Branchiobdellida is an order of freshwater leech-like clitellates that are obligate ectosymbionts or ectoparasites, mostly of astacoidean crayfish.

The American zoologist Perry C. Holt wrote his doctoral thesis on branchiobdellids and devoted his 45 years of research to the taxon.

Forty years later, molecular data from rDNA and mitochondrial DNA studies has shown that he was correct, and that Oligochaeta, Branchiobdellida, Acanthobdellida and Hirudinea form a monophyletic group and that each should be considered an order.

There is no prostomium, and the peristomium and next three segments are modified into a sucker, surrounded by small tentacles, with the mouth at its centre.

An Appalachian brook crayfish was found to have one species of branchiobdellid in the gill chambers, one on the oral and ventral surfaces of the body and one on the chelae.