Abstract
Ectoparasitic tantulocaridan crustaceans, Microdajus aporosus sp. nov., were found attached to the tanaidacean crustacean Meromonakantha macrocephala (Hansen) from 568 m in the Ross Sea. A single host bore on its pereiopods five expanded tantulus larvae with gestating males and two isolated cephalons of the parasite. Microdajus langi Greve is newly reported from the Gullmarfjord, Sweden. A recent comparison of tantulocaridan thoracopods to maxillopodan naupliar appendages is evaluated in the light of recent morphological and ontogenetic findings.