Microcotyle is a genus which belongs to the phylum Platyhelminthes and class Monogenea. Species of Microcotyle are ectoparasites that affect their host by attaching themselves as larvae on the gills of the fish and grow into adult stage. This larval stage is called oncomiracidium, and is characterized as free swimming and ciliated.
Species of Microcotyle have only one host in their entire life cycle. Different species of Microcotyle inhabit marine and freshwater and they can also infect different species of fishes. They are uniquely characterized by their haptor having a lot of tiny clamps on the lateral margins.
Although not really known to cause that much damage in marine wildlife, some of them are reported to cause agricultural problems like Microcotyle sebastis as an example. Microcotyle sebastis commonly affects Sebastes schlegeli, a maricultured fish in Korea.[1]
Individuals of species of Microcotyle, like any typical polyopisthocotylean monogenean, have an anterior organ called prohaptor, which is mainly used for feeding and attachment. Although the prohaptor is not the primary attachment organ, it is used to anchor the body of the parasite while the opisthaptor is being repositioned. The opisthaptor is found in all Microcotyle species and it is an important attachment organ that allows these ectoparasites to latch onto their hosts.
Located at the anterior part of the worm is the funnel-shaped mouth that is connected to the pharynx, followed by the esophagus that is smaller in diameter compared to the pharynx. About one tenth of the entire length of the worm, the esophagus then divides into intestinal crura, which extends further posteriorly. The cruca is divided into pouches, which extend between vitellaria. Vitallaria are glands that secrete yolk around the egg. This digestive pathway is observed to be continuous throughout the entire worm. Food particles were observed to be passing back and forth along these pathways in vivo.[2]
The worms are hermaphroditic, containing both male and female organs. Each worm has reproductive organs such as vas deferens, testis, uterus, vitelline duct, ovary, and vitellaria.[2] They also have flame cells that function as a kidney and remove waste material. A short duct that opens to the outside on the dorsal surface is composed of four canals on each side, two posterior and two anterior, that come together laterally to the cirrus. During observation on immature specimens, these canals can still be seen. However, on adults, these canals are concealed by vitellaria.[2]