Unit 5.1 Phylum Platyhelminthes

Phylum Platyhelminthes Flat worms Triploblastic – three primary germ layers Acoelomate – no body cavity Bilateral symmetry Hermaphroditic Monoecious – Having both sperm and egg producing parts One opening for digestive system – located ventrally. Food is eaten and excreted through the same tube.

Phylum Platyhelminthes Paired lateral nerve cords & cerebral ganglion – very simple Flame cells – specialized “kidney” cells No specialized circulatory or respiratory systems – must be flat so nutrients & oxygen can diffuse throughout the body

Echinodermata Uniramia Chelicerata Chordata Crustacea Protochordates Lophophorates Crustacea Protochordates Arthropoda Annelida Hemichordata Mollusca Other pseudocoelomates Nemertea Platyhelminthes Nematoda Ctenophora Cnidaria Mesozoa Placozoa Sarcomastigophora Ciliophora Porifera Apicomplexa Microspora Myxozoa

Acoelomate Ectoderm Mesoderm Endoderm Coelom – A fluid filled space that is completely surrounded by mesoderm

Fig. 14.1

Acoelomate Phylum Platyhelminthes: Class Turbellaria Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Platyhelminthes: Class Turbellaria Acoelomate

Pseudocoelomate Ectoderm Mesoderm Endoderm Coelom – A fluid filled space that is completely surrounded by mesoderm

Coelomate Ectoderm Mesoderm Endoderm Coelom – A fluid filled space that is completely surrounded by mesoderm

Nervous System Lateral nerve cord Cerebral ganglion Connectives Eye spot Auricle

Brain Auricle Cerebral ganglion Paired nerve cords

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Excretory System

Fig. 14.6a

Fig. 14.6b

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Turbellaria

Class Turbellaria Eye spots – detect simple light gradients. Ciliated skin surface secretes mucous and aids in movement. May be aquatic or terrestrial. Terrestrial species are all nocturnal. Most are free-living – not parasites but predators/scavengers.

Class Turbellaria Planarians have the ability to regenerate new body parts or to generate an entirely new organism from pieces of themselves.

Fig. 14.2

Class Trematoda Flukes Parasites Holdfast devices Complex life cycle Most possess these Complex life cycle Intermediate host Animal with juvenile stage Definitive host Animal with adult stage

Fig. 14.7

Clonorchis sinensis Oral sucker Intestine Uterus Yolk gland Ovary Testes Ovary Seminal recepticle

Clonorchis sinensis Chinese liver fluke 50 million people infected. Cirrhosis of liver – liver tissue is replaced by non-functioning scar tissue that impairs overall liver function Diarrhea Edema – fluid beneath the skin. Severe gut pain.

Fig. 14.12

Fascioloa hepatica Sheep liver fluke Sheep, cattle and man Weight loss Eat vegetation contaminated with metacercariae – small capsules that house the intermediate stage of the fluke.

Life Cycle of the Sheep Liver Fluke Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of the Sheep Liver Fluke

Fasciolopsis buski Intestinal fluke 10 million people Man and pigs Hemorrhage and abscesses of small intestine

Paragonimus westermani Lung fluke Carnivores, pigs, rodents and man May be fatal

Schistosoma Blood flukes – parasitize mesenteric blood vessels. 200 million people infected. 1 million deaths/year. Second most deadly parasite behind malaria. Males wrap around females & they exist in pairs throughout adult lives.

Life Cycle of a Schistosome Fluke Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle of a Schistosome Fluke Eggs are expelled in urine or feces to fresh water where the larvae pass through an intermediate stage involving a snail host and then enter through the skin of a passing human host.

Schistosoma The eggs all have a hook that tears bodily tissues throughout the human host causing more damage as they are passed. Larvae have a forked tail that assist them in borrowing through human skin.

Schistosoma

Swimmers Itch – Related to Blood Fluke

Swimmers Itch Need avian hosts to complete their life cycle. Humans are “accidentally” infected and develop a rash for around a week. Sores develop around burrowing sites but the larvae die within a few hours of entering the skin

Class Cestoidea Tapeworms No digestive system – suck in pre-digested nutrients from the intestines of the host that are directly utilized in metabolic processes. Can grow up to 100 feet long. Human tapeworms may reach 60 feet in length.

Class Cestoidea The scolex, or head, is equipped with suckers designed to anchor the worm to the intestinal wall and to suck in nutrients. The proglottids are hermaphroditic segments, each able to detach from the body and produce eggs.

Class Cestoidea Infections are usually asymptomatic other than lethargy and/or dull abdominal pain. The lethargy is due to a lack of nutrients caused by the tapeworms’ feeding. This leads to weight loss. People may purposefully infect themselves with tapeworms to lose weight.

Scolex

Proglottid Testes Uterus Vas deferens Seminal receptacle Ovary Yolk gland

Pork Tapeworm (Taenia solium) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pork Tapeworm (Taenia solium)

Taenia saginata

Echinococcus granulosus A tapeworm that causes a potentially fatal parasitic disease called hydatid disease. Herbivores, and sometimes humans, become the intermediate hosts after ingesting eggs on vegetation.

Echinococcus granulosus The eggs then hatch into embryos that lodge in tissues and grow into huge cysts containing thousands of tapeworm larvae. When the cysts finally cause the host to die or become easy prey, they are ingested by the scavenger/predator and become adults in their intestinal tracts.

The End