Arxellia tracheia, 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 : 272-273

Arxellia tracheia n. sp.

( Figs 6 , 70–74 )

Clade A, sp. 3— Williams et al., 2013.

Type material. Holotype (6.7 x 6.4 mm) MNHN IM- 2009-15183.

Type locality. Papua New Guinea, Vitiaz Strait, BIOPAPUA, stn CP3721, 6°03’S, 147°37'E, 542– 554 m.

Material examined. Papua New Guinea, Vitiaz Strait. BIOPAPUA: stn CP3721, 6°03’S, 147°37'E, 542–554 m, 1 lv (holotype).

Distribution. Only known from the type locality.

Description. Shell: Size moderate for genus (height 6.7 mm, width 6.4 mm), conical, slightly higher than wide; height 1.05x width, 2.9x aperture height; periphery subangular. Protoconch paucispiral, diameter approximately 350 µm, rounded, with minute, crisp granules and 6 thin, more or less equally spaced spiral threads, adapical threads arising at half whorl; terminal lip straight, without varix. Teleoconch of up to 5.4 whorls; first two whorls moderately convex, subsequent whorls almost straight; shoulder horizontal on first three whorls, evanescing on later whorls; whorls sculptured with up to 9 spiral cords; cords thin and nearly smooth on first two whorls, thicker and beaded on following whorls; beads of adapical cords much stronger. Suture shallowly canaliculate on early whorls, not so on final whorl. First whorl convex, sculptured by 5 thin, more or less equally spaced spiral cords arising immediately except P1 appearing a little later; P1 at rim of shoulder, P5 just above suture; faint, close-set axial threads in cord intervals. On second whorl, all cords similar in size; P5 partially covered by suture; axial threads evanescing in middle of whorl. Prosocline axial folds arise during third whorl, stronger on subsutural area and adapical part, rendering P1 beaded; P1 and P4 strongest, both beaded, P1 stronger than P4; P4 forming suprasutural carina; P3 weakening; secondary cord S3 arising in middle of whorl, rapidly equalling P 3 in strength. On fourth and fifth whorls, P1 and P4 strongest, P2, P3 and S3 weakest, P5 of intermediate strength. On last whorl, T1 arising at start of whorl, between P1 and P2; T2 arising at same time, between S3 and P4, both subgranular; S5 arsing at periphery. Aperture roundly quadrate, weakly oblique; peristome incomplete; outer and inner lips moderately thick at rim; angulation at base of columella weak. Columella vertical, shallowly concave, with small basal flange fused to strong callus and forming one lobe at midpoint, partially overlapping umbilicus. Base almost flat, with 4 thin, smooth outer cords, intervals between cords twice width of cords; median area smooth; a single strong cord with coarse, axially elongated beads marking angulate rim of umbilicus. Umbilicus superficially wide (diameter ca. 23% of shell width), but funnel-shaped and thus narrowing internally, its wall sculptured with thin axial threads.

Colour: Early teleoconch whorls greyish-blue, later whorls pinkish; base nacreous white; suture white; protoconch brownish-pink.

Remarks. Arxellia tracheia most closely resembles A. trochos ( Figs 1 , 12–24 ) from southern New Caledonia, but though of similar size, that species has a more rounded periphery and differs in numerous sculptural features, namely: P5 (not P4) forms the suprasutural carina, all the teleoconch spiral cords are more or less similar in size, the shoulder is still present on the last whorl, there are 2–3 (rather than one) strong, beaded cords around the umbilicus. In the molecular analysis of Williams et al. (2013), A. tracheia forms a clade with A. boucheti and A. helicoides .

Etymology. Uneven, rough (Greek: ταχζ, εια, υ, adjective)—with reference to the different size of the spiral cords on the shell whorls.

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 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 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.