''Microphallus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

trematode Trematoda is a Class (biology), class of flatworms known as trematodes, and commonly as flukes. They are obligate parasite, obligate Endoparasites, internal parasites with a complex biological life cycle, life cycle requiring at least two Host ( ...

s (flukes) in the family Microphallidae. The Greek name means "tiny

penis A penis (; : penises or penes) is a sex organ through which male and hermaphrodite animals expel semen during copulation (zoology), copulation, and through which male placental mammals and marsupials also Urination, urinate. The term ''pen ...

Hosts

They are parasitic on a variety of

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s, and

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, some species having complex life cycles involving more than one host. For example, '' Microphallus piriformes'' parasitizes the rough periwinkle (''

Littorina saxatilis ''Littorina saxatilis'', common name the rough periwinkle, is a species of small sea snail, a marine (ocean), marine gastropod mollusc in the family Littorinidae, the winkles or periwinkles. First identified in the 1700s, it has been misidentifie ...

''); when these are eaten by

herring gull Herring gull is a common name for several birds in the genus ''Larus'', all formerly treated as a single species. Three species are still combined in some taxonomies: * American herring gull (''Larus smithsonianus'') - North America * European h ...

s it infects the bird and lays its eggs in the bird's feces to infect new periwinkles. Other

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

s include, for example New Zealand mud snail ''Potamopyrgus antipodarum'' and others.

Parasite-host interactions

Several species are notable for manipulating or influencing their hosts. '' Microphallus piriformes'' causes its host, the rough periwinkle, to move upwards, making it more vulnerable to predation by

s. '' Microphallus pseudopygmaeus'' chemically castrates (

parasitic castration Parasitic castration is the strategy, by a parasite, of blocking reproduction by its host, completely or in part, to its own benefit. This is one of six major strategies within parasitism. Evolutionary strategy The parasitic castration strateg ...

) its host, the snail '' Onoba aculeus'', and causes it to grow larger than normal (it is not clear if this gigantism benefits the host or parasite or if it is a non-adaptive side-effect). '' Microphallus papillorobustus'' causes its host, the lagoon sand

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

('' Gammarus insensibilis'') to swim upwards, making it more vulnerable to predation.Thomas F., Fauchier J. & Lafferty K. D. (2002)
Conflict of interest between a nematode and a trematode in an amphipod host: test of the "sabotage" hypothesis
. ''Behav. Ecol. Sociobiol.'' 51: 296-301. Some species of this genus "hitch-hike" on the manipulations of other species; for example, '' Microphallus hoffmanni'' parasitizes the same sand shrimps as ''Microphallus papillorobustus'' but does not manipulate the shrimps itself, instead benefiting from the latter's manipulation of the host.

Life cycle

An undescribed ''Microphallus'' species is a widespread and locally common parasite in New Zealand lakes and streams. Multilocus

allozyme Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. These are opposed to isozymes, which are enzymes that p ...

genotype data show that this ''Microphallus'' is a single outbred species with high levels of gene flow among South Island populations. The parasite exclusively uses '' Potamopyrgus antipodarum'' as the intermediate host, and the final hosts are

waterfowl Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which i ...

. Embryonated ''Microphallus'' eggs are ingested from sediment and hatch in the snail's gut, penetrate the intestine, and migrate to the

gonads A gonad, sex gland, or reproductive gland is a mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, ...

and

digestive gland The hepatopancreas, digestive gland or midgut gland is an organ of the digestive tract of arthropods and molluscs. It provides the functions which in mammals are provided separately by the liver and pancreas, including the production of digestive ...

. Following successful establishment, the parasite then undergoes

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...

, replacing much of the host's reproductive tissue and digestive gland, which results in complete sterilization of the snail. The first visible parasite developmental stages ( blastocercariae) are detectable after approximately 75 days post-exposure and metacercariae are common by 90 days post-exposure at 16 °C in the lab. The life cycle is completed when snails containing metacercariae are consumed by waterfowl.

References

The article incorporates CC-BY-2.0 text from reference.Osnas E. E. & Lively C. M. (31 May 2005) "Immune response to sympatric and allopatric parasites in a snail-trematode interaction". ''

Frontiers in Zoology ''Frontiers in Zoology'' is a peer-reviewed open access scientific journal covering all aspects of zoology. It was established in 2004 and is published by BioMed Central on behalf of the German Zoological Society. The editors-in-chief are Jürge ...

'' 2: 8. {{Taxonbar, from=Q3382391 Plagiorchiida genera