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Worms
Flatworms
Flatworms are invertebrate.
It has a head, or anterior end,
and tail, or posterior end.
Like most animals, flatworms
are bilaterally symmetrical.
Examples: Tape worms & blood flukes.
Bilateral Symmetry
 Body plan in which an animal can be divided
into two equal sides.
Structure
 Gastrovascular cavity – gut with a single
opening.
 Cephalization – concentration of sensory
organs towards the anterior end.
Digestion & Excretion
 Pharynx – takes up
food.
 Enzymes excreted to
break down material.
 Nutrients diffuse to
other parts of the body.
 Flame cells – collect
excess water.
 Water travels through
network of tubules
and is eliminated
through pores on the
body surface.
Roundworms (Nematodes)
 Examples: hookworms,
pinworms
 Pseudocoelomates:
hollow fluid filled cavity
- lined by mesoderm on
the outside and
endoderm on the side.
The body of a roundworm
It has a complete digestive tract:
 Two openings: mouth and an anus at opposite ends.
 Food only travels one way.
Segmented Worms:
Annelids
 Their bodies are
divided in segments,
or sections.
 Example: Earth Worm,
leeches
Characteristics
 Symmetry – Bilateral
 A segmented coelom – allows different parts
of the body to move independently.
 Setae – external bristles.
Coelom
 The body cavity of annelids is called coelom.
 A coelom is a fluid-filled cavity completely lined by
tissue that originated from mesoderm tissue.
Structure and Movement
 Anchor middle section
using setae.
 Contraction of the
longitudinal muscles
causes the worm to
move forward.
Feeding and Digestion
 Pharanx – muscular structure that sucks in soil.
 Esophogus – food passes through here.
 Crop – temporary storage
 Gizzard – grinds soil, breaking
up organic matter.
 Intestine – absorbs organic
compounds and nutrients.
 Anus – expels waste.
Circulation
 O2, CO2, nutrients &
wastes transported
through blood vessels.
 Aortic arches connect
the dorsal and ventral
blood vessels.
 Contraction of vessels
and arches circulates
the blood.
Respiration
 Obtaining Oxygen:
– Diffusion through skin
 Nephridia:
– Tubes that eliminate excess water and wastes.
Reproduction
 Hermaphrodites
 Setae and mucus secreted by the clitellum hold
the worms together.
 Secrete sperm into the
mucus and it is stored
in the seminal receptacle.
Reproduction
 After they separate the clitellum secretes a
tube made of mucus and chitin.
 This tube picks up the worm’s eggs and
sperm  fertilization.