Branchiura sowerbyi are relatively large worms, brownish with whitish, more transparent margins. They have a bluntly conical prostomium and no eyes. The body with 70-180 segments. Dorsal setae start from segment II, with 3-7 setae per bundle, decreasing to one posteriorly. Cylindrical gills are segmentally arranged in the posterior part of the body. The gill-bearing segments lack hair setae, and the length of hairs varies within the same bundle.