Phragmomphalina vilvensi Herbert & Williams, 2020

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 : 89-90

Phragmomphalina vilvensi Herbert & Williams, 2020

Fig. 35E–H

Phragmomphalina vilvensi Herbert & Williams in Williams et al., 2020: 19, fig. 7a, d–f.

Type loc.: east of Leven Bank (12°26′ S, 48°13′ E), off NW Madagascar, northern Mozambique Channel, depth 580 m.

Phragmomphalina vilvensi – Vilvens 2022: 56, fig. 8a–n.

Material examined

WALTERS SHOAL – slopes • 1 empty shell; stn DW4892; 33°12′ S, 44°01′ E; depth 624–646 m; 4 May 2017; MNHN • 1 empty shell; stn CP4901; 33°09′ S, 44°01′ E; depth 647–672 m; 6 May 2017; MNHN • 1 living specimen; stn CP4902; 33°08′ S, 44°02′ E; depth 700–711 m; 7 May 2017; DNA tissue sample; MNHN-IM-2013-67169 • 1 living specimen; stn CP4905; 33°32′ S, 44°00′ E; depth 1000– 1052 m; 9 May 2017; DNA tissue sample; MNHN-IM-2013-67170 • 1 living specimen; stn CP4905; 33°32′ S, 44°00′ E; depth 1000–1052 m; 9 May 2017; DNA tissue sample; MNHN-IM-2013-67171 • 5 empty shells; stn CP4905; 33°32′ S, 44°00′ E; depth 1000–1052 m; 9 May 2017; MNHN • 1 living specimen; stn CP4906; 33°26′ S, 44°00′ E; depth 799–837 m; 9 May 2017; DNA tissue sample; MNHN- IM-2013-67172 • 16 empty shells; stn CP4906; 33°26′ S, 44°00′ E; depth 799–837 m; 9 May 2017; MNHN • 1 living specimen; stn CP4907; 33°27′ S, 44°00′ E; depth 880 m; 9 May 2017; DNA tissue sample; MNHN-IM-2013-67173 • 1 living specimen; stn CP4907; 33°27′ S, 44°00′ E; depth 880 m; 9 May 2017; DNA tissue sample; MNHN-IM-2013-67174 • 16 specimens, some living; stn CP4907; 33°27′ S, 44°00′ E; depth 880 m; 9 May 2017; MNHN • 20 + specimens, some living; stn CP4908; 33°29′ S, 44°00′ E; depth 900–950 m; 9 May 2017; MNHN • 2 specimens, living; stn CP4909; 32°45′ S, 44°03′ E; depth 987–989 m; 10 May 2017; MNHN • 20 + specimens, some living; stn CP4911; 32°46′ S, 44°18′ E; depth 964–965 m; 10 May 2017; MNHN • 8 specimens, some living; stn CP4912; 32°49′ S, 44°23′ E; depth 961–966 m; 10 May 2017; MNHN .

Distribution

Known from the northern Mozambique Channel, southern Madagascar and Walters Shoal. On Walters Shoal it has been found on the slopes at depths of 646–1000 m (live-taken material 711–1000 m); obtained mostly by beam trawl on substrata of coarse sand, solitary coral rubble and pteropod shell debris, with living hexacorals, octocorals, decapods, bivalves and echinoids.

Remarks

Specimens of Phragmomphalina vilvensi from Walters Shoal closely resemble those from off NW Madagascar. They differ in that the sculpture is somewhat weaker on the mid-spire whorls, particularly on the third whorl where the spiral lirae are finer and the subsutural pliculae not as strongly developed. Additionally, the whorl periphery is generally more rounded in material from Walters Shoal and there are fewer, coarser axial pliculae radiating around the umbilicus. However, these differences are slight and, since preliminary analysis of CO1 sequence data indicates that samples from Walters Shoal cluster amongst those from off NW Madagascar (S.T. Williams pers. com. 2021), evidently reflect geographic variation within a single species.

Virtually every stage in the development of the septum and closure of the umbilicus is present in this material, but there seems to be limited correlation between septum development and shell size, except that juveniles never have a septum. Large specimens of 4.5 whorls may retain a patent umbilicus with minimal septum development. It is unlikely that the species is sexually dimorphic in this regard since the great majority of adult and subadult specimens evince a degree of septum development. Similarly, there is no evidence that the umbilical cavity is used as a brooding chamber for developing embryos. The umbilicus itself is of more or less uniform size in all individuals, unlike the umbilically brooding species of Cinysca Kilburn, 1970 ( Areneidae ) in which the umbilicus of females is broader than that of males (pers. obs.). Furthermore, at full development the septum in species of Phragmomphalina completely closes the umbilicus and would need to be resorbed in order to release fully developed embryos.

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).