Eudaronia?biconcava ( Thiele, 1925 )

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 : 39-40

Eudaronia?biconcava ( Thiele, 1925)

Fig. 17E–G

Lyocyclus (?) biconcavus Thiele, 1925: 117 [83], pl. 9 figs 18–19.

Type loc.: off Mogadishu , Somalia, Valdivia stn 256 (1°49′ N, 45°29.5′ E), depth 1134 m .

Eudaronia biconcavus [sic] – Warén 1991: 77.

Eudaronia biconcava – Warén 1991: fig. 8A [radula]. — Kano et al. 2009: 401. — Rubio & Rolán 2021: 90, fig. 36a–c [syntype].

Material examined

WALTERS SHOAL • 1 empty shell; south plain, stn CP4913; 33°52′ S, 44°05′ E; depth 1539–1615 m; 11 May 2017; MNHN .

Distribution

Recorded from deep water off Somalia (1134 m) ( Thiele 1925), Réunion (1155–1200 m) ( Warén 1991) and on the plain surrounding Walters Shoal (1539–1615 m); living specimens unknown.

Remarks

Rubio & Rolán (2021) illustrated a syntype of Lyocyclus biconcavus (Museum für Naturkunde, Berlin – ZMB/Moll-109251). When compared to the specimen from Walters Shoal, this syntype, albeit smaller and thus probably subadult (diameter 1.0 mm vs 1.4 mm), has stronger apical and basal keels, and an aperture that is markedly flared where these keels meet the outer lip. My referral of the present material to E. biconcava is thus tentative and is influenced by the shared western Indian Ocean provenance. With only one specimen available and with no data concerning intraspecific variation in species of Eudaronia , I refrain from describing the Walters Shoal specimen as a new species. More western Indian Ocean specimens will need to be examined before a definitive conclusion can be drawn.

With the exception of Eudaronia mikra Hoffman, Gofas & Freiwald, 2020 , Recent species of Eudaronia exhibit only small differences in shell morphology. Judging from the original figures ( Verco 1909) and those provided by Cotton (1959) and Warén (1991), the south Australian E. jaffaensis has a deeper shell with more rapidly expanding whorls than E. biconcava . In E. spirata Hoffman, Gofas & Freiwald, 2020 , from seamounts south of the Azores, the apical and basal insertions of the outer lip are level with the apical and basal keels respectively, whereas in the present material and the Berlin syntype these insertions lie some distance below and above these respective keels ( Fig. 17E ), and the interruption of the peristome thus spans a narrower portion of the penultimate whorl. Eudaronia aperta (Sykes, 1925) from off Portugal is similar in the latter respect, but it is difficult to assess since the published images of the species differ considerably in the relative depth of the whorls and the convexity of the periphery ( Warén 1991: fig. 14c, e; Hoffman et al. 2020: fig. 11). Like E. spirata , the apical part of the protoconch of the Walters Shoal specimen bears distinct spiral threads ( Fig. 17G ). Eudaronia mikra has axially costate early whorls and is more similar to species of Adeuomphalus Seguenza, 1876 .

Figures

Fig. 17. A–D. Bichoristes wareni McLean, 1992. A–B. Apical and apertural views, diameter 2.4 mm, stn DW4886 (MNHN). C. Protoconch of A. D. Protoconch of juvenile with thickened terminal lip, stn DW4893 (MNHN). E–G. Eudaronia?biconcava (Thiele, 1925), stn CP4913 (MNHN). E–F. Apertural and apical views, diameter 1.4 mm. G. Protoconch. Scale bars= 100 μm.