Segmented Worms SWBAT describe the body covering, method of support, and forms of movement used by the earthworm; describe the nervous system of the earthworm; identify the structures of an earthworm’s digestive system and describe the functions of each structure; explain the processes of circulation, respiration, and excretion in the earthworm; define closed circulatory system; evaluate the significance of having earthworms in the soil.

Segmented Worms  What phylum does the earthworm belong in? Annelida  Segmented

Body of an Earthworm  Epidermis Its skin, through which gases are exchanged  Cuticle Thin outer coating that protects it from harmful parasites and substances

Body of an Earthworm  How do earthworms move? An earthworm has two muscle groups that contract and expand its body. It anchors itself using the bristles on its body and then contracts, anchors its other end and releases the front to expand and move forward.

Intestines of the Soil  How do earthworms help the soil? Earthworms digest plant and animal matter so that it becomes usable for plants to gather nutrients from the soil. They also bring soil that is deep, up toward the surface as they burrow, which can affect crop growth.

Earthworm’s Nervous System  Sensory receptor A structure that can sense a stimulus and then start an impulse traveling along a nerve  Describe the nervous system of an earthworm. They have sensory receptors that send impulses through the nerve cord to the ganglia that tell it how to respond.

Earthworm’s Digestive System  Describe the process of digestion in an earthworm. Soil enters through the mouth and into the pharynx, where glands secrete a liquid to lubricate it as it passes through. The esophagus is a tubular passageway that then carries the food to the crop that stores it temporarily. Food then passes into the gizzard which mechanically digests food by contracting and relaxing. The ground up food passes to the intestine where digestive enzymes break the food into a soluble substance that is absorbed into the bloodstream to be distributed to the cells. The indigestible parts leave through the anus, and are called castings.

Earthworm’s Circulatory System  Closed circulatory system Blood never leaves the vessels  Aortic arches Same function as a heart Control blood pressure  Capillaries Tiniest blood vessels – pass blood to arteries  Veins Vessels that carry blood toward the heart

Earthworm’s Circulatory System  Explain the process of circulation in an earthworm. The circulatory system is a continues network of blood vessels. The large dorsal blood vessel of the earthworm works with the aortic arches to pump blood and control blood pressure. The bloodstream is used to pass substances between an earthworm’s tissues.

Earthworm’s Respiratory and Excretory Systems  Explain the processes of respiration and excretion in and earthworm Earthworm’s exchange gases through its epidermis (no lungs). Most of the segments in a worm have a coil of tubes that collects waste from the blood and then passes it out through tiny pores on the surface.