Pseudophyllid cestodes (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...

 pseudophyllidea) are a kind of flatworm

Flatworm

The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...

 with multiple "segments" (proglottids) and two bothria

Tentacle

A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...

 or "sucking grooves" as adults. Proglottids are identifiably pseudophyllid as the genital pore and uterine pore are located on the mid-ventral surface, and the ovary

Ovary

The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...

 is bilobed ("dumbbell

Dumbbell

The dumbbell, a type of free weight, is a piece of equipment used in weight training. It can be used individually or in pairs .-History:...

-shaped").

Eggs have one flat end (the operculum

Operculum (gastropod)

The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...

) and a small knob on the other end. All pseudophyllid cestodes have a procercoid stage in their 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...

, and most also have a plerocercoid

Plerocercoid

Plerocercoid refers to last larval form found in the second intermediate host of many Cestoda with aquatic life cycles....

 stage.

The most important family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of pseudophyllid cestodes is Diphyllobothriidae, which infect mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s as their definitive hosts and use either 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 (a group of small crustaceans found in the sea and nearly every freshwater habitat, e.g. Spirometra

Spirometra

Spirometra is a genus of Pseudophyllid cestode that reproduces in canines and felines but which can cause pathology in humans. As an adult, this tapeworm lives in the small intestine of its definitive host and produces eggs that pass with the animal's feces. The eggs hatch into coracidia which...

) or both copepods and fish as in the broadfish tapeworm as 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.
The hermaphroditic Schistocephalus solidus

Schistocephalus solidus

Schistocephalus solidus is a tapeworm of fish, fish-eating birds and rodents.This hermaphroditic parasite belongs to the Eucestoda subclass, of class Cestoda. It parasitizes fish and fish-eating water birds. The fish-eating water bird is the definitive host and reproduction occurs in the bird's...

parasitizes fish and fish-eating water birds, with a cyclopoid copepod as the first intermediate host.

When humans harbor plerocercoid

Plerocercoid

Plerocercoid refers to last larval form found in the second intermediate host of many Cestoda with aquatic life cycles....

s of pseuddophyllidean cestodes outside the small intestine, it can cause sparaganosis.