(Figs 2, 25– 41, Table 3)
Clade A, sp. 4 — Williams et al., 2013.
Type material. Holotype (11.5 x 12.7 mm) MNHN IM- 2009-17850. Paratypes: 5 MNHN IM- 2009-17851, IM- 2009-17849, IM- 2009-17852, IM- 2007-18220, IM- 2009 -31844, 1 NHMUK 20140007, 1 coll. C. Vilvens CV 2014-18220.
Type locality. Southern New Caledonia, Norfolk Ridge, NORFOLK 2, stn DW2057, 24° 40 'S, 168 ° 39 'E, 555– 565 m.
Material examined. Southern New Caledonia and Norfolk Ridge. CHALCAL 2: stn DW73, 23° 40 'S 168 ° 38 'E, 573 m, 19 lv, 1 dd juv.—Stn DW74, 22° 40 'S 168 ° 3, 650 m, 17 lv, 1 dd sub.—Stn DW75, 24° 39 'S 168 ° 40 'E, 600 m, 20 lv.—BATHUS 2: stn CP760, 22° 19 'S, 166 ° 11 'E, 455 m, 1 dd sub.—BATHUS 3: stn DW838, 23°01'S, 166 ° 56 'E, 400–402 m, 5 lv sub.— NORFOLK 1: stn DW1693, 24° 55 'S, 168 ° 21 'E, 564–1144 m, 7 lv, 3 sub lv, 3 juv lv.—Stn DW1694, 24° 40 'S, 168 ° 39 'E, 575–589 m, 25 lv, 40 sub lv.—Stn DW1695, 24° 40 'S, 168 ° 39 'E, 562–587 m, 25 lv, 10 sub lv.—Stn DW1697, 24° 39 'S, 168 ° 38 'E, 569–616 m, 15 lv, 15 sub lv, 17 juv lv.—Stn DW1699, 24° 40 'S, 168 ° 40 'E, 581–600 m, 2 lv, 6 sub lv.—Stn DW1700, 24° 40 'S, 168 ° 40 'E, 572–605 m, 3 lv, 3 sub lv.—Stn DW1701, 24° 40 'S, 168 ° 39 'E, 564–586 m, 7 lv, 6 sub lv.—Stn DW1704, 23° 45 'S, 168 ° 16 'E, 400–420 m, 1 lv.—Stn DW1707, 23° 43 'S, 168 ° 16 'E, 381–493 m, 5 lv.— NORFOLK 2: stn DW2056, 24° 40 'S, 168 ° 39 'E, 573–600 m, 3 dd, 2 sub lv, 5 juv lv.—Stn DW2057, 24° 40 ’S, 168 ° 39 'E, 555–565 m, 8 lv (holotype and paratypes MNHN IM- 2009-17851, IM- 2009-17849, IM- 2009-17852, IM- 2007-18220, IM- 2009-31844, NHMUK 20140007, coll. C. Vilvens CV 2014-18220).—Stn DW2058, 24° 40 'S, 168 ° 40 'E, 591–1032 m, 12 lv.—Stn DW2060, 24° 40 'S, 168 ° 38 'E, 582–600 m, 12 lv, 8 sub lv, 4 juv. —Stn DW2067, 25° 16 'S, 168 ° 56 'E, 614–690 m, 1 dd.—Stn DW2073, 25° 24 'S, 168 ° 19 'E, 609 m, 7 dd.—Stn DW2074, 25° 24 'S, 168 ° 20 'E, 623–691 m, 5 dd.—Stn DW2075, 25° 23 'S, 168 ° 20 'E, 650–1000 m, 5 dd.—Stn DW2077, 25° 21 'S, 168 ° 19 'E, 666–1000 m, 1 dd.—Stn DW2084, 24° 52 'S, 168 ° 22 'E, 586–730 m, 2 lv, 2 juv lv.
Distribution. Southern New Caledonia and Norfolk Ridge, 402–666 m, living at 402– 650 m.
Description. Shell: Size relatively large for genus (height up to 11.8 mm, width up to 13.0 mm), slightly wider than high, conical; height 0.9 x width, 2.6–3.2 x aperture height; periphery weakly angular to almost rounded. Protoconch paucispiral, diameter approx. 330 µm, rounded, with 5 thin, equally spaced spiral threads; terminal lip straight, without varix. Teleoconch of up to 6.2 whorls; first two whorls convex, subsequent whorls almost straight; shoulder oblique with angulate rim, except on last whorl where shoulder horizontal; whorls with up to 20 spiral cords; cords thin and nearly smooth on first two whorls, thicker and beaded on subsequent whorls, beads of adapical cords stronger. Suture canaliculate on early whorls, not so on later whorls. First whorl sculptured by 6 thin, more or less equally spaced, cords; cords arising immediately after protoconch; P 1 and P 2 slightly stronger than other cords; P 1 forming rim of shoulder; close-set axial threads between cords. On second whorl, axial threads hard to distinguish and evanescing at end of whorl; P 6 at suture. Prosocline subsutural axial folds develop at start of third whorl, rendering P 1 and P 2 subgranular; P 1 and P 2 the strongest with secondary cord S 2 arising and rapidly reaching strength of P 3; P 5 thickening after middle of whorl, smooth and forming a weak suprasutural carina. On fourth whorl all adapical cords beaded, abapical cords subgranular; S 4 and S 1 arising; P 1 stronger than other cords; P 5 almost as strong as P 1, forming prominent carina above suture; shoulder more or less horizontal, suture not canaliculate; axial folds weaker, but still visible. On fifth whorl, P 6 emerging from suture; tertiary cords arising by intercalation between P 1 and S 1 and/or between S 4 and P 5. On last whorl, numerous additional tertiary cords arising, resulting in a total of up to 20 cords; carina on P 5 weaker than on penultimate whorl. Aperture subcircular; peristome incomplete; outer and inner lips thin; columella vertical, concave, the middle portion slightly reflected and overlapping umbilicus; a small flange at columella base. Base moderately convex, with 15–18 spiral cords; peri-umbilical region with approx. 30 axial pleats, rendering 5–8 most inner cords beaded; cord at umbilical rim 1.5 –2.0x wider than penultimate cord and strongly beaded with coarse, pointed beads; outer basal cords thin, smooth, becoming weakly beaded in central part of base, intervals between cords 1.5 –2.0x width of cords. Umbilicus deep, relatively narrow (diameter ca. 9–13 % of shell width), with angulate rim; internal wall almost straight, with 6–8 strong, subgranular to beaded spiral cords; cord closest to rim coarsely beaded; intervals between cords approx. 0.5 –1.0x width of cords.
Colour: Teleoconch whorls nacreous, pinkish to orange; base white to grey; protoconch white.
External anatomy (based on observation of rehydrated bodies removed from dry shells) (Fig. 41): Typical of the family. Propodium with prominent lateral lobes; snout broad with lips modified into a fringe of digitiform processes; cephalic tentacles well-developed, papillate; eyes black, situated on short stalks fused to outer side of tentacle base; right eye-stalk with a small subocular tentaculiform process; left neck lobe present as two short, nonpapillate tentacles, the right one as a trigonal outgrowth just behind eye-stalk; three papillate epipodial tentacles present on each side, of more or less equal size; between the anterior pair on both sides is a smaller tentacle-like projection, that on the right appearing to arise from the underside of an epipodial flap. Preservation of material inadequate to determine presence and position of any epipodial sense organs. Operculum corneous, straw-brown, shallowly concave, multispiral with central nucleus; growing margin short.
Remarks. The shell of Arxellia boucheti is distinctive on account of its large size, numerous spiral cords and rounded periphery. The external anatomy is almost identical to that illustrated by Warén (1993) for Solariella obscura and S. varicosa, and is also close to that of Spectamen (Herbert 1987). In the molecular analysis of Williams et al. (2013), this species forms a clade with A. tracheia and A. helicoides.
Etymology. Named after Philippe Bouchet (MNHN), whose dynamic leadership of Indo-Pacific expeditions and skilful management of malacological human resources have led to great advances in systematics and the discovery of many species new to science.