Phylum Annelida - "Segmented Worms"
Three Classes:
• Oligochaeta - "few bristles" ex. earthworm
• Polychaeta - "many bristles" ex. sandworm
• Hirudinea - ex. leech
Advancements:
• first true coelomic cavity
• complete digestive tract with regions that have special jobs
• central nervous system with brain and nerve cord
• closed circulatory system
• segmentation of body structure permits greater specialization
Note: segments separated internally by wall of tissue called septum
Title: Jun 1­6:12 AM (1 of 10)
Dissecting Tools
dissecting pins
teasing/dissecting needle
dissecting probe
forceps
scalpel
dissecting scissors
Title: Jun 1­4:37 AM (2 of 10)
Rule of Thumb: Use the dullest instrument possible to
get the job done without damaging tissues and organs!
The Earthworm
External Features
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cylindrical, tapered
100-175 segments (somites)
darker, rounded dorsal surface
lighter, flat ventral surface + setae
prostomium
clitellum
anus
prostomium
clitellum
anus
Movement
• digs front setae (bristles) in, pulls along
• digs back setae in, pushes forward
External Pores
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#2,4 male genital pores (seg 15, 26)
#5 female genital pores (seg 14)
#6 openings of seminal receptacles (seg 9-10)
#3 sperm grooves
Title: Jun 1­5:00 AM (3 of 10)
Circulatory System
• aortic arches (around esophagus)
• into ventral blood vessel
• sm vessels, capillaries in tissues
• back through dorsal blood vessel
dorsal blood vessel
Nephridium
Aortic Arches
("hearts")
suprapharyngeal ganglia ("brain")
Ventral Nerve Cord
(with ganglia)
ventral blood vessel
Title: Jun 1­5:42 AM (4 of 10)
Digestive System
• mouth
• buccal cavity
• pharynx
• esophagus
• crop
• gizzard
• intestine
• rectum
* crop has flexible walls to expand for storage of food
• anus
(under aortic arches)
* gizzard has muscular walls to help crush and grind food (pebbles)
These two parts they have in common with birds! Gizzards allow them
to break their food down into smaller pieces since they have no teeth!
Title: Jun 1­5:12 AM (5 of 10)
Excretory System
• nephridia
- look like tiny white coils in each section
Nephridium
Aortic Arches
("hearts")
suprapharyngeal ganglia ("brain")
Ventral Nerve Cord
(with ganglia)
Title: Jun 1­5:12 AM (6 of 10)
Nervous System
• nerve collar around pharynx
• suprapharyngeal ganglia = "brain"
• ventral nerve cord
• ganglia (swellings in each section)
Nephridium
Aortic Arches
("hearts")
suprapharyngeal ganglia ("brain")
Ventral Nerve Cord
(with ganglia)
Title: Jun 1­5:12 AM (7 of 10)
Reproductive System
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hermaphroditic - must cross fertilize
1 pr testes
3 lobed seminal vesicles (store)
sperm released out male genital pores
move along sperm grooves
kept in seminal receptacles of other worm
1 pr ovaries
eggs released and stored in body coelom
pass out female genital pores
fertilized by sperm outside body (in cocoon)
Title: Jun 1­5:12 AM (8 of 10)
Respiratory System
• diffusion through skin
Title: Jun 1­5:12 AM (9 of 10)
Class Polychaeta
• segmented body
• "many bristles" for protection + traction
• marine worms
• some live on bottom, some burrow, some build tubes
• some free-swimming, some parasitic
• flat, fleshy projections on sides = parapodia
• parapodia help in locomotion + gas exchange
Class Hirudinea
• segmented body
• 75% are external parasites
• attach to host, cut through skin, suck blood
• salivary glands produce hirudin which keeps
host's blood from clotting
• used in early years when "blood letting" was common
• still used to prevent clots and pressure build up in small
veins when trying to reattach fingers, etc.
Title: Jun 3­6:19 PM (10 of 10)
parapodium