A new species of Euplectellidae (Porifera: Hexactinellida: Lyssacinosida) from the northwestern Pacific Ocean

A new species of the deep-sea sponge Dictyaulus is described from materials collected by the research vessel Ke Xue during its three cruises between 2014 and 2017 to survey seamount biodiversity. The newly described species was one of the only two sponge species found living on all three seamounts investigated. It may be a common species living on seamounts in the tropical western Pacific. All seven known species of Dictyaulus Schulze, 1896 contain floricomes, but each species has special spicules. The new species is easily distinguishable by the presence of discasters, which have previously been reported only in Dictyaulus starmeri Tabachnick and Levi, 2004, but the latter species possesses sigmatocomes, which are not present in the new species. The five specimens collected display large variation in size, with total lengths from 55 to 610 mm. The specimens differ in the abundance of microsclere types which we consider to be caused not only by differences of their life history stages but also to a greater extent by differences in their living environments.