Amalda alabaster, Kantor & Castelin & Fedosov & Bouchet, 2020

Kantor, Yuri I., Castelin, Magalie, Fedosov, Alexander & Bouchet, Philippe, 2020, The Indo-Pacific Amalda (Neogastropoda, Olivoidea, Ancillariidae) revisited with molecular data, with special emphasis on New Caledonia, European Journal of Taxonomy 706, pp. 1-59 : 36-40

Amalda alabaster sp. nov.

urn:lsid:zoobank.org:act:48866CE5-477F-4ED8-9FDF-D323C1126E56

Figs 13 D–E, 15

Diagnosis

Shell small, up to 27 mm, ovate fusiform, with low broad conical spire and small low dome shaped protoconch (diameter of first whorl ca 0.8 mm). Primary callus smooth, shallowly impressed on left side at last whorl suture, secondary callus weakly microshagreened. Olivoid groove very shallow and indistinct. Anterior band separated by distinct fasciolar ridge into upper and slightly broader lower bands. Colour uniformly white.

Etymology

The specific epithet refers to the white and semitransparent shell. Used as a noun in apposition.

Type material

Holotype

SOUTHERN NEW CALEDONIA • 22°06′ S, 167°03′ E; 190–200 m deep; TERRASSES; stn DW3093; MNHN IM-2007-43627; sequenced.

Material examined

Sequenced material

9 sequenced specimens ( Table 1).

Not sequenced material

NEW CALEDONIA • 1 lv; type locality; IM-2007-43633 • 3 lv; Bassin des Loyauté ; 21°45′ S, 166°37′ E; 253–266 m deep; HALIPRO1; stn CP852 • 3 dd; 17 lv; 21°45′ S, 166°37′ E; 241–250 m deep; HALIPRO1; stn CP853 • 6 dd; east coast of mainland New Caledonia ; 21°48′ S, 166°41′ E; 239–250 m deep; BATHUS 1; stn DW649 • 8 dd; 21°48′ S, 166°41′ E; 264–269 m deep; BATHUS 1 ; stn DW650 • 5 dd; 21°17′ S, 165°57′ E; 237–298 m deep; BATHUS 1 ; stn DW654 • 42 lv; 4 dd; 21°45′ S, 166°37′ E; 250 m deep; BATHUS 1; stn CP713.

Description (holotype)

MEASUREMENTS. SL 26.7 mm, AL 13.5 mm, SW 10.7 mm.

SHELL. Small, ovate fusiform with relatively broad base, SW/SL 0.40; body whorl evenly weakly convex on right side, and slightly bulging on left side due to strong callus, greatest width of body whorl median. Protoconch nearly completely covered by callus with part of first whorl exposed, low dome shaped. First protoconch whorl diameter 0.79 mm. Spire low, broadly conical; primary callus thick and covering all whorls except part of protoconch, shallowly impressed on left side at last whorl suture. Surface of callus glossy, smooth, with weak indistinct spiral ridges, secondary callus thick, with distinct anterior border, joining parietal callus without visible border, extending to right ventral side of last whorl and continuing up to form a thick, tongue-shaped pad that reaches suture of antepenultimate whorl. Surface of secondary callus weakly shagreened. Body whorl cloak weakly glossy, smooth, not microshagreened. Olivoid groove very shallow and indistinct, terminating in short, broadly triangular, labral denticle. Rear edge of anterior band very sharp and distinct. Anterior band subdivided into upper and lower parts by distinct fasciolar ridge. Both upper and lower bands very weakly evenly convex, nearly flat. Plication plate with deep and broad groove at upper third, separating adapical largest spiral ridge, and two slightly smaller ridges similar in size. Columella smooth. Aperture irregularly oval, rounded posteriorly due to callus, widest medially; outer lip medium thick, orthocline in side view, nearly straight, with slight, blunt labral denticle; siphonal notch shallow, symmetrically U-shaped. Colour uniformly white.

RADULA (n =3) ( Fig. 13 D–F). Similar in all specimens. Central tooth tricuspid, with central cusp slightly longer than lateral ones. Cusps smooth, but lateral flaps strongly serrated and bearing longitudinal grooves between cusplets. 1–4 additional small cusplets between central and lateral major cusps.

Remarks

All sequenced specimens of A. alabaster sp. nov. are very similar to the holotype. In addition to pure white specimens, some are light ivory in colour of the upper teleoconch whorls or even of the entire shell (MNHN IM-2007-43583, Fig. 15 C–D).

Conchologically Amalda alabaster sp. nov. is extremely similar to white specimens of A. montrouzieri . The slight differences may be the more regularly oval outline and the more cyrtoconoid spire of A. montrouzieri , but those differences are very subtle. The new species is recorded at larger depths than

most of specimens of A. montrouzieri (180–210 versus 10–70 m), but A. montrouzieri can occasionally occur at the same depths as A. alabaster sp. nov.

Although A. montrouzieri and A. alabaster sp. nov. are closely related, a large genetic distance between them confirms their distinction. Furthermore, there appears to be a minor difference in the radula. In A. montrouzieri the central cusp of the central tooth is clearly shorter than the lateral ones, but in A. alabaster sp. nov. the situation is opposite – the central cusp is distinctly longer. The illustration of the radula of A. montrouzieri by Kilburn & Bouchet (1988: figs 51, 53) shows a central tooth with a morphology similar to that in our A. alabaster sp. nov. Regrettably, the authors did not present the station data of the specimen from which the radula was extracted and, therefore, it is not clear whether they indeed examined A. montrouzieri . All our sequenced specimens originated from only two stations off south and south-eastern New Caledonia at depths of 180–210 m, but numerous non-sequenced specimens (see Material) were collected in the depth range of 237– 298 m. Some have a light yellowish spire callus and upper anterior band.

One specimen (MNHN IM-2013-63897, Fig. 15 H–I) from a station more to the North on the east coast of New Caledonia is sister to A. alabaster sp. nov., with a very high support. Conchologically it differs from A. alabaster sp. nov. in having a stouter shell with thicker primary callus and a more pronounced colouration. It may represent a geographical morph (although it was collected very close to the type locality of A. alabaster sp. nov.) or even a separate species, but at the moment the lack of additional sequenced material does not allow to draw firmer conclusions. So, we refer to this and similar specimens as A. cf. alabaster sp. nov. The ABGD analysis also attributed A. cf. alabaster sp. nov. to the same PSH as A. alabaster sp. nov.

Distribution

South-eastern New Caledonia, in 180– 280 m.

Figures

Fig. 13. Radulae of species of Amalda H. Adams & A. Adams, 1853. A–C. A. montrouzieri (Souverbie, 1860). A–B. Île Ouen – Baie du Prony, LAGON, stn DW239, 22°24.3′ S, 166°57.8′ E, 42–43 m, SL 20.2 mm. C. Grand Récif Sud, LAGON, stn DW544, 22°50.8′ S, 166°48.5′ E, 25 m, SL 25.4 mm (shell on Fig. 12I). D–E. A. alabaster sp. nov. D. Holotype, MNHN IM-2007-43627, SL 26.7 mm (shell on Fig. 15A–B). E. MNHN IM-2007-43636, SL 17.6 mm. F. A. cf. alabaster, MNHN IM-2013-63897, SL 18.1 mm (shell on Fig. 15H–I). G. A. allaryi Bozzetti, 2007, MNHN IM-2013- 68272 (shell on Fig. 17A). H. A. coriolis Kilburn & Bouchet, 1988, MNHN IM-2013-63899 (shell on Fig. 18H–I).

Fig. 15. Amalda alabaster sp. nov. A–B. Holotype, MNHN IM-2007-43627, SL 26.7 mm. C-D. MNHN IM-2007-43583, SL 24.8 mm. E. MNHN IM-2007-43621, SL 27.1 mm. F. MNHN IM-2007-43626, SL 22.2 mm, specimen not sequenced. G. MNHN IM-2007-43633, SL 22 mm, specimen not sequenced. H–I. A. cf. alabaster, MNHN IM-2013-63897, SL 18.1 mm. Shells at the same scale, all specimens except F–G sequenced.