Talassia laevapex sp. nov.

urn:lsid:zoobank.org:act: DBCBECED-6660-4330-8074-1D5D4F524D1F

Figs 31–43

Etymology

The specific epithet refers to the smooth protoconch.

Type material

Holotype MAURITANIA – Tamxat Mounds • 1 shell (Figs 36–39); 17.5410° N, 16.6666° W; depth 486 m; 15 Nov. 2010; box core in coral rubble with silty mud; MSM16/3-GeoB14905; SMF358967.

Paratypes MAURITANIA – Tamxat Mounds • 2 shells (Figs 34–35, 40–43); same collection data as for holotype; SMF358968 • 13 shells; same collection data as for holotype; SMF358969 • 4 shells; 17.5427° N, 16.6634° W; depth 510 m; 15 Nov. 2010; box core in coral rubble with silty mud; MSM16/3-GeoB14904; SaM79757.

Other material examined

MAURITANIA • 1 shell; Arguin South 3 Canyon; 19.7378° N, 17.1459° W; depth 493 m; 7 Nov. 2010; bottom grab in silty mud; MSM16/3-GeoB14860; SaM79747 • 3 shells (Figs 31–33); Banda Mounds; 17.6794° N, 16.6684° W; depth 450 m; 8 Jan. 2007; box core in coral rubble with mud; POS346- GeoB11579; SaM79753 .

Description

Elevated shell with rounded whorls, fine irregular axial sculpture, flexuous lip and smooth, glossy translucent protoconch, cream white. Holotype dimensions: height 2.2 mm, width 1.1 mm, apical angle 34°.

PROTOCONCH. Elevated paucispiral shell with globular nucleus and 1¼ whorls (Figs 33, 35, 37); smooth, numerous shallow micro pits visible under high magnification; faint spiral lines below upper suture in last part whorl; lip straight yet oblique at 17° with spire axis (Fig. 35); width 0.35 mm.

TELEOCONCH. Elevated spire with 3 rounded whorls and deep suture (Figs 31–32, 34, 36, 40–41). Axial sculpture coarse with numerous irregularly spaced flexuous growth lines; opisthocline below upper suture. Many spiral lines composed of aligned raised dots and dashes (Figs 38–39, 42–43); fine on the first whorl, coarser and more irregular on subsequent whorls. Narrow, deep, elongated umbilicus at base body whorl partly covered by parietal lip (Figs 31–32, 36, 40–41).

APERTURE. Oval outline, flattened on parietal side; smooth inside (Figs 31–32, 36, 40). Parietal and columellar lip sharp; external lip not thickened, blunt, flexuous with notches above the periphery and at base (Fig. 41). Aperture height 0.9 mm.

VARIABILITY. The growth lines on teleoconch vary in roughness. Occasionally, umbilical slit is nearly closed. The observed range for apical angle is 34°–36°. No variability observed in adult height (2.2 mm).

Distribution

NE Atlantic Ocean, Mauritania, latitude 17.5°– 19.8° N, known depth range 450– 510 m.

Remarks

The radula and the soft parts of the new species are unknown. Only empty shells were found in or near coral debris with silty or muddy sand.

Differential diagnosis

All hitherto known NE Atlantic species have a protoconch sculpture with spiral lines composed of raised dots and dashes. Talassia dagueneti shows an axial sculpture of regular raised flexuous riblets on the teleoconch and finely aligned spirals of raised beads on the protoconch (Warén & Bouchet, 1988; Fig. 5) whereas T. laevapex sp. nov. has finer irregular growth lines (Figs 38–39, 42–43) and a smooth protoconch (Figs 33, 35, 37). Talassia tenuisculpta has similar fine growth lines and spiral lines as the new species but its protoconch has a clear spiral sculpture of raised dotted lines (de Folin 1873; Warén & Bouchet 1988; Figs 9–10). Talassia coriacea is larger and has a large pyriform aperture (Warén & Bouchet 1988; Fig. 1). Talassia philippeswinneni has a protoconch with shallow micro-pits and its teleoconch has spiral cords (Rolán & Swinnen 2016: 120–124, figs 1–4). Talassia coriacea and T. philippeswinneni live on the shelf whereas the new species is found on the upper bathyal slope.