Covers the general features of cestodes: their segmented body, scolex, proglottids, tegument, nervous and excretory systems, and cysticercus larvae. It then traces the life cycle of Diphyllobothrium latum through its two intermediate hosts, crustaceans and fish, to human infection by raw or undercooked fish. The note adds a recap of questions and answers and four mnemonics for body parts, the life cycle, larval stages and class traits.
Topic 90 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 4 sections, about 861 words (6 min of reading), with 10 flashcards.
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Class Cestoda. Diphyllobothrium latum.
Class Cestoda (Tapeworms)
Genus Diphyllobothrium
Mnemonics
Class Cestoda (Tapeworms)
General Features
Cestodes are parasitic flatworms that belong to the Phylum Platyhelminthes.
They are commonly known as tapeworms.
Tapeworms have a ribbon-like, elongated, and segmented body structure, making them distinct from other flatworms.
The entire body of the adult worm is called the strobila.
The head of the worm is referred to as the scolex, which is used for attachment to the host’s intestinal wall. It contains a pair of cerebral ganglia that form part of the nervous system.
Body Structure
The worm’s body is divided into multiple segments called proglottids. Some tapeworms may have between one thousand to two thousand proglottids.
Each proglottid can function independently to some extent and may contain reproductive organs.
A detached proglottid can continue to move for a short time and retain some sensory function.
Sensory and Nervous Systems
Tapeworms lack complex sensory organs. Instead, their tegument, or outer surface, acts as a sensory interface with the external environment.
The nervous system consists of two lateral nerve cords running along the length of the worm and a pair of cerebral ganglia located in the scolex.
Excretory System
The excretory system includes two longitudinal excretory canals that are connected by transverse canals.
Excretion is aided by flame cells, which are specialized cells that help filter waste from the body.
Larval Forms
The larval form of a cestode that develops inside the intermediate host is called a cysticercus.
A cysticercus is a fluid-filled cyst that is either round or oval and can be seen without a microscope.
Cysticerci may vary in size depending on the species and are commonly found in organs such as the muscles, liver, skin, or brain of the intermediate host.
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