Pterobranchia

The Flügelkiemer ( Pterobranchia ) are marine hemichordate. The millimeter -sized worm-like animals live mostly colonial on the ocean floor where they filter food particles with their characteristic tentacle apparatus from the water. They were originally known only by Dredgeproben from the deep sea, but were now also detected in the shallow waters of warm seas.

Characteristics and relationship hypotheses

The body of the Flügelkiemer can be subdivided into the food serving fishing tentacle region, subdivide the housing be built and the rostral saccular, viscera and gonads containing hull. Coelomräume exists only in rostral and in the tentacle region. The hull is dark colored in most species, the tentacles reddish. On the front of Rostralschilds located below a red ribbon.

Due to the tentacle apparatus was seen in the Flügelkiemern also possible close relatives of the Lophophorata ( syn.: Tentaculata ), so a large group of horseshoe worms ( Phoronida ), brachiopods ( Brachiopoda ) and bryozoans ( Bryozoa ). This relationship hypothesis was of great importance for the system of two-sided - symmetrical animals ( Bilateria ) because it brought together the Flügelkiemer as a supposedly primitive deuterostomes with the Lophophorata as a supposedly primitive protostomes. They were considered in some of these interpretations even as representatives of the most primitive bilaterians.

Molecular biological studies, however, such a primitive state of Flügelkiemer can not confirm, so that is now assumed that their Percolator Percolator is not homologous to the Lophophorata, and otherwise no close relationship exists to protostomes.

These studies are the result Flügelkiemer rather a highly specialized Deuterostomiergruppe that emerged from acorn worm-like precursors most likely ( once they were for the Hemichrodata rather the reverse course of evolution to, ie emergence of acorn worms from flügelkiemerartigen precursors ).

On the basis of deep sea pictures described in the 1970s intermediate forms between Flügelkiemern and acorn worms called " Lophenteropneusten ", were identified in 2005 after first catch these animals as specialized acorn worms that can only be brought with the very hypothetical Flügelkiemern in conjunction.

Inside systematics

There are two trims and two extant families. The families are distinguished by the tentacle apparatus, the Gebäusebaus and other anatomical features.

• Order Cephalodiscoidea Family Cephalodiscidae, four to nine pairs of tentacles with up to 50 leaflets per tentacle. Genus Atubaria Sato, 1936 ( nomen dubium )
• Genus Cephalodiscus
• Genus Pterobranchites Kozlowski, 1967 †

• Genus Diplohydra Kozlowski, 1949 †
• Genus Graptovermis Kozlowski, 1949 †
• Family Rhabdopleuridae Genus Eorhabdopleura Kozlowski, 1970 †
• Genus Fasciculitubus OBut & Sobolevskaya, 1967 †
• Genus Kystodendron Kozlowski, 1959 †
• Rhabdopleura genus, only a tentacle pair with up to 15 to 30 leaflets per tentacle.
• Genus Rhabdotubus Bengtson & Urbanek, 1986 †

Close relatives of the extinct graptolites are Flügelkiemer that were distributed worldwide by the middle Cambrian to Lower Carboniferous and important index fossils for the Ordovician and Silurian are. In addition to sessile forms of them are also many genera known that pelagic lived with the help of floating bodies. The fossilierbaren parts of Flügelkiemers Cephalodiscus graptolithoides are the fossils of graptolites so similar that some scientists believe that must be filed with the Pterobranchen the graptolites.