chapter 37-2 annelida. phylum: annelida annelid: means “little rings” many body segments can...
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CHAPTER 37-2
Annelida
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Phylum: Annelida
Annelid: means “little rings” Many body segments
Can include marine species Earthworms Leeches
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Characteristics and Classification
Bilateral Symmetry Coelomates Segmented (important evolution) Developed organ systems External Bristles and Fleshy Protrusions
Setae #
Parapodia Presence or absence
Determine which class division Oligochaeta, Polychaeta, Hirudinea
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Oligochaeta
Live in soil or fresh water Look for adaptations
for burrowing Have no parapodia Name means “few
bristles” Have few Setae
Most familiar member is the Earthworm
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Oligochaeta – Structure and Movement
Earthworm body divided in more than 100 virtually identical segments
Locomotion method Worm anchors some middle segments by
setae Contracts muscles in front of those segments
This increases pressure on coelomic fluid Elongates the animal and pushes anterior end
forward Anterior setae then grip ground, pulling the
posterior segments forward
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Oligochaeta – Feeding and Digestion
Ingest soil as they burrow through Sucked into mouth by the pharynx Esophagus – crop – gizzard – intestine - anus
Play an important role to maintain soil fertility Decomposition Release nutrients Oxygen penetration Loosen soil
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Oligochaeta – Circulation
Closed circulatory system Blood travels to posterior end through
ventral blood vessel Blood returns to anterior end through
dorsal vessel Aortic arches link the two blood vessels at
the anterior end
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Oligochaeta – Respiration and Excretion
No specialized respiratory organs Oxygen and CO2 diffuse
directly through skin Gas exchange only happens if
skin is moist Secrete mucus and have a thin
cuticle Eliminate cellular waste and
excess water Excretory tubules called
nephridia Each segment (except first 3
and last 1) contain a pair
Nephridia
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Oligochaeta – Neural Control
Nervous system Chain of ganglia connected by a ventral nerve
cord Most segments contain a single ganglion
Nerves branch from each ganglion Several ganglia fused to form “brain” (cerebral
ganglia) Main function is to process simple info from sensory
structures Present in all segments, but concentrated at
anterior
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Oligochaeta – Reproduction
Hermaphrodites (Cannot self fertilize) Mating: 2 worms press ventral surface
together, anterior pointing in opposite directions Held together by:
Setae & Mucus Secreted by clitellum (thickened section)
Sperm moves through mucus to seminal receptacle
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Oligochaeta – Reproduction Cont’d
The worms separate After several weeks the clitellum secretes a
tube Made of mucus and chitin Tube slide forward and picks up eggs and sperm
Fertilization occurs within tube Young worm develops inside for 2-3 weeks
before hatching
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Polychaeta
2/3 of all annelids “many bristles” Mostly marine Have antennae and specialized
mouthparts
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Hirudinea
Smallest class, about 300 species
Leeches Mostly freshwater No setae or parapodia Sucker at each end of body Some are carnivores, but
many are parasitic Suck blood from host Secrete anesthetic and anti-
clotting substance