Bruceina areneformis, 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 : 69-73

Bruceina areneformis sp. nov.

urn:lsid:zoobank.org:act:63AE5EA2-1B6D-4D73-A783-86AB41A26F83

Figs 28C–F , 29A–C, G

Diagnosis

Shell turbiniform, height up to 5.4 mm; height ≈ diameter; base narrowly umbilicate; protoconch hexagonally reticulate; teleoconch sculpture of strong spiral cords, nodular on spire whorls; P3 forms carina-like shoulder cord on spire whorls with S3 present below P3; start of last adult whorl with four strong rounded spiral cords above and including peripheral one, final half-whorl with additional intermediaries, shoulder cord no longer prominent, upper two cords remaining nodular; base with 5–6 rounded spiral cords; aperture subcircular, peristome somewhat flaring at base of columella; shell uniformly whitish.

Etymology

From Arene H. Adams & A. Adams, 1854 and the Latin “ forma ” – “shape”; in reference to the superficial resemblance of the species to some members of the areneid genus Arene .

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn DW4893; 33°16′ S, 43°58′ E; depth 623–629 m; 4 May 2017; MNHN-IM-2000-35699 .

Paratypes

WALTERS SHOAL – slopes • 3 empty shells; stn DW4879; 33°17′ S, 43°52′ E; depth 288–300 m; 1 May 2017; MNHN-IM-2000-35700 • 1 living specimen, juvenile; stn DW4880; 33°17′ S, 43°51′ E; depth 275–318 m; 1 May 2017; MNHN-IM-2000-35701 • 19 empty shells; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN-IM-2000-35702 • 14 empty shells; same collection data as for holotype; MNHN-IM-2000-35703 • 7 empty shells; stn DW4897; 33°09′ S, 43°59′ E; depth 490–584 m; 5 May 2017; MNHN-IM-2000-35704 .

Other material

WALTERS SHOAL – slopes • 1 empty shell; stn DW4877; 33°10′ S, 43°49′ E; depth 217–256 m; 1 May 2017; MNHN • 50 + empty shells; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN • 10 + empty shells; stn DW4885; 33°17′ S, 43°55′ E; depth 272–380 m; 3 May 2017; MNHN • 30 + empty shells; stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN • 3 empty shells; stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN • 30 + empty shells; stn DW4890; 33°09′ S, 43°59′ E; depth 492–588 m; 4 May 2017; MNHN • 2 empty shells; stn DW4892; 33°12′ S, 44°01′ E; depth 624–646 m; 4 May 2017; MNHN • 1 empty shell; stn DW4894; 33°09′ S, 43°50′ E; depth 199–261 m; 5 May 2017; MNHN • 1 empty shell; stn DW4895; 33°09′ S, 43°49′ E; depth 238–283 m; 5 May 2017; MNHN • 1 empty shell; stn DW4898; 33°09′ S, 44°01′ E; depth 652– 668 m; 6 May 2017; MNHN .

Description

SHELL. Small (height up to 5.4 mm), turbiniform; height and diameter approximately equal or slightly higher than wide; spire prominent (height approximately equal to that of aperture), with indented suture; whorls evenly rounded, sculptured by strong spiral cords, nodular on spire whorls; umbilicus present, deep and rather narrow; teleoconch of up to 4.0 whorls. First teleoconch whorl with an axial growth flaw shortly after terminal protoconch varix (at 0.1–0.2 whorl); initially sculptured only with fine, close-set spiral lirae, weak uneven growth-lines and occasional irregular, ill-defined, subsutural riblets ( Fig. 28F ); a single strong spiral cord soon develops midway between sutures, creating distinct, somewhat undulant shoulder; shoulder cord stronger and carina-like on second whorl (= P3 of Marshall 1988), with undulant coronations linked to broad, low, axial riblets ( Fig. 28E ); near end of first whorl a second cord develops between P3 and abapical suture (= S3 of Marshall 1988), followed during second whorl by a third cord (P1) on shoulder slope, just below adapical suture ( Fig. 29G ); fine spiral liration of first whorl evanesces near end of second whorl; a fourth cord (P4) also evident at whorl periphery, level with abapical suture; cords rendered nodular where crossed by axial riblets; start of last adult whorl with four strong rounded spiral cords above and including peripheral one (P1, P3, S3, P4); equivalent of P2 not present; in final half-whorl, second and third intervals with finer intermediary cord arising (T1 and T2 respectively); adapical cord slightly weaker than others, shoulder cord no longer as prominent; upper two cords remaining nodular, but axial riblets no longer evident; third and fourth cords shallowly undulant or almost smooth; cord intervals with close-set, microscopic collabral threads. Base typically with 5–6 rounded spiral cords, their intervals slightly narrower toward umbilicus; in some specimens cords in mid-region of base reduced or obsolete, rarely basal cords almost completely lacking; umbilicus narrow and deep, with funicle-like cord spiralling into it at mid-columella level ( Fig. 28D ); peri-umbilical region sometimes with fine close-set spiral lirae, most obvious in juveniles. Aperture subcircular, peristome incomplete; columella lip concave, basal half somewhat reflected, flaring at junction with basal lip; outer lip thin, crenulated by spiral cords; interior nacreous.

PROTOCONCH ( Fig. 28F ). Diameter 330–340 μm; surface sculptured with hexagonal network of interconnected ridges; terminal varix well developed, rib-like.

COLOUR. Uniformly milky-white to pale buff, cord intervals with a faint pink/green iridescence in the freshest specimens.

DIMENSIONS. Holotype, height 4.3 mm, diameter 4.2 mm; largest specimen, height 5.4 mm, diameter 5.3 mm.

OPERCULUM. Corneous, pale golden-brown; whorls narrow and numerous.

RADULA AND EXTERNAL ANATOMY. Unknown.

Distribution

Known only from the slopes of Walters Shoal, at depths of 256–652 m (live-taken specimen 275– 318 m); dredged on coarse sandy substrata with octocorals and solitary corals.

Remarks

Although this species might at first glance appear referable to the Areneidae , its operculum lacks the characteristic calcareous granules of the areneid operculum and the hexagonal protoconch microsculpture clearly places it in the Calliostomatidae . Within this family, the overall shell facies, in particular the turbiniform profile and the ontogeny of the spiral sculpture, notably the relatively high position of the primary spiral cord on the first two teleoconch whorls (P3 of Marshall 1988), ally the species to the thysanodontine genus Bruceina , a taxon to date known only from the continental shelf and upper slope (50–500 m) off south-eastern Africa (four species). Bruceina areneformis sp. nov. has a broader, less elevated spire when compared with B. cognata ( Marshall, 1988) , B. eos ( Marshall, 1988) and B. meimiaoae Huang, 2020 , and all three of these species have more numerous spiral cords and are typically of bright pinkish colour (occasional specimens of B. eos may be uniformly whitish). Bruceina chenoderma (Barnard, 1963) has a more similar shape, but it too is usually pinkish in colour and it has more numerous spiral cords (5 vs 3 above periphery at the start of the last adult whorl) ( Herbert 1995). In addition, the granules on the adapical cords of the spire whorls are more angular in B. chenoderma . All four South African species attain a larger size (height 7–9 mm) than B. areneformis .

Another thysanodontine species, Carinastele wareni Vilvens, 2014 from off southern Madagascar, is of relevance here. When describing this species, Vilvens (2014) used a different system for numbering the spiral cords compared to that of Marshall (1988). Thus, the prominent keel-like shoulder cord on the first whorl is P2 for Vilvens and P3 for Marshall. In turn P3 for Vilvens corresponds with S3 for Marshall. Since Marshall defined Carinastele as lacking S3, I consider Carinastele wareni , which possesses an S3 (sensu Marshall), to be referable to Bruceina rather than to Carinastele . It was based on a single small specimen (height 2.5 mm), which I believe to be a juvenile specimen of B. cognata . It differs from B. areneformis sp. nov. in lacking nodules on the two adapical spiral cords on the spire.

Bruceina areneformis sp. nov. exhibits considerable variation with respect to the strength and number of spiral cords on the base. Typically, there are 5–6 basal cords, plus an additional funicle-like cord spiralling into the umbilicus. In some specimens, however, the cords in the mid-region of the base are absent and in such specimens the fine peri-umbilical spiral lirae are often more evident, particularly in juveniles. Above the periphery the cording is usually more consistent, but the adapical cord may become weak or obsolete on the last adult whorl. There is also variation in the strength of the nodules on the cords on the apical surface. Whereas these are usually distinct on the two adapical cords on the spire whorls ( Fig. 28C ), they often become weak or obsolete on the last adult whorl.

Calliostoma cyrtoida Gofas & Hoffman, 2020 from upper bathyal depths on the South Azorean Seamount Chain is remarkably similar to Bruceina areneformis sp. nov. in its general facies. It differs from the latter in having a narrower umbilicus, and the first teleoconch whorl lacks fine spiral lirae and is distinctly bicarinate with more numerous, stronger axial ribs.

Figures

Fig. 28. A–B. Calliostoma pantopunctatum sp. nov., holotype (MNHN-IM-2013-67275). A. Oblique view of apex showing development of spiral sculpture. B. Sculptural detail of protoconch and early teleoconch. C–F. Bruceina areneformis sp. nov., paratypes C. Side view of spire. D. Umbilical region showing funicle-like cord within. E. Oblique view of apex showing development of spiral sculpture. F. Sculptural detail of protoconch and early teleoconch (C–D = MNHN-IM-2000-35700, E–F =MNHN- IM-2000-35704). Scale bars: A, C= 1.0 mm; B, F =100 μm; D= 500 μm; E =200 μm.

Fig. 29. A–C. Bruceina areneformis sp. nov., holotype, height 4.3 mm (MNHN-IM-2000-35699). D–F. Carinastele achrosta sp. nov., holotype, height 8.7 mm (MNHN-IM-2000-35705). G–H. Portions of the above holotypes to illustrate numbering of spiral cords, following Marshall (1988). G. Bruceina areneformis sp. nov.H. Carinastele achrosta sp. nov. The equivalent of P2 is not present inB. areneformis sp. nov.