The Earthworm

Question 1

Classification

Answer 1

• earthworms are invertebrates (lacking backbone)
• they are segmented worms, the segments are separated by septa
• they are coelomate, so they have a complete body cavity lined by a membrane called a peritoneum

Question 2

Digestion

Answer 2

• worms eat decaying vegetation in the soil
• they ingest food using a muscular pharynx, then an esophagus carries food to the crop for storage
• food is mechanically digested in the gizzard
• their intestine absorbs digested nutrients into their blood
• the surface area of the intestine is increased by the typhlosole

Question 3

Gas exchange

Answer 3

• worms have a high surface area to volume ratio and can obtain enough oxygen directly through their skin
• the skin must be kept moist therefore they live underground
• when it rains, their tunnels fill with water and they must come out of their burrows to breathe

Question 4

Reproduction

Answer 4

• earthworms are hermaphroditic
• when worms copulate, they collect sperm form their partner and store it in seminal receptacles
• worms deposit their eggs in a mucus ring made by the clitellum
• as they slide the ring over their heads, the sperm are deposited in the ring to fertilize the eggs

Question 5

Excretion

Answer 5

• earthworms have two metanephridia per segment that filter the blood
• a ciliated funnel opens into the body cavity at the anterior end
• the other end leads to the outside of the body
• as urine passes along the tubule, salts are reabsorbed, producing a very dilute urine

Question 6

Locomotion

Answer 6

• earthworms move by a peristalsis-type mechanisms
• most segments have 4 pairs of setae that anchor an end of the worm to the soil
• when the front is anchored, the circular muscles relax and the longitudinal muscles contract, pulling the posterior end
• when the back is anchored, the longitudinal muscles relax and circular muscles contract, pushing the head