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Annelida- the segmented worms

3 4 Phylum Annelida: “ringed worms”

5 Class Oligochaeta: earthworms

•  Little cephalization •  Closed Circ. System •  Paired nephridia w/ circulatory association •  Hermaphroditic: clitellum •  Specialized digestive tract •  Cutaneous respiration •  No free-swimming larval stage

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Peristaltic movement

•  Contracted longitudinal muscle

•  Contracted circular muscle

Creepy Crawly

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External Morphology

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Internal Morphology

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Cross-Section

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Nephridia

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Class Polychaeta: segmented marine worms

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Polychaete cross-section

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Class Hirudinea: leeches •  Mainly freshwater, flattened segmented worms •  Parasitic, scavengers, predatory •  Lack coelomic compartments •  Reproduction is similar to earthworms •  Secrete anesthetic and anticoagulant •  Medically significant

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Medical Leeches

•  1500s B.C.!

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The trochophore larva!

2nd larval stage-Veliger larva of snail

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Annelid development

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Requirements for Animal Life •  The demands of 3 unique environments

–  Marine, freshwater, terrestrial •  Gas exchange •  Nutrition •  Distribution and transport •  Disposal of cellular wastes •  Internal water and salt balance •  Reproduction and development •  Support and movement