''Microphallus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

parasitic 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 ha ...

trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive h ...

s (flukes) in the family

Microphallidae ''Microphallidae'' is a family of trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction ...

. The Greek name means "tiny

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...

Hosts

They are parasitic on a variety of

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, and

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

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 gastropod mollusc in the family Littorinidae, the winkles or periwinkles. First identified in the 1700s, it has been misidentified as a new spe ...

''); 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 The New Zealand mud snail (''Potamopyrgus antipodarum'') is a species of very small freshwater snail with a gill and an operculum. This aquatic gastropod mollusk is in the family Tateidae. It is native to New Zealand, where it is found throug ...

''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) 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 Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...

('' 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 pe ...

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 The New Zealand mud snail (''Potamopyrgus antipodarum'') is a species of very small freshwater snail with a gill and an operculum. This aquatic gastropod mollusk is in the family Tateidae. It is native to New Zealand, where it is found throug ...

'' 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 ...

. 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 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, produces sper ...

and digestive gland. 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 ...

, 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

metacercaria Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...

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