Features of the Earthworm

Better known as a night crawler or fish bait, the earthworm is a member of the phylum Annelida. Ranging in size from 1/25 of an inch to 11 feet, the body is actually a tube within a tube; the digestive tube within the long reddish-brown body. As it burrows though the ground, the earthworm loosens and mixes soil, contributing to the growth of plants.

  1. Outer Body

    • The earthworm's head is called the anterior, and its other end is called the posterior. At the anterior tip of the worm's body is a flap of skin, the prostomium, hanging over its mouth. The outer skin of the worm is slimy to the touch, since it requires moisture in order to survive. The worm breathes through its skin. The body is a series of segments, and on each segment, except for the first and last, are small bristles. Called setae, these bristles help the worm to move. Near the anterior of its body is a light-colored band called the clitellum. This is where cocoons are formed. Under the epidermis of the worm is a layer called the cuticle.

    Muscles

    • Inside the outer skin of the worm's body are circular muscles that encircle the body, and inside those are longitudinal muscles that run the length of the body. The circular muscles tighten, making its body long and thin. The longitudinal muscles squeeze together, bringing the posterior of the body forward. Worms can move forward and backward.

    Circulation

    • The earthworm has two blood vessels that run the length of the body. The dorsal vessel runs over the digestive tube and the other, the ventral vessel, below. Five hearts, or aortic arches, pump the blood through the vessels. The aortic arches pump the blood that flows through the body via the dorsal blood vessel and back through the ventral blood vessel.

    Digestion

    • After the worm takes in food through its mouth, it passes through the pharynx. the esophagus, the crop and the gizzard before reaching the intestine. In the esophagus, calciferous glands release calcium carbonate to eliminate excess calcium from the body. The food is stored in the crop before moving onto the gizzard, where any stones the worm ate grind the food. Gland cells in the intestine release fluids to aid in the digestive process. Waste matter is eliminated by nephridia, organs that function as kidneys.

    Reproductive System

    • Earthworms are hermaphrodites containing both male and female reproductive sex organs. Although it creates both sperm and egg, the worm has to mate with another worm in order to reproduce. The clitellum of both worms form a slime tube in which eggs are fertilized. Then the slime tube becomes an egg cocoon that will be deposited in the soil.

    Nervous System

    • The earthworm has a simple nervous system enabling it to react to outside stimulus. There are the cerebral ganglia in the anterior portion of the body, which act as its brain, and the subpharyngeal ganglion and the ventral nerve, which run the length of its body.