Discovery of Petromica Topsent in the Pacific Ocean: a revision of the genus with a new subgenus (Chaladesma, subgen. nov.) and a new species (P.(C.) pacifica, sp. nov.) (Porifera : Demospongiae : Halichondrida : Halichondriidae)

Abstract

Petromica Topsent, a sublithistid demosponge with affinities to Halichondriidae (Demospongiae : Halichondrida), is revised from type material to explore the phylogenetic and biogeographic relationships of a new species, P. pacifica, sp. nov., from the southern Great Barrier Reef and south-eastern Queensland, being the first record of the genus for Australian waters and for the Pacific Ocean. The present work brings the total number of species known worldwide to eight. Phylogenetic analysis confirms the monophyly of the genus and its synonymy with the nominal genus Monanthus. These analyses indicate that the new species is most closely related to two western Atlantic species (southern Brazilian to the central Caribbean), for which a new subgenus Chaladesma, subgen. nov. is proposed. Chaladesma differs from the nominotypical subgenus in its soft consistency confined to the basal portion of the choanosome (v. firm to rigid), reflecting the poorly developed desma skeleton, and lack of desma zygoses; possession of multiple papillae supported internally by sinuous tracts of oxeas (v. either no papillae or papillae supported by spiral plumose tracts); a single size class of oxeas (v. two size classes); and a moderately high proportion of monocrepidial desmas (with visible axial canal) (40–45%) (v. 0–5%, except in P. plumosa, which has 90% monocrepidial desmas).