Atlantilux, HUANG, 2015

GENUS ATLANTILUX HUANG, 2015 View in CoL

FIGURE 24A – H

Type species: Mitra exigua C.B. Adams, 1845 (OD). Diagnosis: Shell small, not exceeding 12 mm, turriform, elongate-fusiform to biconical, with rather wide aperture and stout siphonal canal. Protoconch wide, bulbous, of about 1.5 glossy, convex whorls, or papilliform, with three or more weakly convex whorls. Suture distinct, impressed. Teleoconch whorls typically with wide, slightly concave, subsutural area sculptured with dense, rounded axial riblets; riblets of similar morphology developed on shell base. Periphery strongly convex, typically situated below whorl mid-height, sculptured with strong and wide rounded ribs. Rarely, whorl outline flattened, and sculpture of two rows of nodules developed, one adapical, other situated at whorl periphery. Spiral sculpture absent or represented by regular fine threads throughout whorl height. Last adult whorl strongly convex, siphonal canal typically constricted to stout, sculptured with several strong oblique cords, formed by the continuation of the columellar folds. Siphonal notch shallow or indistinct. Aperture rather wide, outer lip lirate within. Inner lip bearing four narrow, subequal, oblique folds. Shell typically light- to dark-brown or olive green, or pink, with spiral white band on whorl periphery, often intersected by one or two fine brown threads; shell rarely uniform white. Head-foot and siphon dark grey or black, with multiple white and light-yellow spots. Tentacles rather long with eyes situated laterally at their bases. Radula with robust multicuspidate rachidian and sickle-shaped unicuspidate laterals.

Included species: Carribean: Atlantilux exigua (C.B. Adams, 1845) ( Fig. 24A, B.); 1 Atlantilux ampla Huang, 2015 ; 2 Atlantilux gemmata (G.B. Sowerby II, 1874) ; 2 Atlantilux narcisselli Huang, 2015 ; 2 Atlantilux puella (Reeve, 1845) comb. nov. ( Fig. 24C, D). 1

Indo-Pacific: Atlantilux nodospicula ( Cernohorsky, 1970) comb. nov. ( Fig. 24E); 1 Atlantilux rubra (Broderip, 1836) comb. nov. ( Fig. 24F – H). 1

Distribution and habitat: Caribbean, intertidal and shallow subtidal depths; Indo-Pacific, shallow subtidal and bathyal depths.

Remarks: Typically Atlantilux can easily be recognized by its large bulbous protoconch in combinaton with a characteristic whorl profile, with wide, slightly concave subsutural ramp and whorl periphery shifted towards lower suture. A distinctive sculpture pattern, of dense riblets in subsutural area and notably wider folds on whorl periphery, is developed in Atlantilux exigua , Atlantilux ampla , and Atlantilux narcisselli , and is faint in Atlantilux gemmata ( Redfern, 2013) . These four species form a rather distinctive group that we consider to be ‘typical’ Atlantilux (as it includes the type species). One more Caribbean species, Vexillum sykesi (Melvill, 1925) , has stronger spiral elements, but is close overall to typical Atlantilux in shell proportions and whorl outline, and is likely to be closely related to the other four species mentioned.

A bulbous protoconch suggestive of non-planktotrophic development is also present in Austromitra and Pusia (Ebenomitra) . Austromitra species can usually be distinguished from Atlantilux spp. by a weaker sculpture lacking spiral elements, and typically evenly convex whorls. Members of Ebenomitra , in addition to their weaker sculpture compared with Atlantilux , possess a tricuspidate rachidian, whereas it is multicuspidate in Atlantilux .

The Caribbean Atlantilux puella , and Indo-Pacific Atlantilux nodospicula and Atlantilux rubra , are conchologically very divergent from typical Atlantilux , and are placed here in Atlantilux based on currently available molecular data, and pending a more thorough phylogenetic analysis. The Indo-Pacific species assigned here to Atlantilux all have pointed, multi-whorled protoconchs, which readily differentiate them from the Caribbean species. (However, more Indo-Pacific species with paucispiral protoconchs currently placed in Vexillum may turn out to belong to Atlantilux .) The two species of Atlantilux recognized in our phylogenetic analysis differ notably from each other in sculpture and whorl profile, and some minute species of Vexillum (for example Vexillum herosae Herrmann & Salisbury, 2012 ; Vexillum salisburyi Cernohorsky, 1976 , or Vexillum altisuturatum Chino & Herrmann 2014 ), fall well within the range of conchological variation for Atlantilux ; however, Vexillum herosae , at least, is a true Vexillum based on our phylogenetic analysis. Further studies are needed to understand the extension and boundaries of Atlantilux .