What are annelids?
The annelids are humble creatures classified in the animal phylum Annelida, a scientific name meaning little ring. We share ol; world with at least seven thousand different annelids, but most of the time we fail to notice them. For they live quiet, secretive lives, some in the ground, some on the beaches, some in fresh water and some in the sea.
The annelid we know best is the earthworm, that little plowman who does so much to enrich our farmland. He belongs in the class Oligochaeta meaning few spines. The spines are the almost invisible little hairs along the body of the earthworm and Oligochaeta is one of five classes in the sizeable phylum Annelida, the ringed ones.
The rings of an annelid are the round segments which make up the long tube which is the body of the earthworm. This ringed feature is built into the skin of. the annelid with circles of soft tissue separated by circles of more leathery tissue. In most annelid this ringed feature is repeated inside the body. The muscular system, or part of it, may take the form of circles. In some annelids, the nervous and circulatory systems tend to form circles.
The soft bodied, segmented annelids share some features with the mollusks and some with the insects. But they have enough differences to rate them a phylum of their own. The annelids have red blood, though the red comes from hemoglobin dissolved in the blood. In the red blood of the mammals, this vital substance hemoglobin is carried al=g in the red corpuscles.
The annelids of the earthworm class take in oxygen through the skin. Other annelids have simple gills for taking oxygen from the water. One of the most fascinating features of the earthworm is its method of multiplying.
Each earthworm is both male and female, so any two earthworms can be a pair of parents. Some annelids have separate sexes and some mutiply by budding.
Class I of the phylum Annelida includes a group of smallish marine worms. In Class II, we find the beach dwelling clamworm, who somewhat resembles a centipede. Most of his 3,500 cousins are ocean dwellers, The earthworm and its 2,400 cousins are in Class III. Class IV includes the blood sucking leeches and Class V is a group of sausage shaped marine annelids.
Not all the annelids show their ring systems in their soft, moist skins. But these segments, called somites, are always a major feature Inside the body of an annelid. Most of these humble creatures are smallish animals with tubular bodies just a few inches long. A few of the annelids are just big enough to be seen and the giant of the clan is an earthworm perhaps seven feet long.