Alvania adiaphoros Bouchet and Warén, 1993

Gofas, Serge, 2007, Rissoidae (Mollusca: Gastropoda) from northeast Atlantic seamounts, Journal of Natural History 41 (13 - 16), pp. 779-885 : 806-809

Alvania adiaphoros Bouchet and Warén, 1993

( Figures 13–15 , 16H )

Alvania adiaphoros Bouchet and Warén 1993, p 652 , 666.

Type material

Holotype and 15 paratypes from ‘ Monaco’ sta. 2214 (coll. H. Fischer), in MNHN.

Type locality

Off Flores, Azores (39 ° 269N, 31 ° 229W, 650–914 m).

Material examined

Meteor— Seamount 2 sta. DW143, 8 sh. (1.70×1.24 to 1.93× 1.30 mm); DW152, 8 spm. (1.76×1.19 to 1.96× 1.34 mm, drawing SM 169 1.82× 1.20 mm) and 233 sh. (1.72×11.4 to 2.12× 1.42 mm). Hyères— Seamount 2 sta. DW182, 15 spm. (1.74×1.14 to 2.04× 1.32 mm) and ca 1000 sh. (1.70×1.20 to 2.10× 1.42 mm). Irving— Seamount 2 sta. DW208, 1 sh. (1.72× 1.12 mm); DW209, 1 sh. (1.66× 1.12 mm). Atlantis— Seamount 2 sta. DW255, 3 spm. (1.66×1.02 to 1.74× 1.18 mm) and 760 sh. (1.54×1.06 to 2.00× 1.32 mm); DW258, 7 spm. (1.82×0.26 to 2.08× 1.35 mm) and 530 sh. (1.62×1.10 to 2.00× 1.24 mm); TS270, 7 spm (drawing SM 201; 1.56×1.10 to 1.74× 1.24 mm) and 36 sh. (1.64×1.10 to 1.98× 1.30 mm); DW274, 370 sh. (1.46×1.00 to 1.88× 1.26 mm).

Description

Shell with a moderately high spire, quite solid, up to 2.1× 1.4 mm. Protoconch of 1.75 convex whorls; surface of larval whorls covered by minute granules arranged in broad spiral bands.

Teleoconch of 2.75–3 whorls (Meteor), 3–3.25 whorls (Atlantis), with a sculpture of elevated, widely separated axial ribs, minute spiral threads and distinct spiral cords restricted to the abapical area. Ribs ca 18–20 (Meteor) to 25–30 (Atlantis) on the penultimate whorl, with adapical termination hardly prominent along the suture, fading out at the periphery and not extending on the abapical part of the body whorl; ribs becoming attenuated on the body whorl where approaching the outer lip. A distinct spiral cord overhanging adapically the suture, continued on the body whorl; the periumbilical area of the body whorl with some four to five (Meteor, Hyères) or six to seven (Atlantis) additional cords, narrower than the interspaces, decreasing in size towards the umbilical chink. Spiral threads well expressed on the first teleoconch whorl, then attenuated or disappearing on the later whorls, unequal in size and spacing, overrunning the axial ribs, more conspicuous adapically along the suture. Outer lip orthocline, thickened externally mostly in the adapical part, thickened externally at a distance of the edge by a broad rim, then thinning out to a cutting edge; smooth inside. Inner lip thin, bordering a small umbilical chink. Shell colour entirely white, translucent. Operculum thin, paucispiral, with eccentric nucleus.

Cephalic tentacles cylindrical, with rounded tips. Eyes embedded in a slight swelling at the base of each tentacle. Snout somewhat tapering, truncated and bilobed anteriorly, with tiny bright yellow jaws and large bright yellow buccal mass visible by transparency. Large bright yellow granular masses behind each eye. Dorsal rear part of head with a V-shaped black mark (Atlantis only). Sole of foot colourless (Meteor) or tinged with longitudinal yellow bars (Atlantis), with pedal glands inconspicuous. Metapodial tentacle trifurcate, short (Meteor) or rather large (Atlantis). Right and left pallial tentacles moderately small. Visceral mass visible by transparency in the spire whorls, brownish with very small black granules.

Remarks

The above description is based on specimens from the seamounts, where the species is common. The holotype collected off the Azores has a quite faint axial sculpture but another shell from the type locality illustrated by Bouchet and Warén (1993, Figure 1487) resembles the dominant morphology found on Atlantis seamount .

Specimens from Meteor and Hyères differ from those on Atlantis in having a more solid shell with fewer ribs, and by details in the colour pattern of the head-foot. The species was only found as two shells on Irving ( Figure 16H ), and those show some features which are transitional to the Alvania funiculata n. sp. found in deeper water on Cruiser.

Alvania adiaphoros somewhat resembles the mainland species A. electa (Monterosato, 1874) in general shape and in having a strong suprasutural cord separated from the suture by a channelled interspace. It differs in lacking spirals in the adapical part of the whorls, in a lesser extension of the ribs towards the abapical part, and in being less umbilicate. The protoconch is also different, the granules tending to form definite spiral threads in A. electa .

Figures

Figure 13. Alvania adiaphoros Bouchet and Warén, 1993. (A) Shell from Meteor seamount, DW152 (470 m), actual size 1.86 mm; (B) protoconch, same locality; (C, D) shells from Hyères seamount, DW182 (480 m), actual sizes 1.94 and 1.96 mm; (E) protoconch, same shell as (D); (F) shell from Atlantis seamount, DW255 (340 m), actual size 1.86 mm; (G) protoconch, same shell. Scale bars: 100 Mm.

Figure 14. Alvania adiaphoros Bouchet and Warén, 1993. (A) Living specimen from Meteor seamount, DW152 (470 m), actual size 1.82 mm; (B) detail of head and propodium; (C) detail of opercular lobes and metapodium.

Figure 15. Alvania adiaphoros Bouchet and Warén, 1993. (A) Living specimen from Atlantis seamount, TS270 (330 m), actual size 1.74 mm; (B) detail of head and propodium; (C) detail of opercular lobes and metapodium.

Figure 16. (A) Alvania funiculata n. sp. Holotype (sh.) from Hyères seamount, DW203 (845 m), actual size 1.84 mm; (B) paratype (spm.), same locality, actual size 1.76 mm; (C) protoconch of the holotype; (D–F) shells from Cruiser seamount, DW237 (670 m), actual sizes 1.60, 1.70, and 1.60 mm; (G) protoconch, same as (F); (H) shell from Irving seamount, DW208 (790m) attributed to A. adiaphoros, actual size 1.70 mm. Scale bars: 100 Mm.