The Invertebrates The Worms

General Characteristics soft-bodied, long, legless bilateral symmetry cephalization a distinctive sensitive anterior region having a collection of nerve tissue with which to make decisions three cell layers epidermis – outer layer; protection and locomotion mesooderm – middle layer; muscular contractions during locomotion gastroderm – inner layer; lines the digestive track Many phyla, we will look at 3 most common

Phylum Platyhelminthes the “flatworms”

The Flatworms thin flattened body most are parasitic tapeworms flukes some are free-living planarians 3 classes

Planarians (Life process chart) Class Turbeliaria – free-living freshwater approximately 1cm long anterior region has 2 cross-eyed eyespots on the dorsal surface that are sensitive to light

Planarians

Planarians movement cells on the ventral surface secrete slime and then the ciliated cells can move across the slimy surface muscles in the mesoderm can contract to help with movement

Planarians nutrition eats small animals, eggs, liver releases digestive enzymes out of its mouth and onto their prey pharynx extends out of mouth and draws up the digested particles into the branched intestine enzymes in the intestine break down the food further food is diffused throughout the body waste is egested through the pharynx

Planarians excretion flame cells – hollow bulbs located at the end of a system of tubes in the mesoderm, empty waste into the environment by the means of excretory pores helps maintain water balance by excreting excess water

Planarians Response anterior mass of nervous tissue, ganglia, act as a “brain” two longitudinal nerves extend from the “brain” and transverse nerves join the longitudinal nerves together sensitive to touch, chemicals, light

Planarians eyespots longitudinal nerves transverse nerves

Planarians asexual reproduction fission: planarian can pull itself apart behind the pharynx and each half can regenerate into new animals sexual reproduction hermaphroditic: both male and female reproductive organs cross-fertilize each other and release eggs enclosed in a capsule eggs will hatch in about 1 months time

Planarians

Parasitic Flatworms depend on host for nourishment harm their host, but do not kill them few sense organs as adults no external cilia in adults thick tegument (protective covering) suckers and/or hooks for attaching to the host

Parasitic FLukes Class Trematoda – The Flukes Opisthorchis sinensis Intermediate host - an animal that temporarily harbors the immature form of a parasite (snail) cannot live outside of host for very long Read page 353-354 in textbook

Parasitic FLukes flukes sheep liver fluke mouth intestine sucker ovary testes

Parasitic Tapeworms Class Cestoda – The Tapeworms Do not resemble flukes Pork tapeworm Ribbon-like body that can be as long as 6m in length Lives in intestines of a vertebrate host, animal or human Scolex – small bulb-shaped head Suckers and hooks on scolex attach worm to host

pork Tapeworms (cont.) body is divided into proglottids that contains both testis and ovaries no mouth or digestive organs absorbs and uses only food that the host’s body has already digested tegument protects it from harsh digestive juices deprives host of food, but usually pose no physical dangers UNLESS tapeworm grows so long as to clog the intestines humans eat the proglottids and cysts form in their muscles