Rotifers

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Rotifers
Keratella cochlearis

Keratella cochlearis

Systematics
without rank: Multicellular animals (Metazoa)
without rank: Bilateria
without rank: Primordial mouths (protostomia)
Trunk : Rotifers
Scientific name
Rotifera
Cuvier , 1817

Rotifers ( Rotifera , obsolete Rotatoria ) are 0.1 to 0.5 millimeter ( Acanthocephala up to 70 centimeters) long multicellular animals with a genetically determined, constant number of cells ( Eutelia ). On the head there are movable eyelashes, the wheel organ . So far around 2000 species have been described worldwide, some of them very different , of which around 550 occur in Germany .

habitat

Rotifers occur in many habitats. They are just as at home on land, in trees, in damp moss or between soil particles as they are in the sea or in fresh water. They don't mind the cold Antarctica any more than the heat of thermal springs .

The various species of rotifers live either permanently attached to plants or floating freely in water or detritus .

morphology

Rotifers when hunting and eating.
Rotifers. The eyes, the wheel organ and the chewer are easy to see.
Rotifers.
Rotifers Ptygura pilula

The appearance of the rotifers is very diverse, but the body can be roughly divided into three sections:

  • Head with wheel organ - The wheel organ consists of eyelash fields and / or eyelash rings that are almost constantly in motion. On the one hand it is used for locomotion and on the other hand it is used to swirl in food particles.
  • Trunk - In the middle of the body is the trunk. In some species, the hull is stiffened, then one speaks of armor. The armor does not come from a cuticle, but from the sclerotization of a layer in the trunk epidermis, the dense layer . The trunk epidermis does not consist of individual cells, but of a syncytium that was created by the fusion of the epidermal cells. Some rotifers, such as Macrochaetus collinsi, have long spines on their trunk. Taphrocampa selenura in turn has a sticky epidermis. Most species can pull their head and foot into their torso.
  • Foot - The rotifer's foot has two appendages, the toes. There are glue glands in the foot that open onto the toes. With the help of the adhesive glands, the rotifer can temporarily or permanently attach itself to a chosen surface. However, some planktonic rotifers, such as Asplanchna , have no foot.

Due to their body shape, rotifers have various options for locomotion: gliding, swimming, crawling like a tensioner, running with the eyelashes of their head or swirling.

In order to survive dry periods, bdelloid rotifers give off part of their body fluid and shrink to a spherical shape. In this very resistant permanent stage , also called dry rigidity, they can survive for up to four years.

Individual eggs or egg packets, which have a similarly high resistance to environmental influences as the adult animals, can hang on the trunk or foot.

The chewing stomach (Mastax, Pl. Mastaces) typical of the Rotifera shows jaw-like, complex frameworks made up of individual rod-shaped, shield-shaped or plate-shaped hard parts containing chitin, the so-called trophi (Sg. Trophus). They can be moved against each other and, depending on their shape, can perform different functions such as sucking in, grinding, crushing or grasping prey. In the Monogononta, the trophi are shaped very differently depending on the species and are an important feature for the precise taxonomic determination of individual species. In the species of the Bdelloida they show a rather similar structure among the individual species, it is also spoken of the typical ramaten mastaces or the ramaten trophi of the Bdelloida (English ramate trophi).

nutrition

Most species feed on algae or detritus . Brachionus calyciflorus, for example, feeds on unicellular algae and bacteria. It whirls this up with its wheel organ. Lindia torulosa feeds on blue-green algae , the threads of which they pinch off with the chewing device. But there are also predatory rotifers , such as the floscularia ( floscularia ), which catch very small organisms and particles from the water thrown up by their rudder organs, or the cephalodella, which also live predatory. Asplanchna brightwelli is about a millimeter in size and also feeds predatory. It secretes a peptide , the so-called asplanchnine, into the water, which is often called kairomone and induces thorns in the prey organisms. Pleurotrocha petromyzon , in turn, feeds scavengers on dead water fleas . The Collotheca , Cupelopagis vorax but also Stephanoceros fimbriatus have a different way of hunting. They catch their food with wide open funnels at the top of their bodies. The two species of the primordial genus Seison live in the sea as parasites on species of the crustacean genus Nebalia . Freshwater forms like Proales are also considered parasites because they live in and feed on algae like Volvox and Vaucheria .

Multiplication and Life Expectancy

The different genera of the rotifers perceive different possibilities of reproduction. Under favorable conditions (usually in the summer months) asexual reproduction takes place (see also: Parthenogenesis ), under unfavorable conditions (mostly in autumn) sexual reproduction takes place.

Some species, such as Adineta vaga, are able to incorporate genetic material from other living beings into their genome, which offsets the disadvantages that result from asexual reproduction. This reproductive strategy was first demonstrated in rotifers by Eugene Gladyshev and was previously only known in bacteria. In addition, A. vaga renounces sexual reproduction and meiosis .

Rotifers have different life expectancies. The average is around a week.

Taxonomy

The first scientific observer of the rotifers is Antoni van Leeuwenhoek , who observed the rotifers with his self-made microscope . Since its magnification was not very great, he could only imprecisely observe the flickering mouth opening, but described its wheel-shaped appearance.

Today the rotifers are still accepted as an animal phylogeny, according to phylogenetic examinations of both the morphology and molecular biological comparisons, however, the scratch worms (Acanthocephala) , which were previously also regarded as an animal phylum, must be regarded as a sister group of the Bdelloida within the rotifers. The comprehensive group (Rotifera i. E. S., Seisonacea, Acanthocephala) is occasionally called "Syndermata", but most authors prefer to use the name Rotifera in the broader sense for this group. The order Seisonacea (with the only family Seisonidae, 2 species) is classified by some systematics as the only order (monotypical) in its own class "Pararotatoria".

The following relationships within the rotifers are assumed to be one of the current hypotheses:

 Rotifers  

 Seisonacea


  NN  

 Bdelloida and scratchworms (Acanthocephala)


   

 Monogononta




In the past, rotifers were placed in a group of " tube worms" or roundworms (nemathelminthes), an embarrassment taxon without clear delimitation, which has not been recognized as monophyletic in more recent systematics . More recent investigations on a morphological, but above all on a genetic basis have now consistently shown that the rotifers form a clade with two small, little-known groups, the jaw mouths (Gnathostomulida) and the Micrognathozoa (with the only species Limnognathia maerski ) , which after one morphological feature, the similar fine structure of the jaw apparatus Gnathifera ("jaw support") has been called. The arrowworms (Chaetognatha) , which have long been puzzling in their position, would be closely related. In the meantime, the fossil species Amiskwia sagittiformis Walcott 1911 from the Central Cambrian Canadian Burgess slate has been identified as a possible morphological intermediate form. The togetherness of the groups is also supported by the identical structure of the Hox genes , which are important for development .

Fossils

The only known fossil from the tribe Rotifera is the find of a member of the class Bdelloidea (order Bdelloida) in Tertiary Dominican amber . At the same time, this find provides evidence that parthenogenesis has existed for at least 25 to 40 million years.

supporting documents

  1. ↑ Alois Herzig et al. (Ed.): Rotifera X. Rotifer Research: Trends, New Tools and Recent Advances, Proceedings of the Xth International Rotifer Symposium, held in Illmitz, Austria, 7-13 June 2003. Springer, Dordrecht 2005, ISBN 978-1-4020 -4408-3
  2. ↑ Heinz Streble , Dieter Krauter : Life in the water drop. Microflora and microfauna of freshwater. An identification book. Franckh-Kosmos Verlag, Stuttgart 2008, ISBN 978-3-440-11966-2
  3. ^ Eugene A. Gladyshev, Matthew Meselson, Irina R. Arkhipoval: Massive Horizontal Gene Transfer in Bdelloid Rotifers . In: Science . 320, No. 5880, May 30, 2008, pp. 1210-1213. doi : 10.1126 / science.1156407 .
  4. ↑ Jean-François Flot, Boris Hespeels a. a .: Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga. In: Nature. 500, 2013, pp. 453-457, doi : 10.1038 / nature12326 .
  5. ↑ James R. Garey, Thomas J. Near, Michael R. Nonnemacher1, Steven A. Nadler: Molecular evidence for Acanthocephala as a subtaxon of Rotifera. Journal of Molecular Evolution 43 (3), 1996; Pages 287–292 ( doi: 10.1007 / BF02338837 )
  6. ↑ Martín García-Varela, Gerardo Pérez-Ponce de León, Patricia de la Torre, Michael P. Cummings, SSS Sarma, Juan P. Laclette: Phylogenetic Relationships of Acanthocephala Based on Analysis of 18S Ribosomal RNA Gene Sequences. Journal of Molecular Evolution 50 (6), 2000; Pages 532–540 ( doi: 10.1007 / s002390010056 )
  7. ↑ Ferdinand Marletaz, Katja TCA Peijnenburg, Taichiro Goto, Noriyuki Satoh, Daniel S. Rokhsar (2019): A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans. Current Biology 29: 312-318. doi: 10.1016 / j.cub.2018.11.042
  8. ↑ JakobVinther & Luke A. Parry (2019): Bilateral Jaw Elements in Amiskwia sagittiformis Bridge the Morphological Gap between Gnathiferans and Chaetognaths. Current Biology 29 (5): R152-R154. doi: 10.1016 / j.cub.2019.01.052
  9. ↑ Andreas C. Fröbius & Peter Funch (2017): Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans. Nature Communications 8, Article number 9. ( open access )
  10. ↑ George O. Poinar, Jr .: Life in Amber . 350 pp., 147 figs., 10 plates, Stanford University Press, Stanford (Cal.) 1992. ISBN 0-8047-2001-0

literature

Web links

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