1) Each segment of an earthworm has setae (bristly hairs), structures that enable the worm to have a grip as it burrows through the soil. The earthworm has longitudinal and circular muscles that enable it’s movements as it burrows in the soil.
2) When an animal exhibits cephalization, it has a concentration of nerves ending in one pole of the body, that is considered the head. While earthworm ahs ganglions in each segment in its body, its largest ganglion is found at the anterior end (the ‘head’), hence shows some degree of cephalization.
3) The earthworm eats up the soil and digests its organic matter while Ascaris lumbricoides, that is a parasite, absorbs nutrient through its body from the extracellular environment (host). Therefore an earthworm has a more developed digestive system than that of an Ascaris lumbricoides.
4) Their digestive system has a mouth and an anus. However, that of the Ascaris lumbricoides is primitive compared to that of the earthworm. Actually, flatworms have no body cavity. This is why the Ascaris is considered to be a pseudocoelomate as opposed to the earthworm that is a coelomate (contains a true body cavity).
5) Annelids recycle soil nutrients. By eating up the soil and digesting organic matter, they break it down to simple components that can e absorbed by the plants. As they burrow in the soil, they aerate it hence benefiting plants roots. These are important benefits in agriculture.
6) Annelids have a complex organ system (true coelomates) compared to roundworms. Additionally, unlike roundworms, annelids have a segmented body. They also exhibit more cephalization than either nematodes (roundworms) or platyhelminths (flatworms).