تبلیغات
گفتمان خاكشناسی - earth worms _ part 1

گفتمان خاكشناسی

به امید روزی كه قدر خاك را هم بدانیم

Earthworm

From Wikipedia, the free encyclopedia

Jump to: navigation, search
Earthworms
Lumbricus terrestris, the Common Earthworm
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata
Order: Haplotaxida
Suborder: Lumbricina
Families

Acanthodrilidae
Ailoscolidae
Alluroididae
Almidae (disputed)
Criodrilidae
Eudrilidae
Exxidae
Glossoscolecidae
Hormogastridae
Lumbricidae
Lutodrilidae
Megascolecidae
Microchaetidae
Ocnerodrilidae
Octochaetidae
Sparganophilidae

Earthworm is the common name for the largest members of Oligochaeta (which is either a class or subclass depending on the author) in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female. Theoretical cladistic studies have placed them instead in the suborder Lumbricina of the order Haplotaxida, but this may again soon change. Folk names for the earthworm include "dew-worm", "rainworm", "night crawler" and "angleworm" (due to its use as fishing bait).

Earthworms are also called megadriles (or big worms), as opposed to the microdriles (or small worms) in the families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a distinct clitellum (which is much more obvious than the single-layered one of the microdriles) and a vascular system with true capillaries.

Contents

[hide]

[edit] Anatomy

The basic body plan of an earthworm is a tube, the digestive system, within a tube, the muscular slimy, moist outer body. The body is annular, formed of segments that are most specialized in the anterior. Earthworms have a simple circulatory system. They have two main blood vessels that extend through the length of their body: a ventral blood vessel which leads the blood to the posterior end, and a dorsal blood vessel which leads to the anterior end. The dorsal vessel is contractile and pumps blood forward, where it is pumped into the ventral vessel by a series of "hearts" (aortic arches) which vary in number in the different taxa. A typical lumbricid will have 5 hearts. The blood is distributed from the ventral vessel into capillaries on the body wall and other organs and into a vascular sinus in the gut wall, where gases and nutrients are exchanged. This arrangement may be complicated in the various groups by suboesophageal, supraoesophageal, parietal and neural vessels, but the basic arrangement holds in all earthworms. Most earthworms are decomposers feeding on undecayed leaf and other plant matter, others are more geophagous.

[edit] Reproduction

Earthworm reproduction

Earthworms are hermaphrodites: They typically have two pairs of testes, surrounded by 2 pairs of testes sacs. There are 2 or 4 pairs of seminal vesicles which produce, store and release the sperm via the male pores, and ovaries and ovipores in segment 13 that release eggs via female pores on segment 14. However, most also have one or more pairs of spermathecae (depending on the species) that are internal sacs which receive and store sperm from the other worm in copulation. Some species use external spermatophores for transfer instead.

Earthworm cocoons

Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The clitellum becomes very reddish to pinkish in color. The cocoon, or egg case, is secreted by the clitellum band which is near the front of the worm, but behind the spermathecae. Some time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator (cocoon) in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for a lack of the sex structures, which develop later in about 60 to 90 days. They attain full size in about one year. Scientists predict that the average lifespan under field conditions is 4–8 years, still most garden varieties live only one to two years. Several common earthworm species are mostly parthenogenetic, that is, with asexual reproduction resulting in clones.

[edit] Regeneration

Earthworms have the facility to regenerate lost segments, but this ability varies between species and depends on the extent of the damage. Stephenson (1930) devoted a chapter of his monograph to this topic, while G.E. Gates spent 20 years studying regeneration in a variety of species, but “because little interest was shown”, Gates (1972) only published a few of his findings that, nevertheless, show it is theoretically possible to grow two whole worms from a bisected specimen in certain species. Gates’s reports included:

  • Eisenia fetida (Savigny, 1826) with head regeneration, in an anterior direction, possible at each intersegmental level back to and including 23/24, while tails were regenerated at any levels behind 20/21 [1].
  • Lumbricus terrestris Linneus, 1758 replacing anterior segments from as far back as 13/14 and 16/17 but tail regeneration was never found.
  • Perionyx excavatus Perrier, 1872 readily regenerated lost parts of the body, in an anterior direction from as far back as 17/18, and in a posterior direction as far forward as 20/21.
  • Lampito mauritii Kinberg, 1867 with regeneration in anterior direction at all levels back to 25/26 and tail regeneration from 30/31; head regeneration was sometimes believed to be caused by internal amputation resulting from Sarcophaga sp. larval infestation.
  • Criodrilus lacuum Hoffmeister, 1845 also has prodigious regenerative capacity with ‘head’ regeneration from as far back as 40/41.[2]

An unidentified Tasmanian earthworm shown growing a second head is reported here

نظرات() 
Buy generic viagra
سه شنبه 23 مرداد 1397 03:11 ق.ظ

You have made your point!
where can i buy viagra from viagra at pharmacy cheap generic viagra uk how to buy viagra online safely buy viagra cheap uk buy viagra online canadian pharmacy viagra buy no prescription buy brand viagra buy viagra canadian pharmacy viagra uk price
babecolate.com
یکشنبه 21 مرداد 1397 11:42 ب.ظ

Good stuff. Thank you.
prix cialis once a da cialis tablets weblink price cialis achat cialis en europe cialis 10 doctissimo miglior cialis generico tesco price cialis usa cialis online we use it 50 mg cialis dose cialis 5 mg
Cialis pills
دوشنبه 7 خرداد 1397 02:29 ق.ظ

Factor very well utilized.!
cialis venta a domicilio purchase once a day cialis cialis patentablauf in deutschland we use it 50 mg cialis dose click now cialis from canada cialis wir preise generic cialis levitra warnings for cialis cialis sans ordonnance we recommend cialis info
Cialis pills
پنجشنبه 20 اردیبهشت 1397 04:01 ق.ظ

Whoa a lot of helpful material!
only here cialis pills generic cialis tadalafil dose size of cialis cialis price thailand how do cialis pills work cialis online holland cialis usa cost acheter cialis meilleur pri dosagem ideal cialis order a sample of cialis
Buy cialis
جمعه 7 اردیبهشت 1397 07:05 ب.ظ

Nicely put, With thanks!
we use it 50 mg cialis dose purchasing cialis on the internet enter site 20 mg cialis cost cialis online napol cialis generico lilly cialis generico online cialis generico lilly cialis generic cialis in sconto cialis kaufen wo
Generic for viagra
سه شنبه 4 اردیبهشت 1397 04:15 ق.ظ

You actually mentioned it wonderfully.
vigra sildenafil generic price where to buy viagra in stores how buy viagra online viagra uk buy buy internet viagra viagra generic viagra generic find viagra how to buy cheap viagra
Cialis canada
جمعه 17 فروردین 1397 07:55 ب.ظ

You suggested this terrifically.
cialis ahumada cialis prices generic cialis review uk prescription doctor cialis click here to buy cialis cialis 5 effetti collaterali acheter cialis kamagra cialis generique look here cialis cheap canada cialis online deutschland
Buy cialis
جمعه 3 فروردین 1397 04:24 ب.ظ

Nicely put, Kudos.
rx cialis para comprar cialis sans ordonnance cialis rezeptfrei canada discount drugs cialis cialis for sale south africa i recommend cialis generico cialis price in bangalore 40 mg cialis what if i take miglior cialis generico cialis coupon
Cialis canada
یکشنبه 27 اسفند 1396 11:20 ب.ظ

You explained it superbly!
can i take cialis and ecstasy prix de cialis cialis 5 mg buy what is cialis cialis lilly tadalafi cialis tadalafil cialis 10mg prix pharmaci cialis savings card cialis generico online rx cialis para comprar
 
لبخندناراحتچشمک
نیشخندبغلسوال
قلبخجالتزبان
ماچتعجبعصبانی
عینکشیطانگریه
خندهقهقههخداحافظ
سبزقهرهورا
دستگلتفکر

نظرسنجی

    وبلاگ را چگونه ارزیابی میکنید ؟










تبلیغات پیامکی تبلیغات پیامکی

آمار وبلاگ

  • کل بازدید :
  • بازدید امروز :
  • بازدید دیروز :
  • بازدید این ماه :
  • بازدید ماه قبل :
  • تعداد نویسندگان :
  • تعداد کل پست ها :
  • آخرین بازدید :
  • آخرین بروز رسانی :