PHYLUM PLATYHELMINTHES

Biology 11

What is a flatworm?

Acoelomates

Thin, solid bodies

Can be 1mm to several meters

14,500 species

Marine, freshwater, and moist habitats on land

Ex. Tapeworms, flukes, planarians

Flatworms

1. Class Tubellaria (Planaria)

Soft, flattened bodies covered in cilia

Live in aquatic or moist environments

Scavengers

2. Class Trematoda (Flukes)

Parasitic: therefore, they have a tough outer

covering and two suckers to anchor to a host and

feed at the same time.

Example: Schistosoma (liver fluke).

Lung Fluke

Zombie Snail

mailto:http://animal.discovery.com/tv-shows/monsters-inside-me/videos/the-lung-fluke.htmmailto:http://www.youtube.com/watch?v=Go_LIz7kTokhttp://animal.discovery.com/tv-shows/monsters-inside-me/videos/the-lung-fluke.htm

3. Class Cestoda (Tapeworm)

Parasitic: live

in digestive

tract of host.

Organization

3 true cell layers (endoderm, mesoderm, ectoderm)

Simple organs (cephalization, excretory, pharynx,

ect.)

Acoelomates

Motility

All

Bilateral symmetry

Mobile

Planaria

Move by gliding over a slime track they secrete

Anterior

Dorsal

Posterior

Ventral

Feeding

Planarians / Flukes

Extracellular digestions: enzymes secreted by mouth

A muscular tube, the pharynx, is extended out though

the mouth. The food is sucked in through the pharynx

and passes into the intestine and digestive glands.

Tapeworm

Intracellular digestion: tapeworms absorb the digested

nutrients of their hosts, so they have no need for a

mouth

Digestion and Excretion

Planarians / Flukes

Incomplete digestive system: food enters through the

same opening by which undigested wastes leave.

Extracellular digestion: enzymes secreted onto slow-

moving or dead prey.

Excretory system consists mainly of FLAME CELLS; small,

bulb-like structures that remove water and chemical

wastes through the body pores by using beating cilia.

Digestion

Excretion

Digestion/ Excretion Con’t.

Tapeworms

No digestive system, since they absorb nutrients

already digested by their host. The SCOLEX is a knob-

shaped head with hooks or suckers or both, with which

the tapeworm attaches to its host.

Nervous System

Planaria / Flukes

Two anterior ganglia serve as a simple brain

(cephalization)

A ladder-like network of nerves runs the length of the

body

React to light, chemical, food

Nervous System Con’t.

Tapeworm:

The nervous system is reduced

The main nerve center, ganglion, is in the scolex

Smaller nerves travel down the body to muscular and

sensory ending

Some nerves are only temporary

Reproduction

Planaria / Flukes

Asexual: through fragmentation and regeneration

Sexual: individuals are hermaphrodites, but individuals

cannot fertilize their own eggs. Eggs are laid in a

protective cocoon and take 2-3 weeks to hatch

Planaria Reproductive Picture

https://www.youtube.com/watch?v=wn3xluIRh1Y

https://www.youtube.com/watch?v=wn3xluIRh1Y

Reproduction Con’t.

Tapeworm

Behind the SCOLEX is a region

from which PROGLOTTIDS are

produced and eventually shed.

PROGLOTTIDS are body sections

that contain a complete

hermaphrodite reproductive

system.

Tapeworms have at least two hosts

in their life cycles

Proglottid

Circulation

Planarians / Flukes / Tapeworms:

None

Diffusion of nutrients to body cells

Overview