Lumbricina

Of the Lumbricina , subdivision of Haplotaxida of the Annélides, gathers the whole of the ground worms, are 13 S and more than 5.000 S described (and of very many not yet known, especially in the tropical areas).

The ground worm, also called lombric is a digger Animal. Its activity and its ecology make of it a major actor in the structuring of the grounds.

Anatomy

Group coelomate, tripoblastic protostomien, pertaining to the subclass of Oligochètes, the order of Haplotaxida and the sub-order of Lumbricina.

Appearance of a metamerized coelomic cavity. These cavities are homonomists, therefore regular with repetition of the néphridies and the ganglia. Metamerized body made up of named successive rings segments. Those are surrounded by a longitudinal musculature and a circular musculature.

Ventral nervous chain (hyponeurien), closed circulatory system.

The body generally goes from the pink to chestnut, sometimes iridescent with purple reflections. Some species are very coloured (orange or turquoise, in particular at some Trigaster of Central America. Because of a cutaneous respiration (the ground worms do not have lungs), the body must remain wet to allow breathing.

Each segment is furnished with four pairs of short silks on the ventral face (moderate worms) or of a silk line around (many tropical species), which helps with displacement. The first two segments and the last do not have silks and have a particular role: point for the first, stops for the second and Anus for the last. The first segment is called Prostomium, the second Peristomium and the last Pygidium.

The circulatory system includes/understands a large contractile dorsal vessel where blood is propelled forwards. Five to seven pairs of side hearts take again blood and send it towards the back in a ventral vessel. The digestive tract is enough worked out and includes/understands a mouth, a Pharynx which can be used of suction cup to draw food in the galleries and as crusher to triturate them. The food passes then in the Jabot, receives a contribution of calcium Carbonate of the Glandes of Morren, passes in the Gésier which continues crushing and reaches finally the Intestin. It is there that is produced the argilo-humic Complexe.

General biology

Food

They are generally nourished by ingurgitant ground to digest and absorb the organic matter of it of it (Litière, Micro-organisme S…).

Reproduction

The lombrics are Hermaphrodite S with crossed fecundation, carrying at the same time male reproductive bodies and female. They must nevertheless be coupled to reproduce.

As example at the lombric common European, two testicles, independent but connected to the spermiductes by ciliés conduits leading sperm towards the male genital pore (on segment 15), passing by 10th and 11th segments (the 13th container a pair of ovary). The cells which will give the spermatozoa maturent in seminal blisters in 9th, 11th and 12th segments where the sperm is constituted which is finally collected in the 15th segment. The ovaries produce eggs which will be stored in the 14th segment then " pondus" in a cocoon of Mucus.

Before the coupling, the clitellum located 33e at the 38e segment inflates and secretes a sticking mucus which helps two individuals to be joined head-digs. One of the partners emits sperm which will be temporarily preserved in the seminal receptacles of 9th and 10th segments of the other.

The coupling is done head-digs. After the coupling, a sleeve of Mucus is produced by the clitellum (the most reinflated zone, generally in the first third of the body of the animal). The Ovule S of the lombric and the Sperme of its partner are inserted in this sleeve when it slips forwards and passes on genital glands. The ends of this sleeve are stuck when it arrives at the head lombric to form a Cocon. The egg segments in Spirale and forms a Larve type Trophopore. With the birth, the youthful ones have the morphology of the adults, except the Clitellum which appears with sexual maturity.

Others

While moving in the ground, the ground worms dig galleries and fill them of their Turricule S (dejections). They air, loosen and fertilize thus the grounds, from where them great interest for the Agriculture. The density of worms is very variable and depends on the type of ground and the Climat. In a French meadow, it can go from 1 to 2 million, even 4 million individuals per hectare. The world biomass of ground worms is higher than that of the human ones. In France, the principal predatory ones are the Taupe, the Crapaud, the Musaraigne and especially the Hérisson as well as many Oiseau X. Certain tropical species are partially or completely watery and have a quadrangular body (Almidae, for example). Others were found alive with several tens of meters in the trees (Europe, Amazonia).

Ecology and role in the structuring of the grounds

The ground worms are omnipresent in all the grounds tropical or moderate and their taxonomic diversity is very important (3 627 species lombricians listed in 1994; estimated at 7.000, even much more, on the whole). It is not rare to find 200 to 250 ground worms per m ² in meadows moderate. Censuses generally show that this abundance is much more reduced within the agricultural pieces plowed and mono farming. Indeed, for one century, certain grounds have passed from 2 tons of worms of ground to the hectare to 50 kg.

In 1881, Charles Darwin already underlined in a test “Formation of the topsoil due to the action of the ground worms” ( The Formation off Vegetable Mould Through the Action off Worms With Observations one Their Habits ) the total importance of the activity of the ground worms in the Fertilité of the grounds just like the Climat, the nature of the Bed rock on which the ground in question develops, and the type of litter brought to the ground.

By their activity in the ground, these animals control a certain number of physical, chemical and biological processes of the ground. Because of that, these animals are generally called organizations Engineers of the ground, just like the Termite S, the Fourmis, etc Can be called engineer of the ground any organization which by its activity modifies its habitat in a direction which is “favorable” but also favorable for him to the other pledged organizations to this habitat (in fact the Bactérie S or the Champignon S of the ground, etc).

It is now well established that the ground worms influence the structure and the fertility of the ground through their activities of excavation, of excretion of macro-aggregates, ingestion of Organic matter, etc Ainsi, these animals act directly on the structuring of the grounds by creating galleries. These galleries are preferential ways by which the infiltration and the circulation of water, the aqueous solutions and gases are facilitated. Mucus, Urine and Fèces are deposited on the walls of the galleries and confer to them particular biogeochemical properties (enrichment in Sucre S, etc). The ground worms also produce dejections (“  Turricule s ”) which constitutes macro-aggregates of ground of organomineral properties modified compared to the surrounding ground (pH neutralized, greater stability of the aggregates, etc).

While acting on their habitat, these animals would indirectly control the activity, the diversity and the spatial distribution of the communities of Micro-organisme S of the ground. This influence is capital since the micro-organisms of the ground are responsible, in last spring,

1. of the Minéralisation of the organic matter in nutrients given to the provision of the roots of the plants buckling the cycle of the life (see biogeochemical Cycles)
2. of the formation of the Humus (the shape of Séquestration of carbon in the grounds).

The ground worms would however not influence all in the same way the properties of the ground and the processes which result from this. Indeed, some would exclusively nourish litter on the surface of the ground and live there permanently (épigés, of the Greek ear on and Ge ground), others would nourish litter of surface which they hide in generally vertical galleries (the anéciques ones, of the Greek anesis elasticity), others finally would exclusively nourish humus of the ground which they introduce on their passage, creating of vast networks of galleries without never going back to the surface of the ground (endogés, of the Greek endo inside).

These three ecological types would constitute as many strategies of exploitation of the resources selected during the evolution of the ground worms. The limits between these types do not seem however very frank and it remains to explain their determinisms. In all the cases, this heterogeneity of behavior undoubtedly induces influences distinct in their contribution to the fertility from the ground. In the ideal, épigés, endogés and the anéciques ones would act in concert in the formation and the maintenance of the fertility of the grounds.

The recent awakening of the impact growing of the human activities on the ecological systems is in the beginning many work studying the relation between the diversity of living and the total operation of these systems (see ecology). For the agricultural grounds, some practical farming like the Ploughing, the use of plant health products (see Manure, Pesticide S), etc have as a consequence a reduction in the diversity of the ground worms and could induce a deterioration of the operation of the grounds of the agro ecosystem S. From the point of view of the conservation and of the Réhabilitation of the grounds, the identification of species playing an important role (“key species”) in the ground seems a research topic impossible to circumvent in ecology of the ground.

They also contribute to the Bioturbation, and thus to the vertical and horizontal transfer of certain pollutants (in a way differentiated according to the pollutants and the species considered.

In spite of a very great quantity of research on aspects varied of the ecology of the ground worms and their behaviors, quantitative information on key aspects such as the formation of the galleries and the activities associated still miss. It is generally assumed that the functional role of the various species lombricians can be induced starting from the characteristics of the ecological types to which they are attached (anecic, épigée, endogée). However, this assumption was only tested very little in experiments. Research on the activities of the ground worms is difficult to undertake because of opaque nature of the ground where they live. However, of advanced methodological recent using techniques such as the Tomography with the X-rays (see Tomodensitométrie), the Radio-marking of the individuals and the modeling of the activities constitute powerful novel methods to apprehend the ground worms and the networks of galleries which they dig under the surface of the ground.

Threats

The number of ground worms per m ³ of ground strongly regresses in the zones of intensive agriculture. It is protected better by the Organic farming which is made an ally of it, and is most present in the Prairie S. Some Pesticide S are conceived for especially killing the lombrics (for examples for the football, golf courses, etc); they are the Lombricide S.

Economic use

Certain species of lombrics high ( lombriculture ) and are sold for the production of Compost, or for the fishing.

Ecotoxicology

The guiding line of OECD for the tests of chemicals “ Worm of Ground, Essais of Acute Toxicity ” makes it possible to release CL50 products tested.

Taxonomy and principal geographic origins

Order: Haplotaxida; Sub-order: Lumbricina

Principal families

• Lumbricidae : moderate zones of the Northern hemisphere
• Hormogastridae: Europe
• Sparganophilidae: North America
• Almidae: Africa, South America
• Acanthodrilidae: Africa, Central America and of the South
• Ocnerodrilidae: Africa
• Octochaetidae: Central America, India, New Zealand, Australia
• Megascolecidae: Asia, Africa, Oceania, Australia, North America
• Glossoscolecidae: Central America and of the South
• Eudrilidae: Africa
• Lutodrilidae: The United States
• Microchaetidae: Africa
• Biwadrilidae: Japan
• Ailoscolecidae: France
• Moniligastridae: India, Asia

Species

There exist very many species of lombrics distributed on all the surface of the sphere, largest living in tropical zone.

In the language running, the term “ lombric ”, that one believes to allot to only one species, indicates in fact several of the species with for example in France: Lumbricus terrestris , Lumbricus rubellus or Eisenia fetida which is most frequent. Certain species live in the Deadwood and the matter in decomposition. Others circulate in the ground primarily horizontally, and others still vertically (it is those which leave characteristic turricules on the surface).

• Megascolides australis - Driloleirus macelfreshi