Archiannelida
The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.
Archiannelida in Berthold Hatschek Archiannelides ( "Urringelwürmer") and Ray Lankester Haplodrili ( "Simple earthworms") is the name of a historic, mostly as fine categorized taxon of annelids in the class of polychaete , the mostly very small, only in sand gap system living Species in seas around the world that mostly feed on bacteria on the sand particles. According to recent research results, they can be divided between the two taxa Protodriliformia and Orbiniida, which are not closely related .
features
Despite their small size, the Archiannelida have a large number of segments and a prostomium on which a pair of " tentacles " ( palps ) sit. The nervous system consists of a simple brain and a ventral nerve cord that is closely connected to the epidermis and has no individual ganglia. The well-developed coelom is divided by partitions into segment-wise chambers in which the intestinal canal is suspended from complete longitudinal mesenteries . The nephridia are simple and open to the coelom. The closed blood vessel system has a simple structure and consists of a back and abdominal vessel as well as paired side vessels connecting them. Many species, such as the genus Polygordius , do not have bristles , while these are found in Saccocirrus , for example . Simplified, free-floating or parasitic forms with only a few segments, such as Dinophilus and Histriodrilus , which lack celomial septum and blood vessel system, were also included.
Systematics
The term Archiannelida implies that these annelids were similar to the common ancestor of all annelids, which according to this would have to have been an inhabitant of sand gaps, and accordingly have original characteristics. In 1868 Friedrich Anton Schneider described a new genus of annelid worms from the sand gap fauna, Polygordius , with the species Polygordius lacteus and Polygordius purpureus . In 1878, Berthold Hatschek described this genus, in which there are “still” no bristles ( Chaetae ), as the “most primitive” of the annelid worms, and saccocirrus , even if it also has bristles, was primitive. In 1891 he described the subclass Archiannelides within the Annelida with the genera Protodrilus and Polygordius , each of which he granted the status of a family: Protodrilidae (in the sea, in the sand) and Poygordiidae (in the sea, beach region). He expressly ruled out other families that were put here by other researchers, which he understood under Archiannelides essentially a group in the range of the later taxon Protodriliformia. The concept of the archiannelida as primitive annelids lasted until at least 1969, when Hermans described the archiannelida as a polyphyletic group , whose representatives had developed convergent in the interstitium of the sand to very similar formulas, so that Kristian Fauchald followed this argument and in 1977 the families no longer followed as Archiannelida summarized. Günter Purschke and Claude Jouin-Toulmond argued in 1988 that at least some of the Archiannelida families form a monophyletic group and compared the taxon Protodrilida, in which they included the genera Parenterodrilus , Protodriloides , Protodrilus and Saccocirrus , with the sister group of the Spionida , while Kristian Fauchald and Gregory Rouse could not recognize such a relationship in 1997 and placed the three families Protodrilidae , Protodriloididae and Saccocirridae as well as other families of the Archiannelida as familiae incertae sedis in the order Canalipalpata or the subclasses Palpata or Scolecida .
New investigations led to the opinion that the former Archiannelida belong to two monophyletic groups, but neither of which are closely related to each other. Struck, Golombek and other established in 2015 phylogenetic due to investigations on a molecular genetic basis for a taxon Protodriliformia on, consisting of the orders Protodrilida and Polygordiida as sister group consisting of the (sub) systems Eunicida and Phyllodocida existing Aciculata with which it, the group the (newly delimited) Errantia forms, on the other hand the taxon Orbiniida in a new extent from the families Orbiniidae , Parergodrilidae , Diurodrilidae , Dinophilidae and Nerillidae , which in turn represents a sister group to a clade that consists of the Clitellata , Terebellida , Arenicolidae , Opheliidae , Capitellidae , Echiura , Spionida , Sabellida , Cirratulidae and Siboglinidae , and with this forms a group called Sedentaria , which is much more extensive than the earlier taxon Sedentaria. From this work, it appears that the in sand gap systems living (Interstitia) Orbiniida - Parergodrilidae, Diurodrilidae, Dinophilidae and Nerillidae - by Progenese , reached adaptation to this habitat while not specifically related other Annelidengruppe the Protodriliformia by dwarfing in ever finer sediments to now known tiny forms developed. The Archiannelida taxon is no longer considered a natural kin group.
Based on the work of Struck, Golombek and others in 2015, the following cladogram can be drawn:
| Annelida s. lato |
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literature
- Anton Schneider (1868): About the construction and development of Polygordius. Archives for Anatomy, Physiology and Scientific Medicine, 1868, pp. 51–60, panels II – III.
- Berthold Hatschek (1878): Studies on the history of the development of the Annelids. A contribution to the morphology of bilaterals. Works from the Zoological Institute of the University of Vienna and the Zoological Station in Trieste 1, pp. 277–404.
- Berthold Hatschek (1881): Protodrilus leuckartii. A new genus of archiannelids. Works from the zoological institutes of the University of Vienna and the zoological station in Trieste 3 (1), pp. 79–92.
- Berthold Hatschek: (1888-1891). Textbook of zoology, a morphological overview of the animal kingdom as an introduction to the study of this science. Volume 3. Gustav Fischer, Jena 1891. vol. 1 [1888], pp. i-iv, 1-144, vol. 2 [1889], pp. 145-304; vol. 3 [1891], pp. 305–432, here 1st subclass of the annelids. Archiannelides. Pp. 411-415, here p. 415.
- Colin O. Hermans (1969): The systematic position of the archiannelida. Systematic Zoology 18, pp. 85-102.
- Kristian Fauchald (1977): The polychaete worms, definitions and keys to the orders, families and genera. Natural History Museum of Los Angeles County: Los Angeles, CA (USA), Science Series. 28, pp. 1 - 188, here Order Orbiniida , p. 14.
- Günter Purschke, Claude Jouin (1988): Anatomy and ultrastructure of the ventral pharyngeal organs of Saccocirrus (Saccocirridae) and Protodriloides (Protodriloidae fam. N.) With remarks on the phylogenetic relationships within Protodrilida (Annelida: Polychaeta). Journal of Zoology, London 215 (3), pp. 405-432.
- Gregory W. Rouse, Kristian Fauchald (1998): Recent views on the status, delineation, and classification of the Annelida. (PDF). American Zoologist. 38 (6), pp. 953-964. doi: 10.1093 / icb / 38.6.953
- Torsten Hugo Struck, Anja Golombek, Anne Weigert, Franziska Anni Franke, Wilfried Westheide, Günter Purschke, Christoph Bleidorn, Kenneth Michael Halanych (2015): The Evolution of Annelids Reveals Two Adaptive Routes to the Interstitial Realm Current Biology. Current Biology 25 (15), pp. 1993-1999. DOI: 10.1016 / j.cub.2015.06.007
- Anne Weigert, Christoph Bleidorn (2016), Current status of annelid phylogeny. Organisms Diversity and Evolution 16 (2), pp. 345-362. DOI: 10.1007 / s13127-016-0265-7