Oligochaeta contains all the animals commonly thought of as 'earthworms'. Long thin worms with no obvious appendages to their bodies and greatly reduced heads so that when the animal is still it is not sometimes obvious which end is the head and which is the tail. As a group they are all morphologically similar and taxonomic division is often made far more on the basis of internal characteristics, particularly the positioning of the genitalia. The Oligochaeta are the second largest group of the Annelida, with 3,100 known species they make up about one third of the phylum. within this diversity of species there are aquatic forms, both freshwater and marine and also many terrestrial species. In terms of diet, the smaller species are often predatory while the larger species are soil or mud feeders. There are also a few parasitic species.
Author: Mary K