Ascidiacea

The ascidies ( Ascidiacea ) are marine animals which belong to the subphylum of the urochordés , or Tunicier S. Of the recent discoveries suggests that the ascidies are a group Paraphylétique.

The ascidies are regarded as an evolutionary group with the hinge between the invertebrates and the vertebrate ones. They are divided into 2 different morphological groups: ascidies “known as” recluses and colonial ascidies. The body, generally in form of in addition to, is covered with a cellulose tunic. It is about the only animal partially made up of cellulose, molecule generally characteristic of the plants.

List orders and families

According to ITIS:
  • order Enterogona
    • sub-order Aplousobranchia Lahille, 1887
      • family Clavelinidae Forbes and Hanley, 1848
      • family Didemnidae Giard, 1872
      • family Polycitoridae Michaelsen, 1904
      • family Polyclinidae Milne-Edwards, 1841
    • sub-order Phlebobranchia Lahille, 1887
      • family Agnesiidae Michaelsen, 1898
      • family Ascidiidae Herdman, 1882
      • family Cionidae Lahille, 1887
      • family Corellidae
      • family Diazonidae Garstand, 1891
      • family Hypobythiidae Sluiter, 1895
      • family Perophoridae Giard, 1872
  • order Pleurogona
    • sub-order Stolidobranchia Lahille, 1887
      • family Molgulidae Lacaze-Duthiers, 1877
      • family Pyuridae Hartmeyer, 1908
      • family Styelidae Sluiter, 1895

Anatomy

At the adult state, the ascidies resemble bags with two openings:

  1. the oral Siphon where the water current enters, pulled by beats of lashes,
  2. the cloacal siphon or expirator where water is rejected.
A gelatinous or cartilagineuse tunic, made up of Tunicine, a variety of Cellulose, and organic matter, recovers the body. The interior of the ascidie is called the room péripharyngienne. The pharynx is equipped with many slits branchiales.

The tube neural which is present in the larva, disappears at the time of the metamorphosis as an adult. The nervous system of the adult is limited to a cerebral Ganglion. A Cœur in the shape of tube is the propellent body of the circulatory apparatus. It sends the Sang in sines dug in the conjunctive Tissu. Flow changes direction both to three minutes. The blood of the ascidies consists of several kinds of Globule S. the digestive system is composed of a Estomac and a Intestin emerging by a Rectum and a Anus.

The Larve resembles small a Têtard of frog, composed of a large “head” and a tail swimmer containing a nervous tube and a spinal cord. The cord and the tube neural, characteristic of twisted, disappear when the animal fixes itself on its substrate.

Reproduction

The ascidies are Hermaphrodite S. Testicules and ovaries release their gamètes in the room péripharyngienne where incubation takes place. The larva resembles a tiny frog tadpole outside. She swims little of time, fixes herself at a support and undergoes a deep metamorphosis. The asexual reproduction and regeneration have a big role, especially at the colonial forms.

Nutrition

The food particles (planktonique micro-organisms) being in water are filtered by a Mucus secreted by the ventral face interns cavity pharyngienne, then conveyed by lashes in the stomach then the intestine.

Ecology, Lifestyle

The ascidies populated all the oceans of the world, represented in addition to 2  300 identified species. The fixed species colonize all the mediums, since the rocks of seaside, the funds littoral to the ropes in the ports and under the hulls of the Bateau X. Ascidies are also found with great depths (more than 400 meters).

The ascidies live fixed on a support. The tunic makes it possible to adhere to the substrate. One can distinguish from the solitary ascidies like the very common Ciona intestinalis and from the ascidies forming colonies. In this case, all the individuals are coated in only one tunic and can sometimes divide bodies in commun runs. The individuals can come from/to each other by budding.

At certain seasons, many ascidies can undergo a transformation: their bodies degenerate and it persists only of the undifferentiated mésenchymateuses cells, which will be able to reform new individuals thereafter.

A whole Biocénose can live around the ascidies. Foraminifère S are encrusted on the tunic, of the Algue S can at it be fixed. Lamellibranche S can live on the level of the gills. parasite S and Symbiote S can also exploit various bodies of the ascidie.

See too

Bibliographical references

  • Noriyuki Satoh, 1994. Developmental Biology off Ascidians. Cambridge University Near.

Related articles

External bonds

  • http://www.ascidians.com

Random links:Pentalog | Andres | Guillaume d' Awans | Edward Donovan | Lucien Jerphagnon | Liste_de_fleuves_en_Virginie_Occidentale