Microcotyle fusiformis has the general morphology of all species of Microcotyle, with a flat symmetrical body, fusiform in outline, comprising an anterior part which contains most organs and a posterior part called the haptor. The haptor is symmetrical, continuous with the rest of the body and bears clamps, arranged as two rows, one on each side. The clamps of the haptor attach the animal to the gill of the fish. There are also two small septated buccal suckers at the anterior extremity. The digestive organs include an anterior, terminal mouth, a muscular pharynx, and a posterior intestine with two lateral blind-ending branches; the left branch is longer. Each adult contains male and female reproductive organs. The reproductive organs include an anterior genital atrium opening a little anterior to midway between the hinder end of the pharynx and that of the oesophagus, armed with small conical spines, a dorsal vagina situated behind the common genital opening two-fifths the whole distance between this and the front end of the ovary, a single ovary nearly shaped as an interrogation-point, and few testes of moderate size, posterior to the ovary and occupying a comparatively small area about one-sixth the whole length of the body.
