Cryptonatica undetermined

Cryptonatica sp. (Fig. 11B 1-B 3) MATERIAL AND DIMENSIONS. — Maximum height 9.2 mm, width 8.3 mm. — RGM.1364921 (188), leg. WG; RGM.1365004 (200+), leg. ACJ; RGM.1365218 (1), leg. AWJ; RGM.1310339 (1), leg. AWJ; RGM.1365107 (500+), leg. AWJ; RGM.1365265 (1 damaged operculum), leg. AWJ. SPECIES CHARACTERISATION. — Globular smooth shell. Three squared teleoconch whorls separated by deep suture. Base covered by a large collumelar lip. Large umbilicus, closed by a thick columellar callus. DISTRIBUTION. — Lower Pleistocene: Atlantic, Selsoif, NW France (this paper). REMARKS At present, two closely similar extant Cryptonatica species are recognised; Cryptonatica affinis, a cold water species present in shallow water of the Arctic Sea, Greenland, Island and Norway, but occurring rarely further southwards into the Bay of Biscay at greater depths, and therefore in colder waters, and C. operculata (Jeffreys, 1885), a warmer water species extending from the Bay of Biscay to North Africa, where it occurs in shallow water settings. The species were differentiated by Bouchet & Warén (1993) based on protoconch diameter. The diameter of the first half whorl of the warm water C. operculata is larger (0.6-0.7 mm) than that of the cold water C. affinis (below 0.5 mm). Specimens from Selsoif are intermediate, having a first half whorl diameter of 0.56 mm (based on 8 specimens). Material from the Naturalis collections was re-examined (RP). Five specimens from northern Norway and Nova Zembla gave a first half whorl diameter of 0.44 to 0.48 mm (mean 0.46), agreeing with Bouchet & Warén’s C. affinis measurements of <0.5 mm given for that species. Three specimens from northern Scotland had a mean first half whorl of 0.22 mm (0.20-0.23), less than half the size of C. affinis, and similar in size to specimens in the Naturalis collection from Mauritania wrongly identified as C. operculata. It is therefore likely that this group is composed of a species complex of more than two species.Detailed morphometric and genetic work is needed to clarify the taxonomic status of the Recent species, which is beyond the scope of this work. We also prefer not to erect a new taxon based on the Selsoif fossil specimens.