Integrative systematics of clathrinid sponges: morphological, reproductive and phylogenetic characterisation of a new species of Leucetta from Antarctica (Porifera, Calcarea, Calcinea) with notes on the occurrence of flagellated sperm

Abstract

Our study reports on the occurrence of a new species of Leucetta (Calcinea, Calcarea) from the Southern Ocean, Leucetta giribeti, sp. nov., collected in the shallow waters (15m depth) of Deception Island, South Shetland Islands. This new taxon is described based on a combination of morphological and molecular data, including the description of oocytes, embryos, larvae and sperm found in the choanosome. While female reproductive elements showed great similarities with those of other calcineans, sperm is reported here for the first time in the whole Calcinea subclass. Sperm cells are flagellated and possess a typical spermatic mid-piece, which is usually observed in cnidarians. In our phylogenetic analyses, we recovered Leucetta giribeti, sp. nov. as sister species of a clade formed by species of the genera Leucetta, Pericharax and Leucettusa. Although the clade in which Leucetta giribeti, sp. nov. is placed is supported by molecular and morphological features, we cannot propose a new genus due to uncertainties regarding the type species of the genus, Leucetta primigenia Haeckel, 1872. Our study reinforces the relevance of integrative approaches in the description of new taxa and contributes to resolving the poorly known reproductive patterns of Antarctic sponge species.