The Earthworms Kidney

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What about the earthworm's "kidneys": do they reflect the workings of an aquatic or a terrestrial animal?

centratedurine (having about the same concentration as blood). The mammals and birds have taken kidney design a step further and are able to combine both high filtration rates and high degrees of water conservation; they produce urine that is more concentrated than the blood.

When we apply physiological criteria to deciding what the proper habitat of an earthworm might be, it is hard to escape the conclusion that they are not really terrestrial. Rather, earthworms seem to belong in a freshwater habitat. Let us see why.

Annelids do not have kidneys as such, but rather a series of small water balance organs called nephridia, one pair per segment (although not every segment has them). Each nephridium is essentially a coiled hollow tube connecting the water space inside the worm, the coelom, with the outside (Fig. 7.1). At one end of a nephridium, a nephridiostome (literally "nephridium mouth") opens into the coelom and thence into the hollow tube, the tubule. The tubule opens at its other end to the outside through a nephridiopore, through which urine is voided.

Earthworm nephridia, like the nephrons of the vertebrate kidney (Fig. 2.5), produce urine through filtration, reabsorption, and secretion, but with a few differences. In the vertebrate nephron, for example,

Figure 7.1 "High filtration" nephridia of annelids. a: Sketch of the nephridium of Pontoscolex corethrurus, showing open nephridiostome, long and extensively folded tubules, and capacious bladder, opening to the exterior through a nephridiopore. [From Goodrich (1945)] b: Schematic diagram of the nephridium of the common earthworm, Lumbricus terrestris, showing multiple loops that promote the reabsorption of salts. [After Boroffka (1965)]

Figure 7.1 "High filtration" nephridia of annelids. a: Sketch of the nephridium of Pontoscolex corethrurus, showing open nephridiostome, long and extensively folded tubules, and capacious bladder, opening to the exterior through a nephridiopore. [From Goodrich (1945)] b: Schematic diagram of the nephridium of the common earthworm, Lumbricus terrestris, showing multiple loops that promote the reabsorption of salts. [After Boroffka (1965)]

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Responses

  • Alina
    What type of kidney earthworm have?
    2 years ago

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