Caryophyllidea
Encyclopedia
The Caryophyllideans are a group of tapeworms that infect fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

s (segmented worms) with a simple scolex or "head." Worms in this 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...

 only have one proglottid, which is believed to be the primitive condition for tapeworms. They are generally less than 10 centimetres long.

In the Caryophyllidean life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...

, adults live in fish, who pass the tapeworm eggs in their feces. Annelids eat the eggs, where they hatch into oncosphere larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e that move through intestinal wall and become procercoid larvae in the body cavity. When the annelid is eaten by a fish, the tapeworm matures.

Catfish
Catfish
Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...

, sucker
Catostomidae
Catostomidae is the sucker family of the order Cypriniformes. There are 80 species in this family of freshwater fishes. Catostomidae are found in North America, east central China, and eastern Siberia...

s, and minnow
Minnow
Minnow is a general term used to refer to small freshwater and saltwater fish, especially those used as bait fish or for fishing bait. More specifically, it refers to small freshwater fish of the carp family.-True minnows:...

s are among the fishes that can serve as definitive hosts.
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