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The first body segment (segment number 1) features both the earthworm's mouth and, overhanging the mouth, a fleshy lobe called the prostomium, which seals the entrance when the worm is at rest, but is also used to feel and chemically sense the worm's surroundings. Some species of earthworm can even use the prehensile prostomium to grab and drag ...
In earthworms, the clitellum can only be seen when the worm is sexually mature. It may be white, orange-red or reddish-brown in colour. Earthworms are ready to mate when their clitellum is orange. [2] In leeches, the clitellum appears during mating season, where it is used for both sexual reproduction and the secretion of a cocoon for the eggs. [4]
Chloragogen cells, also called y cells, are star-shaped cells in annelids involved with excretory functions and intermediary metabolism. These cells function similar to the liver found in vertebrates. Chloragogen tissue is most extensively studied in earthworms. [1]
Parts of the mesothelium, especially on the outside of the gut, may also form chloragogen cells that perform similar functions to the livers of vertebrates: producing and storing glycogen and fat; producing the oxygen-carrier hemoglobin; breaking down proteins; and turning nitrogenous waste products into ammonia and urea to be excreted. [8]
However, 'earthworm' can be a source of confusion since, in most of the world, other species are more typical. For example, through much of the unirrigated temperate areas of the world, the "common earthworm" is actually Aporrectodea (=Allolobophora) trapezoides, which in those areas is a similar size and dark colour to L. terrestris.
Hydrostatic skeletons are very common in invertebrates. A common example is the earthworm. Also, hydrostatic nature is common in marine life such as jellyfish and sea anemones. Earthworms have rings of muscles that are filled with fluid, making their entire body hydrostatic. A sea anemone has a hydrostatic head, with arms radiating out around ...
Both male and female reproductive organs are present in earthworms because they are monoecious. To breed, two earthworms exchange sperm. Long after they are separated, the egg case is secreted. It forms a ring around the worm, then the worm removes the ring from its body and injects its own eggs and the other worm's sperm into it.
Earthworms are a classic example of biological homonymous metamery – the property of repeating body segments with distinct regions. In biology, metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. [1]