Alvania microstriata Hoenselaar and Goud, 1998

Gofas, Serge, 2007, Rissoidae (Mollusca: Gastropoda) from northeast Atlantic seamounts, Journal of Natural History 41 (13 - 16), pp. 779-885 : 793-795

Alvania microstriata Hoenselaar and Goud, 1998

( Figure 7A–D )

Alvania microstriata Hoenselaar and Goud 1998, p 91 –92.

Type material

Holotype (1.70× 1.08 mm) in Nationaal Natuurhistorisch Museum, Leiden ( NNM 57684), eight paratypes ( NNM 57685) and seven paratypes (private collection of H. J. Hoenselaar) from the type locality.

Type locality

Madeira (32 ° 079N, 16 ° 519W, 360 m).

Material examined Seine— Seamount 1 sta. DE82, 34 sh. (jv. 0.98×0.74 to 1.80× 1.26 mm); sta. DE84, 29 sh.

(jv. 0.96×0.72 to 1.75× 1.08 mm, SEM); Poseidon 309 sta. BG7, 20 sh. (1.90×1.20 to 2.32× 1.25 mm).

Description

Shell with a moderately high spire and a blunt apex, moderately solid, adults up to 2.3× 1.2 mm. Protoconch of 1.25 convex whorls; surface of larval whorls covered by minute granules arranged in five to six blurry spiral bands. Teleoconch of 2.5–3.0 whorls, with a sculpture of axial ribs, minute spiral threads and very faint spiral cords more developed on the abapical area. Ribs ca 20–25 on the penultimate whorl, thin, somewhat flexuous, with adapical termination bulging along the suture, and very gradually fading out on the abapical part of the body whorl. Spiral cords very low and faint, as broad as the interspaces, developed mainly on the periumbilical area of the body whorl, hardly visible on adapical part of body whorl and on spire whorls; a shallow subsutural furrow demarcating the bulging termination of the axial ribs along the suture. Spiral threads very minute but well marked, sometimes overrunning the axial ribs, usually abutting on their crests, separated by interspaces about six to eight times as broad, less distinct on the abapical area. Outer lip orthocline or slightly opisthocline with a flexuous profile, with a thin edge not thickened externally even on large, apparently full-grown specimens, smooth and not thickened inside. Inner lip thin, bordering a narrow umbilicus. Shell colour entirely white, translucent.

Remarks

This species shares with A. adinogramma several characters such as the microsculpture of fine threads and the bands of granules on the protoconch, which indicate that they belong to the same species group. It differs in having the ribs bulging adapically along the suture, with a distinct subsutural furrow instead of an inconspicuous subsutural depression, and in consistently lacking the thickening on the external part of the outer lip.

It is noteworthy that this species was collected only on Seine seamount, situated nearest to the type locality, Madeira .

Figures

Figure 7. (A–D) Alvania microstriata Hoenselaar and Goud, 1998. (A, B) Shells from Seine seamount, DE84 (450–455 m), actual size 1.57 and 1.54 mm; (C) protoconch, same shell as B; (D) microsculpture, same shell as A. (E–H) Alvania seinensis n. sp. (E, F) Holotype (sh.) from Seine seamount, DE72 (165 m), actual size 1.40 mm; (G) protoconch of the holotype; (H) microsculpture. Scale bars: 100 Mm (C, G); 50 Mm (D, H).