Mercuria bayonnensis ( Locard, 1894 )

Boeters, Hans D. & Falkner, Gerhard, 2017, The genus Mercuria Boeters, 1971 in France (Gastropoda: Caenogastropoda: Hydrobiidae). West-European Hydrobiidae, Part 13, Zoosystema 39 (2), pp. 227-261 : 230-232

Mercuria bayonnensis ( Locard, 1894)

( Figs 2 A-E, 3A-E; Table 1)

Bythinia [sic] bayonnensis Locard, 1894: 89 , 114, pl. 6, fig. 18.

ORIGINAL INDICATION OF THE TYPE LOCALITY. — “Lac de la Négresse près Bayonne (Basses-Pyrénées)”.

MATERIAL EXAMINED. — France. (i)-(v) Pyrénées-Atlantiques, (i) Bidart, brook Ouhabia and Herigoin, respectively, depth about 1 m and diameter about 2 m, upstream of the mill south of Mas Bassillour about 3 km East of the coast [distance to (v) 2.5 km; UTM XP11] ( BOE 2250 animals and 3185 shells ex 0364), leg. Boeters 22.IX.1970; (ii) Biarritz, “source dans la falaise” [UTM XP11] ( MNHN), leg. Letellier 1949; (iii) Bayonne, district Saint-Esprit [UTM XP11] (2 samples MNHN); (iv) La Nive close to Bayonne [UTM XP11] ( MHNG-BGT 5483/4 shells with dried soft parts; Bourguignat’s label: “De la Nive, près de Bayonne.- (Bass.-Pyr.)”); (v) Bayonne, Lac de la Négresse [Lac Mouriscot; UTM XP11] ( MHNG-BGT 4943/ 3 syntypes). — Landes, (vi) Le Teich [UTM XQ54] ( MNHN-PAS /3 ex de Folin [8], de Folin’s label: “ Amnicola similis var. Baudoniana Gassies ex auctore ipso Le Teich Gironde”). — Gironde, (vii) La Tresne [Latresne; district of Bordeaux right from the Garonne] [UTM XQ96] ( MNHN-PAS /4 ex de Folin [4]).

Spain. Vizcaya, Bilbao [UTM WN08] ( NMW 92605/3, sub anatina ), leg. Willkomm 1850.

LECTOTYPE. — MHNG-BGT 4943 a (ex 4943/3); H: 3.55 mm, D: 2.47 mm, 4.8 whorls (here designated).

DISTRIBUTION AND ECOLOGY. — Neighbouring Spain, Pyrénées- Atlantiques, Landes and Gironde. Mercuria bayonnensis lives in coastal running waters up to springs; during the last decades it could still be collected alive in a brook at Bidart and in a coastal spring at Biarritz. At Bidart in the brook Ouhabia (Herigoin, respectively) collected with shells of Alzoniella haicabia Boeters, 2000 ; in any case sympatric with Theodoxus sp. (cf. already Folin & Bérillon 1877: 453 [separatum: 31]) and Potamopyrgus antipodarum (Gray, 1843) . As regards reports of M. bayonnensis from the Lac de la Négresse, Le Teich and the district Latresne in Bordeaux, the exact biotopes are unclear.

DESCRIPTION

Shell

Conical, with pointed apex and straight sidelines; last whorl about 46-47% of total height of shell; umbilicated; of transparent milky colour; 4.25-4.50 whorls, swollen and very convex, respectively, separated by a deep suture; last whorl before the aperture neither ascending nor descending on shell wall; aperture obliquely broad ovate, a little narrowed above; peristome continuous, usually touching the shell wall over a short distance; outer margin simple, basal margin and columellar edge faintly broadened, palatal, basal and columellar margin at best slightly thickened.

Measurements

See Table 1.

Operculum

Pale reddish.

Animal

External characters. Pallial tentacle not seen. Pigmented black on both flanks of the head, on both flanks of the foot, on its sole and on the skirt of the mantle. Ctenidium with 24 gill filaments (1 ♂).

Male copulatory organ. Penis with appendix, appendix with a weak bulge; black pigment along the vas deferens and towards the appendix.

Female genital tract. Bursa copulatrix and one receptaculum seminis.

DIFFERENTIATING FEATURES

The shape of the shell of M. bayonnensis varies from less elongated to rather globular which allows a separation from M. baudoniana ( Gassies, 1859) , since the shell of M. baudoniana is even more elongated than that of the most elongated specimens of M. bayonnensis . Further, a striking feature of diffentiation can be seen in the fact that M. bayonnensis can be accompanied by Theodoxus sp. , whereas M. baudoniana is accompanied by Anisus spirorbis (Linnaeus, 1758) and Omphiscola glabra (O.F. Müller, 1774) which tolerate falling of water bodies to dryness which does not apply to Theodoxus sp. In Mercuria bayonnensis the last two whorls are more or less smooth (as from the Nive and at Bidart and Biarritz), except for some irregularities of growth whereas in both subspecies of M. sarahae at least these whorls are striatulate (as at Thouaré-sur-Loire and Locmaria). Further, in males of M. sarahae the appendix of the copulatory organ shows a comparatively pronounced lateral bulge (compare 2B-D with Figures 4B, C and 5 B-D).

REMARKS

Locard’s description (1894) of his Bythinia bayonnensis was based on a sample in Bourguignat’s collection. This type series comprises three specimens with a reddish paucispiral operculum. Thus, Locard was in error when stating: “Opercule assez enfoncé dans l’intérieur de l’overture, orné de stries concentriques peu fortes, presque de même teinte que le reste du test.”

As regards the syntypes, one of them reminds with its elongated shell of M. baudoniana as described by Paladilhe in 1869 as Amnicola lanceolata from Saint-Jean-de-Luz about 10 km distant from the Lac de la Négresse, the type locality of M. bayonnensis . The other two less elongated syntypes (lectotype and one paralectotype) allow us, however, to acknowledge Bythinia bayonnensis as differentiated on species level from M. baudoniana and to attribute all other records of Mercuria from the Pyrénées-Atlantiques to M. bayonnensis . Nevertheless, it is open to question whether M. bayonnensis in our present understanding covers more than one species, since it has been reported from quite different biotopes such as springs, a small river ( BOE 0364), and also the river Nive. Unfortunately, topotypes of Bythinia [sic] bayonnensis have not yet been collected and Locard’s brief indication of the type locality as “Lac de la Négresse” leaves it open whether the three syntypes have been collected in a spring bordering the lake (such as Alzoniella perrisii [ Dupuy, 1851]), the lake itself, a tributary or an outflow.

In view of the fact that the syntypes in comparison to all other examined samples are conchologically not very homogeneous, further investigations are necessary to clarify whether these peculiarities reflect a great variability of M. bayonnensis or whether the syntypes must be attributed to more than one species.

The distribution area of M. bayonnensis extends at least up to Bordeaux. Nevertheless, a sample with shells of Mercuria from Plassac at the Gironde [UTM XQ89]( MNHN-PAS /4 ex de Folin) could not be attributed to this species with certainty since the whorls are somewhat striatulate as in M. sarahae .

The occurrence at Bayonne, Saint-Pierre-d’Irube, Bramepan [UTM XP21] (Folin & Bérillon 1877: 453 [separatum: 31]) could not be confirmed by Boeters on 28.IX.1968 (see Boeters 2000: 160; the area has meanwhile been destroyed [Gittenberger verbally]).

Figures

FIG. 2. — Mercuria bayonnensis (Locard,1894): France, Pyrénées-Atlantiques, Bidart, farm Bassillour,river Ouhabia: Herigoin (BOE 2250 ex 0364); A, shell; B, ♂: head and foot with copulatory organ exposed through slit in mantle; C, D, ♂ head with copulatory organ, ventral (C) and dorsal view (D); E, ♀, body lumen opened to show renal oviductus with receptaculum seminis (rs1) and bursa copulatrix surrounded by intestinal section (partially removed). Abbreviations:bc, bursa copulatrix; in, intestine; op, operculum; pe, penis; ro, renal oviductus; rs1, single receptaculum seminis; vd, vas deferens. Scale bar: 1 mm.

FIG. 4. — Mercuria sarahae sarahae (Paladilhe,1869),France,Loire-Inférieure,Thouaré-sur-Loire,river Loire (BOE 1478 ex SMNS-FAL);A-C, ♂; A, shell; B, C, head and foot with copulatory organ exposed through slit in mantle, ventral (B) and dorsal view (C); D, E (♀); D, shell; E, body lumen opened to show renal oviductus with receptaculum seminis (rs1) and bursa copulatrix surrounded by intestinal section (partially removed). Abbreviations: bc, bursa copulatrix; fp, fecal pellet; in, intestine; op, operculum; pe, penis; ro, renal oviductus; rs1, single receptaculum seminis. Scale bar: 1 mm.

FIG. 5. — Mercuria sarahae vindilica (Paladilhe,1870), France, Morbihan, Locmaria [Belle-Île-en-Mer] (BOE 1448); A, B, ♂; A, shell; B, head and foot with copulatory organ exposed through slit in mantle; C, D, ♂: head with copulatory organ, ventral (C) and dorsal view (D); E, F (♀); E, shell; F, body lumen opened to show renal oviductus with receptaculum seminis (rs1) and bursa copulatrix surrounded by intestinal section (partially removed). Abbreviations: bc, bursa copulatrix; in, intestine; op, operculum; pe, penis; ro, renal oviductus; rs1, single receptaculum seminis. Scale bar: 1 mm.