Based on the combination of molecular, morphological and biogeographical data presented here, we conclude that there are at least two, valid, extant species of Protatlanta in the Atlantic Ocean, P. souleyeti and P. sculpta. DNA barcoding of the CO1 gene supports differences in shell morphology, verifying that P. souleyeti and P. sculpta are separate species. The ability to use shell ornamentation to identify between the two species of Protatlanta ensures that they can be identified in sea floor sediments, in plankton samples and in the fossil record, where P. sculpta is known from the Pliocene (Piacenzian).
Biogeographical data have revealed that P. souleyeti and P. sculpta inhabit different oceanographic provinces in the Atlantic Ocean and are, therefore, ecologically differentiated. Initial analysis of sites from the Indian and Pacific oceans shows that P. souleyeti is found worldwide, whereas P. sculpta may be restricted to the Atlantic Ocean.
Aragonite shelled holoplanktonic gastropods (thecosome pteropods and Atlantidae heteropods) are considered to be threatened by, and important bioindicators of, ocean acidification. However, for many species we still do not have an adequate understanding of their species boundaries and biogeography, which is essential to recognise where to monitor for potential changes and what constitutes significant changes in species distribution. This study demonstrates that using an integrative taxonomic approach to reveal species boundaries is an important step in ensuring accurate species identification, which is crucial to understanding species distribution patterns.