Porosalvania, Gofas, 2007

Gofas, Serge, 2007, Rissoidae (Mollusca: Gastropoda) from northeast Atlantic seamounts, Journal of Natural History 41 (13 - 16), pp. 779-885 : 847-848

Genus Porosalvania n. gen.

Type species. Porosalvania solidula n. sp.

Diagnosis

Shell with a moderately high to quite high spire and a blunt apex, adults in size range 2– 4 mm. Protoconch of paucispiral type, a little more than 1.25 whorls, nearly smooth. Teleoconch of three to five whorls, quite solid, with sculpture of variably developed axial folds and spiral cords, usually not sharply defined, sometimes lacking. Teleoconch microsculpture visible only under high SEM magnification, consisting of minute pits, about 1 Mm in diameter and ca 5–10 Mm apart, usually distributed at random, sometimes loosely aligned parallel to growth lines or spirally. Outer lip orthocline or very slightly prosocline; thickened externally mostly in the adapical part, at some distance from the edge, then thinning out to a cutting edge; smooth inside.

Head-foot with cephalic tentacles slender and tapering, and relatively small eyes at the base of each tentacle. Snout somewhat tapering, bilobed anteriorly. Anterior pedal gland distinct in propodium. Metapodial tentacle forming an axial triangular flap and, laterally to it, two small and unequal rounded lobes. Right and left pallial tentacles present. Operculum thin, paucispiral, with eccentric nucleus.

Radula taenioglossate. Central teeth with a well-developed axial cusp flanked on each side by smaller denticles, a single pair of well-developed basal denticles, and moderately developed U-shaped projection. Lateral teeth elongate, terminating in a broad triangular cusp. Marginals elongate and sickle-shaped, denticulated on their distal part.

Remarks

A new genus Porosalvania is here installed to accommodate several of the rissoid species found on the Meteor group seamounts, which share among other shell characters a microsculpture of minute pits not aligned along spiral lines, an attenuated or very attenuated spiral macrosculpture, and an axial sculpture either absent or constituted of broad axial folds. Some of these species resemble several deep-water rissoids placed in Benthonellania Lozouet, 1990 by Bouchet and Warén (1993). However, the West African type species Benthonellania gofasi Lozouet, 1990 has strongly unequal pallial tentacles, a well-developed neck lobe, a cylindrical rather than bilobed snout, and a large and conspicuous metapodial gland ( Gofas 1999). All these features are very peculiar among the Rissoidae and were not found in Porosalvania solidula which could be observed alive. Characters of the head-foot and tentacle array in the latter resemble Manzonia , Gofasia , or some Alvania s.l., with small, symmetrical pallial tentacles, a small metapodial flap, and the anterior pedal gland more conspicuous than the posterior. The radula resembles that found in Manzonia , Gofasia , and in some species of Alvania s. l. (see Ponder 1985, and Figure 31 herein).

Whether the presence of the pitted microsculpture actually indicates a relationship with Gofasia and Manzonia must be considered with caution. A pitted microsculpture is also found in unrelated species of the subfamily Rissoininae (e.g. Figure 57 herein) and in the protoconch of the Barleeidae (see Gofas 1995). Nevertheless the congruence with the shape of the metapodial tentacle as a triangular flap, and the consistency with a distribution in the North Atlantic seamounts and in Macaronesia, suggest that there is really a relationship. A broader geographic scope is nevertheless needed to test this in the framework of a phylogenetic hypothesis.

Some of the species placed in Benthonellania by Bouchet and Warén (1993) may belong here. Benthonellania fayalensis was examined under SEM for microsculpture, but the shells were too corroded to ascertain whether the Porosalvania microsculpture was present.

Figures

Figure 31. Gofasia josephinae Bouchet and Warén, 1993. (A) Partial view of the radula of a specimen from Ampère seamount, DE95 (197–210 m); one of the outer marginals to the right is upturned and shows the denticles normally facing downwards; (B) detail of the central teeth showing paired basal denticles and U-shaped projection. Scale bars: 10 Mm.

Figure 57. Rissoina meteoris n. sp. (A) Holotype (sh.) from Meteor seamount, DW152 (470 m), actual size 8.25 mm; (B) protoconch of a paratype, same locality; (C) microsculpture of teleoconch whorl; (D, E) operculum of another paratype from Meteor seamount, DW136 (305 m), actual size 1.1 mm; (F) partial view of the radula (laterals and marginals missing on the right), showing faint cusps developed on the upper part of outer marginals, same specimen as (D). Scale bars: 100 Mm (B); 50 Mm (C); 10 Mm (F).