Editing Monogenea (section)

==Characteristics==
Monogenea are small parasitic flatworms mainly found on skin or gills of fish.
They are rarely longer than about 2&nbsp;cm. A few species infecting certain marine fish are larger, and marine forms are generally larger than those found on freshwater hosts. Monogenea are often capable of dramatically elongating and shortening as they move. Biologists need to ensure that specimens are completely relaxed before measurements are taken.<ref name=":0">Roberts, S. Larry & John Janovy, Jr. ''Foundations of Parasitology''</ref>

Monogeneans lack respiratory, skeletal, and circulatory systems but they do have posterior attachment structures in the form of adhesives, clamps, hamuli and suckers.<ref name=":0" /><ref>[http://www.britannica.com/EBchecked/topic/209735/flatworm/64463/Annotated-classification#ref=ref529438 flatworm :: Annotated classification - Britannica Online Encyclopedia<!-- Bot generated title -->]</ref> Like other flatworms, Monogenea have no true [[body cavity]] (coelom). They have a simple digestive system consisting of a mouth opening with a muscular [[pharynx]] and an intestine with no terminal opening ([[anus]]).

Monogenea are Platyhelminthes, so are among the lowest invertebrates to possess three embryonic germ layers—[[endoderm]], [[mesoderm]], and [[ectoderm]]. In addition, they have a head region that contains concentrated sense organs and nervous tissue (brain).

Like all ectoparasites, monogeneans have well-developed attachment structures. The anterior structures are collectively termed the '''prohaptor''', while the posterior ones are collectively termed the '''opisthaptor''', or simply [[haptor]]. The posterior opisthaptor with its hooks, anchors, clamps etc. is typically the major attachment organ.

Generally, monogeneans also are [[hermaphroditic]] with functional reproductive organs of both sexes occurring in one individual. Most species are oviparous, but a few are viviparous.