Microcotyle pacifica is a species of monogenean, parasitic on the gills of a marine fish.

[1] Microcotyle pacifica has the general morphology of all species of Microcotyle, with a symmetrical lanceolat body, comprising an anterior part which contains most organs and a posterior part called the haptor.

The haptor is symmetrical, and bears 46-50 clamps, arranged as two rows, one on each side.

The digestive organs include an anterior, terminal mouth, a circular pharynx, a simple oesophagus and a posterior intestine bifurcates immediately posterior to genital atrium into two lateral branches provided with numerous secondary branches, both extends into the hohaptor, and are confluent.

The reproductive organs include an anterior genital atrium, armed with numerous thorn-shaped spines, a medio-dorsal vagina opening approximately one fourth to one-fifth length of body from anterior end, a single tubular, irregularly looped ovary and 18-30 testes irregular in shape, closely packed and occupy the greatest part of the postovarian interintestinal field.