Past and present of the enigmatic genus Lanayrella Salvador & Cunha, 2020 (Gastropoda: Cephalaspidea) in the southwestern Atlantic Ocean

Abstract

The genus Lanayrella currently comprises two recent, minute gastropods species, Lanayrella vagabunda and L. ringei, both known exclusively from the Magellanic Region. The genus was originally assigned to Acteonidae because it shares with Acteon a relatively wide and thick shell with a moderately elevated spire, a sculpture dominated by spiral elements, and a strong columellar fold. However, it lacks a distinct proto/teleoconch boundary, a diagnostic feature of Acteon. Here, L. ringei is studied for the first time based on shell morphology and gross anatomy, which reveal as key characters a cephalic shield divided into two lobes with lateral tentacular pads and the absence of an operculum. These features strongly suggest that Lanayrella belongs among cephalaspidean gastropods rather than within Acteonidae, a “lower” heterobranch taxon. Furthermore, both shell and radular morphologies are comparable to those of certain species of Toledonia and Bogasonia, leading to Lanayrella bullata n. comb. here proposed. Specimens from the Monte León Formation (lower Miocene) of southern Argentina are herein reported as L. vagabunda representing the first fossil record of the genus. This finding indicates that Lanayrella is part of an ancient lineage of highly distinctive gastropods whose presence in southern South America can be traced back at least 20 million years.