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Topsent, 1928

Definition: The main skeleton is composed of megascleres (monactinal, diactinal or both) and spongin fibres in various stages of development; megascleres are frequently localised to distinct regions; microscleres include meniscoid forms such as chelae (unique to the order) and sigmas, and other diverse forms (toxas, rhaphides, microxeas). Most families are viviparous, with uniformly ciliated parenchymella larvae with bare posterior poles, whereas Raspailiidae is predominantly oviparous (chelae SEM).

Remarks: This order contains more living species than all other Recent Porifera, and includes both marine and some freshwater species. Up to 25 families have been recognised in this order, most being typical in having chelae microscleres but several atypical in lacking these microscleres. The families fall naturally into three distinct suborders:

Suborder Microcionina: megascleres differentiated in choanosomal and ectosomal types; special echinating acanthostyles normally present; chelae are palmate; toxas normally present; sigmas absent.

Suborder Myxillina: megascleres differentiated in choanosomal and ectosomal types; special echinating acanthostyles normally present; chelae are tridentate (arcuate or anchorate) isochelae; sigmas normally present; no toxas.

Suborder Mycalina: megascleres not differentiated; no echinating acanthostyles; chelae are palmate; sigmas and toxas frequently present.

Source: Hajdu et al., 1994; Hooper & van Soest, 2002b.

Order Poecilosclerida