Tetraphyllidea is a large

tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cestodar ...

order that contains some 60

genera 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 nomenclat ...

and about 800 described

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. Tetraphyllideans are remarkable for their

scolex Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of m ...

morphologies, which are the most varied and morphologically complex amongst all tapeworm orders. Tetraphyllidean cestodes also exhibit a remarkable degree of

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

specificity. The

procercoid Procercoid is the first larval stage of some tapeworms, which usually develops inside the body cavity of copepods. Flatworm in this stage is not enclosed in a protective cyst, but is infectious. Procercoids resemble their adult forms in pathways of ...

probably parasitizes

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s, which are eaten by the second

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 a ...

teleost Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...

fishes,

decapods The Decapoda or decapods (literally "ten-footed") are an order (biology), order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, Caridea, shrimp and Dendrobranchiata, prawns. Most ...

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s, which may also serve as

paratenic 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 ...

hosts. The verified definite hosts are

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...

skate Skate or Skates may refer to: Fish *Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongin ...

s and

stingray Stingrays are a group of sea rays, which are cartilaginous fish related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae ( ...

s. Occasionally found in

cetacean Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

s, the role of these

apex predator An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...

s in the tetraphyllidean life cycle is not well known; whales and dolphins may be definite or dead-end hosts. '' Crossobothrium antonioi'' is a recently discovered species in the genus '' Crossobothrium'', which belongs to the order Tetraphyllidea.New species of ''Crossobothrium'' (Cestoda:Tetraphyllidea) from the broadnose sevengill shark, ''Notorynchus cepedianus'', in Argentina
/ref> It is a parasitic tapeworm that infects ''Notorynchus cepedianus'', the broadnose sevengill shark. ''C. antonioi'' was discovered off the coast of Buenos Aires Province, Argentina. ''C. antonioi'' was recovered from the spiral intestine of ''N. cepedianus'' and named after the lead researcher's father, Antonio Ivanov. ''C. antonioi'' is the smallest species in its genus and about 47.4-51.5 mm long; other species in the genus are about twice as long as ''C. antonioi''. It has 4 stalked bothridia ("sucking grooves") on its scolex. Its proglottids, which are the segments of tapeworms that contain the reproductive structures, are longer than wide when immature, and become wider than long at maturity. However, the proglottids at each stage are generally the same shape. ''C. antonioi'' also have crenulated bothridial margins and a microthrix pattern that varies from other species in ''Crossobothrium''. The most notable and unique quality of ''C. antonioi'' is the large amount of testes per mature proglottid. ''C. antonioi'' has more than 700 testes per proglottid, whereas other ''Crossobothrium'' species have ~150-300 testes per proglottid.

References

Cestoda Platyhelminthes orders {{cestoda-stub