Bichoristes wareni McLean, 1992

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 : 37-39

Bichoristes wareni McLean, 1992

Fig. 17A–D

Bichoristes wareni McLean, 1992: 287 , figs 46–53.

Type loc.: Norfolk Ridge (24°55′ S, 168°22′ E) [not 162°22′ E as given], depth 505–515 m.

Material examined

WALTERS SHOAL – slopes • 1 empty shell; stn DW4879; 33°17′ S, 43°52′ E; depth 288–300 m; 1 May 2017; MNHN • 1 living specimen; stn DW4880; 33°17′ S, 43°51′ E; depth 275– 318 m; 1 May 2017; MNHN • 4 empty shells; stn DW4881; 33°16′ S, 43°50′ E; depth 377–382 m; 2 May 2017; MNHN • 17 empty shells; stn DW4886; 33°17′ S, 43°56′ E; depth 573–582 m; 3 May 2017; MNHN • 7 empty shells; stn DW4887; 33°17′ S, 43°57′ E; depth 599–640 m; 3 May 2017; MNHN • 1 empty shell, fresh; stn DW4890; 33°09′ S, 43°59′ E; depth 492–588 m; 4 May 2017; MNHN • 10 empty shells, some fresh juveniles; stn DW4893; 33°16′ S, 43°58′ E; depth 623–629 m; 4 May 2017; MNHN • 1 empty shell; stn DW4897; 33°09′ S, 43°59′ E; depth 490–584 m; 5 May 2017; MNHN • 1 empty shell; stn DW4898; 33°09′ S, 44°01′ E; depth 652–668 m; 6 May 2017; MNHN • 1 empty shell; stn DW4899; 33°09′ S, 44°02′ E; depth 707–720 m; 6 May 2017; MNHN .

Distribution

Until now known only from the type material from the Norfolk Ridge, south-east of New Caledonia. Here recorded for the first time in the Indian Ocean; from the slopes of Walters Shoal, at depths of 300–707 m; dredged on substrata of coarse sand; one live-taken specimen 275– 318 m.

Remarks

Although geographically distant from the original sample discussed by McLean (1992), I can find no consistent differences by which to separate the Walters Shoal specimens from the original Norfolk Ridge material. The holotype (diameter 3.2 mm) is somewhat larger than the specimens from Walters Shoal (diameter of largest specimen 2.5 mm), but this is likely simply a reflection of the number of teleoconch whorls (respectively 3.2 vs 2.7 whorls). Like the holotype, the specimens from Walters Shoal have a smooth protoconch with a relatively small apical bulb (rounded or somewhat ovate) which is followed by an expanding terminal tube, from which it is separated by a relatively deep suture-like groove ( Fig. 17C–D ). The protoconch of species of Choristella is of the same form ( McLean 1992). In several fresh juvenile shells from Walters Shoal, the protoconch has a distinct, rounded terminal varix ( Fig. 17D ), but this appears to be a delicate, superficial structure and is partly or completely eroded in adult specimens.

The holotype was collected alive, but McLean (1992) did not state whether the specimen was found in a spent elasmobranch egg case. However, since he stated that no choristellids were “known to be free living and unassociated with the spent egg cases of elasmobranchs”, it is clear that he considered this to be the habitat of Bichoristes wareni , the planispiral shell of which he believed would facilitate access to the narrower terminal parts of such egg cases. There is no information to indicate whether or not the single live-taken specimen collected on Walters Shoal was living in an elasmobranch egg case. All specimens from Walters Shoal were sorted from sieved samples of dredged substratum.

Zerotula nummaria Powell, 1940 from northern New Zealand (Family: Zerotulidae ) has a superficially similar keeled, planispiral shell, but is smaller (diameter <1.5 mm) and has less distinct, shallowly undulant keels and a rougher surface ( Warén & Hain 1996).

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.