Arxellia trochos, Vilvens, Claude, Williams, Suzanne T. & Herbert, David G., 2014

Vilvens, Claude, Williams, Suzanne T. & Herbert, David G., 2014, New genus Arxellia with new species of Solariellidae (Gastropoda: Trochoidea) from New Caledonia, Papua New Guinea, Philippines, Western Australia, Vanuatu and Tonga, Zootaxa 3826 (1), pp. 255-281 : 261-264

Arxellia trochos n. sp.

( Figs 1 , 12–24 , Table 2 )

Type material. Holotype (5.9 x 5.3 mm) MNHN IM- 2009-23092. Paratypes: 3 MNHN IM- 2009-23109, IM- 2009- 23094, IM- 2009-23089, 1 NHMUK 20140006.

Type locality. New Caledonia, Banc de l’Orne/Walope, EXBODI, stn DW3862, 22°20'S, 169°01’E, 400– 520 m.

Material examined. South-western New Caledonia. BIOCAL: stn DW08. 20°34'S. 166°54'E. 435 m. 16 dd. 8 dd sub. 8 dd juv.—Stn DW83. 20 °35'S. 166°54'E. 460 m. 4 dd. 1 dd juv.—BATHUS 2: stn DW730, 23°03'S, 168°58'E, 397–400 m, 2 dd (one exceptionally large: 6 whorls, 8.4 x 7.0 mm).—EXBODI: stn CP3851, 22°19'S, 168°45’E, 471–510 m, 1 lv (paratype MNHN IM- 2009-23109).—Stn DW3861, 22°19'S, 169°01’E, 425–490 m, 1 lv (paratype MNHN IM- 2009-23094).—Stn DW3862, 22°20'S, 169°01’E, 400–520 m, 3 lv (holotype, paratypes MNHN IM- 2009-23089 and NHMUK 20140006).

Loyalty Islands. MUSORSTOM 6: stn DW410, 20°38'S, 167°07'E, 490 m. 3 dd.—Stn DW413, 20°40'S, 167°03'E, 463 m. 1 dd.

Fiji. BORDAU 1: stn DW1486, 19°01'S, 178°26'W, 395–540 m, 34 dd, 16 dd juv.—Stn DW1492, 18°43'S, 178°23'W, 430–450 m, 4 dd, 1 dd juv.—Stn DW1496, 18°43'S, 178°23'W, 392–407 m, 4 dd.

Distribution. South-western New Caledonia, 400–471 m (living at 471–490 m); Loyalty Islands, 463–490 m (dead); Fiji, 407–430 m (dead).

Description. Shell: Size moderate for genus (height up to 6.8 mm, width up to 6.7 mm), conical, slightly higher than wide; height 1.0–1.1x width, 3.1–3.5x aperture height; periphery subangular. Protoconch paucispiral, diameter approx. 300 µm, rounded, with 5 thin, unequally spaced spiral threads; terminal lip straight, without varix. Teleoconch of up to 5.5 whorls; first two whorls convex, subsequent whorls almost straight-sided; shoulder oblique with angulate rim, except on last whorl where shoulder horizontal; whorls with 8–10 spiral cords; cords thin and nearly smooth on first two whorls, thicker and beaded on subsequent whorls, beads of adapical cords much stronger, intervals between cords narrower than width of cords. Suture canaliculate on early whorls, not so on final whorl. First whorl sculptured by 6 thin, more or less equally spaced, spiral cords; cords arising immediately after protoconch; P1 at rim of shoulder; P6 sometimes partially covered by suture; faint, close-set axial threads between cords. On second whorl, P1 rapidly becoming stronger than other cords; P3 and P4 faint, difficult to distinguish; P2 and P5 of intermediate strength; axial threads evanescing by middle of whorl. Prosocline axial folds develop at start of third whorl, stronger on subsutural area and adapical part, rendering P1 and P2 subgranular; P1 and P5 the strongest cords, P5 stronger than P1, smooth, producing suprasutural (peripheral) carina; P6 totally covered by suture; secondary cord S3 arising at end of whorl, soon attaining size of P3 and P4. On fourth whorl, P1 and P2 strongly beaded, other cords subgranular; P6 partially visible on some samples, weakly subgranular. On fifth whorl, T1 arising at beginning of whorl, between suture and P1; shoulder more or less horizontal, suture not canaliculate; axial folds much weaker, but still visible. On final whorl, P6 arising at periphery; T2 arising above P5, rapidly resembling P4; T3 arising later between P1 and P2, beaded. Aperture subcircular; peristome incomplete; edge of outer and inner lips somewhat thickened; columella vertical, weakly concave, its edge slightly reflected at mid-point and overlapping umbilicus, a small flange at its base. Base weakly convex, almost flat, with 9–10 spiral cords; 3–4 outer cords smooth, relatively strong, their intervals similar to width of cords; cords of median area much weaker, their intervals approx. 1.5x width of cords; 2–3 inner cords much stronger and beaded; innermost cord at rim of umbilicus, twice as wide as penultimate cord and with strong, axially elongate beads. Umbilicus deep, comparatively wide (diameter ca. 17–21% of shell width), with angulate rim; internal wall almost straight, with 3–5 equally spaced, spiral cords of varying strength, crossed by axial grooves; intervals between cords approx. 0.5–1.0x width of cords.

Colour: Teleoconch whorls nacreous, white to greyish-blue, varying between samples; early teleoconch whorls white to deep grey, later whorls and base white to greyish-blue; protoconch white.

Radula ( Figs 23, 24 ): Rhipidoglossate; formula (5–6)+1+4+1+4+1+(5–6), with approx. 30 transverse rows of teeth; rows broadly M-shaped; rachidian cusp trigonal, with finely denticulate lateral margins and a somewhat larger central denticle; two inner lateral teeth similar to rachidian, but asymmetrical, their inner margin straight, the outer one curved; third lateral tooth more slender, fourth lateral tooth elongate and curved, with finer, more irregular denticles; interaction of base-plates complex; a well-developed, elongate-rectangular latero-marginal plate present; marginals 5–6, sickle-shaped, gradually tapering to a sharp point, lacking side denticles.

Remarks. Arxellia trochos cannot be confused with any known Solariellidae species belonging to other genera. Within Arxellia , it is closest to A. maestratii ( Figs 7 , 85–93 ) from Vanuatu and Wallis Island area, but the latter species is smaller, has stronger carina and the intervals between the spiral cords are wider (not narrower) than the width of the cords. The new species may also be compared to A. tracheia ( Figs 70–74 ) from Papua New Guinea and A. erythrea ( Fig. 94–103 ) from Tonga, but in these two species the peripheral carina is formed by P4 (not on P5).

The radula exhibits characteristic solariellid features ( Herbert 1987; Hickman & McLean 1990), especially the reduced number of rows (approx. 30), highly differentiated lateral teeth (2 inner teeth similar to rachidian tooth, fourth tooth elongate and curved) and relatively few marginal teeth per row; the well-developed latero-marginal plate is similar to that found in Archiminolia , Bathymophila , Spectamen and some species referred to Solariella .

This species was not included in the molecular phylogeny of Williams et al. (2013), but unpublished molecular studies confirm that it belongs in Clade A with the other species here referred to Arxellia .

Etymology. Trochos (Greek: τροχζ), a potter's wheel; used as a noun in apposition—with reference to the shape of the shell, the regular whorls of which are reminiscent of a piece of hand-made pottery.

Figures

FIGURES 1 – 9. Arxellia new species, all holotypes except A. tenorioi. 1, A. trochos, n. sp., type species of Arxellia n. gen. 2, A. boucheti n. sp. 3, A. herosae n. sp. 4, A. helicoides n. sp. 5, A. tenorioi n. sp. 6, A. tracheia n. sp. 7, A. maestratii n. sp. 8, A. thaumasta n. sp. 9, A. erythrea n. sp. Scale bar = 5 mm.

FIGURES 12 – 24. Arxellia trochos n. sp., New Caledonia. 12 – 14, holotype MNHN IM- 2009 - 23092, Banc de l’Orne / Walope, 400 – 520 m [EXBODI, stn DW 3862], 5.9 x 5.3 mm. 15 – 18, paratype MNHN IM- 2009 - 23109, Banc Sur Durand, 471 – 510 m [EXBODI, stn CP 3851]. 15 – 16, shell, 6.8 x 6.7 mm. 17, details of protoconch and early whorls; 18, details of columella, umbilicus and aperture. 19, paratype MNHN IM- 2009 - 23094, Banc de l’Orne / Walope, 425 – 490 m [EXBODI, stn DW 3861], 6.6 x 6.0 mm. 20 – 22, MNHN, 435 m [BIOCAL, stn DW 08], 6.3 x 5.8 mm. 23 – 24, paratype MNHN IM- 2009 - 23089, radula. 23, entire width of radula ribbon. 24, central field. Scale bar = 5 mm, except figs. 17, 23: 100 µm, fig. 18: 200 µm, fig. 24: 20 µm.

FIGURES 85 – 93. Arxellia maestratii n. sp., southern New Caledonia, Norfolk Ridge. 85 – 89, holotype MNHN IM- 2000 - 27389, Vanuatu, 487 – 507 m [MUSORSTOM 8, stn DW 972], 4.8 x 4.8 mm. 85 – 87, shell. 7.0 x 7.2 mm. 88, details of protoconch and early whorls. 89, details of columella and umbilicus. 90 – 91, MNHN, Vanuatu, 410 – 505 m [MUSORSTOM 8, stn DW 977], 5.6 x 5.2 mm. 92 – 93, MNHN, Wallis Island, 415 – 420 m [MUSORSTOM 7, stn DW 604], 4.8 x 4.8 mm. Scale bars = 5 mm, except fig. 88: 100 µm, fig. 89: 500 µm.

FIGURES 70 – 74. Arxellia tracheia n. sp., holotype MNHN IM- 2009 - 15183, Papua New Guinea. 70 – 72, shell, 6.7 x 6.4 mm. 73, details of protoconch and early whorls. 74, details of columella, umbilicus and aperture. Scale bar = 5 mm, except fig. 73: 100 µm, fig. 74: 1 mm.

FIGURES 94 – 103. Arxellia erythrea n. sp. 94 – 95, holotype MNHN IM- 2000 - 27391, Tonga, Vava'u group, 440 – 487 m [BORDAU 2, stn DW 1586], 5.5 x 5.4 mm. 96 – 100, paratype MNHN IM- 2000 - 27392, Tonga, Vava'u group, 578 m [BORDAU 2, stn DW 1585], subadult. 96 – 98, shell, 4.1 x 4.1. 99, details of protoconch and early whorls. 100, details of columella and umbilicus. 101 – 103, MNHN, Waterwitch Bank, 325 – 400 m [MUSORSTOM 7, stn DW 537], 5.2 x 5.1 mm. Scale bars = 5 mm, except figs. 99, 100: 100 µm.

Tables

TABLE 2. Arxellia trochos n. sp.: shell dimensions for type specimens.

TW	H	W	HA	H/W	H/HA	H/TW
holotype MNHN IM-2009-23092 5.1	5.9	5.3	1.7	1.11	3.47	1.16
paratype MNHN IM-2009-23109 5.5	6.8	6.7	2.1	1.01	3.24	1.24
paratype MNHN IM-2009-23094 5.4	6.6	6.0	2.1	1.10	3.14	1.22
paratype MNHN IM-2009-23089 5.5	6.6	6.3	2.0	1.05	3.30	1.20
paratype NHMUK 20140006 5.2	6.1	5.7	1.9	1.07	3.21	1.17