Annelids

Phylum Annelida:

15,000 species of Segmented

Worms

Class Oligochaeta

• “Few bristles”

• Earthworms = Lumbricus terrestris

Class Polychaeta

• “Many bristles”

• Marine worms, sandworms

Class Hirudinea

• Leeches

Classification

• Common Name: Earthworm

• Scientific Name: Lumbricus terrestris

• Phylum: Annelida

• Class: Oligochaeta

• Other: Segmented Worms

Characteristics

• Body Plan: Tube within a tube; Segmentation = repeated units

• Body Cavity: Psuedocoelom “False Cavity”

• Symmetry: Radial

• Cell Specialization: Organs and tissues exist; repeated body segments past a certain point; insurance against injury

Life Support Processes

• Absorption: Intestine runs the entire length of the body

• Feeding: Soil enters Mouth > Pharynx (esophagus) > Crop (storage) > Gizzard (grinds food) > Intestine

• Digestion: Intestine = Chemical; Gizzard = mechanical

Life Support Processes

• Respiration: Through the skin, must be kept moist

• Circulation: Closed System - Dorsal Blood Vessel carries blood to head; Ventral Blood Vessel carries blood to back; Ring Vessel = heart (5 Aortic Arches)

• Excretion: Anus = solids; Nephridia = liquids

Life Support Processes

• Secretion: Intestine = digestive enzymes; Clitellum = mucus ring to make egg sac

• Response: Dorsal Ganglia = Brain; no sense organs other than touch receptors in skin

• Movement: Longitudinal and Circular Muscles, Setae

Life Support Processes• Reproduction: Sexual; hermaphrodites

that exchange sperm; Seminal Vesicle = produce sperm, Seminal Receptacle = receive sperm

• Support: Muscle tissues

Ecological Relationships

• Condition Soil; release nutrients

• Detritus Feeders; decompose leaves etc.

Body Systems Compared With Humans

• Nephridia = Kidney

• Intestine = Small Intestine

• Pharynx = Esophagus

Advancements Over Previous Phylum

• Closed Circulation

• Digestive Tract

• Muscles - greater degree of motion

• Segmentation = enables different parts of the body to function independently

Earthworm Diagram

• The largest of the Segmented worms is the African Giant Earthworm (Microchaetus rappi). This huge worm can reach a length of as much as 22 ft and can weigh over 3.1 lb!