Unsegmented 5. Earthworms are invertebrates. An earthworm's body is streamlined and every segment contains a number of bristles called setae. They don't reproduce asexually, however; only half (and likely the head half) of an earthworm split in two will regenerate into a full worm once again [source: Tomlin]. If each segment moved together without being â¦ Physical characteristics. As earthworms in general are not very large, some of these characters are require a microscope to investigate the characters in detail, but if you don't have a microscope a strong hand lens can work ok on larger species. To feed itself, an earthworm pushes its pharynx out of its mouth to grab its food, then takes the food back into its mouth and wets it with saliva. Another bodily feature that facilitates the earthworm's movement is its setae, bristly hairs that are all over the earthworm's body. The important external features are as follows: Shape: Earthworm is elongated, long, narrow, cylindrical or vermiform shaped. The setae provide traction, allowing earthworms to move through the soil more easily. The anterior end is tapering while the posterior end is more or less blunt. There are no eyes or other discerning facial features, only a simply opening for a mouth. Although native to Europe, earthworms are found throughout North America and western Asia. Their food consists of decaying plants and other organisms; as they eat, however, earthworms also ingest large amounts of soil, sand, and tiny pebbles. Earthworms leave the burrow only during the rainy season when their burrows are flooded with water. The earthworm has evolved certain structural, physiological and behavioral characteristics to help it grow, reproduce and survive in its environment. These annuli are ridged and covered in minute hairs that grip the soil allowing the worm to move as it contracts its muscles. The reddish-gray colored body of the earthworm is segmented, and the vital organs are present in particular segments. External Morphology of Earthworm. It is about 8 to 21 cm long and 3 to 4 mm in thickness. Mouth cavity: entrance to the digestive tract of an earthworm. Earthworms have long, segmented bodies, covered in microscopic setae, or bristles, which help to anchor and pull the worm via longitudinal muscle contractions. It is to be noted that the body of the earthworm is essentially a double tube. She writes about science and health for a range of digital publications, including Reader's Digest, HealthCentral, Vice and Zocdoc. To survive changing environmental conditions, like hot or dry soil, an earthworm sometimes goes through diapause or hibernation. 3. Typically only a few inches (7 or 8 centimeters) long, some members of this species have been known to grow to a snakelike 14 inches (35 centimeters). The average earthworm is a reddish brown color, with a pointed posterior and anterior end. Internal Anatomy of Earthworm: If a worm is cut open from the anterior to the posterior end by an incision through the body wall in the mid-dorsal line, the internal structures may easily be studied. Segmentation helps the worm to be flexible and strong in its movement. Some species of earthworm burrow, and their mucus creates a binding substance to stop the walls of their burrow caving in. The dorsal surface is dark purplish brown, and the ventral surface is paler in color. Look at the labeled picture to help you find the following features: Pharynx: This is the light-colored organ just inside the mouth.Its muscular contractions pass food on down to the esophagus. The Best 20 Gallon Fish Tank Guide – 2020, The Best Aquarium Vacuum Buyers Guide – 2020, The Best Goldfish Food Buyers Guide – 2020, The Best Aquarium Rock Buyers Guide – 2020. 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