Mercuria meridionalis ( Risso, 1826 )

Mercuria meridionalis ( Risso, 1826) View in CoL

( Figs 9 View FIG D-H, 10, 11A-C; Table 7)

Bithynia meridionalis Risso, 1826: 100 View in CoL , pl. 3, fig. 28.

Mercuria confusa View in CoL – Boeters 1971: 175 [partim].

Mercuria similis View in CoL – Giusti 1979: 7, figs 4c1-4c4. Erroneous determination.

ORIGINAL INDICATION OF THE TYPE LOCALITY. — “[…] de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes Maritimes” (title of the book) and “Fossés aquatiques. App.[arition] Printemps”.

MATERIAL EXAMINED. — France. (i)-(iii) Bouches-du-Rhône , Région Étang de Berre : (i) between Port-de-Beau-Rivage and Mauran, Merveille, “ruisselets se jettant dans l’étang” [UTM FJ62] ( BOE 0315 /shells), leg. Berner 25.X.1967; (ii) outflow of a spring below road from La Fare-les-Oliviers to Saint-Chamas between Mas Suriane and Mas Meyroux [UTM FJ62] ( BOE 3205 ex 0262), leg. Boeters 28.IX.1969; (iii) Source-du-Canet South of road from La Fare-les-Oliviers to Saint-Chamas [UTM FJ62] ( BOE 0263 ), leg. Boeters 28.IX.1969. — (iv) Var, Draguignan, Foux-de-Draguignan [UTM KP92] ( BOE 0302 ex Meier-Brook), leg. Berner V.1930; ( BOE 2151 /animals and 2414/shells ex 0261) , leg. Boeters 27.IX.1969. — (v)-(viii) Alpes-Maritimes: (v) Nice? [UTM LP53] ( MNHN-RIO / 4 syntypes of Bithynia meridionalis Risso 1826 ); (vi) “marais des Environs de Nice ” [UTM LP53] ( MNHN/204 About MNHN ), leg. Risso; (vii) “Fossés du Var près Nice ” [UTM LP53] ( MNHN); (viii) Nice [UTM LP53] ( MNHN/22 About MNHN ex Caziot; MNHN-LOC/5 ; MNHN-PAS/4 ex de Folin [11]; SMF 119945 About SMF /20 and 266447/3) .

TYPES. — France, Alpes-Maritimes , Nice? MNHN-RIO/4 shells and 4 preparations of rehydrated soft parts; original historical label: “ Bythinia [sic] Meridionalis Risso ”. Lectotype MNHN- IM-2000-32539 [ H: 4.35 mm, D: 3.05 mm, 5.0 whorls] and 3 paralectotypes MNHN-IM-2000-32540 preselected by Giusti in 1998 (here designated).

IDENTIFICATION. — In the Mediterranean coastal area two species of Mercuria can be distinguished, M. similis with a whip-like penis and the species in question with a wedge-like penis. From the west to the East, M. similis is distributed in the departments Pyrénées- Orientales, Aude, Hérault, Gard and Bouches-du-Rhône, but does not reach the Étang-de-Berre, whereas the species in question lives farther East, nowadays in the department Bouches-du-Rhône at the shore of the Étang-de-Berre, and at least in the department Var. From two paralectotypes of Bithynia meridionalis from presumably Nice, male soft parts have been isolated by Giusti, one of them in such a good condition that the wedge-like penis can be seen (see Fig. 12).

DISTRIBUTION AND ECOLOGY. — In the department Alpes-Maritimes likely to be extinct. In the department Var collected live at one single locality (Foux-de-Draguignan) and in the department Bouches-du- Rhône live at two localities (shore of Étang-de-Berre).

In the department Alpes-Maritimes, fossés at the destroyed mouth of river Var, accompanied by Valvata sp. , Bithynia sp. and Belgrandia varica (J. Paget, 1854) . A portable case of a Trichoptera-larva with several specimens of Mercuria meridionalis glued living on it, with Belgrandia varica and a taxonomically problematic Valvata sp. , collected by G. de Mortillet in 1851 (MNHN) shows the former richness of those lost biotopes ( Fig. 9 View FIG G-H).

Caziot (1910: 471) described the occurrence of Mercuria in the destroyed “Fossés aquatiques” at Nice, as follows: “Espèce très commune dans tous les fossés de la rive gauche du Var, près de son embouchure”. These “fossés” were the “fossés de Californie”, ditches or side-brooks with runnig water, indicated by by Caziot (1910: 474, 476) also for “ Valvata piscinalis ” (O. F. Müller, 1774) , “ Valvata depressa ” C. Pfeiffer, 1821 and “ Neritina fluviatilis niciensis Caziot, 1910 ”.

In the departments Var and Bouches-du-Rhône in springs and their outflow, in the Foux-de-Draguignan sometimes amphibious; temperature 21° C (one single determination; BOE 0262).

In the department Var sympatric with Theodoxus sp. , Corrosella astierii ( Dupuy, 1851) (the generic allocation follows Delicado et al. 2015: 414) and Belgrandia marginata (Michaud, 1831) (all BOE 2151).

In the department Bouches-du-Rhône occasionally sympatric with Theodoxus sp. (BOE 0263), Potamopyrgus antipodarum (Gray, 1843) (BOE 0263) and Pseudamnicola ( P.) chamasensis Boeters, 2000 (BOE 0262). For further information on former or recent biotopes in Bouches-du-Rhône and for accompanying molluscs see Coutagne (1881: 23).

DESCRIPTION

Shell

Conical with pointed apex and straight sidelines (as for M. similis ); last whorl about 49-53% of total height of shell; umbilicated; of transparent milky colour; 4.67 [4.5-5.0] (n = 3) whorls, swollen and very convex, respectively, separated by a deep suture; last whorl towards aperture neither ascending nor descending; 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 reflexed, columellar edge slightly thickened.

Measurements

See Table 7.

Operculum

Colour of horn up to weak chestnut-reddish.

Animal

External characters. Pallial tentacle present. Except for a weak band on the snout, head and ommatophores pigmentless; mantle with the exception of its skirt, and visceral hump not brownish but blackish. Ctenidium with 22-24 gill filaments ( Boeters 1971: 178 and fig. 6, ♂).

Male copulatory organ. Penis short and wedge-like, not extending beyond its appendix, both of about the same length; socket of the copulatory organ in its inactive state with transversal folds, immediately in front of the appendix

Fig. 10 View FIG . — Continuation. Mercuria meridionalis ( Risso, 1826) : F, G, ♂, France, Bouches-du-Rhône, between La-Fare-les Oliviers and Saint-Chamas, Sourcedu-Canet ( BOE 0263 ) ; F, shell with partially retracted animal; G, head with copulatory organ exposed through slit in mantle; H -L, France, Var , Draguignan, La Foux-de-Draguignan ( BOE 2151 ex 0261) ; H, ♂: shell partially broken away and mantle slitted to expose copulatory organ ; I -J, ♂: copulatory organ (dorsal and ventral view); K -L, ♀; K, shell with partially retracted animal; L, body lumen opened to show renal oviductus with receptaculum seminis (rs1) and bursa copulatrix surrounded by intestinal section. Abbreviations: bc, bursa copulatrix; in, intestine; op, operculum; pe, penis; pl, pedal lobe; ro, renal oviductus; rs1, single receptaculum seminis. Scale bars: 1 mm.

with a dorsal thickening; appendix like a disk with a lateral bulge; area of the furcation of penis and appendix blackish ( Fig. 11D View FIG ; Boeters 1971: 178, fig. 7; Giusti 1979: 7, figs 4c2 and 4c4).

Female genital tract. Bursa copulatrix and one receptaculum seminis ( Boeters 1971: 178, fig. 8; Giusti 1979: 7, fig. 4c3).

DIFFERENTIATING FEATURES

Versus M. similis: Penis does not extend beyond appendix as in M. similis . Mercuria meridionalis prefers running waters whereas M. similis is also known from stagnant water bodies.

REMARKS

Draguignan is already of record in the Collection Dupuy (Toulouse).

Bérenguier (1882: 42-44) gave a detailed description of the Foux-de-Draguignan and listed Amnicola compacta Paladilhe, 1869 and Amnicola anatina as from Trans[-en-Provence]. One should know that the Foux is situated South-East of Draguignan immediately in front of Trans-en-Provence.

A photograph of a shell of this species from Le Muy about 8 km far from Draguignan can be found in Germain (1931: pl. 17, fig. 496). We have not checked whether M. meridionalis still lives there.

For records of Mercuria from the Alpes-Maritimes which we could not definitely attribute to M. meridionalis see discussion under Bithinia [sic] moutonii Dupuy, 1849 , first paragraph of the chapter “Taxa uncertain”.