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Annelida
Segmented Worms
Main Characteristics
Bilateral symmetry
 Unique annelid head
 Metameric-body segmentation
 Protostomes
 Triploblastic

Main Characteristics (cont.)
They have setae (needle-like structure
of the integumentary system)
 Closed Circulatory System
 Ganglia and Nerve Cords

Locomotion
Use circular and longitudinal muscles
 Can use setae as anchors
 Use hydrostatic pressure
 Use of parapodia (paired appendages)

Annelida
Evolution
Classes of Annelids
Oligochaeta
 Polychaeta
 Hirudinea

Class Oligochaeta

Have a clitellum
– For mucus secretion
– Used in copulation
– Used to form cocoons
No parapodia (appendages)
 Few setae
 Earthworms

Class Oligochaete
Reduced eyes
 Sensitive to chemical or mechanical
stimuli
 Chloragogen tissue-aide in elimination
of nitrogenous wastes and in food
transport

Oligochaete Reproduction
Hermaphroditic
 Must line up clitella
 Held together by mucus sheath
 Cocoon formed

– Fertilization occurs here
– No larval stages

Some freshwater species asexual
Oligochaete Feeding
Scavengers and/or detritovores
 Path of food

– Mouth
– Pharynx
– Crop
– Gizzard
– Stomach
– Intestine
Class Hirudinea
No parapodia
 Circular, longitudinal and oblique
muscle layers
 Leeches

Class Hirudinea
Gas exchange by diffusion
 Nervous system

– Photoreceptors
– Can sense temperature
– Sensory papillae
10-17 pairs of metanephridia for waste
 Chloragogen tissue

Hirudinea Reproduction
All monecious
 All sexually reproducing
 Have a penis for sperm transfer
 Clitellum seen during breeding season
 No larval stages

Hirudinean Feeding

Many carnivorous
– Small invertebrates
– Body fluids
Mouth in the anterior sucker
 Produce “hirudin” – anticoagulant

Class Polychaeta




Largest class
Head distinct w/ eyes and tenticles
Mostly marine
Parapodia-one paired lateral processes on
each side of segments for locomotion,
respiration, or feeding
 Cuticle
 Prostomium-segments of the head (anterior
to mouth)
 Peristomium-segment with mouth
Class Polychaete
Respiration by diffusion
 2-4 pairs of eyes on/near prostomium
 Chemoreceptors
 Statocysts-for sensing equilibrium
 Chloragogen tissue for protein
metabolism

Polychaete Reproduction
Can regenerate
 Asexual reproduction

– Budding
– Fission

Sexual reproduction
– Most fertilization external

Can have alternation of generations
– Epitoke (sexual) vs. Atoke (asexual)
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
