Phylum Platyhelminthes

Presentation Transcript

Flatworms

Flukes

Tapeworms

Phylum Platyhelminthes

The phylum consists of four classes

Turbellaria
Trematoda
Cestoda

Triclad Flatworm

Reproduction

Almost all are simultaneous hermaphrodites
Parasitic species (flukes and tapeworms) have complex lifecycles, with various hosts and several different larval stages
Incredible powers of regeneration

Nervous System

Free-living species usually have a well-developed sensory system
Parasites generally have less elaborate systems.

WHY?

Taxonomic Summary

Phylum Platyhelminthes (Flatworms)

Class Turbellaria
Class Cestoda
Class Trematoda
Class Monogeneans

Class Turbellaria

Most are free–living, tiny and inconspicuous

Primarily marine and freshwater

Free-living

Flatworm

Flatworm Body Plans

Exhibit bilateral symmetry, acoelomate, and are triploblastic
Parenchyma tissue

Digestion and Excretion

Mouth is usually located at the anterior end or mid-body on ventral surface
Excretory system

Contains flame bulbs

Regeneration

Many species posses remarkable powers of regeneration and repair wounds

Turbellarian Lifestyles

Most are benthic
Posses several nerve cords with a centralized ganglia (brain)

Some species also have a protrusible pharynx that captures food and transfers it into the mouth

Can be carnivores or scavenge on dead animals and detritus

Turbellarian Habits

Reproduction

Reproduction occurs with the reciprocal exchange of sperm
Fertilized eggs are released and usually develop directly into flatworms

Muller's larva

Defining characteristics

Scolex

Proglottids

Class Cestoda (Tapeworms)

Proglottids

Proglottids

Each animal can be 3,000 – 4,000 per animal
Amazing reproductive output
Each may contain several ovaries and 1,000 distinct testes

Beef tapeworm

Problems of a parasitic existence

Reproduce within the definitive host
Get fertilized eggs out of the host
Contact a new and appropriate host
Obtain entrance into the host
Locate the appropriate environment within the host
Maintain position within the host
Withstand an often anaerobic environment
Avoid digestion or attack by the hosts immune system
Avoid killing the host, at least until reproduction is completed

Class Trematoda (Flukes)

All are external and internal parasites of other animals
Leech-like bodies with a sucker at each end
Have a gut and well-developed reproductive system, never segmented

Trematoda Lifecycles

The lifecycle is complex with up to 4 different hosts and several larval types

Schistosomiasis

Deadly prominent disease in many regions of the world

Bores into the skin of the definitive host and travels in the circulatory system to the heart the lungs and the kidneys where it feeds and grows

Inflammation is caused by eggs becoming trapped in the hosts tissues

Chinese liver fluke

Lives in the bile duct of humans, cats, and dogs (1-2 cm.)

Goes through two intermediate hosts

Infection occurs from ingestion of raw fish

Trematodes of Concern