15 Monogenea Characteristics & Life Cycle

Monogenea is referred to as monogenean trematodes that belong to the phylum Platyhelminthes. Monogeneans are characterized by an anterior-prohaptor and posterior holdfast organ, the opisthaptor. Let us see what are these monogeneans, their characteristics and other related facts.

Characteristics of Monogenea are listed below:

  1. Monogenea is a hermaphrodite, as both male and female structures are found in the same organism.
  2. Monogenea is mostly oviparous but some species are also viviparous and are cross-fertilizing.
  3. Monogeneans are bilaterally symmetrical, and acoelomate with tissue-organ system level of organization.
  4. The body of Monogenea is unsegmented. Mesoderm is present in between ectoderm and endoderm.
  5. The anus is absent while the mouth is present. Food uptake is by the general body surface via the process of osmotrophy.
  6. Digestive, nervous and excretory systems are present inside Monogenea. Flame cells, protonephridia or solenocytes are the excretory organs present in Monogeneans.
  7. Monogeneans are ammoniotelic as ammonia and fatty acids are excretory products.
  8. Monogeneans do not have a circulatory, respiratory or skeletal system.
  9.  In response to parasitising the fish, Monogeneans cause irritation and tissue damage, rupture of epithelial cells, and excess mucus secretion causing hyperplasia. In addition to this, oedema in lamellae and capillaries leads to malfunctioning of the respiratory system and leading to the death of the host.
  10. Monogeneans are host specific and feed upon both freshwater and marine fishes, for example, Pseudorhabdosynochus lantauensis in Epinephelus coioides, Dawestrema cycloancistrium in Arapaima, and Gyrodactylus salaris in Atlantic salmon.
  11. In a few species like Polystoma integerrimum, and Ancyrocephalus chiapanensis, adaptation to terrestrial habitat is also observed and may exist as an internal parasite.
  12. Other examples are Diclidophora nezumiae, Diplozoon paradoxum, Dactylogyrus vastator, Neobenedenia sp., and Diclidophora sp.
  13. A species of Monogenea, Oculotrema hippopotami use to parasitize the eyes of Hippopotamus.
  14. Monogeneans seem to be colourless as compared to Turbellarians and are the oldest on earth but evolved from Turbellarians.
  15. Monogeneans have hooks and discs for adhering and attachment to the host body surface for the uptake of nutrients.

Monogenea life cycle

The life cycle is defined as different stages crossed and performed by an organism whether it is flora or fauna throughout its lifespan. Let us see the life cycle of monogeneans.

Monogeneans are monogenetic and have a direct life cycle. They are obligate parasites but the larvae oncomiracidium are free-swimming and must have to infect the host cells to complete their lifecycle. They require multiple hosts of back-to-back (fish-to-fish) cells to complete their lifecycle.  

The life cycle of Monogeneans shows the release of eggs by adults followed by larvae formation.

Specifically, they do not have any intermediate hosts. The two most important examples are Gyrodactylus (viviparous) and Dactylogyrus (oviparous). These organisms can only reproduce one time throughout their life which is why grouped under the class monogenean. Eggs have also one or two thread structures which help in attachment with the filaments of fish gills and scales.


Monogeneans are benthic invertebrates and are parasitic upon aquaculture most specifically freshwater fishes. Most of them produce eggs which undergo embryonic development and grow into a ciliated larva, oncomiracidia, which further develops into an adult individual of class Monogenea.

Read more about Turbellaria

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