Annelids - Cloudfront.net
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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