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The ventral vessel branches off to a pair of ventro-tegumentaries and ventro-intestinals in each segment. The subneural vessel also gives out a pair of commissurals running along the posterior surface of the septum. The pumping action on the dorsal vessel moves the blood forward, while the other four longitudinal vessels carry the blood rearward.
Blood is carried forward in the dorsal vessel (in the upper part of the body) and back through the ventral vessel (underneath), before passing into a sinus surrounding the intestine. Some of the smaller vessels are muscular, effectively forming hearts; from one to five pairs of such hearts is typical.
Adapted with permission from. [ 1 ] The ventral nerve cord is a major structure of the invertebrate central nervous system. It is the functional equivalent of the vertebrate spinal cord. [ 2 ] The ventral nerve cord coordinates neural signaling from the brain to the body and vice versa, integrating sensory input and locomotor output. [ 1 ]
The ventral sucker is located halfway to the middle of the body on the ventral side. They are both used for attachment to intestinal wall and blood vessels. The detailed structure of the suckers, presence or absence of hooks, and their exact position on the body are major taxonomic keys between species.
The two main blood vessels furnish smaller vessels to supply the parapodia and the gut. Blood flows forward in the dorsal vessel, above the gut, and returns down the body in the ventral vessel, beneath the gut. The blood vessels themselves are contractile, helping to push the blood along, so most species have no need of a heart.
Earthworm head. Lumbricus terrestris is relatively large, pinkish to reddish-brown in colour, generally 110–200 millimetres (4.3–7.9 in) in length and about 7–10 millimetres (0.28–0.39 in) in diameter. It has around 120–170 segments, often 135–150. The body is cylindrical in the cross section, except for the broad, flattened ...
Microchaetus rappi, the African giant earthworm, is a large earthworm in the family Microchaetidae, the largest of the segmented worms (commonly called earthworms). It averages about 1.4 meters (4.5 feet) in length, but can reach a length of as much as 6.7 meters (22 feet) and can weigh over 1.5 kilograms (3.3 pounds).
Both of the major vessels, especially the upper one, can pump blood by contracting. In some annelids the forward end of the upper blood vessel is enlarged with muscles to form a heart, while in the forward ends of many earthworms some of the vessels that connect the upper and lower main vessels function as hearts. Species with poorly developed ...