Unsegmented Worms Phylum Platyhelminthes. I. Unsegmented worms A. = Worms that are not divided into…

Unsegmented Worms

Phylum Platyhelminthes

I. Unsegmented worms

A. = Worms that are not divided into sections externally & internally

B. E.g.1. Phylum Platyhelminthesaka flatworms

2. Phylum Nematodaaka Roundworms

C. What is a coelom?

= fluid-filled body cavity

between body wall

& digestive tract

Kinds of coelom

1. Acoelomate= no coelomi.e. body cavity is

NOT fluid filled

Kinds of coelom2. Pseudocoelomate= Fluid filled

body cavity

BUT

No mesentary or

peritoneum

Kinds of coelom3. Eucoelomate

=

True coelom

w/ mesentary (holds gut in place)

& peritoneum

(mesodermal

lining of body cavity

D. Phylum Platyhelminthes

1. Class : Turbellaria – planarians

2. Class : Trematoda – flukes

3. Class : Cestoda – tapeworms

D. Phylum Platyhelminthes

Also Acoelomate:• Phylum Nemertea – ribbon worms• Phylum Gnathostomulida-

jaw worms

E. General Info re: Flatworms

1. = “platy” = flat “helminth” = worm

2. Body structure a. Size range 1 mm ------►

many meters (Cestoda) b. Shape – flattened dorso-ventrally c. Only several cell layers thick

E. General Info re: Flatworms

Cells fill body cavity (not fluid)

F. Level of Organization

= organ system

G. Symmetry

• bilateral • (has forward movement & cephalization)

I ‘m a little bilateral animal

too!

H. Habitat

• aquatic (freshwater or marine) • moist soil

• endoparasites of vertebrates

I. Feeding - Class Turbellaria

Planarians-

mostly free-living carnivoreorscavengers

– Incomplete digestive tract – one opening (no anus)

– Mouth on ventral side– Protrusible pharynx– Gastrovascular cavity

(GVC) – “Intestine” very

branched – Enzymes digest food

I. Feeding - Class Turbellaria

I. Feeding - Class Trematoda

• Parasitic flukes• endoparasites of vertebrates• need only minimal digestive tract• E.g. Human Liver fluke

I. Feeding – Class Cestoda

tapeworms–Endo-parasites–Scolex w/ hooks & suckers–NO need for dig. tract – absorbs nutrients from gut of host

suckers

scolex

J. Respiration

• - via diffusion • (only a few cell layers thick)

K. Internal transport

• via diffusion

Marine flatworm

L. Excretion – via diffusion

• EXCEPTION:

planarians have • flame cells ( w/

flagella • that help move

waste to • excretory pores,

then out of the body

M. Response – (Nervous system)

1. Primitive brain – anterior ganglia ganglion = cluster of nerve cells2. Two Longitudinal nerves (the length of the

body)3. Ladder-like cross-bridges of nerves

M. Response – (Nervous system)

M. Response – (Nervous system)

4. Sense organs: (flatworms)a. Ocelli – eyespots / photodetectorsb. Auricles -

contain chemoreceptors (chemicals) & thigmoreceptors (touch)

c. Statocysts – balanced. Rheoreceptors – sense

direction of water current

N. Locomotion - Planaria – use cilia, slime, circular and

longitudinal muscles

to GLIDE

– Trematoda, Cestoda – little motion

cilia

O. Reproduction

1. Asexual – Regeneration (Planaria only)2. Sexual –

a. pattern = monoecious (hermaphrodites)b. cross- fertilization (swap sperm)

P. Ecological Roles

1. Scavengers/ predators – recycle nutrients to ecosystem (Class Turbellaria)

2. Prey for fish & birds (Class Turbellaria)3. Endo-parasites (cause disease)

(Class Trematoda & Class Cestoda)