New genus and species of Polymastiidae (Demospongiae: Hadromerida) from the Antarctic deep sea

Abstract

A new sponge genus and species, Astrotylus astrotylus, is described from the Antarctic abyssal zone. Its peculiar microscleres, herein referred to as astrotylostyles, combine the features of asterose spicules and tylostyles. Similar spicules are observed in Hymeraphia and Discorhabdella (order Poecilosclerida). But this similarity is convergent as far as a radial choanosomal skeleton composed by principal tylostyles and a cortical palisade of small tylostyles in Astrotylus undoubtedly confirm its allocation to the order Hadromerida and most likely to the family Polymastiidae. Atergia, Acanthopolymastia and Tylexocladus have the closest affinities with Astrotylus that calls for the phylogenetic analysis of their relations. Meanwhile astrotylostyles of Astrotylus, cladotylostyles of Tylexocladus and grapnel-like exotyles of Proteleia may be the remnants of non-monaxonic ancestral spicule type in Polymastiidae that calls for reconsideration of the relations between hadromerid families.