Clathria (Cornulotrocha) rosetafiordica sp. nov. from a south-east Pacific fjord (Chilean Patagonia) (Microcionidae: Poecilosclerida: Demospongiae: Porifera)

This article reports on a new species originating from the northern Chilean fjord region, which argued for the resurrection of Cornulotrocha, here classified as a new subgenus of Clathria, for sponges with choanosomal acanthostyles, ectosomal quasidiactinal monactines and rosettes of palmate (an)isochelae. Clathria (Cornulotrocha) rosetafiordica sp. nov. was collected at 23 m depth at Quintupeu fjord (∼42°S), and is unique within this very large genus, in possessing rosettes of palmate anisochelae. The new species is compared to the only other known Clathria (Cornulotrocha), viz. C. (Cornulotrocha) cheliradians n. comb.; to the single other Clathria known with anisochelae, viz C. (Thalysias) dubia; to other crustose Clathria from southern South America, the subantarctic and Antarctic areas; and also to other sponges bearing rosettes; and is considered clearly distinct from all. The phylogenetic significance of rosettes is discussed, a likely adaptive value being discarded in view of the variable location of such structures in the distinct poecilosclerid taxa in which they occur.