Common Group Name Annelids Phylum Annelida Examples Oligochaetes

Common Group Name: Annelids

Phylum: Annelida Examples: • Oligochaetes (earthworms) • Leeches • Polychaetes (mostly marine)

Body Plan • Annelids have bilateral symmetry • Body segments present, separated by septa- or internal walls. • Segments are similar and may specialize in function. • They have a true coelom • Contain a digestive tract with a mouth and anus.

Feeding • Range widely from filter feeders to predators. • More advanced digestive system. • In earthworms: food is collected by the 1)pharnyx- 2)esophagus 3)crop- 4)gizzardnutrients absorbed in 5)intestine.

Respiration • Aquatic annelids breathe through gills- organs specialized for gas exchange underwater. • Land annelids exchange gases through their moist skin.

Circulation • Typical annelids have a closed circulatory system- blood is contained in a network of vessels. • Earthworms have a dorsal vessel and an ventral vessel connected by smaller vessels that supply blood to organs. • Blood flow: Dorsal- tail to head, Ventral- head to tail.

Excretion • Digestive waste leaves through the anus. • Cellular (metabolic)wastes leave through organs called nephridia.

Response • Well-developed nervous system with brain and cords. • Specialty adaptations: – Tentacles – Chemical receptors – Statocysts- gravity detectors – Eyes

Movement • Muscles that are Longitudinal- make the worm shorter and fatter. Circular- make the worm longer and thinner. • Movement= alternating contraction between the two groups. • Marine annelids have appendages for swimming.

Reproduction Most annelids reproduce sexually. n Some use external fertilization with separate sexes. n Others are hermaphrodites producing sperm and egg. n The process: Worms attach to each otherexchange sperm- store sperm- eggs and sperm go into a special ring (clitellum) for fertilization- ring slips off worm body- birth weeks later. n

Other Information • Most unique feature: Segmented body type. • Oligochaetes- streamlined bodies; in freshwater and soil • Leeches- external parasites that suck the blood of their hosts • Polychaetes- marine annelids with paired paddlelike appendages.

Earthworms and the Environment n Earthworms are considered beneficial to the environment because: 1) Their castings contain nutrients. 2) They aerate the soil as they move through it 3) They break up the soil in which they live