User:Tonei/Notepad/Earthworm

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Earthworm

There is definitely material here which could be incorporated into the earthworm article, but also some errors. I have made notes (in italics) where appropriate. -- WormRunner | Talk 04:23, 18 May 2005 (UTC)

==Introduction

not a phylum. an order at best.

Earthworms (also known as angleworms) are any one of the over 1,800 species of terrestrial worms who are members of the phylum Annelida, class Oligochaeta. There are 17 native species and 13 introduced European species of earthworm in the United States. The most common earthworm in the U.S., L. terrestris, grows to about 25 centimetres, although some species grow as long as 3.3 metres. Earthworms can be found almost everywhere where the moisture and makeup of the soil are appropriate to sustain them.

Only a handful of the earthworm species are in the genus Lumbricus. There are 32 described native earthworms in the Pacific states alone. There are over 20 introduced lumbricids, plus many introduced megascolecids. This is an English language wikipedia, not a US one, so US-only info should be used sparingly.

Contents

[edit] Digestion and excretion

The earthworm has a simple digestive system compared to other creatures. It possesses an esophagus, which serves the same purpose as it does in higher animals: to carry food. However, the worm esophagus leads to the crop and gizzard rather than to a stomach (which earthworms do not possess). The crop and gizzard combined serve the purpose of a human stomach. The crop holds food while the gizzard grinds it down mechanically. The gizzard leads into the intestine, which follows the length of the earthworm’s body to the anus. This passage from mouth -> esophagus -> crop -> gizzard -> anus constitutes the entire digestive system.

The lumbricids have this pattern but it is not the only one. Most earthworms have the gizzard in the anteriormost segments, and many have no gizzard at all. The primary function of the esophageal region in most earthworms (including the lumbricids) is calcium carbonate secretion. The usual patterns are below.
mouth>pharynx>gizzard>esophagus>intestine
mouth>pharynx>esophagus>crop>gizzard>intestine
mouth>pharynx>esophagus>intestine


Most of the earthworm’s segments possess a pair of excretory organs known as nephridia. Each of these is a coiled tube which opens up into the body cavity. The internal opening of the tube (nephridiostome) has cilia which propel fluid from the body cavity into the nephridia. The nephridia are surrounded by capillaries that reabsorb the useful substances, leaving metabolic wastes (such as urea), salt, and water to be discharged through the nephridium’s outer opening (nephridopore).

essentially correct

[edit] Nervous system

The nervous system of earthworms consists of a dorsal brain (a mass of nervous tissue found in the prostomium), a pair of nerves which form the ventral nerve cord, and one ganglion (a structure containing a number of nerve cell body..................)

[edit] Reproduction

Earthworms are hermaphrodites, which means that each of them has functional reproductive organs of both sexes. However, the eggs of one individual must be fertilized by the sperm of another. While mating, the two earthworms excrete a sticky mucous which binds them together while each of them transfers sperm to the other. The worms then separate and form cocoons. The cocoons move forward along the earthworm’s body, picking up eggs at segment 14 and sperm from the other earthworm at the 9th and 10th segments. The cocoon then slides over the earthworm’s head, and the eggs are fertilized. The cocoon is then deposited into the soil within the next 24 hours. Miniature earthworms usually emerge in two to four weeks, reaching sexual maturity in two to three months and their full adult size within a year.

Not all earthworms have a mucus tube, many adhere by glandular papillae. The spermathecae may be found in other segments than 9 and 10 in non-lumbricids. While reaching "their full adult size within a year" is probably true for most species, the larger ones may take several years to reach full size.


hey hey!!

[edit] Circulation and Respiration

Earthworms have closed circulatory systems. This consists of a ventral blood vessel which carries blood to the worm’s posterior end, and a dorsal blood vessel which leads to the anterior end. The dorsal vessel contracts and pumps blood forward, where it is pumped into the ventral vessel by the worm’s hearts. The blood is then distributed to capillaries on the body wall and other organs as well as a vascular sinus in the gut wall. This sinus is where gases and nutrients are exchanged.

Oxygen and carbon dioxide exchange takes place through the skin. Although it can be transported directly in the blood, it is usually carried by a respiratory pigment such as hemoglobin. The method of oxygen release depends on the habitat of the worm. Some worms release oxygen to tissues only under extreme oxygen deficiency, while others take up oxygen from the normal atmosphere but release it only when tissue oxygen is low, thus preventing oxygen poisoning.

An inline reference for this would be good.


[edit] Locomotion

The worm’s process of locomotion consists of extending the body, anchoring it to a surface, and contracting the body muscles. When a worm begins forward movement, the circular muscles near the anterior end contract, which extends the head forward. The anterior end lifts up from the surface at the same time to help the forward movement. A wave-like contraction then occurs from the circulatory muscles to the posterior end. When the wave reaches the middle of the body, the longitudinal muscles contract. A wave of longitudinal muscle contraction occurs, and the process is repeated. Earthworms are also capable of moving backwards by reversing the waves of contractions.

[edit] Symmetry and special characteristics

Earthworms are bilaterally symmetrical.


[edit] Resources

"earthworm." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 15 May 2005 <http://www.britannica.com/eb/article?tocId=9031737>.

Oetinger, David F. "Earthworm," The World Book Multimedia Encyclopedia, Mac OS X 2002 Edition, World Book, Inc., 2002.

"worm." Britannica Student Encyclopedia. 2005. Encyclopædia Britannica Premium Service 15 May 2005 <http://www.britannica.com/ebi/article?tocId=210501>.

Haines, Elizabeth and Varghese, Rimini. “The Digestive System: Dissecting the Earthworm.” Rutgers University. http://www.rci.rutgers.edu/~dougproj/earthworm.htm.

"Earthworm." Wikipedia, the free encyclopedia. 14 May 2005, 18:39 UTC. 15 May 2005 <http://en.wikipedia.org/wiki/Earthworm>.

Upper School Science Dept. home page. 12 May 2005. Sidwell Friends School, Washington D.C. 15 May 2005 <http://www.sidwell.edu/us/science/>. (LANA)