The tantulus larva ofMicrodajus langi is redescribed using Scanning Electron Microscopy. Thoracopods 2–5 have poorly developed but fully armed endites. Thoracopods 1–5 are biramous, with each ramus represented by a minute segment. A new species,M. pectinatus, is described from a tanaid host collected in the Rockall Trough, off the west coast of Scotland. A system of homologies for the portopodal segments of the thoracopods of the tantulus larva is proposed. Some aspects of the musculature of the adult male are described for the first time.