Deep-sea "lithistid" assemblages from the Norfolk Ridge (New Caledonia), with description of seven new species and a new genus (Porifera, Demospongiae)

Some seamounts are regarded as deep sea "island systems" of extraordinary biomass and richness, containing assemblages of highly unique taxa, often with restricted species ranges. Here we report on some unique "lithistid" sponges from South Pacific seamounts along the Norfolk Ridge (New Caledonia). The polyphyletic "lithistid" Demospongiae are characterized by the presence of choanosomal articulated spicules (desmas), which form an extremely rigid skeleton in most genera. Sponge assemblages were sampled from 10 seamounts over a depth range that straddles the subtidal-bathyal transition (236-583 m) using a beam trawl and Waren dredge (average sampling time 2.25 hrs per seamount), yielding a diverse "lithistid" fauna of 16 species belonging to 10 genera (one new) and six families. "Spot endemics" (species restricted to a single site) dominated the fauna. Species richness per seamount varied considerably. Of these 16 species found seven were new to science (Corallistes australis n. sp., Herengeria vasiformis n. sp., Isabella mirabilis n. gen., n. sp., Neoschrammeniella norfolkii n. sp., N. castrum n. sp., Homophymia pollubrum n. sp., Reidispongia tuberculata n. sp.) including the new genus Isabella n. gen. within the family Corallistidae. In addition, the genera Herengeria and Neoschrammeniella (family Corallistidae) were redefined based on new findings from this study.