Phylum:
Annileda
Annelida
Origin of the word Annelida: Latin for little rings
Common Examples: Earthworms, tube worms, and
leeches
Symmetry: Bilateral Symmetry
Type of body cavity: Coelom
General Annelid Body Plan
Characteristics of Annelids
Segmentation: The formation of repetitive segments.
Occurs in all phyla that evolved after.
Each segment is divided by a septa
Movement: Via contracting or expanding individual
segments
Characteristics of Annelids
Closed Circulatory System: Flows through a
system of tubes (Like our own)
Hydroskeleton: Used to support the muscles
(similar to nematodes). With annelids the
muscles allow the segments to move
individually.
Characteristics of Annelids
Digestive System: Composed of specialized
organs. Two new organs
1) Crop: used to store food
2) Gizzard: used for mechanical digestion
Excretory System
Consists of two parts:
1) Excretory pore: Opening to
the outside of the body.
First found in
platyhelminthes
2) Nephridium: Filters and
collects waste products
from blood and fluid in
coelom. First seen in
annelids carries on into
mammals
Polychaetes and Oligochaetes
Class Polychaeta: Marine annelids. Groups of
worms with many setae.
Setae: Setae are found on parapodia
Parapodia: Paddle like appendages. One pair
per segment. Used for digging swimming and
breathing
Cephalization: sense
Organs located on
the head portion
include eyes
Oligochaetes
Class Oligochaeta: Have few setae per segment.
Including the earthworm
Setae: Found on the ventral side. Used for
digging. Muscle contractions in each segment
move the setae like a paddle pushing it along
the ground
Parapodia: Lacking in
oligochaetes
Cephalization: No real
head region
Hirudinea
Class Hirudinea: Parasitic annelids. Leeches
Modifications:
Suckers: One small sucker at the anterior end and a
larger one on the posterior end.
Lack setae: Move by swimming. Do not burrow. Or
travel along the ground = lost setae over time
Hirudin: A chemical released into the hosts blood to
prevent the blood from clotting
Anaesthetic : This chemical numbs the area where
the leech feeds so the host doesn’t feel it.
Medical Leeches
Uses: Medical leeches are
used during plastic and
reconstructive surgeries.
How does it work:
- Reduce the swelling in the
tissues by removing pooled
blood
- Assists with healing by
allowing fresh oxygenated
blood move in.
Segmentation
Evidence of segmentation in annelids
1) Rings on the outside of the body
2) Septa membranes with are found between
segments inside the body
3) One pair of nephridia in most segments
4) Branching blood vessels in each segments
5) Ganglia and lateral nerves on each side
6) Setae on most segments
• Shape Of Life 4/8 Explosion Of Life (PBS
Documentary)
• Start at ~25 min