Atlanta fragilis Richter, 1993
This species has not been well recorded in publications and small specimens are likely to have been mistaken as A. peronii. Despite relatively few records, this species has now been found to in the Atlantic, Indian and Pacific oceans.
Shell extremely transparent and very large in the adult form of up to 9 mm.
The keel is tall and inserts between the final and penultimate whorls, leaving a large space between these two whorls (looks partially uncoiled, but with the keel filling the space).
The eyes are type b and, in adult forms are extremely tall (~1 mm).
The spire consists of 3¼ to 3½ whorls. It is similar to A. peronii and some times impossible to identify with certainty. The whorl sutures are often a purple colour, but the shell is colourless.
The shell is assumed to be very thin and fragile, however it is of moderate thickness (~4 μm) compared to other Atlanta species.
Operculum type b, radula type II.
Further reading and images:
Richter, G. 1993. Zur Kenntnis der Gattung Atlanta, 5. Die Atlanta peroni-Gruppe und Atlanta gaudichaudi (Prosobranchia: Heteropoda). Archiv für Molluskenkunde, 122: 189–205.
Seapy, R.R. 2011. Atlantidae. In: Tree of life web project. Available at http://tolweb.org/Atlantidae accessed 1 April 2017.
Wall-Palmer, D., Burridge, A.K., Goetze, E., Stokvis, F., Janssen, A.W., Mekkes, L., Moreno-Alcántara, M., Bednaršek, N., Schiøtte, T., Vinther Sørensen, M., Smart, C.W., Peijnenburg, K.T.C.A. Biogeography and genetic diversity of the atlantid heteropods. Progress in Oceanography, 160:1–25. doi: 10.1016/j.pocean.2017.11.004
Wall-Palmer, D., Metcalfe, B., Leng, M.J., Sloane, H.J., Ganssen, G., Vinayachandran, P.N., Smart, C.W. Vertical distribution and diurnal migration of atlantid heteropods. Marine Ecology Progress Series, 587: 1–15. doi: 10.3354/meps12464.
Wall-Palmer, D., Smart, C.W., Kirby, R., Hart, M.B., Peijnenburg, K.T.C.A., Janssen, A. 2016. A review of the ecology, palaeontology and distribution of atlantid heteropods (Caenogastropoda: Pterotracheoidea: Atlantidae). Journal of Molluscan Studies, 1-14.