Nematodes and
Annelids
Phylum Nematoda (Roundworms)
•Non-segmented
•Bilateral symmetry
•Organization - 3 germ layers – endoderm,
ectoderm, & mesoderm – organ level
•Pseudocoelomates (body cavity) – filled with fluid
– space for organs
•Tube-within-a-tube body plan – complete digestive
tract with mouth and anus.
•Habitat – fresh or salt water, soil, inside host (both
plants & animals)
Life Processes
•Internal transport - fluid in pseudocoelom
transports nutrients & oxygen
•Support – fluid in pseudocoelom provides
support (hydrostatic skeleton).
•Respiration - Breathe through their skin diffusion.
•Movement - longitudinal muscles – move
with whiplike motion – inefficient in water,
good in soil & host.
•Excretion – waste is removed through the
anus
•Feeding & digestion –
•Feed using muscular pharynx which
shoots out from mouth
•Food is digested in intestine
•Gender - appear as separate males &
females
•Sexual reproduction – male injects sperm
into female, she lays eggs.
Roundworm anatomy
Types of
nematodes:
• Ascaris
• Contracted
when one
eats
vegetables
contaminated
with human
waste.
• Trichina
worm:
• Trichinosis
is contracted
when eating
undercooked
pork
containing
encysted
larvae.
•Filaria worm:
•Carried by
mosquitoes
and causes
elephantiasis
by blocking
lymphatic
drainage.
•Pinworms:
•Common
infections in
children.
•Hookworm:
•Once common
in the southern
United States.
•Person
becomes
infected when
walking in soil
contaminated
with human
waste
•Guinea worm:
•Person
becomes
infected when
drinking water
with water fleas
contaminated
with guinea
worm eggs.
•Worm emerges
from leg once
fully grown.
Phylum Annelida (segmented worms)
• Symmetry - bilateral
• Organization - 3 germ layers – organ level
• Coelomates -have a body cavity – more
complex organs
• Segmented
• Habitat – fresh or salt water, soil
• Tube-within-a-tube body plan – specialized
organs in digestive tract (see earthworm later)
• Support - hydrostatic skeleton.
• Respiration - breathe through their skin diffusion.
• Internal transport - closed circulatory
system with 5 aortic arches (hearts) and
blood vessels that run the length of the body
and branch to every segment.
• Excretion –
– Nephridia (tiny tubes found in each segment)
remove nitrogen waste through openings in
body wall
– Anus removes waste from digested food.
•Movement - alternating contraction of
longitudinal and circular muscles found in each
segment.
•Response - brain connected to a ventral nerve
cord .
•Three classes –
•Polychaeta – marine worms
•Oligochaeta – earthworms
•Hirudinea - leeches
Earthworm, Lumbricus
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Mouth
Pharynx
Esophagus
Crop
Gizzard
Intestine
Anus
Aortic arches (hearts)
Dorsal blood vessel
Ventral blood vessel
Brain
Ventral nerve cord
Clitellum
Setae
Clitellum
Testis
Sperm reservoir
Ovary
Seminal
receptacle
Excretory pore
Nephridium
Tubule
H. Intestine
I. Coelom
J. Muscle
K. Muscle
L. Epidermis
L1. Cuticle
M1. Blood vessel
M2. Blood vessel
N. Nerve cord
O. Nephridium
P. Setae
Earthworms
• Have pairs of setae in each segment; when
muscles contract in each segment, setae anchor
in the soil, and aid locomotion.
• Diet - leaves & decaying matter
• Digestion: Mouth  Pharynx (swallows food)
 Esophagus (connects pharynx & crop) 
Crop (stores food)  Gizzard (grinds food –
contains small stones swallowed by the worm)
 Intestine (digests food)
•Gender - hermaphroditic.
•Reproduction
•Meet at clitellum (smooth part of worm),
which secretes a ring of mucus
•Each injects sperm into mucus
•Tube slides forward, picking up eggs
•Tube slides off body & is left behind
•Fertilization occurs within tube
•Worms hatch in a few weeks – no larval
stage
•Two sets of young
Leeches
• Most in fresh water, some in soil or salt water.
• 2 suckers (1 small anterior, 1 large posterior) to feed.
• Some are free-living predators; most are fluid
feeders that attach themselves to open wounds.
• Bloodsuckers cut through tissue with 3 saw-like
jaws – leaves “Y” – shaped wound.
• Anesthetic in saliva prevents victim from feeling
attack and dilates blood vessels; anticoagulant
(hirudin) in their saliva keeps blood from clotting;
pouches in crop allows for storage of up to 5 times
their weight – long time between feedings.