Oligochaetes — Class Oligochaeta

Earthworms are the best-known members of this class. Oligochaetes (Oligo="few"; chaeta="hairs") have no appendages, a simple brain, and segmented bodies that are usually shorter than 10 cm. Tiny bundles of hairs on every segment are characteristic of all species in this group and they are used both as basic touch sensors and as anchors in the sediment to facilitate movement.

There are approximately 25 oligochaete species inhabiting the arctic marine environment, including Enchytraeus hyalinus, a worm with four bundles of straight hairs per segment, and Lumbricillus sp., whose hairs are typically curled. These worms often thrive in nearshore waters, where the mixture of freshwater and saltwater creates a favourable environment. Like most oligochaetes, these species are benthic dwellers and feed continuously on the surrounding sediments. Consequently, they have no need for eyes to seek prey. Sediments are largely composed of organic matter, including plant matter, decomposing organisms, feces, and the bacteria that grow on all three. Oligochaetes rarely stop eating, digesting what they can and getting rid of the rest as quickly as possible to make room for more.

Marine oligochaetes occur on the ocean's floor, often within kelp beds or the bottom sediments.

Oligochaetes have both female and male reproductive parts, and most species rely on copulation with another individual for reproduction. After mating, eggs are released into a cocoon formed by several segments near the front of the body, and the sperm fertilizes the eggs within. The edges of the cocoon close while the eggs are developing. Upon hatching, the ends reopen and tiny worms escape to the outside environment.