Microhabitat use by nine species of caprellid amphipods in the genus Caprella inhabiting a Japanese Sargassum bed could be divided into three major categories. Differences in the patterns of use were closely related to the nature of the mother–young association and morphological characteristics of young. Pattern A was shown by three species Caprella danilevskii, C. okadai and C. subinermis that produced large first instar young (>1.6 mm in body length, BL) with no maternal care, and directly use Sargassum thalli as habitat substrata throughout their lives. Two different patterns of microhabitat use occur in the six other species, which produce small first instar young (<1.3 mm BL) and have trouble using Sargassum thalli as their primary habitat. Pattern B comprised of C. decipiens, C. monoceros and C. scaura in which females care for their young until they become large enough to disperse onto the seaweed thalli. The first instar young of these three maternal care species have specialized pereopods. In Caprella monoceros and C. scaura, which show a ‘cling-to-mother’ type of maternal care, each pereopod has a concaved margin on the propodus and a long dactylus, well adapted for clinging to the mother, and C. decipiens, which show a ‘stay-around-mother’ type of maternal care, have comparatively slender and longer pereopods to hold onto seaweed branches near their mother. Pattern C included C. arimotoi, C. glabra and C. penantis which showed no maternal care and use thin branches of epizoites such as epiphytic hydroids as their primary substrata. It is concluded that caprellids that live on seaweed with thick thalli and branches such as Sargassum patens have different solutions to the problem of where the small first instar young can live: species with larger young emerge directly onto seaweed thalli, but species with smaller young use an epiphytic secondary habitat or depend on maternal care.