiERIA, Vol. 65, No. 1-3,2001 spec. nov.; Palaospemn hessoni Tebenacqensis subspec. nov.; (?) Palaospeu1n nanum spec. nov.; Alwaie/la jaaqlla Boeters, 2000; Bylhillella smmiaiaaa (Paladilhe, 1870); Bylhiaella er. IIbi­ CIIIIIS (Paladilhe. 1874). The four representatives of A1oitessieria, Palaospeu7n and Alwniella 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 clu Lez north of Montpellier, are not inhabited by more than seven species of these two families: Moitessieria 1'OlalldiollQ Bourguignat. 1863; Paladilltia plellrotoma Bourguignal, 1865; P conica Paladilhe, 1867; Argaaiella exilis (Paladilhe. 1867); Bythiosp"'1/! bOllrglligaoli (Paladilhe. 1866); Belgraadiagibba (Draparnaud, 1805); BytMllella elllrepha (Paladilhe. 1867). 2. Speciation Gorthner & Meier-Brook (1985) stressed the following three factors as being essential for speciation resulting in endemism in freshwater molluscs in Lake Ochrid: (1) a great age (Lake Ochrid is dated as Late Pliocene); (2) low temporary fluctuation of abiotic fac· tors; (3) the presence ofvarious ecological niches. In 1991 Boeters & Muller discussed whether these factors could also explain the origin of the rich subterranean prosobranch fauna of the Rhone basin if this basin is roughly understood as a lake-like subterranean area. They cameJ.o the conclusion that factors (I) and (2) do not apply to the RJ10ne basin and that the subterranean prosobranchs of the Rhone basin might have invaded the valley from the neighbouring karst. As regards the subterranean prosobranchs of the Nez, the following can be concluded. Factor (I). In view of the fact that the waters of the Nez originate from karst of the Cretaceous period in a region which has not been covered by marine waters any more (Delfaud, 1980), it 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 Arudy was covered by ice during periods ofglaciation, it cannot be excluded that the kar­ stic labyrinth of the Nez was not constantly, entirely frozen and remained at least partly inhabitable for freshwater organisms. Reference is made to Bythiospeum spec. living at a temperature of 4.50 C (in May) at the cave Angerioch (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 two species of Gyraulus. G. lydl1lidicus lives, fat example, on rocky limestone bottoms of the littoral zone at a depth of not more than 1 m, whereas G. tmpezoides lives on soft bottoms covered by Cham beds at a depth of 6 to 15 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: "Si nous considerons les st.ations les plus riches ... nous remarquons que les especes sont inegalement reparties. Les genres Salelltinella, Microclta1'On, Stenasellus, et Bathynella sont ahondants dans la nappe des puits tubes alors que Plipltargus gineti et Asellus albigen­ sis se rencontrent essentiellcment dans les sources, sur la peripherie des nappes. n Notenboom (1986: 81) found HaplogillglYlIIlIs and PselldollipllOrglls species together in some hyporheic habitats in t.he lower course of a river but added: "In the river system of Boe/ers & Bertmnd: A freshwater prosobranchJauna iu S. France 3 30 km GAVE D'OLERON SPAIN FRANCE NEZ REBENACQ • L'OBIL DU NEZ GAVE D'OSSAU SEVIGNACQ 1---...., 1 km Fig. 1. Map of southwestern France (top), with an enlarged detail. 4 BASTERlA, Vol. 65, No. 1-3,2001 the Rio Deva (Picas de Europa) which was investigated at several localities, Haplogillglymus shows a preference for the upper courses, while PseudonijJltarglls prefers the lower courses." These observations show at least indirectly that even subterranean waters may offer different niches for speciation. I!. MOITESSIERIIDAE AND HYDROBIIDAE I1 THE VALLI~E DU 'EZ As far as the Vallee du Nez has been examined, the valley is inhabited by three repre­ sentatives of the Moitessieriidae and three species of Hydrobiidae: ;\1oilessieria nezi spec. nov., Palaospeum bessoni rebenacqellSis subspec. nov., (?) Palaospell11L nonU1n spec. nov" AlZOlliello )lIl1qllo Boeters, 2000, Bylhillello servoilliallo (Paladilhe, 1870), and Bylhillello ef. utriculus (Paladilhe. 1874). Details of these species are given below. Abbreviations used for collections: BOE, colln H.D. Boeters, Munchen; MNHN, Museum national d'Histoire naturelle, Paris; RMNH, I ationaal I atuurhistorisch Museum (formerly Rijksmusellrn van Natullrlijke Historie), Leiden. Moitessieria nezi spec. novo (fig. 34) Material. - France, Pyrenees-Atlantiques, spring below the farms Hiqueres and Junqua, 1.35 km WSW. ofthe center of Rebenacq (UTM YNI8]; Boeters leg. 20.ix.2000 (MNHN holotype ex HOE 1483, shell; BOE 1483/2. shells) and 3/4.vd998 (BOE 1446/1, shell). Shell. - Shell cylindro-conicaL Spire with 6.25 convex whorls, separated by a deep suture. The first three whorls of about the same size; the following ones, up to the aper­ ture, gradually increasing in size. Rows of pits form a spiral sculpture (21 rows above the edge of the aperture). The last whorl ascends very slightly on the shell wall. The apertu­ rallip is 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. Aperture ovoid and slightly oblique. Viewed from the side, the edge of the aperture is curved like a question mark. Height and width of shell 2.35 and 0.8 mm, height and width of aperture 0.6 and 0.5 mm (holotype). Anatomy. - Unknown. Differentiating features. - J\!foilessieria nezi spec. novo occurs close to l\t{oitessien'a lesclte­ rae Boeters, 1981, in the west, and Moitessieria simoniana (Saint-Simon, 1848) in the east. The shell ofM. les-cheraediffers by a partially scalaroid last whorl and closely arranged spi­ ral ridges. (Closely arranged spiral ridges are also shown by two samples of Moilessieria spec. from the Pyrenees-Atlantiques, both collected by Bertrand, at Tardets in deposits of the Saison and at Aleay). As regards M. simaniona, Bodon & Ciust; (1991) have publis­ hed a biometric analysis of six shells of this species from deposits of the Garonne at Toulouse and found the ratios 3.3-3.6 for 'total heighLwidth of second to last whorl' and 1.4-1.5 for 'height oflast whorl;width ofsecond to last whorl'. For the holotype ofM. nezi spec. novo these ratios are 3.3 and 1.5. The data for J\!f. nezi spec. novo show that the size of the whorls scarcely increases before the fourth whorl. Further, according to photo­ graphs of four of the shells examined by Bodon & Ciusti (1991; 3, fig. lA-DJ, the height ofthe shell in M. simonliwa is only 1.55-1.85 mm and never reaches 2.35 mm.