Family Spirasigmidae Hallmann, 1912

Abstract

Spirasigmidae Hallmann (Demospongiae, Spirophorida) contains two genera, both known only from single specimens from remote islands of the Pacific and Indian Oceans. They are thinly encrusting to small conical shapes, with radial skeletons that fan out and become plumose in the periphery where they become nearly tangential at the surface, composed of large strongyloxeas. One genus (Spirasigma) also has a secondary disorganised skeleton of roughened ‘microxeas’. Both lack triaenes, and their allocation to Spirophorida is based on possession of true sigmaspires, although it is included in Spirophorida as a family incertae sedis.