5)PHYLUM ANNELIDA (p 594-601)

PHYLUM ANNELIDA – Segmented Worms
PHYLUM ANNELIDA – Segmented Worms
 Annelids are worms with segmented bodies
 Includes earthworms & some marine worms
 Annelida means “little ring”
PHYLUM ANNELIDA – Segmented Worms
 Annelids are worms with segmented bodies
 Includes earthworms & some marine worms
 Annelida means “little ring”
A. General Characteristics
 Although annelids look like round worms and flat
worms, they are very different. In fact, they are
probably more closely related to clams and snails
than the other worm phylums.
 Annelids have a complex organ system.
 Annelids, like homo sapiens, have a true coelom.
A. General Characteristics
B. Body Systems
1. Circulatory System
 Well developed “closed” system (not open to air)
 Blood is pumped thru 2 vessels that run the length of
the body


dorsal (top vein - back)
ventral vessels (bottom vein - front)
 5 circular hearts & 2 primitive hearts near the
anterior (head) end connect dorsal and ventral
vessels
.
B. Body Systems
B. Body Systems
2. Respiratory System
 Diffusion across the skin
 Dependent on the skin being moist
dry worm = dead worm
 oxygen can only cross moist membranes as water is
needed to carry oxygen across the membrane

 Some marine worms have gills
B. Body Systems
2. Respiratory System
 Diffusion across the skin
 Dependent on the skin being moist
dry worm = dead worm
 oxygen can only cross moist membranes as water is
needed to carry oxygen across the membrane

 Some marine worms have gills
B. Body Systems
3. Digestive System
 Mostly detritivours – eat rotting organic material
 All annelids have a complete system
Mouth>Pharynx>Esophagus>Crop>Gizzard>Intestines>Anus
 Pharynx forces food down esophagus with muscular




contractions
Esophagus tube to carry food to the crop
Crop flexible storage sac for later digestion
Gizzard mechanically grinds up food
Intestine actual digestion and absorption of food
B. Body Systems
B. Body Systems
4.
Excretion System
 each segment have NEPHRIDIA to expel
nitrogenous wastes
 mostly located in posterior end
B. Body Systems
5.
Nervous System
well developed with a primitive brain.
 have chemical and touch sensors
 bristles (setae) aid in touch sense



Setae also hold the worm in the ground when pulled
from above
some marine species have primitive eyes!
B. Body Systems
B. Body Systems
6.
Reproduction
 asexually – regeneration of lost segments
 sexual reproduction to increase genetic diversity
 earthworms are hermaphrodites
 self-fertilization is ruled out because the two worms come
together to exchange sperm which is then stored in the
seminal recepticle of the other worm. Later the clitellum
slides forward to pick up the sperm and eggs, fertilization
occurs, and the clitellum slides off the anterior end to act as
a cocoon for the young to develop in
B. Body Systems
6.
Reproduction
C. Classification
There are 3 classes of Annelids
 1. Class Oligochaetes – earthworms
 -name means fewer, less obvious bristles (setae)
C. Classification
There are 3 classes of Annelids
 1. Class Oligochaetes – earthworms
 -name means fewer, less obvious bristles (setae)
C. Classification
There are 3 classes of Annelids
 2. Class Polychaetes: “many bristles”, marine worms
 many have paddle-like appendages, developed from bristles
 Neries worms have “jaws” developed from bristles
 tube worms-live in self-secreted tubes of CaCO3, filter feeders
C. Classification
There are 3 classes of Annelids
 2. Class Polychaetes: “many bristles”, marine worms
 many have paddle-like appendages, developed from bristles
 Neries worms have “jaws” developed from bristles
 tube worms-live in self-secreted tubes of CaCO3, filter feeders
C. Classification
There are 3 classes of Annelids
 3. Class Hirudinea: leaches
 appear to be unsegmented, but segments are present inside
 External parasites that suck the blood from the host
 used in medicine to
• stop blood clotting, as anesthetics, contain antibiotics
C. Classification
There are 3 classes of Annelids
 3. Class Hirudinea: leaches
 appear to be unsegmented, but segments are present inside
 External parasites that suck the blood from the host
 used in medicine to
• stop blood clotting, as anesthetics, contain antibiotics
D. Ecology of Annelids
 Earthworms play a vital role in converting large
amounts of organic matter into rich and fertile soil.
 They are key components of food chains.
 By burrowing through the soil, they allow oxygen
and water to reach plant roots.
 Earthworms enrich the soil by adding nitrogen,
phosphorus and potassium, which promote vigorous
plant growth.
The End