Tetraphyllidea is a large tapeworm order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 that contains some 60 genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 and about 800 described species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. Tetraphyllideans are remarkable for their scolex morphologies

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

, which are the most varied and morphologically complex amongst all tapeworm orders.

Tetraphyllidean cestodes also exhibit a remarkable degree of host

Host (biology)

In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...

 specificity. The procercoid probably parasitizes copepod

Copepod

Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...

s, which are eaten by the second intermediate host

Intermediate host

A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...

s: teleost fishes, decapods

Decapoda

The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...

 or cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s, which may also serve as paratenic

Paratenic

In parasitology, the term paratenic describes a host which is not needed for the development of the parasite, but nonetheless serves to maintain the life cycle of the parasite. Alaria americana may serve as an example: the so-called mesocercarial stages of this parasite reside in tadpoles, which...

 hosts. The verified definite hosts are shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s, skate

Skate

Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....

s and stingray

Stingray

The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...

s. Occasionally found in cetaceans, the role of these apex predator

Apex predator

Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...

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. 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.