Minchin, 1900b
Definition: Demospongiae in which the fibre skeleton, though usually present, is reduced in relation to soft tissue and is virtually absent in some genera. The skeleton arises from a continuous spreading basal plate, and adopts either a dendritic skeleton or—in contrast with the name of the group—an anastomosing or reticulate skeleton. The fibres are always pithed and strongly laminated, usually quite stout , and frequently incorporate cellular elements. Free fibrous spicules (spiculoid) may occur in addition to the main skeleton. The choanocyte chambers are large and sac-like or tubular-elongate. Mesohyl volume is low in relation to chamber and canal volume, and the mesohyl is only weakly infiltrated by collagen. This, in conjunction with the generally reduced fibres skeleton, makes the sponges soft and fragile. The pith in the fibres is markedly distinct from the bark elements, and in structure is close that in the Verongida. It is common to find dark fibre pigmentation contrasting with the mesohyl pigmentation, which is uniform throughout the sponge. (Dictyodendrilla sp.) (Aplysilla rosea) (Aplysilla cross section)
Remarks: Larvae are either large, incubated parenchymella larvae with complex structure and histology, always with a terminal clump of long cilia, or simple parenchymellas lacking terminal long cilia.
Biochemically, members of this group are very diverse and interesting, with distinct family patterns.
Two to four families are distinguished in the order, viz. Family Darwinellidae (Aplysillidae of authors), Family Dictyodendrillidae (secondary reticulate skeleton, not represented in the area), Family Dysideidae (in literature previous to 1985 considered a Dictyoceratid group, possibly to be a separate (sub-)order), and Family Halisarcidae (recently considered a separate order). References: Bergquist, 1980; Bergquist et al., 1990; Boury-Esnault et al., 1990.
Source: Hooper's Internet Sponge Guide.
Families not represented in the area:
Dictyodendrillidae.