Life Cycle of Monogenea

Monogenea describes a class of small parasitic flatworms that live on the outside of the host's body rather than internally. In order to accomplish this feat, monogenean parasites have highly developed attachment appendages located at the rear of the organism and are usually comprised of a suction device, pinscers, hooks or spines.

General Characteristics

As with most other parasites, monogenean parasites depend on several hosts to facilitate maturation and dispersion. Most monogenean parasites will have a predominantly aquatic host, such as fish and aquatic mammals, such as whales, although some target semi-aquatic species, like frogs. In most cases, the intermediate host will be eaten by the primary host.

Reproduction

Each parasite within this class has its own distinct characteristics regarding its life cycle, but the overall process is much the same. Monogeneans possess the simplest life cycle of all the parasitic platyhelminths. Most monogeneas are hermophroditic, meaning they can reproduce either sexually or asexually, depending on the conditions and availability of a mate. Most species are egg bearing, but some are known to deliver live young, like G. elegans

Early Development

Once the eggs hatch, the larvae will either float in the water, where they use fine hairlike appendages called cilia to maneuver in the water in search of a new host, or the pregnant female will release her eggs inside the new host when the intermediate host has been consumed. In this stage, the larvae are known as oncomiracidium. Once the larvae have invaded the new host, the cycle begins again.

Primary Hosts

Monogeneans have not been documented as having ever infected birds, even aquatic birds, though one species has been documented parasitizing a mammal. Oculotrema hippopotami can be found attached to the eye of the hippopotamus.

Interesting Facts

One particularly interesting monogenean is the Gyrodactylus elegans. Each adult gives birth to a single live larva. This newly born organism contains the embryo of another G. elegans, which in turn contains another, which contains another. As each larva groes, it gives birth to the resident embryo, allowing the original mother to be able to produce four offspring for each egg. Diplozoon paradoxum will not become sexually mature until they come in contact with another organism of their species. After they achieve maturity and mate, the two organisms are joined for life, creating a single organism out of the two individuals.

References

• Monogenea