Fifteen Seconds of Mediocrity

Specimen assigned to 'Gemmula aff. G. asukana' by MacNeil (1960).

This is going to be another one of those posts where I try to actually build something on the back of some obscure taxon about which I've only managed to find enough to fill about two sentences. You have been warned.

Kuroshioturris asukana was described as Drillia asukana by Yokoyama in 1926 in the Journal of the Faculty of Science, Imperial University of Tokyo. That might in itself explain why I haven't been able to access the original description (for my American readers, the appropriate issue is on Google Books here, in case this is another one that Google is only making available within the United States). The species is a Pliocene member from Japan of the gastropod superfamily Conoidea, the 'poison-tongued' gastropods, in the family Turridae. The exact position of asukana in the turrids has shifted around a bit: it has appeared in Clavatula, in Gemmula, in (the most horrifying turrid genus of all) Pleurotoma, before Powell (1966) placed it into Kuroshioturris (treated by Powell as a subgenus of Ptychosyrinx, but as a separate genus by later authors such as Beu 2011). A second specimen other than the holotype assigned by Yokoyama to Pleurotoma asukana in 1928 may not in fact be the same species, and MacNeil (1960) noted that the holotype appeared to be a juvenile, further complicating identification.

The type species of Kuroshioturris, K. hyugaensis, from the East China Sea. Photo from here.

Powell (1966) stated that Kuroshioturris was restricted to the Miocene and Pliocene of Japan, but this was an error. Two of the species listed by Powell (including the type species of the genus) are in fact members of the Recent fauna. Beu (2011) also assigned two species from the Pliocene to Recent of New Zealand to Kuroshioturris. Powell distinguished Kuroshioturris from Ptychosyrinx sensu stricto on the basis of the protoconch morphology, noting that the adult shell was otherwise nearly identical. However, other cases of conoid genera being separated solely on the basis of protoconch form have since been regarded as invalid (Beu 2011). Protoconch morphology often reflects to mode of larval lifestyle for the animal: a tall, narrow protoconch (such as in Ptychosyrinx) indicates an actively feeding, planktotrophic larva, while a blunt, short protoconch indicates a lecithotrophic larva nourished by yolk reserves. Changes from one nutritional mode to another seem to have happened repeatedly, leading to cases such as the lecithotrophic 'genus' Maoritomella turning out to be a polyphyletic assemblage of Tomopleura species that had independently abandoned planktotrophy. Many such genera have now been synonymised, but many (such as Kuroshioturris?) still require examination.

REFERENCES

Beu, A. G. 2011. Marine Mollusca of isotope stages of the last 2 million years in New Zealand. Part 4. Gastropoda (Ptenoglossa, Neogastropoda, Heterobranchia). Journal of the Royal Society of New Zealand 41 (1): 1-153.

MacNeil, F. S. 1960. Tertiary and Quaternary Gastropoda of Okinawa. Geological Survey Professional Paper 339.

Powell, A. W. B. 1966. The molluscan families Speightiidae and Turridae: an evaluation of the valid taxa, both Recent and fossil, with lists of characteristic species. Bulletin of the Auckland Institute and Museum 5: 1-184, pls 1-23.