The morphology of the sphaeromatid brood pouch (Crustacea: Isopoda: Sphaeromatidae)

The structure of the brood pouch and mouthparts of ovigerous female sphaeromatids is described. Taxonomically, these are shown to be important generic characters and some attempt is made to relate structure to function. Expanded maxillipeds (which produce a current of water through the marsupium) are shown to occur only in genera which have oostegites overlapping in the mid-line and reaching the mouthparts anteriorly. The reduction of the mouthparts of some genera cannot be explained, but it may conserve energy at the final moult. No platybranchiate genera (subfamily Cassidininae) have the mouthparts reduced but some have the maxilliped expanded. Some correlation between brood pouch structure and habitat is suggested. Genera with a brood pouch composed only of oostegites (and hence liable to disruption by turbulence and particle abrasion) occur sublittorally or, if intertidal, adopt a protected, crevice dwelling habit. Genera with a brood pouch composed of large opposing pockets (which are more able to resist disruption) occur intertidally or in shallow water, and may be found in wave-washed sand. Some wood-boring species of the genus Sphaeroma Latreille show a reduced number of oostegites when compared with non-boring species. This presumably relates to their burrowing habit.