Today’s Objectives

Explore the diversity, success, body
plans, organ systems and economic
importance of phylum Annelida.
Phylum Annelida
Annelida
Segmented Worms
Main Characteristics

Bilateral symmetry
 Metameric
 Tagmatization
 Protostomes
 Triploblastic
 Setae
 Closed Circulatory System
 Ganglia and Nerve Cords
 Metanephridia
Phylum Annelida
Classes of Annelids
Polychaeta – Nereis, Arenicola
 Oligochaeta – Lumbricus, Tubifex
 Hirudinea - Hirudo

Phylum Annelida
Class Polychaeta
Mostly marine
 Parapodia
 Cuticle
 1st segment – prostomium
 2nd segment – peristomium

Phylum Annelida
Polychaeta Feeding

Most carnivorous
– Some have venom
– Gut is straight tube

Some are detritovores
– Extract nutrition from sediment (or soil)
– Gut has crop and gizzard
Many are filter feeders
 Some can get food by diffusion

Phylum Annelida
Other polychaete Systems
Respiration by diffusion
 2-4 pairs of eyes on/near prostomium
 Chemoreceptors
 Statocysts
 Metanephridium for excretion
 Chloragogen tissue for protein
metabolism

Phylum Annelida
Polychaete Reproduction
Can regenerate
 Asexual reproduction

– Budding
– Fission

Sexual reproduction
– Most fertilization external

Can have alternation of generations
– Epitoke (sexual) vs. Atoke (asexual)
Phylum Annelida
Oligochaeta
Terrestrial, freshwater, some marine
 Have a clitellum

– For mucus secretion
– Used in copulation
– Used to form cocoons
No parapodia
 Few setae

Phylum Annelida
Oligochaete Locomotion
Use circular and longitudinal muscles
 Can use setae as anchors
 Use hydrostatic pressure

Phylum Annelida
Oligochaete Feeding
Scavengers and/or detritovores
 Path of food

– Mouth
– Pharynx
– Crop
– Gizzard
– Stomach
– Intestine
Phylum Annelida
Other Oligochaete Systems
Most ganglia fused
 Reduced eyes
 Sensitive to chemical or mechanical
stimuli
 Use metanephridia for excretion
 Chloragogen tissue

Phylum Annelida
Oligochaete Reproduction
Hermaphroditic
 Must line up clitella
 Held together by mucus sheath
 Cocoon formed

– Fertilization occurs here
– No larval stages

Some freshwater species asexual
Phylum Annelida
Hirudinea
Terrestrial, freshwater or marine
 No parapodia
 Secondary annuli on segments
 Circular, longitudinal and oblique
muscle layers

Phylum Annelida
Hirudinean Feeding

Many carnivorous
– Small invertebrates
– Body fluids
Mouth in the anterior sucker
 Produce “hirudin” – anticoagulant

Phylum Annelida
Other Hirudinea Systems
Gas exchange by diffusion
 Nervous system

– Photoreceptors
– Can sense temperature
– Sensory papillae
10-17 pairs of metanephridia for waste
 Chloragogen tissue

Phylum Annelida
Hirudinea Reproduction
All monecious
 All sexually reproducing
 Have a penis for sperm transfer
 Clitellum seen during breeding season
 No larval stages

Phylum Annelida