Hinea nucleola ( Moerch , 1876) Strong & Bouchet, 2020

Strong, Ellen E. & Bouchet, Philippe, 2020, Hidden in plain sight: two co-occurring cryptic species of Supplanaxis in the Caribbean (Cerithioidea, Planaxidae), ZooKeys 991, pp. 85-109 : 85

Hinea nucleola ( Moerch, 1876) comb. nov. Fig. 3E

Planaxis nucleola Mörch, 1876: 126

Holotype.

U.S. VIRGIN ISLANDS • 7.8 mm in height; St Croix; 1849; Ørsted leg.; ZMK 152749 (Fig. 3E ).

Other material.

U.S. VIRGIN ISLANDS • 1 spm; St. John, Caneel Bay; USNM 1620829.

Description.

Shell. Shell small for the genus, solid, littoriniform, high-spired, consisting of 5+ (apex broken or corroded in the two known specimens) weakly convex whorls separated by impressed suture, last whorl occupying ca 80% of total shell height. Shell surface smooth, except incised spiral grooves, 0-2 adapically below suture and 2-8 on shell base. Aperture ovoid, occupying ca 40% of total shell height, with 0-4 low internal lirae, with distinct siphonal notch, narrow callus adpressed to parietal and columellar areas, parietal tooth strong, blunt. Color dark brown olive in holotype, to light orange brown with white parietal tooth and columellar callus. Height 7.8-8.4 mm.

Remarks.

Planaxis nucleola was described based on a single specimen, and the "probable holotype" (Fig. 3E ) is in the Statens Naturhistoriske Museum [formerly Naturhistorisk Museum], Copenhagen. The type locality was St Croix, then in the Danish Virgin Islands [currently U.S. Virgin Islands].

Planaxis nucleola was explicitly separated from P. nucleus by Mörch (1876) by its much less acutely pointed shell and spiral grooves restricted to the base. It had never been illustrated, and we have not traced any citation of that species since Mörch (1876). It is currently indexed in MolluscaBase in the synonymy of S. nucleus based on Rosenberg (2009).

The genus-group name Angiola Dall, 1926, has long been in use for Caribbean planaxids ( Houbrick 1987; Rosenberg 2009), but was synonymized with Hinea by Ponder (1988).

Discussion.

The sympatry and syntopy of Supplanaxis nucleus and S. nancyae raise the question of the evolutionary mechanism that might have led to the emergence of two species. Unexpectedly, the phylogenetic tree did not resolve S. nucleus and S. nancyae as sister taxa. A specimen of the Panamic Supplanaxis planicostatus (G.B. Sowerby I, 1825) from Panama City [type locality: Galapagos Is; Fig. 3B ], sequenced only for the 16S gene, is placed as sister to S. nancyae , albeit with no support. A further eastern Pacific Supplanaxis species is S. obsoletus (Menke, 1851) [type locality: Mazátlan, Pacific coast of Mexico]. The Caribbean and the Panamic species of Supplanaxis have obviously shared a long part of their evolutionary history, and more phylogenetic work needs to be done to properly assess their relationship.

Figures

Figure 3. Type specimens of Supplanaxis nucleus and relevant planaxids. A Buccinum nucleus Bruguiere, 1789. Neotype, MNHN-IM- 2000 - 35804 B Planaxis planicostatus G. B. Sowerby I, 1825. Syntype NHMUK 1966623 (© The Trustees of the Natural History Museum, London, http: // creativecommons. org / licenses / by / 4.0 /; https: // data. nhm. ac. uk / object / 4767541 c-a 5 d 1 - 41 db-aa 0 c- 0 c 03724 e 970 a) C Planaxis (Supplanaxis) nancyae Petuch, 2013. Holotype, FMNH 328402 (© Field Museum of Natural History-CC BY-NC; https: // collections-zoology. fieldmuseum. org / catalogue / 2877223) D Planaxis niger Quoy and Gaimard, 1833. Syntype, one of 22 specimens, MNHN-IM- 2000 - 27769 E Planaxis nucleola Moerch, 1876. Probable holotype, ZMK 152749. Scale bar: 1 cm.