Microcollonia miniata, 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 : 75-78

Microcollonia miniata sp. nov.

urn:lsid:zoobank.org:act:C2937537-9556-4126-A1F7-2F42FEECA6C5

Figs 30 , 32C–F

Diagnosis

Shell small, turbiniform, very thick, diameter up to 3.0 mm; anomphalous in adult; sculpture dominated by strong spiral cords; early teleoconch whorls with three un-beaded spiral cords, a fourth cord arises below adapical suture on third whorl, bearing bead-like nodules toward end of whorl; suture descending toward insertion of outer lip; base with three spiral cords; adult umbilicus glazed over by columella callus; exterior of outer lip with subterminal swelling; early whorls milky-white, subsequent whorls uniformly vermilion; umbilical region white.

Etymology

From the Latin “ minium ” – “cinnabar”, “ miniatus ” – “painted red with cinnabar”; in reference to the vermilion colour of the shell.

Material examined

Holotype

WALTERS SHOAL • living specimen; summit area, south-west, stn WS03; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; DNA tissue sample; MNHN-IM-2013-67278 .

Paratypes

WALTERS SHOAL • 1 living specimen; same collection data as for holotype; DNA tissue sample; MNHN-IM-2013-67279 • 1 living specimen; summit area, south, stn WB05; 33°15.1′ S, 43°54.5′ E; depth 26–30 m; 1 May 2017; DNA tissue sample; MNHN-IM-2013-67280 • 1 living specimen; summit area, south, stn WB05; 33°15.1′ S, 43°54.5′ E; depth 26–30 m; 1 May 2017; DNA tissue sample; MNHN-IM-2013-67281 • 1 living specimen, juvenile; summit area, south, stn WB05; 33°15.1′ S, 43°54.5′ E; depth 26–30 m; 1 May 2017; SEM of protoconch; MNHN-IM-2000-35709 • 16 specimens, some living; summit area, north-west, stn WB10; 33°09.1′ S, 43°51.8′ E; depth 30 m; 6 May 2017; SEM of operculum; MNHN-IM-2000-35708 .

Other material

WALTERS SHOAL – summit area, north-west • 19 empty shells; stn WB09; 33°13.8′ S, 43°55.8′ E; depth 27–30 m; 4 May 2017; MNHN. – summit area, south-west • 50 + empty shells; stn WS03; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN • 40 + specimens, some living; stn WS04; 33°12.2′ S, 43°50.8′ E; depth 40 m; 30 Apr. 2017; MNHN • 2 empty shells; stn WR01; 33°12.2′ S, 43°50.8′ E; depth 36 m; 30 Apr. 2017; MNHN. – summit area, south-east • 50 + specimens, some living; stn WS08; 33°13.7′ S, 43°55.9′ E; depth 30–33 m; 3 May 2017; MNHN. – summit area, south • 8 specimens, some living; stn WS06; 33°15.1′ S, 43°54.5′ E; depth 26 m; 1 May 2017; MNHN • 50 + specimens, some living; stn WS07; 33°15.4′ S, 43°52.2′ E; depth 30–33 m; 2 May 2017; MNHN • 10 empty shells; stn WB05; 33°15.1′ S, 43°54.5′ E; depth 26–30 m; 1 May 2017; MNHN .

Description

SHELL. Small (diameter up to 3.0 mm) and very thick; profile turbiniform, spire of moderate height; diameter slightly greater than height; sculpture dominated by strong spiral cords; anomphalous in adult; teleoconch of up to 3.0 whorls. First two teleoconch whorls with three spiral cords, the lowest one level with or just above abapical suture; cords smooth, lacking granules or beads; a fourth spiral cord arises below adapical suture on third whorl; this shoulder cord initially with low undulations which strengthen and become almost bead-like toward outer lip; abapical suture level with peripheral cord on last adult whorl, descending distinctly immediately prior to insertion of outer lip; cords on last adult whorl have an indistinct spiral thread on their crest; intervals between cords deep, their width equal to or slightly narrower than cords; no significant axial sculpture evident, only microscopic collabral growth striae. Base usually with three spiral cords; outer two cords like those above periphery, inner one broader and with low, ill-defined beads; middle basal spiral cord missing in one specimen ( Fig. 30E ); umbilicus narrowly patent in juveniles and subadults, but usually glazed over by columella callus in adult, though still remaining somewhat sunken. Aperture subcircular, peristome almost complete, glazed with smooth, glossy callus; columella lip concave, with a very slight swelling at its base; outer lip thick, lacking internal ornamentation, but its edge rendered undulant by spiral cords; exterior of outer lip strengthened by low, broad, subterminal swelling ( Fig. 30C ); interior not obviously nacreous.

PROTOCONCH ( Fig. 32C ). Translucent milky-white; diameter ± 280 μm, ca 1.25 whorls, apical bulb rounded; sculptured by three relatively strong subspiral threads, one close to abapical suture, with additional somewhat irregular subspiral thread-like features in their intervals; terminal lip straight, slightly flaring; step-like junction with teleoconch clearly demarcated.

COLOUR. First whorl of teleoconch translucent milky-white like protoconch, becoming progressively more pinkish-red toward end of whorl; subsequent whorls more or less uniformly vermilion; above periphery no colour difference between spiral cords and their intervals except in faded post-mortem specimens ( Fig. 30D ); basal coloration similar, but cords sometimes paler than their intervals, sometimes not; innermost basal cord uniformly white; peristome and interior of aperture white; vermilion colour of exterior subsequent to subterminal swelling fading to white at lip edge.

DIMENSIONS. Holotype, height 2.7 mm, diameter 3.0 mm (= largest specimen).

OPERCULUM ( Fig. 32D ). White, paucispiral and thickly calcified; nuclear region slightly domed, but extensively pitted particularly near its centre; nuclear region bounded by a broad raised ring sculptured by a fine anastomosing network of ridges; this ring terminating in a pointed tongue-like extension in the parieto-columellar region; peripheral region adjacent to basal and outer lips of aperture bounded by a narrow flattened ledge.

RADULA ( Fig. 32E–F ). Formula ∞+5+1+5+∞, length ca 1.0 mm, with 40–45 transverse rows of teeth; rows with a shallow central posterior indentation. Rachidian tooth with angular kite-shaped base-plate leading to small trigonal shaft with no cusp, behind which hood-like secondary flap; wings of kite joined by curved thickening of base-plate, close to anterior margin. Innermost lateral teeth with trigonal expansion of shaft, expansion progressively diminishing toward evenly curved shaft of fifth lateral; tooth overlap extensive; lateral tooth cusps asymmetrically trigonal, increasing in size from first to fifth, outer edge curved and blade-like with 2–4 smaller denticles at outer base. Marginal teeth progressively smaller toward edge of ribbon, their cusps narrow and strongly recurved, with denticulate edges.

Distribution

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

Remarks

Microcollonia miniata sp. nov. resembles M. rubricinctum (Mighels, 1845) from Hawaii, Japan and the Philippines, but that species has more numerous spiral cords (± 10 vs 7 on last adult whorl), and the cords are paler than their intervals, resulting in a spirally striped colour pattern ( Sasaki 2000b; Hasegawa 2018, Poppe et al. 2023). Such a colour pattern is evident in C. miniata only in older post-mortem specimens in which the intensity of the colour on the spiral cords has begun to fade ( Fig. 30D ). Similar, more geographically proximate species include Circumcollonia purpurata (Deshayes, 1863) from Réunion and Microcollonia carminea (Bartsch, 1915) from South Africa. The former is smaller (diameter 2.0 mm), has ±12 spiral cords on the last adult whorl, and the base is largely white, with only a narrow deep red band midway between the periphery and the umbilicus. The latter, though of similar size, has more numerous spiral cords (up to 20 on last adult whorl) and the cords are also generally paler than their intervals.

There are additional colloniine samples from deeper water (256–660 m) on the slopes of Walters Shoal, but this material is all in poor condition. One or more species may be involved, and though undoubtedly similar to M. miniata sp. nov., I suspect that they represent different species rather than old material of M. miniata that has been displaced downslope.

Figures

Fig. 30. Microcollonia miniata sp. nov. A–C. Holotype, diameter 3.0 mm (MNHN-IM-2013-67278). D. Faded shell, diameter 2.7 mm, stn WS07 (MNHN). E. Umbilicate subadult specimen with only two basal spiral cords, diameter 2.9 mm (paratype, MNHN-IM-2013-67279).

Fig. 32. A. Cantrainea herosae sp. nov., protoconch (paratype, MNHN-IM-2000-35706). B. Parviturbo cicatricosus sp. nov., holotype, protoconch and axial varices on early teleoconch. C–F. Microcollonia miniata sp. nov.C. Protoconch and early teleoconch (paratype, MNHN-IM-2000-35709).D. Operculum, maximum diameter 1.0 mm (paratype, MNHN-IM-2000-35708). E. Radula, half row (ex stn WS07). F. Radula, rachidian and right lateral teeth (ex stn WS07). Scale bars: A–C =100 μm; D =250 μm; E =25 μm; F = 10 μm.