Sponges from Doumer Island, Antarctic Peninsula, with description of new species of Clathria (Axosuberites) Topsent, 1893 and Hymeniacidon Bowerbank, 1858, and a re-description of H. torquata Topsent, 1916.

Antarctic sponges were mainly studied from trawling or dredging (shallow and deep water) during pioneering oceanographic expeditions carried out since the late 19th century. More recently, sponge collections by SCUBA diving have allowed the detection of species in more cryptic habitats such as rocky walls. In this study, we analyzed Antarctic sponges collected by SCUBA (in 2016 to 2018; shallower than 25 m) around Doumer Island (Palmer Archipelago, Western Antarctic Peninsula-WAP), where only five sponge species have been known. We gathered over 215 specimens, most part identified; 18 known species and one new species. Clathria (Axosuberites) retamalesi sp. nov., is set apart from its congeners on account of the combination of its habit, categories and dimensions of spicules. The East Antarctic material named as Hymeniacidon spec. (3397 m depth) from the Gauss scientific collection has been related to the shallow species H. torquata Topsent, 1916. We described H. torquata based in several specimens (n= 51) from Doumer Island (WAP), only ca. 41 km from Petermann Island (the type locality). Spicules of H. torquata are smaller than the ones present in the Hymeniacidon spec. material, which is here named Hymeniacidon hentscheli sp. nov., since it does not fit into any known cold water species of Hymeniacidon from Antarctica or the Southern Hemisphere, due to a combination of habit, oscula shape, and spicule dimensions. Only five sponge species were previously known from Doumer Island, also collected by SCUBA. Our findings suggest that the ongoing study of collections of sponges assembled at Doumer Island will still yield new taxonomic findings.