Acarnus Gray 1867

Genus Acarnus Gray, 1867 (sensu Hooper, 2002) Type species: Acarnus innominatus Gray, 1867a (by monotypy). Definition: Non-fistular Acarnidae with cladotylote echinating spicules (Hooper, 2002). Diagnosis: Non-fistulose, encrusting to massive growth forms; ectosomal tylotes with microspined ends, forming tangential or paratangential tracts (not brushes); choanosomal skeleton isodictyal, isotropic or anisotropic reticulate, occasionally plumo-reticulate or plumose or hymedesmioid in encrusting species; skeletal tracts cored by smooth styles, echinated by 1 or 2 (exceptionally 3) categories of cladotylotes, echinating acanthostyles present or absent, and smooth tylostyles; microscleres are palmate isochelae, toxas of several morphologies, smooth microxeas and acanthoxeas (emended from Nascimento & Pinheiro, 2023; our additions are in bold).