Gibbula ’ roseosticta, Herbert, 2024

Herbert, David G., 2024, The Vetigastropoda (Mollusca) of Walters Shoal, with descriptions of two new genera and thirty new species, European Journal of Taxonomy 923, pp. 1-119 : 94-96

‘ Gibbula ’ roseosticta sp. nov.

urn:lsid:zoobank.org:act:CE42EB1E-A3B2-4E3A-A4BE-134C435E2E51

Fig. 37

Diagnosis

Shell trochoid-turbiniform, diameter up to 3.7 mm, height ≈ diameter; spire conical with angular periphery; base narrowly umbilicate; penultimate and last whorls with three spiral cords, the uppermost weakest, peripheral one strongest; cord intervals with fine, close-set, axial pliculae; apex whitish, spiral cords on second whorl deep rose-pink, colour pattern subsequently fragmented into dashes and blotches of deep rose-pink on whitish ground; cord intervals washed with pale orange-brown.

Etymology

From the Latin “ roseus ” – “rose-coloured” and the Greek “ stiktos ” (στΙκτΟς) – “spotted”; in reference to the pattern of deep pink spots on the shell.

Material examined

Holotype

WALTERS SHOAL • empty shell; summit area, south-west, stn WS03; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN-IM-2000-35722 .

Paratypes

WALTERS SHOAL • 3 empty shells; same collection data as for holotype; MNHN-IM-2000-35723 • 7 empty shells; summit area, south, stn WS06; 33°15.1′ S, 43°54.5′ E; depth 26 m; 1 May 2017; MNHN- IM-2000-35724 • 12 empty shells; summit area, south-east, stn WS08; 33°13.7′ S, 43°55.9′ E; depth 30–33 m; 3 May 2017; MNHN-IM-2000-35725 .

Other material

WALTERS SHOAL • 6 empty shells; summit area, south-west, stn WS03; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN • 3 empty shells; summit area, south-west, stn WS04; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN • 8 empty shells; summit area, south, stn WS07; 33°15.4′ S, 43°52.2′ E; depth 30–33 m; 2 May 2017; MNHN • 1 empty shell; summit area, south, stn WB05; 33°15.1′ S, 43°54.5′ E; depth 26–30 m; 1 May 2017; MNHN • 1 empty shell; summit area, north-west, stn WB09; 33°13.8′ S, 43°55.8′ E; depth 27–30 m; 4 May 2017; MNHN .

Description

SHELL. Small (diameter up to 3.7 mm), trochoid-turbiniform, height and diameter more or less equal; spire conical with angular periphery; suture shallowly indented; sculpture dominated by strong spiral cords; base narrowly umbilicate; teleoconch of up to 4.5 whorls. First teleoconch whorl with three spiral cords, one peripheral, level with or just above abapical suture, another below adapical suture, and third midway between these; cords strengthen during second and subsequent whorls, particularly middle and peripheral cords; occasional specimens with a fourth, weaker spiral cord above peripheral one on second whorl, but this subsequently evanescing; penultimate and last whorls with three spiral cords, uppermost weakest, sometimes noticeably so, peripheral one strongest; slight thickening immediately below suture may appear as fourth spiral, often enhanced by colour pattern. Microsculpture comprising extremely fine, close-set, axial pliculae, first appearing near beginning of third whorl ( Fig. 37E ); pliculae most obvious in cord intervals, but also cross cords when unworn; peripheral cord usually with a number of finer spiral lirae, traces of such lirae occasionally also on mid-whorl cord. Base with 5–8 low spiral cords, progressively finer and more close-set toward umbilicus; microsculpture as above; umbilicus open, but relatively narrow and steep-sided, partly obscured by upper part of columella, more so when adult. Aperture roundly quadrate, columella slightly oblique to shell axis, somewhat thickened and reflected; outer lip lacking denticles; interior nacreous.

PROTOCONCH ( Fig. 37F ). Somewhat worn in all available specimens; comprising approx. 1.25 whorls, diameter 240–280 μm; apex weakly beaked; terminal lip more or less straight, lacking varix; surface smooth, no superficial microsculpture evident even in freshest juveniles.

COLOUR. Protoconch and early part of first teleoconch whorl milky-white; spiral cords subsequently becoming deep rose-pink, conspicuous on second whorl; on third whorl spiral colour pattern becomes fragmented into dashes and subsequently blotches of deep rose-pink on whitish ground; line of such blotches also present below adapical suture, seeming to delineate weak subsutural cord; cord intervals washed with pale orange-brown when fresh. Base with similar colour pattern, blotches tending to merge into axial bands around umbilicus in adults; umbilicus itself white.

DIMENSIONS. Holotype, height 3.7 mm, diameter 3.7 mm (= largest specimen).

OPERCULUM, RADULA AND EXTERNAL ANATOMY. Unknown.

Distribution

Known only from the summit area of Walters Shoal, at depths of 26–40 m; habitat dominated by encrusting coralline algae; collected by brushing and suction sampling; living specimens unknown.

Remarks

This species is clearly allied to the South African ‘ Gibbula ’ radiation, in particular to ‘ Gibbula ’ multicolor (Krauss, 1848) , which it resembles in both shape and sculpture. That species, however, has a less conical profile, attains a considerably larger size (diameter up to 8.0 mm) and has fine spiral lirae in the cord intervals. It also commonly has blue/green dots and the colour pattern on the apical surface comprises zig-zag axial bands or flames rather than spots aligned in spiral rows. The present species also has a more consistent colour pattern on the second teleoconch whorl, comprising distinctive deep rose-pink spiral lines. In this respect it resembles ‘ G. ’ zonata (Wood, 1828) from the west coast of South Africa, but in that species the spiral lines are greyish-purple and do not become fragmented on later whorls. ‘ Gibbula ’ zonata also has a less angular periphery, more distinct spiral microsculpture and lacks an umbilicus in the adult.

The occurrence of the South African species Sinezona insignis and Vaceuchelus gemmula on Walters Shoal are further examples demonstrating an affinity between the summit area fauna of Walters Shoal and the shallow, warm-temperate South African marine fauna. Further examples are evident in the Columbellidae and Muricidae (respectively Monsecour and Houart pers. com. 2021).

Figures

Fig. 37. ‘Gibbula’ roseosticta sp. nov. A–C. Holotype, diameter 3.7 mm (MNHN-IM-2000-35722). D. Spire whorls showing white apex and deep rose-pink spiral cords on second whorl (paratype, MNHN- IM-2000-35724). E. Oblique apical view showing spirally corded early whorls with fine axial pliculae developing near start of third teleoconch whorl (paratype, MNHN-IM-2000-35723). F. Protoconch, sculptural details, if any, eroded (paratype, MNHN-IM-2000-35723). Scale bars: D–E= 0.5 mm; F =100 μm.