Phylum Annelida The Segmented Worms

Common name: Segmented worms Characteristics: Cephalization: Well-developed nervous system: nerve cord with ganglion in each segment and anterior brain Bilaterally symmetrical Organs within a true coelom (cavity within mesoderm) Compartmentalization of organs / movement of parts of body Closed circulatory system with five pairs of “aortic arches”

Sophisticated digestive system: mouth – food enters pharynx – passes through esophagus – peristalsis crop – storage gizzard – grinding intestine – more digestion anus – waste exits

Intestine Earthworm anatomy Gizzard Esophagus Mouth Crop Pharynx

Appendages: Setae: a stiff hair like or bristle like structure Parapodium: Paired muscular bristle-bearing appendages used in locomotion, sensation, or respiration

Muscles Circular muscles Longitudinal muscles

remove nitrogenous wastes; wets skin No gills/lungs—use diffusion Nephridium: A tubule open to the exterior that acts as an organ of excretion remove nitrogenous wastes; wets skin No gills/lungs—use diffusion Most have red hemoglobin in blood a red protein responsible for transporting oxygen in the blood 

Reproduction Most are hermaphroditic testes in 10th and 11th segments ovaries in 13th segment Clitellum stores eggs and produces “slime band” protective coat around eggs

Classes of Annelids Oligochaeta: earthworms, night crawlers, (aquatic) tubifex worms 20-45 tons of soil/year/acre processed by worms on organic farms each worm processes its own weight each day

Polychaeta: bristleworms, tube worms, featherdusters marine worms with parapodia and (most) jaws

Hirudinea: terrestrial / aquatic leeches some parasitic, some free-living medicinal anticoagulant “hirudin”

Class Hirudinea The medicinal leech is best known as the organism used for blood letting (people used to believe many health problems caused by "bad" blood). They are being used once again to remove blood from hematomas (areas of blood leakage) resulting from surgery (like re-attaching severed limbs, etc.).