Download Phylum Annelida

Phylum
Annelida
Segmented Worms
Phylum Annelida
• Metameric Body Plan
– Bodies are divided into segments
– Separated by septa
– Each segment has own excretory,
nervous and circulatory structures
– Flexible support and efficient
locomotion
Characteristics
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Most complex of all worms
Triploblastic coelomates
Bilateral symmetry
More complex
Closed circulatory system
Characteristics
• Two sets of muscles
– Circular and longitudinal
• Paired epidermal setae
(bristles)
– Ventral side
– Used in movement
Class Polychaeta
“many bristles”
~5300 species
Mostly marine
Largest group
Burrow into sea floor or live in reefs or
tubes
• Carnivores or filter feeders
• Lateral extensions called parapodia with
numerous setae
• Respiratory gases diffuse across the body
wall
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Reproduction
• Remarkable regeneration
– Some have break points that allow
worms to sever themselves when a
predator grabs them
– Lost segments are later regenerated
• Asexual reproduction
– Budding or transverse fission
• Sexual reproduction (most common)
– Dioecious
– Epitokes
Class Clitellata
• Characterizes organisms based
upon clitellum and few or no
setae
• Subclass Oligochaeta
– Earthworms
• Subclass Hirudinea
– Leeches
Subclass Oligochaeta
“few hairs”
~3000 species
Freshwater/terrestrial habitats
Lack parapodia and have fewer,
shorter setae
• Earthworms
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Characteristics
• Mostly live in terrestrial
environments
• Most have 100-150 identical
segments
– Specialized segements 35-37
(clitellum)
• Reproduction
• Moves by anchoring setae then
contracting circular muscles
Digestion
• Takes in soil through pharynx (acts as a
pump)
• Soil moves down esophagus to crop
(storage)
• Moves to gizzard (crushing/grinding)
• Moves to intestine, absorption and
digestion occurs through folds in walls
• Solid waste out through anus
• Valuable to gardeners and farmers
– Break up soil, aerate, and add nutrients
(Nitrogen)
Circulation
• Closed circulatory system
• Blood circulates through series of
vessels
• Blood absorbs molecules and
carries them through dorsal
vessel to five pairs of “hearts”
• “Hearts” pump blood into main
ventral blood vessel and smaller
vessels carry blood to body.
Respiration and
Excretion
• Take in O2 and give of CO2 by diffusion
through skin.
• Must remain moist (not too wet or dry)
• Eliminate liquid wastes through ciliated
tubes called metanephridia (2 per
segment)
• Chloragogen tissue (acts like a liver)
– Amino acid metabolism, converts ammonia
to urea
– Converts excess carbs into glycogen and fat
(store energy)
Nervous Control
• Can respond rapidly due to concentration of nerves
called cerebral ganglion (anterior end).
• Connected to rest of body by ventral nerve cord
• Ganglion connects each segment to cord
• No external eyes or ears
• Receptors in skin will enable reactions (light, sound,
chemical)
– Active mainly at night
• Giant Fibers
– Mediate an escape response
– Responds to stimulus from either end of worm
– Initiates “anchor” and longitudinal muscles contract
to quickly pull worm away from stimulus
Reproduction
• Hermaphroditic
• Female structures anterior, male structures
posterior
• Two worms exchange sperm
– Mucus secretion from clitella holds them together
– Sperm stored in seminal receptacle until just
before eggs are laid
– Clitellum forms a cocoon for the deposition of
sperm and eggs
– Fertilization occurs in the cocoon
– Ends are sealed, deposited in soil, hatches in 1-3
weeks
Subclass Hirudinea
• ~500 species
• Leeches
• Predators (feed on small
invertebrates or feed on body fluids)
• 34 segments, reduced clitellum (only
during reproduction)
• Freshwater (some are marine or
terrestrial)
• Do not have setae
Characteristics
• Flat and tapered body with
suckers on each end
• Attach with anterior suckers
– Three sharp jaws to pierce host skin
– Secrete “hirudin” that prevents
hosts’ blood from clotting
• Reproduce sexually (monoecious)
Interesting Facts
• Used to be used to “detoxify”
blood
– Thought leeches removed toxins
• Plastic surgery
– Used to increase blood flow which
keeps tissue alive long enough for
surgery, re-attachment or tissue
lifting