Family Microcionidae Carter, 1875

Abstract

Microcionidae Carter (Demospongiae, Poecilosclerida), including Clathriidae, Ophlitaspongiidae, contains 77 nominal genera of which only 9 genera and 12 subgenera are considered to be valid (one incertae sedis). There are approximately 470 described (valid) species worldwide, living predominantly in shallow waters with a few recorded from deeper seas, and with many other species still collected but remaining undescribed. Microcionids typically have three skeletal regions delineated by the distribution of different structural megascleres: (1) the choanosomal skeleton (with principal monactinal spicules enclosed within spongin fibres and spined monactinal spicules typically echinating fibres; in two groups this is replaced by a basal or axial renieroid skeleton of smooth or acanthose styles or strongyles, with or without echinating spicules); (2) an extra-fibre subectosomal skeleton (with tracts of larger auxiliary monactinal spicules ascending to the surface); (3) and a non-tangential ectosomal skeleton (with smaller auxillary styles forming a surface crust perpendicular to the surface). Megascleres are predominantly smooth ectosomal and choanosomal styles, with some diactinal and acanthose modifications. Microscleres are palmate isochelae, only exceptionally modified to superficial arcuate-like or anchorate-like forms (produced by torsion of the shaft and detachment of alae), and toxas with diverse morphologies including microxea-like and raphidiform toxas in few species. Skeletal structures range from ‘hymedesmioid’ and ‘microcionid’ in encrusting taxa, to plumo-reticulate and occasionally axially compressed in some species, but usually irregularly reticulate in most taxa. Occasionally spicules are partially or completely replaced by detritus. Two subfamilies are recognised: Ophlitaspongiinae de Laubenfels (with a secondary renieroid spongin fibre and/or spiculose skeleton overlaying a primary reticulate, plumo-reticulate, plumose or hymedesmioid spiculo-spongin skeleton) and Microcioninae Carter (lacking a secondary renieroid reticulate skeleton, having only a reticulate, plumo-reticulate, plumose hymedesmoid, microcionid or axially compressed primary skeleton).