Turrancilla apicalis Kira, 1959

(Fig. 21A–E)

Turrancilla sp. – Habe 1943: 71, pl. 3, fig. 7.

Turrancilla apicalis 1s. Taki MS, Kira 1954 –1958: 63, pl. 31, fig. 2 [nom. nud.]; 1959: 79, pl. 31, fig. 2 [with short description in Japanese].

Ancillus apicalis Ninomya 1988: 146–147, Pl. 1, figs. 9–11; Okutani (ed.) 2017: 332, 995, pl. 288, fig. 1.

Turrancilla suavis (Yokoyama, 1926) – Kira 1962–1968 (different printings of Shells of the Western Pacific in color): 88, pl. 32, fig. 2; Higo et al. 1999: 270, species G3125.

Type material. Holotype of Turrancilla apicalis Kira, 1959 – Osaka Museum of Natural History, 8082. Holotype of Ancillus apicalis Ninomiya, 1988 – NSMT 64458, paratype 1 NSMT 64459.

Type localities: Turrancilla apicalis – Tosa; Ancillus apicalis – Off Daiosaki Point, Shima Peninsula, Japan, 200–250 m in depth.

Remarks. The name was first introduced by T. Kira in the first edition of his Coloured Illustrations of the Shells of Japan (Kira 1954) without any description. Therefore, the name was long considered a nomen nudum. However, in the second edition of the book, Kira (1959) provided a brief description in Japanese, thus validating the name (Bieler & Petit 1990).

In subsequent printings of the book, Kira referred to the species as Turrancilla suavis (Yokoyama, 1926) (a fossil from the Cenozoic: Hijikata Formation). This nomenclature was later adopted by various authors (e.g., Higo et al. 1999). Ninomiya (1988) appears to have overlooked this validation and described the species again under the genus Ancillus, referencing Kira. Consequently, Ninomiya’s name is a junior subjective synonym and a secondary homonym of Turrancilla apicalis Kira, 1959. Comparison of the holotypes of Turrancilla apicalis (Osaka Museum of Natural History; Fig. 21A–C) and Ancillus apicalis (Fig. 21D–E) leaves little doubt that the specimens are conspecific. Ninomiya (1988) also compared the species to Ancilla suavis Yokoyama, 1926, and concluded that it represents a distinct species, differing “in having a remarkably deep depression on the subsutural band, a slender shape, and a larger size” (p. 147). The holotype of Ancilla suavis was deposited in UMUT CM 23364. However, according to the museum’s website, it is currently missing (https://umdb.um.u-tokyo.ac.jp/DKoseibu/en/Collection/ detail.php?umutNo=23364). The existing illustration of the type does not allow for resolution of the synonymy between suavis and apicalis. Thus, we follow Ninomiya’s (1988) opinion and consider them as two distinct species.

T. apicalis is recognized as the only recorded Recent species of the genus in Japan (Okutani 2017). The single specimen we sequenced from Japan falls within T. alcocki but differs from the types of T. apicalis by having a broader shell and a higher aperture. Nevertheless, it is important to emphasize that we are working with very limited material, and interspecific variation remains unstudied.

The species is very similar to T. glans, if distinguishable at all. A minor difference is that, in T. glans, the colour band crossing the columella (corresponding to the lower anterior band) is distinct and narrow. In contrast, in T. apicalis, it is either absent (as in the holotypes of A. apicalis and T. apicalis) or represented by a broad band with blurred edges (as seen in the paratype of A. apicalis). Due to the limited material from Japan and the lack of molecular data, the variability of the species could not be examined.

Considering the large geographic distance between specimens confidently identified as T. apicalis and our specimens of T. glans, we take a conservative approach and regard T. apicalis as a separate species, pending additional molecular data from Japan.