''Polystoma integerrimum'' is a
flatworm
The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegme ...
(platyhelminth) from the class
Monogenea
Monogeneans are a group of ectoparasitic flatworms commonly found on the skin, gills, or fins of fish. They have a direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they have both male and female reprod ...
found in
amphibians in Asia and Europe. It is an
endoparasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
of
frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" '' Triadobatrachus'' is ...
s and toads and has an unusual
life cycle
Life cycle, life-cycle, or lifecycle may refer to:
Science and academia
* Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring
* Life-cycle hypothesi ...
which synchronises with that of its host.
Description
''P. integerrimum'' is a leaf-like flatworm that can grow to a maximum length of about . At the anterior (head) end are the mouth and a pair of suckers, and at the posterior end is the main device by which the parasite attaches to its host, the
opisthaptor, with its three pairs of suckers, a pair of hooked anchors and marginal hooks.
The flatworm's mouth is connected to a muscular pharynx, an oesophagus and a gut, but it has no anus.
[
]
Ecology
''P. integerrimum'' inhabits the bladder of a frog or toad where it feeds on blood, mucus and the sloughed cells of its host. Unlike many species of flatworm, the adults are either male or female, with functional testes or ovaries.[ The eggs are produced throughout the year but are stored in the host's bladder and only pass out into the water when the amphibian returns there to breed; in this way, the flatworms synchronise their reproductive cycle with that of their amphibian hosts.][ After hatching, the flatworm ]larvae
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
T ...
, called oncomiracidia, make their way to the gills of developing tadpole
A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found ...
s, where they attach. Here they stay until the tadpoles undergo metamorphosis, at which time they crawl over their hosts' bodies and enter their bladders through their cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds ...
s.[
Some of the flatworm larvae develop in a different way, particularly when developing on younger tadpoles, becoming prematurely sexually mature while still attached to the gills of the tadpole. These ]neotenic
Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compare ...
individuals are capable of producing viable eggs which pass out into the water and develop in the normal way.
References
{{Taxonbar, from=Q5033330
Polyopisthocotylea
Parasites of amphibians
Endoparasites