All specimens of Protatlanta (Table S1) were assessed for shell ornamentation. Following the results of this study, specimens with shell ornamentation were identified as P. sculpta and non-ornamented specimens were identified as P. souleyeti (Fig. 5). These specimens (N=1003) indicate that P. sculpta is distributed throughout the Atlantic (Fig. 5a). However, quantitative sampling along the meridional transect of AMT24 shows that P. sculpta is rarely found within the subtropical gyres, being most abundant in the equatorial upwelling region (Figs 5a, 6). Conversely, quantitative sampling shows that P. souleyeti, although widespread in the Atlantic Ocean, has a preference for the northern and southern oligotrophic subtropical gyres (Figs 5b, 6). This suggests that the two species have different ecological preferences, with P. souleyeti preferring oligotrophic regions and P. sculpta preferring more nutrient rich waters.
Samples from the Indian and Pacific oceans permitted initial investigation of the wider distribution of these two species. Specimens of P. souleyeti were found worldwide, however, only a single specimen of P. sculpta was found outside of the Atlantic Ocean. This single specimen of P. sculpta (ZMUC_GAS_782) was collected in the Marquesas Islands and a specimen of P. souleyeti was collected at the same site.