Nanaphora decollata (Rolán & Fernández-Garcés, 1994)

(Fig. 11 A-E)

Cheirodonta decollata Rolán & Fernández-Garcés, 1994: 20, figs 19- 21, 23-24, 30CD; 2007: 20, pl. 1, figs 6-11. — Zhang 2011: 99, fig. 289. — Redfern 2013: 127, fig. 361. — Lamy & Pointier 2018: 284, pl. 91, fig. 2.

Nanaphora decollata – Fernandes & Pimenta 2015: 502. — Rolán & Fernández-Garcés 2015: 53, fig. 4V.

TYPE MATERIAL. — Holotype. Cuba • sh; MNCN 15.05/11142. Paratypes. See the original description.

TYPE LOCALITY. — Cuba: Marianao beach, La Habana.

MATERIAL EXAMINED. — Guadeloupe. KARUBENTHOS 1 • 1 sh; sta. GB09; MNHN.

GEOGRAPHIC DISTRIBUTION. — Bahamas (Redfern 2013); Cuba (Rolán & Fernández-Garcés 1994); Cayman (this study); Antigua (Zhang 2011); Guadeloupe (Rolán & Fernández-Garcés 2015; Lamy & Pointier 2018; this study).

BATHYMETRIC DISTRIBUTION. — Recorded depth in Guadeloupe: 6 m. Previous recorded depth in the West Atlantic: 2 m (Rolán & Fernández-Garcés 1994) to 14 m (Redfern 2013).

REMARKS

Nanaphora decollata was originally described in Cheirodonta Marshall, 1983, a genus with only two confirmed species, i.e., the type species Cheirodonta pallescens (Jeffreys, 1867) from the East Atlantic and Cheirodonta dupliniana (Olsson, 1916) from the West Atlantic, plus a third species [ Cheirodonta labiata (A. Adams, 1854), from Australia] with a tentative allocation (Marshall 1983; Fernandes & Pimenta 2015). The Atlantic species of Cheirodonta have radula with multicuspid teeth, of which the marginal are much elongated (Bouchet & Guillemot 1978; Bouchet 1985; Fernandes & Pimenta 2019b). In fact, there are significant similarities between the radula of N. decollata (Rolán & Fernández-Garcés 1994) and those of Cheirodonta, mainly in the morphology of the lateral teeth, with the central and marginal teeth of N. decollata being also similar to those of C. dupliniana, but slightly different from those of C. pallescens, which shows central tooth with a diastema and marginal teeth with cusps restricted to the distal part of the basal plate. The protoconch of N. decollata is also slightly similar to that of Cheirodonta, bearing granules on the embryonic shell and two spiral cords on the larval shell (Fig. 11E), although the former protoconch is shorter and its whorls are more convex. The most discrepant differences between N. decollata and Cheirodonta rely on teleoconch features, with the former showing a small and ovoid shell shape, nodules much larger (including the subperipheral and basal cords) and a much reduced suture (Fig. 11A). These conditions are also observed in other West Atlantic species, which, perhaps prematurely, led Fernandes & Pimenta (2015) to include them in Nanaphora, a probably non-monophyletic genus which shows species with different patterns of embryonic and larval shell sculptures, and whose type species has a paucispiral protoconch (hindering comparisons) and unknown radula (Marshall 1983; Fernandes & Pimenta 2015). Citing Fernandes & Pimenta (2015: 502), “the affinity among the genera Nanaphora, Opimaphora Laseron, 1958 and Cheirodonta makes necessary a taxonomic revision of them to achieve a precise delimitation of each genus”, including a further molecular phylogeny.

Two unusual teleoconch features of N. decollata were indicated by Rolán & Fernández-Garcés (1994) and Redfern (2013), and are confirmed here. The presence of micro-sculpture (Fig. 11B) is not widespread in Triphoridae (Marshall 1983; Fernandes & Pimenta 2020), but some species currently allocated in Nanaphora may show it (Marshall 1983; see also the next species). Another remarkable feature of N. decollata is the emergence of the median spiral cord not between the adapical and abapical cords, as observed in most triphorids, but derived from a split of the adapical cord on the body whorl (Fig. 11C), after the adapical cord had become axially elongated – it does not seem a supranumerical cord (Bouchet 1985; Fernandes & Pimenta 2015). The splitting of one spiral cord into two cords is observed in some species of Cerithiopsidae H. Adams & A. Adams, 1853, and it was reported in a Triphoridae species from Ascension Island (Bakker & Swinnen 2021), although with a different formation and major divergences in the shell.

Rosenberg (2009) cited two new localities for the Caribbean range of Nanaphora verbernei (Moolenbeek & Faber, 1989), i.e., Cayman and Grenada, based on material from the ANSP collection. After checking images of the single lots for such localities (ANSP 200078, Grand Cayman Is., 2 m - 2.8 mm long, with protoconch; ANSP 296542, Prickly Bay, Grenada, 0-1 m - 3.5 mm long, without protoconch), the material from Cayman actually refers to N. decollata, whereas that from Grenada is worn and precludes further identification (although it seems N. decollata). The main difference between both species is the spiral sculpture of the protoconch, since N. decollata has always two spiral cords (Fig. 11E). Shells without apex may be much similar owing to the ovoid shape and bifurcating adapical spiral cord of teleoconch (for N. verbernei, see Fig. 13B and Moolenbeek & Faber 1989: fig. 8). Rolán & Fernández-Garcés (1994) argued that the white band is only seen in the adapical cord of N. decollata, but it can be also present in the abapical cord in the penultimate whorl of N. verbernei, which is seen in most shells from Martinique without apex (Fig. 11 F-I); even though, it is preferred to name these decollate shells as N. cf. verbernei, and so far N. decollata is absent from Martinique.