Anatomy of Animals

Annelids

Circulatory - The earthworm has an extensive closed circulatory system. Hemoglobin-containing blood moves anteriorly in a dorsal blood vessel and then is pumped by five pairs of hearts into a ventral blood vessel. As the ventral blood vessel takes blood toward the posterior regions of the worm's body, it gives off branches in every segment.
Digestive - The earthworm feeds on leaves or any other organic matter, living or dead, that can be taken conveniently into its mouth along with dirt. Food drawn into the mouth by the action of the muscular pharynx is stored in a crop and is ground up in a thick, muscular gizzard. Digestion and absorption occur in a long intestine, whose dorsal surface is expanded by a typhlosole that allows additional surface area for absorption. Notice that the tube-within-a-tube plan has allowed specialization of the digestive system to occur.
Endocrine (neuro) - It is known that annelid reproduction is controlled by some kind of endocrine system.
Excretory - The excretory system consists of paired nephridia, or coiled tubules, in each segment. Nephridia have two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall. Between the two openings is a convoluted region where waste material is removed from the blood vessels about the nephridium.
Immune - Earthworms have a highly effective immune system since cancer cannot be induced in them nor does it seem to occur in natural populations. They possess a highly evolved, unique and efficient immune system that has facilitated long-term survival.
Musculo-skeletal - Locomotion in the earthworm is suitable to its way of life, and each segment of the body has four pairs of setae, or slender bristles. The setas are inserted into the dirt, and then the body is pulled forward. Both a circular layer and a longitudinal layer of muscle in the body wall make it possible for the worm to move and to change its shape. Muscle contraction is aided by the fluid-filled coelomic compartments, which act as a hydrostatic skeleton.
Nervous and Sensory - The nervous system consists of an anterior, dorsal, ganglionic mass, or a brain, and a long ventral solid nerve cord with ganglionic swellings and lateral nerves in each segment. When invertebrates are compared to vertebrates, it often is said that the former have a ventral solid nerve cord, while the latter have a dorsal hollow nerve cord. The earthworm lacks obvious cephalization.

Reproductive - The earthworms are hermaphroditic, with a complete set of organs for both sexes. The male organs of an earthworm are the testes, the seminal vesicles, and the sperm ducts; the female organs are the ovaries, the oviducts, and the seminal receptacles. Copulation occurs when two worms lie ventral surface to ventral surface with the heads pointing in opposite directions. The clitellum, a smooth girdle about each worm secretes mucus, after which the sperm leave the sperm ducts and travel to the seminal receptacles of the partner. The clitellum later produces a slime tube, which is move along over the head of the worm by muscular contractions. Into this tube are deposited eggs from the oviducts and sperm from the seminal receptacles. The slime tube forms a cocoon within which the miniature worms develop. There is no larval stage.

Respiratory - A earthworm has no respiratory organ. It takes in oxygen directly through its skin and gives off carbon dioxide. Its skin is always moist for allowing efficient absorption of oxygen dissolved efficient in the water.