Minchin, 1900b
Definition: One of the so-called "keratose sponge" orders, lacking mineral spicules, although detritus and contaminating spicules may be acquired; sponges are usually tough, difficult to tear, and frequently with differences in pigmentation between the surface and subectosomal regions; the main skeleton consists of a reticulation of spongin fibres (Spongia officinalis fibres), often organised into primary, secondary and sometimes tertiary networks (fasciculated fibre); fibres are usually homogenous or lightly laminated in cross-section, with or without central pith, and collagenous spongin filaments may be scattered within the mesohyl. Larvae are large, incubated parenchymella larvae, evenly covered with short cilia except at one pole where tufts of large flagella occur, and both poles have rings of pigmented cilia-free cells.
Remarks: Three families are traditionally included in the Dictyoceratida, differentiated by their fibre characteristics: Spongiidae, Thorectidae and Dysideidae. Recently Dysideidae was moved to Dendroceratida based on affinities inferred by comparative choanosomal ultrastructures. The group of sponges possessing special spongin filaments (Ircinia c.s.) have been recently separated from Thorectidae in a separate family Irciniidae, thus the number of families in this order stays 3, each with representatives in the area:
Family Spongiidae: simple unpithed fibres.
Family Thorectidae: strongly laminated fibres and with diffuse pith.
Family Irciniidae: strongly laminated fibres and with diffuse pith, with knobbed filaments (ircinid filament ).
Source: Bergquist, 1980.