Order HAPLOSCLERIDA Topsent, 1928

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Diagnosis

Encrusting, massive, lobate, tubular, arborescent, flabellate or excavating sponges. Habit, colour and oscular features broadly variable. Consistency generally compressible to soft, brittle or hard and incompressible in one group. Ectosomal skeleton usually unispicular, tangential, regular reticulation of single spicules, bundles or spongin enforced fibres. It may be frequently absent or occasionally developed into a thick impenetrable crust. Choanosomal skeleton a regular isodictyal reticulation of megascleres encased in variable amounts of spongin. The reticulation may take the form of a strictlyunispicular-isotropic skeleton. Frequently it is anisotropic with thicker or thinner ascending tracts interconnected by single spicules or thin tracts. In some groups the skeletal tracts are arranged in thickly alveolar fashion in which meshes may become rounded and result in a disoriented reticulation. Spicules usually are relatively short fusiform sharply pointed oxeas (‘cigarshaped’), which in general may be easily differentiated from oxeas in other orders. Strongyles are also common and it is not infrequent that they derive from juvenile oxeote stages. Oxeas and strongyles may also occur together, then often in different size categories, the smallest of which may be functional microscleres and then are dubbed microxeas or microstrongyles. These are usually concentrated in the ectosome. Megascleres are usually smooth, but in one suborder are frequently finely spined. Microxeas occurring in that same group are also invariably spined. Further microscleres in the order are sigmas, toxas and raphides. In one suborder there is a unique microsclere type, the amphidiscs, associated with the gemmule resting stage. Sigmas and toxas are often characteristically angularly bent, making them distinct from such microscleres in other orders. Two of the three suborders share secondary metabolites of the pyridine and acetylene compound types. One monotypical genus has a sclerosponge basal skeleton.

ID Keys

KEY TO THE SUBORDERS OF HAPLOSCLERIDA
(1) Marine sponges ---------------------------------------------------------------------------------------------------------------- 2
Freshwater sponges ------------------------------------------------------------------------------------------------ Spongillina

(2) Skeleton anisotropic, i.e., consists of clearly recognizable ascending spicule tracts or fibres interconnected at regular distances by secondary spicule tracts or fibres. Larvae are incubated -------------------------Haplosclerina
Skeleton isotropic, i.e., consists of a reticulation without a clear orientation and without distinction in primary ascending and secondary interconnecting spicule tracts or fibres, skeleton densely confused. Larvae unknown, presumably oviparous ----------------------------------------------------------------------------------------------- Petrosina

Diagnosis References

van Soest, R.W.M. & Hooper, J.N.A. 2002. Order Haplosclerida Topsent, 1928. pp. 831-832 in Hooper, J.N.A. & van Soest, R.W.M. (eds). Systema Porifera: A guide to the classification of sponges. New York : Kluwer Academic/Plenum Publishers Vol. 1. [831]

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