earthworms

earth worms 

An earthworm is a tubular, segmented worm of the phylum Annelida. They occur worldwide and are commonly found in soil, eating live and dead organic matter. An earthworm's digestive system runs the length of its body. It respirates through its skin. It has a double transport system made of coelomic fluid that moves within the fluid-filled coelom and a simple, closed circulatory system. It has a central and a peripheral nervous system. Its central nervous system consists of two ganglia above the mouth, one on either side, connected to a nerve running along its length to motor neurons and sensory cells in each segment. Large numbers of chemoreceptors concentrate near its mouth. Circumferential and longitudinal muscles edging each segment let the worm move. Similar sets of muscles line the gut, and their actions move digesting food toward the worm's anus.^[1]

Earthworms are hermaphrodites: each carries male and female sex organs. As invertebrates, they lack a true skeleton, but maintain their structure with fluid-filled coelom chambers that function as a hydrostatic skeleton.

"Earthworm" is the common name for the largest members of Oligochaeta (which is a class or subclass depending on the author). In classical systems, they were in the order Opisthopora, since the male pores opened posterior to the female pores, although the internal male segments are anterior to the female. Theoretical cladistic studies have placed them in the suborder Lumbricina of the order Haplotaxida, but this may soon change. Folk names for the earthworm include "dew-worm", "rainworm", "night crawler", and "angleworm" (from its use as fishing bait).

Larger terrestrial earthworms are also called megadriles (translates to "big worms"), opposed to the microdriles ("small worms") in the semiaquatic families Tubificidae, Lumbricidae, and Enchytraeidae. The megadriles are characterized by a distinct clitellum (more extensive than that of microdriles) and a vascular system with true capillaries.