PHYLUM ANNELIDA – segmented worms Biology 112. Annelids Representative species: common earthworm.

PHYLUM ANNELIDA – segmented worms

Biology 112

Annelids

• Representative species: common earthworm

Class Oligochaeta: Earthworms

``It may be doubted whether there are any other animals which have played so important a part in the history of the world as the earthworm.``

-Charles Darwin, 1881

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Body complexity

• Coelom – fluid filled body cavity surrounded by a mesoderm (room for organs)

• Peritoneum - membrane in the coelom in which all organs are attached

• 2 sets of muscle tissue– 1. body wall muscles to move the worm – 2. digestive system muscles to move food

Class Oligochaeta: Earthworms

• ~ 2500 species• Many more cell layers than flat and round worms

• Circulation: have blood to carry gases to and from body tissues

• Blood in earthworms contains a red protein hemoglobin (just like in us!)

• Have 5 hearts near the anterior end

Class Oligochaeta

• More complex digestive system than other worm phyla

• They consume dirt (food and sand particles) via mouth, esophagus, pharynx, and then stores it in the crop.

• After storage, food moves to the gizzard to be ground down, then to the intestine for digestion and absorption into the blood stream.

• Undigested food moves out the anus

Earthworm digestion

http://www.youtube.com/watch?v=FK-Oo7NwPiQ

Class Oligochaeta• Setae are bristles that aid in movement– Each segment has 4 setae (except first and last ones)

• Complex nervous system

• Reproduce sexually– Hermaphrodites

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Worm Charming??• http://www.youtube.com/watch?

v=OnwEJEDsWBc

Other members of Phylum Annelida

• Class Hirudinea – leeches (blood sucking parasites)

http://www.youtube.com/watch?v=cePKpt5nOJ0&feature=fvw

Other members of Phylum Annelida

• Class Polychaeta – marine worms