Definition: Hymedesmiidae with subectosomal spicule tracts of acanthose tornotes, fanning out at the surface forming an ectosomal palisade. Choanosome a confusedly plumose arrangement of acanthostyles, acanthose tornotes, arcuate isochelae and thin sigmas. Areolate pore-fields are absent.
Diagnosis: Stalked, flabellate Hymedesmiidae with subectosomal spicule tracts fanning out at the surface forming an ectosomal palisade. Subectosomal tracts and ectosomal palisade consist of acantho-tornotes. The choanosome is a confusedly plumose arrangement of all spicule types: acanthostyles, acantho-tornotes and microscleres, sometimes vague plumose tracts of acanthostyles are recognizable near the ectosome. Microscleres are arcuate isochelae and thin sigmas.
Remarks: The ectosomal spicules are straight diactines, isodiametric, acanthose, with mucronate, sometimes unequal ends and thus conform to the definition of tornotes except for the fact that the tornotes of Acantorna are completely acanthose. Previously known tornotes are smooth or might have micro-spined ends. We suggest to name these acantho-tornotes acantornotes.
Type species: Acantorna tahoma n. sp.
Etymology. The genus Acantorna is named after the unique acantornotes not known from other taxa of Poecilosclerida.