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2007-05-22 04:57:04 · 3 answers · asked by godrics 2 in Science & Mathematics Biology

3 answers

depend upon intake of food input

2007-05-22 05:03:04 · answer #1 · answered by abr 1 · 0 1

Earthworms have a circulatory system and a digestive tube that runs their length. What may restrict their skin thickness is respiration since they have no lungs or specific organs for this. They respire, exchange oxygen and CO2, across their skin into their blood. The distance gas can diffuse limits the skin thickness. This doesn't limit their length as their entire skin respires.
They suck the soil in as they travel. Movement through soil is easier with long slender bodies so they evolved a shape to allow constant forward movement through a very dense medium. Processing the soil takes place along the entire inner tube with digestion in the last half. So effective forward movement limits their circumference. Then tensile strength of their skin may set a top length limit. The skin has to resist tearing as the worm moves, pushing forward against the soil, but be thin enough to respire across.
Each species has adapted to its environment so has a set adult size just as rabbits, shrimp, or mollusks do. There are families of large worms and of small. To enable them to reach a larger size they have evolved a more complex circulatory system with true capillaries in the larger families.
The small species remain small and the largest species grow to their adult size of up to 7-8 feet long but still under an inch in diameter. Big worm families include the Lumbricus terrestris that gets to 10 inches. These are the common earthworm, in many places, due to range of habitat and size.

The largest earthworm is Australian and lives in moist, clay soil. The next is from a nearby region, the Palouse. The palouse worm lives in a bunch grass prairie with volcanic ash deposits that are very fertile.

Speculating I would guess larger worms can burrow deeper to water retentive soil levels and surface to volume ratio lets them store more water while they have to come up for food. This lets them survive periods of drought. All worms require moisture in the environment. Their skins do not resist either UV or desiccation.

2007-05-22 07:22:23 · answer #2 · answered by gardengallivant 7 · 0 0

The earthworm has no digestive, respiratory, or circulatory systems. The digestion happens from cell to nutrient contact, the respiration happens from cell to air contact through simple diffusion (hence the mucus, and the reason they come out of the ground in heavy rain). If the worm gets to large in either length or diameter the cells on the inside of the body would quickly starve and be overrun by waste product.

2007-05-22 05:12:36 · answer #3 · answered by Anonymous · 1 1

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