Parviturbo cicatricosus Herbert 2024, sp. nov.

Parviturbo cicatricosus sp. nov.

urn:lsid:zoobank.org:act: 9128AAA8-ECB0-4E9B-8BD1-C6579D59DB86

Figs 32B, 34

Diagnosis

Shell small, turbiniform, diameter up to 2.8 mm, whorls rounded; umbilicus moderately wide; sculpture of strong angular spiral cords (± 11 on final whorl) and distinct axial varices or growth scars; growth scars becoming more numerous in final quarter whorl; subperipheral cord level with insertion of outer lip; outer lip notched at ends of spiral cords; uniformly milky-white.

Etymology

From the Latin “ cicatrix ” – “a scar”, “ cicatricosus ” – “full of scars”; in reference to the frequent axial varices and growth flaws.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn DW4879; 33°17′ S, 43°52′ E; depth 288–300 m; 1 May 2017; MNHN-IM-2000-35710.

Paratypes

WALTERS SHOAL – slopes • 1 empty shell; same collection data as for holotype; MNHN- IM-2000-35711 • 1 empty shell; stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN-IM-2000-35712 • 1 empty shell; stn DW4893; 33°16′ S, 43°58′ E; depth 623–629 m; 4 May 2017; MNHN-IM-2000-35713 • 1 empty shell; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN-IM-2000-35714.

Other material

WALTERS SHOAL – slopes • 2 empty shells; stn DW4880; 33°17′ S, 43°51′ E; depth 275–318 m; 1 May 2017; MNHN • 2 empty shells; stn DW4885; 33°17′ S, 43°55′ E; depth 272–380 m; 3 May 2017; MNHN • 1 empty shell; stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN.

Description

SHELL. Small (diameter up to 2.8 mm), turbiniform, wider than high, with rounded whorls and indented suture; periphery evenly rounded, close to mid-whorl; base rounded, with moderately wide umbilicus; teleoconch of up to 2.25 whorls. First teleoconch whorl initially with 3 spiral lirae and strong axial varix at about 0.25 whorls (Fig. 32B); lirae strengthen with growth to form angular cords; further axial varices or scars occur, often at intervals of approx. 0.25 whorls, becoming more numerous in final quarter of last whorl (Fig. 34C); additional cord arises below adapical suture during second whorl, and a fifth emerges from abapical suture just prior to aperture, at whorl periphery; intervals between spiral cords with weak, close-set axial threads; base similarly sculptured with six cords, subperipheral one level with insertion of outer lip; umbilicus of moderate width, its margin evenly rounded, but narrowing rapidly and with steep sides after innermost basal cord. Aperture subcircular; peristome complete, somewhat flattened in parietal region; columella concave, at most slightly reflected; outer lip notched at ends of spiral cords; interior lacking conspicuous nacre.

PROTOCONCH (Fig. 32B). Glassy with faint corneous tinge; diameter ± 350 μm, ca 1.25 whorls, apical bulb rounded; sculptured with distinct subspiral threads; terminal lip straight, slightly flaring.

COLOUR. Apical whorls translucent, becoming less so with growth; last adult whorl uniformly milky-white.

DIMENSIONS. Holotype, height 2.2 mm, diameter 2.7 mm; largest specimen, height 2.4 mm, diameter 2.8 mm.

OPERCULUM, RADULA AND EXTERNAL ANATOMY. Unknown.

Distribution

Known only from the slopes of Walters Shoal, at depths of 300–623 m; dredged on substrata of coarse sand with octocorals and solitary corals; living specimens unknown.

Remarks

Herbert (2015) referred three South African species to Parviturbo and two of these somewhat resemble Parviturbo cicatricosus sp. nov., namely P. agulhasensis (Thiele, 1925) and P. alfredensis (Bartsch, 1915), but both have fewer spiral cords than P. cicatricosus and are respectively smaller (diameter 1.8 mm) and larger (diameter 4.8 mm) than P. cicatricosus. The third species, P. sola (Barnard, 1963), has a much stronger axial sculpture.

In their global revision the genus, Rubio et al. (2015) recorded no species of Parviturbo from the tropical Indian Ocean, but described four new species from the tropical south-west Pacific. Of these, P. pombali Rubio, Rolán & Fernández-Garcés, 2015 from Vanuatu is perhaps the most similar to P. cicatricosus sp. nov., but P. pombali is smaller (diameter 1.08 mm), and has fewer spiral cords with stronger axial sculpture in their intervals. With respect to their sharp spiral cords and distinct protoconch sculpture, species of the Parviturbo rehderi Pilsbry & McGinty, 1945 group from the Caribbean also somewhat resemble P. cicatricosus, but these too are smaller and have fewer spiral cords. None of the described species of Parviturbo has the distinctive growth scars exhibited by P. cicatricosus.