Crossing the polar front—Antarctic species discovery in the nudibranch genus Tritoniella (Gastropoda)

Abstract

Tritoniella belli is the only valid species of a nudibranch genus endemic to the Southern Ocean. Recent exhaustive sampling and molecular analyses led to the discovery of several new lineages. A total of 69 specimens were collected from 25 sites across the Weddell and Scotia Seas, from 5 to 751 m depth. In this study, we provide morphological and anatomical characters to describe five new Tritoniella species, namely T. gnocchi n. sp., T. prinzess n. sp., T. gnathodentata n. sp., T. schoriesi n. sp., T. heideae n. sp. Detailed descriptions of colouration, external morphology, digestive and reproductive organs, distribution, and ecology are presented in a systematic context. These are compared to the type material from the Ross Sea of T. belli and its synonym T. sinuata, whose status requires additional sampling to be solved. Discrete differences in external characters, including the shape of dorsal notum ridge and mantle edges, support the species hypotheses delimited by Moles, Berning et al. (2021). Moreover, detailed scanning electron microscopy images of the masticatory border of the jaws, radula teeth, and penial papilla were provided and their differences discussed. The gut content of all species revealed sclerites of Primnoidae gorgonians as their preferred prey. Pseudo-cryptic radiations along the Scotia Arc, explained by the combination of distribution reduction due to glacial cycles and the existence of refugia, and enhanced by their direct development, could explain the allopatric speciation events in Tritoniella species.