Phylum: Annelida Earthworms

The Anatomy of an Earthworm Section 27-3 Anus Clitellum Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel Ganglion Brain Mouth Dorsal blood vessel Crop Gizzard Body segments Setae

Annelid: animal in the annelida phylum meaning “little rings” which refer to many body segments A. Characteristics 1. Segmentations: divided into different compartments 2. Coelom: body cavity filled with fluid and internal organs a) Segmented coelom allows different parts of the body to contract or expand independently

3. Setae: external bristles 4. Parapodia: fleshy protrusions Characteristics B. Earthworm: few setae on each segment, no parapodia, and live in soil or freshwater 1. Structure and movement: divided into more than 100 segments

a) Move: worm anchors some of the. middle a) Move: worm anchors some of the middle segments by setae and contracts muscles in front segment which elongates the animal and pushes the anterior (front) forward b) Anterior end setae then anchor and pull the posterior (back) end forward Moving

2. Feeding and digestion: ingest soil as they burrow through it and the soil is sucked into the mouth with overhanging prostomium a) Soil passes through esophagus b) Crop: temporary storage area c) Gizzard: muscular part of the gut where it grinds the soil releasing and breaking up organic matter

d) Passes through the long intestine and digested d) Passes through the long intestine and digested organic compounds in the soil are absorbed by the blood e) Typhlosole: infolding of the intestinal wall that increases the surface area for digestion and absorption f) Undigested material is eliminated through the anus Feeding

3. Circulation: closed system that transports oxygen, carbon dioxide, nutrients, and wastes a) Ventral blood vessel: blood travels through to posterior end b) Dorsal blood vessel: blood travels through to anterior end c) Aortic arches: five pairs of muscular tubes that force blood through vessels

4. Respiration: no special organs a) Oxygen and carbon dioxide diffuse through skin b) Takes place if skin is moist 5. Excretion a) Nephridia: “tiny kidneys” excretory tubules that eliminate wastes and are located in each segment

6. Neural control: chain of ganglia connected by a ventral nerve cord a) Ganglia: carries impulses to muscles and from sensory cells in the segment b) Cerebral ganglia: brain used to process information

a) Two earthworms press their surfaces together in opposite directions 7. Reproduction: hermaphrodites: has both male and female reproductive organs a) Two earthworms press their surfaces together in opposite directions b) Clitellum: secretes mucus from each worm c) Each earthworm injects sperm into mucus d) Sperm move through seminal receptacle where they are stored

e) Worms separate and clitellum secretes a tube e) Worms separate and clitellum secretes a tube of mucus called chitin that picks up the worm’s egg and the stored sperm f) Fertilization occurs in the tube and young worms develop inside the case for 2-3 weeks

The Anatomy of an Earthworm Section 27-3 Anus Clitellum Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel Ganglion Brain Mouth Dorsal blood vessel Crop Gizzard Body segments Setae

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