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Crossobothrium antonioi is a recently discovered species in the genus Crossobothrium. It is a parasitic tapeworm that infects Notorynchus cepedianus, the broadnose sevengill shark.

Discovery
C. antonioi was discovered off the coast of Buenos Aires Province, Argentina. Samples were caught in February 2000, November 2002, and November 2005 in Puerto Quequén. As it is an endoparasite like all other tapeworms, C. antonioi was recovered from the spiral intestine of N. cepedianus. The cestode was named after the lead researcher's father, Antonio Ivanov.

Morphology
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 (the head of tapeworms).

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.

All of the Crossbothrium genera except for C. laciniatum have been found only in hexanchid sharks.