Phragmomphalina candida, 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 : 90-92

Phragmomphalina candida sp. nov.

urn:lsid:zoobank.org:act:B355BF8F-2C1E-4A84-888A-15FF66F50B88

Figs 35I–L , 36F–G

Diagnosis

Shell elevated-lenticular to subglobose, diameter up to 12.8 mm; whorls convex, lacking shoulder; suture somewhat sunken on second and third whorls; spire whorls with fine spiral lirae and third whorl with weak subsutural pliculae, but remainder of shell smooth and glossy; base umbilicate in juveniles and subadults, covered with thin septum in adults; columella with lustreless granular callus deposit; shell uniformly whitish, often with very faint pinkish wash on adapical surface.

Etymology

From the Latin “ candidus ” – “white”; in reference to the colour of the shell.

Material examined

Holotype

WALTERS SHOAL • empty shell; slopes, stn CP4902; 33°08′ S, 44°02′ E; depth 700–711 m; 7 May 2017; MNHN-IM-2000-35716 .

Paratypes

WALTERS SHOAL – slopes • 1 empty shell; same collection data as for holotype; MNHN- IM-2000-35717 • 5 empty shells; stn DW4898; 33°09′ S, 44°01′ E; depth 652–668 m; 6 May 2017; MNHN-IM-2000-35718 .

Other material

WALTERS SHOAL – slopes • 5 empty shells, juvenile; stn DW4898; 33°09′ S, 44°01′ E; depth 652– 668 m; 6 May 2017; MNHN • 6 empty shells, juvenile; stn DW4899; 33°09′ S, 44°02′ E; depth 707– 720 m; 6 May 2017; MNHN • 4 empty shells, juvenile; stn DW4900; 33°10′ S, 44°01′ E; depth 660– 670 m; 6 May 2017; MNHN .

Description

SHELL. Moderate to relatively large (diameter up to 12.8 mm), elevated-lenticular to subglobose, diameter greater than height; spire prominent, with convex whorls and strongly indented suture; spire whorls lacking an obvious shoulder, but suture somewhat sunken (channelled), distinctly so on second and third whorls ( Fig. 36F ), less so with subsequent growth and not so on last adult whorl; periphery below mid-whorl, very slightly angled; sculpture weak, shell essentially smooth and glossy save for fine spiral lirae on early spire whorls and very weak subsutural pliculae on third whorl; base less convex, umbilicus closed by thin septum at maturity; teleoconch of up to 5.0 whorls. First teleoconch whorl with 5–7 low spiral lirae, increasing to 8–10 on third whorl through intercalation; no obvious shoulder present, but adapical region of whorl strongly convex and suture thus sunken; uppermost lira may lie atop subsutural convexity and appear as low subsutural cord; axial sculpture on these early whorls indistinct (at most close-set, microscopic threads), but low subsutural pliculae develop during third whorl resulting in weak beading below suture ( Fig. 36F ); spiral lirae evanesce toward end of third whorl and subsutural pliculae likewise weaken and become obsolete during fourth whorl; last adult whorl smooth and glossy with only microscopic growth-lines and indistinct traces of uneven spiral sculpture; base similarly smooth in adult, but with growth-lines strengthening somewhat toward and into umbilicus, juveniles usually with fine spiral lirae on base; umbilicus patent in juvenile and subadult specimens, steep-sided, with strong cord defining its margin; in large specimens this cord not rendered obviously plicate by growth-lines and base lacking additional peri-umbilical spiral cords; however, in some juveniles the peri-umbilical cord is beaded and there may be weak pliculae radiating from umbilicus with some additional indistinct peri-umbilical spiral sculpture. Aperture subquadrate to roundly D-shaped; peristome interrupted in parietal region; columella slightly oblique to shell axis, shallowly concave and covered with lustreless, granular callus deposit; in holotype callus spreading as thin septum over umbilicus (somewhat damaged or deformed); septum lustreless, but not obviously granular; junction of columella and basal lips rendered angular by peri-umbilical cord; outer lip thin and simple; interior nacreous, lacking labral ornamentation.

PROTOCONCH ( Fig. 36G ). Translucent milky-white; diameter 340–350 μm, ca 1.25 whorls, apical beak lacking; sculptured by 6–7 fine spiral threads; terminal lip straight, not thickened.

COLOUR. Shell uniformly whitish, often with very faint pinkish wash on adapical surface of last whorl of larger specimens. No living or freshly dead specimens available and any translucence or iridescence lost in samples examined.

DIMENSIONS. Holotype, height 9.2 mm, diameter 12.8 mm (= largest specimen).

OPERCULUM, RADULA AND EXTERNAL ANATOMY. Unknown.

Distribution

Known only from the slopes of Walters Shoal, at depths of 670–707 m; dredged on sandy substrata with solitary corals; living specimens unknown.

Remarks

The overall shell facies and the thin calcareous septum closing the adult umbilicus ally this species with Phragmomphalina . Although no undamaged adult specimens are available, the material examined clearly evinces consistent conchological characters that differentiate it from other species of Phragmomphalina . The co-occurring P. vilvensi differs in having well-developed, coronate subsutural sculpture and strongly plicate spiral cords around the umbilicus. In addition, P. candida sp. nov. has a less conical profile and more convex spire whorls with a slightly sunken suture.

In comparison with species of Phragmomphalina from elsewhere, P. diadema (Marshall, 1999) , a species widespread in the south-western Pacific ( Williams et al. 2013), possesses a distinctly nodular subsutural spiral cord and strong peri-umbilical spiral and axial sculpture, whereas P. alabida (Marshall, 1999) , from off northern New Zealand, is smaller relative to the number of whorls (10.7 mm at 5 teleoconch whorls vs 12.8 mm at 5 teleoconch whorls) and more elevated. Phragmomphalina tenuiseptum (Marshall, 1999) from the Three Kings Rise, has a more similar shape and shares a sunken suture on the spire whorls, but it has rounded collabral axial folds on the spire whorls, as well as spiral threads and axial folds on the inner third of the base.

Solariella incisura Melvill, 1909 from the Saya de Malha Banks (265 m) has much stronger, more well-defined spiral lirae on the first two teleoconch whorls, its suture is not channelled on the mid-spire whorls, the umbilical rim is strongly angled and delineated by a beaded cord with strong radiating pliculae and the interior of the umbilicus bears distinct spiral lirae. The two syntypes (NHMUK 1910.3.17.8–9) are almost certainly juvenile, but specimens of P. candida sp. nov. of the same size have a weaker umbilical angle, lack radiating pliculae and the spiral sculpture within the umbilicus is scarcely evident. However, the similarity of the two species is sufficient to indicate that Melvill’s taxon is also referable to Phragmomphalina rather than to Solariella .

Figures

Fig. 35. A–D. Bathymophila williamsae sp. nov., holotype, diameter 8.5 mm (MNHN-IM-2013-67177). E–H. Phragmomphalina vilvensi Herbert & Williams, 2020. E–G. Walters Shoal, stn CP4907, diameter 14.7 mm (MNHN-IM-2013-67173). H. Large specimen with weak subsutural sculpture, Walters Shoal, stn CP4907, diameter 15.3 mm (MNHN). I–L. Phragmomphalina candida sp. nov. I–K. Holotype, diameter 12.8 mm (MNHN-IM-2000-35716). L. Subadult lacking umbilical septum, diameter 9.0 mm (paratype, MNHN-IM-2000-35718).

Fig. 36. A–C, H–I. Solariella asaphea sp. nov. A, C. Apertural and oblique basal views of holotype, diameter 4.1 mm (MNHN-IM-2000-35719). B. Apical view of paratype, diameter 3.3 mm (MNHN- IM-2000-35720). H. Subsutural sculpture, holotype. I. Protoconch (paratype, MNHN-IM-2000-35720). D–E. Bathymophila williamsae sp. nov., paratype (MNHN-IM-2013-67176). D. Oblique view of spire showing detail of apical sculpture. E. Sculptural detail of protoconch. F–G. Phragmomphalina candida sp. nov., paratype (MNHN-IM-2000-35718). F. Oblique view of spire showing sunken suture and detail of apical sculpture. G. Sculptural detail of protoconch. Scale bars: D, F =500 μm; E, G, I= 100 μm; H =200 μm.