Talassia mexicana Hoffman & Freiwald 2022, sp. nov.

Talassia mexicana sp. nov.

urn:lsid:zoobank.org:act: E2C0E1CB-44AB-4CF4-A2ED-0085E043B89D

Figs 22–30

Etymology

The specific epithet refers to the distribution area, the Gulf of Mexico.

Material examined

Holotype MEXICO – off Yucatan, Campeche Slope • 1 shell (Figs 25–28); 23.4907° N, 87.1703° W; depth 566 m; 22 Mar. 2012; box core in coral rubble with calcareous mud; MSM20/4-GeoB16310; SMF358964.

Paratypes MEXICO – off Yucatan, Campeche Slope • 2 shells (Figs 22–24, 29–30); same collection data as for holotype; SMF3658965 • 7 shells; same collection data as for holotype; SMF358966.

Other material examined

MEXICO – off Yucatan, Campeche Slope • 22 shells; 23.8335° N, 87.1338° W; depth 640 m; 24 Mar. 2012; box core in coral rubble with calcareous mud; MSM20/4-GeoB16321; SaM83497.

USA – off SW Florida • 2 shells; 26.3370° N, 84.7598° W; depth 507 m; 27 Mar. 2012; box core in coral rubble with mud; MSM20/4-GeoB16337; SaM83194.

Description

Elevated shell with rounded whorls, flexuous axial ribs and fine spiral cordlets, flexuous lip and smooth, glossy protoconch, cream white. Holotype dimensions: height 4.1 mm, width 1.5 mm, apical angle 29°.

PROTOCONCH. Elevated paucispiral shell with globular nucleus and 1 ½ whorls (Figs 23–24, 26); smooth; lip flexuous, ophistocline on exposed area (Fig. 26); width 0.44 mm.

TELEOCONCH. Elevated spire with 5 rounded whorls with impressed suture (Fig. 25). Axial sculpture sharp flexuous ribs, approximately 18 per whorl on first 3 whorls; more irregular on body whorl. Microsculpture composed of aligned raised beads on first whorl (Fig. 27); coarser and more irregular on subsequent whorls (Fig. 28). Narrow, deep, elongated umbilicus at base body whorl partly covered by parietal lip (Figs 22, 25, 29–30).

APERTURE. Oval outline, flattened on parietal side; smooth inside (Figs 22, 25, 30). Parietal lip very thin, occasionally strongly reclined; columellar lip sharp; external lip not thickened, blunt, flexuous with notches below suture and at base (Fig. 29). Aperture height 1.4 mm in holotype.

VARIABILITY. Number and strength of axial riblets and micro-sculpture is variable. Spiral cordlets sometimes faint or irregular, more frequently distinct and regular. Apical angle 29°–30°. Known range of adult height 3.6–4.1 mm.

Distribution

Gulf of Mexico, off Yucatan and off western Florida, known depth range 507– 640 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

This species is the largest in Talassia; adult size is more than 3.5 mm whereas all other species measure less than 3 mm. The protoconch is also largest with a diameter exceeding 0.4 mm; all other known congeneric species have a smaller protoconch diameter. Talassia sandersoni from off the SE USA is smaller, has 9–10 spiral lines on the last ¼ whorl of the protoconch and the sculpture of the teleoconch lacks the axial ribs (Warén & Bouchet 1988: fig. 48; Figs 12, 16–17, 19). The protoconch of the new species is smooth (Figs 23–24, 26) and the teleoconch has sharp axial ribs (Figs 22, 25, 29–30). All hitherto known NE Atlantic species (Talassia coriacea, T. tenuisculpta, T. dagueneti) have a protoconch with spiral cordlets composed of raised dots and dashes; the new species has a smooth protoconch. Talassia dagueneti shows more flexuous riblets on the teleoconch (Warén & Bouchet 1988; Figs 4, 6). Talassia coriacea has a large pyriform aperture (Warén & Bouchet 1988; Fig. 1).