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Phylum Annelida: Segmented Worms
Chapter 27~~~ IN 121
A. General Characteristics Phylum: Annelida
1. Annelid: means“tiny rings”
2. Class: Oligochaeta
3. Examples: bristleworms, earthworms, leeches.
4. Bilateral animals w/ 2 body openings (mouth and anus).
5. Segmented Body
6. Live soil or freshwater
7. Nocturnal burrowing worm
8. Feeds on dirt filtering out organic matter
9. Beneficial to the soil: aeration (opening up soil to allow air to circulate
better), fertilization
10. Respiration: oxygen diffuses across moist skin
11. Sexual Reproduction- hermaphrodites (Earthworms & Leeches)
12. Closed circulatory system: blood contained within vessels,
13. Well Developed Nervous System
B. Earthworm Parts
1. Crop: temporary storage sac after mouth
2. Gizzard: sac w/muscular walls to grind soil
3. Intestine: long intestine stretches length of body to
aid in digestion of soil
4. Ganglion: brain-like organ
5. Aortic Arches: Heart of worm; really 5 enlarged
blood vessels.
B. Earthworm Parts
6. Anus: wastes are removed
7. setae: bristles used for movement located
on ventral side
8. Clittelum: enlarged reproductive segment,
secretes mucus which helps hold worms
together during reproduction
Pathway of Digestion in
an Earthworm
1. Prostonium (lip)
2. Mouth
3. Pharynx (the throat)
4. Esophagus
5. Crop
6. Gizzard
7. Intestine
8. Anus
C. Leeches:
1. Class: Hirudinea
2. Parasitic segmented worm
3. Most live in fresh water
4. Have no bristles for movement, move w/muscular
contractions
5. Suckers at each end of body
6. Medical Uses
a.
Anesthetic
b. Increase circulation
c.
Secretions act as anticoagulants during
feedings
d. Reattachment of digits
e.
Reduce swelling
f.
Cosmetic surgery
Segmented Worm Quiz
1. The term “annelid” means ___.
a. Round worm
b. flat worm
2. Annelids have ___symmetry and ___ body openings.
a. Radial, 1
c. bilateral, 1
b. radial, 2
d. bilateral, 2
3. True/False: Earthworms have 5 true hearts.
4. To keep you from feeling it, the leech secretes an ___ when
it bites into you to feed.
a. Anesthetic
b. toxin
c. anticoagulant
5. True/False: Leeches serve a useful purpose to man.
Section 27-3
Compare/Contrast Table
Comparing Flatworms, Roundworms, and Annelids
CHARACTERISTIC
FLATWORMS
ROUNDWORMS
ANNELIDS
Shape
Flattened
Cylindrical with tapering
ends
Cylindrical with tapering
ends
Segmentation
No
No
Yes
Body cavity
Acoelomate
Pseudocoelomate
Coelomate
Digestion and
excretion
Gastrovascular cavity with
one opening only; flame
cells remove metabolic
wastes
Tube-within-a-tube
digestive tract; opening at
each end; metabolic
wastes excreted through
body wall
Tube-within-a-tube
digestive tract; opening at
each end; nephridia
remove metabolic wastes
Respiration
Through skin; no
respiratory organs
Through skin; no
respiratory organs
Through skin; aquatic
annelids breathe through
gills
Compare/Contrast Table
continued
Section 27-3
Comparing Flatworms, Roundworms, and Annelids
CHARACTERISTIC
FLATWORMS
ROUNDWORMS
ANNELIDS
Circulation
No heart, blood vessels,
or blood
No heart, blood vessels,
or blood
Blood circulated through
blood vessels in closed
circulatory system
Response
Simple brain; nerve cords
run length of body;
eyespot and other
specialized cells that
detect stimuli
Several ganglia in head
region; nerve cords run
length of body; several
types of sense organs
Well-developed nervous
system with brain and
several nerve cords; many
sense organs
Movement
Gliding, twisting,
and turning
Thrashing
Forward peristaltic
movement
Reproduction
Sexual (hermaphrodites);
asexual (fission)
Sexual (primary males and
females)
Sexual (some are
hermaphrodites; some
have separate sexes)