Earthworm

  Found in Phylum Annelida.

Annelida means "little rings"

                have cylindrical bodies which are divided into seguments (externally and internally).

 

Covering:                thin skin called epidermis

                   Gases are exchanged through the thin epidermis and carried to the animal's tissues by tiny blood vessels.

                   The epidermis is covered with a thin, protective cuticle which must be kept moist to permit its passage of oxygen through it.

 

protection: by body covering - cuticle

movement:                2 muscle layers work together for forward movement:

                                Circular muscles - contract and make worm longer and thinner

                                Longitudinal- contract and draws posterior end forward.

                                setae are tiny bristles that anchor the worm

  support: 2 muscles layers

  digestion: feeds on vegetation, refuses, and decayed animal matter in soil

  digestion:  the breaking down of food into smaller substances

  digestive system:  a group of tissues and organs that work together to digest the food of an organsism

  digestive tract:  a long tube through which food passes as it is being digested

                                                    mouth - where food enters
  
                                                 anus - where nondigested food leaves

  Digestion of food can be divided into two processes:

                (1)  Mechanical digestion: the process of breaking food into smaller pieces and mixing it with
                                                            digestive juices

                (2)  Chemical digestion: the breaking down of food into substances usuable by cells

  absorption:  the movement of digested food from the digestive tract into the body of an organism

                                 mouth

                                 pharynx

                                 esophagus

                                 crop- temp. stored

                                 gizzard- grinds the food by mechanical digestion

                                 intestine- chemical digestion and absorbtion

                                 anus

                The mouth of the earthworm secretes fluids that moisten the soil as it enters the earthworm

                food-laden soil is drawn into the mouth through the muscular pharynx and passed down the esophagus to the crop, where it is temporarily stored

                food is passed into the gizzard where muscular contractions grind the food against the soil and break the food into small pieces

                food is then digested in the intestine, where digestive enzymes break it down (this is chemical digestion)

                the intestinal tract is straight and tubular; food is absorbed by blood circulating through its walls and indigestible materials are expelled through the anus.  These solid wastes are called casts (or castings). This enriches and improves the soil.

                                The burrows dug by earthworms permit the passage of oxygen and water deep into the ground and enable plants to send down roots much more easily.

                The feeding process of a single earthworm will produce approximately 1/2 pound of rich, fertile humus in one year.

                An estimated 18 tons of earth per acre per year is brought up from below and deposited on the surface by earthworms.

Giant earthworms, found in tropical regions, may be 12 ft. long and have 500 segments. They are located by the gurgling sounds they make as they move underground.

 

  respiration: the process of supplying O2 to and removing CO2 from the body of an organism

                                   The earthworm has no special respiratory organs.

                                   Gas exchange is made through the moist skin by diffusion.

             worm's outer surface must remain moist

                if an earthworm is dried by the sun, it will die of suffocation

                if they remain in water-soaked earth, they will drown

 

circulation: the movement of substances throughout the body of an organism.

                                   closed circulatory system

                                   red blood (contains hemaglobin)

             2 major blood vessels (dorsal and ventral)

             5 major pairs of aortic arches

                Closed circulatory system:  a type of circulation in which the blood remains in vessels

 

                Dorsal blood vessel:  it is the pumping organ (acts as the heart)

                                  pumps blood forward to the 5 pairs of aortic arches

                aortic arches:  chief function - maintain a steady pressure of blood into the ventral blood vessel

                                   Blood passes through the aortic arches down to the ventral blood vessel

                Ventral Blood Vessel:  (serves as the aorta) receives blood  from the aortic arches and delivers it to the brain and the rest of the body through smaller arteries to capillaries to veins and back to the dorsal blood vessel


excretion: the removal of wastes from an organism's body.

                The organs of excretion are the nephridia, a pair which are found.

                nephridia:  tiny looped tubes that collect wastes from the earthworm's blood (filters waste from the
                                  blood)

                Wastes are collected in the nephridia and are passed out of the body through tiny holes (called nephridiopores) on the in all body segments except the 1st, 3rd, and last one.

 

Nervous System:

                                Most animals control their bodies through neurons.

neuron:  nerve cell

nerve:  a bundle of neurons wrapped in protective coverings

ganglion:  cluster of nerve cells (acts as a relay station)

                                 a mass of nerve tissue; sometimes called a simple brain in many invertebrates

brain:  an organ that coordinates the bodily functions

stimulus:  anything that causes a response in an organism

 

THE EARTHWORM'S NERVOUS SYSTEM

 

Sensory receptors are distributed over the animal's entire body.

sensory receptor:  a structure that can sense a stimulus

                                                    They are sensitive to light, touch, and certain chemicals, with a high concentration at its front end.

impulse travels from sensory receptor (in front) to two large ganglions in the third segment

sensory receptors in other areas carry impulse to the nerve cord along nerve cord there is one small ganglion in each segment;  inside the ganglions the impulses are transferred to the proper neurons; neurons carry impulses to muscles, bristles, etc.

                                ganglia in 3rd segment (a mass of nervous tissue)

                                double ventrical nerve cord with smaller ganglia- 1 for each segment

                                nerves leading to muscles and sensory structures  (light, touch, certain, chemicals, and
                                                                                                            electricity)

 

reproduction: normal mode is sexual (some species can regenerate)

                                    hermaphrodite

                                    male organs are testes (2 pairs) in 10th and 11th segments

                                    female organs are ovaries (1 pair) in the 13th segments

                                    in sexual reproduction, the 2 worms must exchange sperm.

 

Giant earthworms, found in tropical areas, may be 12 ft. long and have 500 segments.  They are located by the gurgling sounds   they make as they move underground.