''Corynosoma autrale'' is a species of

acanthocephala Acanthocephala ( Greek , ' 'thorn' + , ' 'head') is a group of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses t ...

n (also known as thorny-headed worms, or spiny headed worms). This species usually infects

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...

s; the semi-aquatic fin-footed marine mammals most commonly known as

seals Seals may refer to: * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impress an emblem, used as a means of a ...

and

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

s. Pinniped infections are not exclusive, recently ''C. australe'' has been discovered in

Magellanic penguin The Magellanic penguin (''Spheniscus magellanicus'') is a South American penguin, breeding in coastal Patagonia, including Argentina, Chile, and the Falkland Islands, with some bird migration, migrating to Brazil and Uruguay, where they are occas ...

s (''Spheniscus magellanicus'').

Life cycle

This species follows a

biological life cycle In biology, a biological life cycle (or just life cycle when the biological context is clear) is a series of stages of the life of an organism, that begins as a zygote, often in an egg, and concludes as an adult that reproduces, producing an offsp ...

similar to many other of the same phylum. Starting with eggs being released in the feces of the host from a mature female, the eggs are then ingested by an

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

, the parasite's first

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 ...

. Typically for ''C. australe'' the first host is an

amphipod Amphipoda () is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphipod species cur ...

, a relatively small (usually less than 10 millimeters) shrimp-like

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 ...

. Within the crustacean a spindle-shaped

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

is released from the eggs and then subsequently develops into an acanthella, the juvenile infective form of an acanthocephalan. The acanthella then moves into the

body cavity A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, a ...

via the

gut wall The gastrointestinal wall of the human gastrointestinal tract, gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut (the Lumen (anatomy), lumen) outwards, these are the mucosa, the submucosa, the ...

encyst A microbial cyst is a resting or dormant stage of a microorganism, that can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion. ...

s within and begins developing into the infective form known as a cystacanth. When the first intermediate host is consumed, either by its

definitive 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 ...

or by a

paratenic 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 a ...

, the parasitic worm is released. Once within the definitive host, the cystacanth becomes an adult, encysts, then pierces the gut wall after its proboscis has been everted. Once through the gut wall it sexually matures by developing its sexual organs after feeding. After sexual maturation, the adult worms mate, the embryos develop within the female and the life cycle repeats. In contrast, within a paratenic host like a fish, the parasitic worm just forms a cyst.

Magellanic penguin infection

Fish serve as a paratenic host to the ''Corynosoma australe'' parasite given that their infection by the parasitic worm is not necessary for the success of the parasite's life cycle. Nonetheless, paratenic hosts such as fish are still important because they allow the parasite access to a variety of hosts given many animals eat fish as their primary food source, in this case Magellanic penguins. Since penguins typically consume the same food as seals and sea lion it became apparent how penguins acquire a parasitic infection endemic to

s. Likewise, since seals and sea lions share a comparable physiological similarity with penguins, cross species infection is more than possible. Though, ''C. australe'' can only produce viable eggs from within the

host. C''. australe'' can survive perfectly well within the penguins as its host, with female worms growing bigger within the guts of Magellanic penguins. In addition, though ''C. australe'' can survive well within Magellanic penguins, egg viability is lessened within this non-native host. Likewise, the

sex ratio A sex ratio is the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. However, many species deviate from an even sex ratio, ei ...

of the parasitic worm is highly skewed toward females within the gut of the penguins as the host. Though Magellanic penguins are not the definitive host of ''C. australe'', they serve well as a suitable candidate.

References

{{Taxonbar, from=Q2188058 Polymorphidae Parasites of birds Parasites of mammals Animals described in 1937