Annelids Section 29.2

Segmented worms Coelomates 2/3rds are marine Each segment contains digestive, excretory, circulatory and locomotor organs and is separated from other segments by septa Some segments also contain areas responsible for specific functions such as reproduction, feeding or sensation A primitive brain – the cerebral ganglion – is located at the anterior end, with a nerve cord that runs the length of the body

Key Characteristics Coelom – located inside the mesoderm Organ systems – including a closed circulatory system and a one-way gut with specialized organs Bristles – stiff, external setae which provide traction for crawling; some also have fleshy legs called parapodia

Marine Worms The largest group of annelids Have parapodia for movement Many are burrowing; some secrete a glue-like material that sticks grains of sand together to make a tube Some are free-swimming predators

Marine Tube Worms glue grains of sand together to make their tubes

Marine Feather Duster Tube Worms

Marine bristle worm with parapodia

Earthworms No parapodia Only a few seta on each segment No eyes, but they do have light and touch sensitive areas on each end of their bodies Highly specialized scavengers Body shape is maintained by a hydrostatic skeleton They are hermaphrodites

Earthworms are hermaphrodites but don’t fertilize their own eggs

Leeches Have suckers at each end Most are predators or scavengers Some are parasites of vertebrates or crustaceans No seta or parapodia No internal segments

Leeches can be useful medicinally