Vosmaer, 1886
Definition: Demospongiae with a plumoreticulate skeletal architecture built of interchangeable styles and oxeas and intermediate spicules, of widely diverging sizes and not functionally localized (Van Soest, Diaz and Pomponi, 1990). Scopalina ruetzleri, Axinella polypoides, Axinella Vosmaer, Acanthella Vosmaer, confused
Remarks: The plumoreticulate skeletal architecture maybe a synapomorphy for a much wider group of Demospongiae (see Van Soest, 1991). This character is progressively lost in the family Halichondriidae. However, a basic plumorecticulate or plumose architecture is found even there with few exceptions. Although the combination of styles and oxeas is also found in a few Raspailiids and Poecilosclerids, these groups show localization or categorization in them. For instance, in Myxillids stylote choanosomal spicules are combined with ectosomal diactines; in the Raspailiid Echinodictyum choanosomal oxeas are arranged into tracts which are echinated by (acantho-)styles. Indiscriminate occurrence of styles and oxeas is not found. Localized spicules in Didiscus , Myrmekioderma and Higginsia are considered microscleres.
Sinuous longer or shorter diactinal spicules are found in Axinella cannabina , Phakellia , Auletta , Bubaris , Acanthella , Dactylella , some Axinyssa and some Topsentia . This distribution may be interpreted as retention of ancestral spicules, possibly related to lithistid spicules (through Monocrepidium and fossil genera such as Cephalorhaphidites and Megaloraphium ) and thus constitute an underlying synapomorphy.
Isonitriles are organic compounds found in Axinella , Acanthella , Ciocalypta , Axinyssa , "Epipolasis ", "Stylotella ", "Halichondria " and "Hymeniacidon " (names between quote marks represent doubtful generic assignments) (personal communication Dr. J. C. Braekman), and thus may turn out to be a good underlying synapomorphy, too.
The families of the Halichondrida sensu Van Soest et al., 1990 (emended to include a separate family Bubaridae which were previously merged with Axinellidae):
Family Axinellidae Ridley and Dendy, 1887: Halichondrida with axially condensed and extra-axially plumoreticulate choanosomal skeletons.
Family Bubaridae Topsent, 1904: persistently encrusting Halichondrida, with single
styles or rhabdostyles erect on a basal mass of curved or twisted spicules; the latter may be oxeote, strongylote or stylote, entirely smooth or provided with spines and or swellings.
Family Desmoxyidae amily Desmoxyidae Hallmann, 1917: Halichondrida with a reticulate-fasciculate choanosomal skeleton of spongin-enveloped tracts with a fleshy, corrugate/ridged surface.
Family Dictyonellidae Van Soest et al., 1990: Halichondrida with spongin-enforced dendritic skeleton of choanosomal spicule tracts and a fleshy conulose surface.
Family Halichondriidae Vosmaer, 1887 (emended): Halichondrida with a choanosomal skeleton consisting of (1) a high density of spicules arranged in (2) vague, ill-defined, directionless tracts, and with (3) spicules in confusion.
Source: Van Soest et al., 1990.