POSTMARSUPIAL DEVELOPMENT OF MUNNOPSURUS-ATLANTICUS (BONNIER, 1896), A DOMINANT ASELLOTE ISOPOD FROM THE UPPER CONTINENTAL-SLOPE OF THE BAYOF BISCAY

The asellote isopod Munnopsurus atlanticus is a dominant species in th e bathyal suprabenthic assemblages from the south margin of the Cap-Fe rret Trench; it is therefore a valuable subject for studies of postmar supial development and population biology in bathyal Isopoda. In this introductory paper, its postmarsupial development is described on the basis of size frequency analysis and morphological discrimination. Eig ht developmental stages are recognized within the Biscayan population: mancas 1-2; manca 3, juvenile and copulatory males; manca 3, juvenile , preparatory and brooding females. The number of successive instars d epends on the sex of the individuals; at least 8 instars for the femal es and 5 instars for the males. The female may be iteroparous, reverti ng to a preparatory condition before brooding once more. The larger ad ults are found over muddy sediments, probably reflecting more favourab le environmental conditions for growth increment in the deepest part o f the investigated area.