Newcomers

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Newcomers
In new mouths, the original mouth (blastopore) becomes the anus (anus), the mouth opening is newly formed.

In new mouths, the original mouth (blastopore) becomes the anus (anus), the mouth opening is newly formed.

Systematics
without rank: Multicellular animals (Metazoa)
without rank: Epitheliozoa
without rank: Tissue animals (Eumetazoa)
without rank: Bilateral animals (bilateria)
without rank: Kidney Animals (Nephrozoa)
Over trunk : Newcomers
Scientific name
Deuterostomia
Grobben , 1908

The new mouths ( new mouth animals, deuterostomia) represent an overstem of the bilateral animals ( bilateria ), of which the back string animals ( chordates , chordata - including humans) and the echinoderms (echinodermata) are the main taxa . One of the two common characteristic features of the deuterostomia is the further development of the original mouth in the embryonic development . Here, in the course of gastrulation, the original mouth becomes the anus and the mouth arises again (deuterostomy). The second characteristic is the dorsal (back) position of the central nervous system (CNS). In the other two-sided animals, the protostomia, however , the original mouth becomes the mouth and the anus breaks through secondarily; the CNS lies ventrally (on the abdomen).

term

The nineteenth century saw the beginning of developmental biology . Early stages of embryonic development were closely observed and described under the microscope. The achievements of the German-Baltic naturalist Karl Ernst von Baer and the German zoologist Ernst Haeckel proved to be particularly groundbreaking and influential . The scientists recognized that the digestive tract is established in two different ways among the three-seeded animals: on the one hand the original mouth becomes the later mouth, the future intestinal tract grows through the embryo and the anus finally breaks through; at other times the original mouth becomes the later anus, the future intestinal tract grows through the embryo and the mouth finally breaks through.

This developmental difference was first interpreted in terms of evolutionary biology by the British biologist Thomas Henry Huxley in 1875 and published twice. Huxley saw in the constitution of the digestive tract a trait that had been developed by very distant ancestors and has since been inherited more and more through diversifying progeny. As a result, all three-seeded animals living today either descended from an ancestor whose embryonic primal mouth became the later mouth - primal mouths; or else they came from an ancestor whose embryonic original mouth became the later anus - new mouths. Huxley called the first group of animals the Archaeostomata and the second group of animals the Deuterostomata .

Both terms were introduced to a wider public in his textbook by the Irish anatomist Alexander MacAlister as early as the next year . However, the knowledge of the Archaeostomata and Deuterostomata remained limited to the English-speaking specialist audience. The words could not establish themselves in the German-speaking area. That is why the Austrian zoologist Berthold Hatschek coined the new word Zygoneura twelve years later for the group of animals that Huxley had previously referred to as the archaeostomata. On the other hand, Hatschek did not offer a synonym for Huxley's deuterostomata.

This technical language gap was only closed in 1908 by the Austrian zoologist Karl Grobben . For his treatise The Systematic Division of the Animal Kingdom , Grobben initially adopted the term Zygoneura from Berthold Hatschek, but added his own synonym Protostomia to it in the course of the text . And he contrasted the protostomia with that group of tricotyledonous animals whose original mouth becomes the later anus. Grobben called this group Deuterostomia .

Thirty-three years after Huxley's Deuterostomata , Karl Grobben had coined an almost identical word for the same concept. During the twentieth century Grobben's pair of terms prevailed in developmental and evolutionary biology. Berthold Hatschek's Zygoneura fell into oblivion as well as Thomas Henry Huxley's Archaeostomata and just like his deuterostomata . The biological terminology today normally only uses the terms protostomia and deuterostomia .

“New age” as an ordering characteristic

After the new age (deuterostomy) was discovered, it served to bring together the very different animal groups of the chordates (chordata), gill animals ( hemichordata ) and echinoderms (echinodermata) to form a common community of descent. The community of descent was given the name “new mouths” ( new mouths , second mouths) or Deuterostomia (from ancient Greek δεύτερο- deutero “second” and στόμα stoma “mouth”).

However, there are other animals that also show deuterostomous embryonic development. New age can be observed in arrow worms ( Chaetognatha ), as well as in some wreath antennae ( Lophophorata ) and some string worms ( Nematomorpha ) and arthropods ( Arthropoda ). For decades it was controversial whether the animals should belong to the deuterostomia. With the help of molecular biological relationship research ( phylogenomics ), great clarity has been achieved on this question. According to this, chordates, gill animals and echinoderms actually form a community of descent. The remaining animal groups mentioned do not belong to it. Instead, their deuterostomies each evolved convergently independently of one another .

Systematics

The new mouth animals (Deuterostomia) represent a large group within the system of animals . Its sister taxon are the primordial mouth animals (Protostomia). With them they form the community of descent of the kidney animals ( Nephrozoa ). The kidney animals are combined with the Xenacoelomorpha to the bilateral animals (Bilateria).

External systematics of Deuterostomia (Neumünder)
  • Bilateria (bilateral animals)
    • Xenacoelomorpha
    • Nephrozoa (kidney animals)
      • Protostomia (primordial mouth animals)
      • Deuterostomia (new mouth animals)

Several animal groups are in turn assigned to the new mouths. Five of them still exist, so they're recent . Taxonomically , each is considered a stem or sub-stem . Because of certain similarities, the five groups can be assigned to a pair of even broader ancestral communities. Based on phylogenomic and comparative developmental findings, the two strains of Ambulacraria are compared to the three strains of the back-stringed animals.

Large groups of recent Deuterostomia (Neumünder)

The system of recent newcomers, however, only gives a sketchy idea of ​​the diversity of the animal group. Because it does not take into account that other Neumünder branches had evolved in past periods of the earth's history. Those branches are only known from fossils today. They can still be built into the existing system. However, the positions of the extinct Vetulicolia and Vetulocystida remain uncertain. Currently they are placed on the same level as the groups of echinoderms and back-string animals as a separate branch of Neumünder.

Systematics of recent and fossil deuterostomia (Neumünder)
 Deuterostomia 
 Ambulacraria 
 Echinodermata 

Echinodermata bilateralia a †


   

Echinodermata asymmetrica b †


 Echinodermata radiata c 

triradiary symmetric echinodermata d †


 pentaradio-symmetric Echinodermata e 

Crinozoa f


   

Eleutherozoa g






 Hemichordata 

Enteropneusta


   

Pterobranchia




   
 Chordata 

Leptocardia h, i


 Olfactores 
 Cristozoa j 

Myllokunmingiida h †


   

Pikaiidae h, k †


   

Conodontophora h, l †


   

Craniata m





   

Tunicata





   
 Vetulicolia 

Vetulicolida †


   

Banffozoa †



   

Vetulocystida †



Template: Klade / Maintenance / 3

a : The group of mirror-symmetrical echinoderms. Echinodermata bilateralia belonged to the Paraphylum of the Homalozoa .
b : The group of asymmetrical echinoderms. Echinodermata asymmetrica belonged to the Paraphylum of the Homalozoa.
c : The group of radially symmetrical echinoderms.
d : Echinodermata radiata with a threefold radial symmetry.
e : Echinodermata radiata with five-fold radial symmetry. They also include the groups of Crinozoa and Eleutherozoa , into which all recent echinoderms are classified.
f : The Crinozoa included the extinct groups of the Eocrinoidea , Paracrinoidea , Cystoidea , Blastoidea and Parablastoidea . They also include the group of Crinoidea , which includes all recent representatives of the Crinozoa. These are sea ​​lilies and hair stars from the subclass of the Articulata .
g : The Eleutherozoa include the recent groups of Echinozoa with sea whales ( Holothuroidea ) and sea urchins ( Echinoidea ) and the asterozoa with starfish ( Asteroidea ) and brittle stars ( Ophiuroidea ).
h : The animals belong to the skullless group ( Acrania ). These are creatures without a skull and with a back string that extends from the tail end to the head region. With the inclusion of the fossil new mouths, the skullless become a paraphylum.
i : Only the three genera of recent lancet fish ( Asymmetron , Epigonichthys , Branchiostoma ) are assigned to the class of skullless lancetfish ( Leptocardia ) .
j : The Cristozoa include all animals with neural crest formations .
k : The only known genus of the skullless Pikaiidae family is called Pikaia .
l : The skullless conodont animals ( Conodontophora ) are known almost exclusively for their fossilized mouthparts. The few finds with preserved soft tissue anatomy suggest a close relationship to the skull animals (craniata).
m : The group of cranial animals (Craniata) included the extinct paraphylum of the shell-skins ( Ostracodermi ) in addition to the more recent groups of round-mouthed ( Cyclostomata ) and jaw-mouthed ( Gnathostomata ).

In the illustrated system specific group names are different reasons no longer uses: Acrania (Paraphylum from Leptocardia, Myllokunmingiida, Pikaiidae and Conodontophora) ambulacrals ( synonym to ambulacraria) Anencephala (synonym to Leptocardia) Branchiotremata (synonym to Hemichrodata) Cephalochordata ( synonymous with Acrania) Cirrostomi (synonymous with Leptocardia) Chordonia (synonymous with Chordata) Coelomorpha (synonymous with ambulacraria) craniota (synonymous with Craniata) Deuterostomata (synonymous with Deuterostomia) Encephalota (synonymous with Craniata) Enterocoelomata (Synonyms to Deuterostomia) Euchordata (synonym to Notochordata) Myomerozoa (synonym to Notochordata) Notochordata (Paraphylum from Acrania and Craniata) Notoneuralia (synonym to Deuterostomia) Pachycardia (synonym to Craniata) Pharyngobranchia (synonym to Leptocardia), Proto Chordata ( Paraphylum from Acrania and Tunicata), Urochordata (synonym for Tunicata), Vertebrata (synonym for Cristozoa o that of Craniata), Xenambulacraria (Paraphylum from Xenacoelomorpha and Ambulacraria), Yunnanozoa (controversial synonym for Myllokunmingiida).

evolution

The new mouth animals are assigned to the group of kidney animals (Nephrozoa) within the bilateral animals (Bilateria). Their sister group consists of the primordial mouth animals (Protostomia). The last common ancestors of new mouth animals and primitive mouth animals therefore consisted of mirror-symmetrical kidney animals. The body of these animals had a main direction of movement ("front"). Correspondingly, more nerve cells and sensory cells were created at the front end of the body ( cephalization ). The body organs, which also included nephridia , developed from three cotyledons .

Phylogenomic studies with a molecular clock suggest that these kidney animals must have lived in the Upper Proterozoic . More precisely, they should have existed during the geological period called Cryogenium in the middle of the Sturtic Ice Age about 680 million years ago, before the lines of the new mouth animals and the primitive mouth animals finally separated. Already about 30 million years later, the new mouths split into the two groups still occurring today, the ambulacraria and the back animals (chordata). The split occurred in the warm period between the Sturtic Ice Age and the Marino Ice Age . The Cryogenium was followed by the Ediacarium . During this period there were further splits. Echinodermata (Echinodermata) and gillfish (Hemichordata) as well as lancetfish (Leptocardia), cristozoa and tunicates (Tunicata) thrived in their own lines before the Cambrian began. The soft-skinned animals were probably only a few millimeters tall. The search for their fossils has so far been unsuccessful. It was not until the fossil deposits of the Lower Cambrian that organisms were extracted that most certainly belonged to the new mouth animals. These animals, too, were hardly longer than a few centimeters. Only representatives of the new mouth branch of the Vetulicolia achieved greater body lengths, whereby the species Vetulicola longbaoshanensis represented the utmost possible with just under a decimeter.

Oldest fossil genera of Deuterostomia a, b, c
Ambulacraria • Echinodermata • Echinodermata bilateralia
Ambulacraria • Echinodermata • Echinodermata asymmetrica
Ambulacraria • Echinodermata • Echinodermata radiata
Ambulacraria • Hemichordata • Enteropneusta
Ambulacraria • Hemichordata • Pterobranchia
  • --- d
Chordata • Leptocardia
Chordata • Olfactores • Cristozoa
Chordata • Olfactores • Tunicata
Vetulicolia
Vetulocystida
a : Many of the fossils come from two Cambrian fossil sites. The Maotianshan slates from southern China are 520 to 525 million years old. The Burgess Shales from western Canada are approximately 508 million years old.
b : Because of its uncertain taxonomic classification, the genus Yunnanozoon (= Cathayamyrus = Zhongxiniscus , = Haikouella ) is not considered here. Perhaps it was an ancestor of the string animals (chordata).
c : Because of their uncertain taxonomic classification, the Cambroernida group with its genera Herpetogaster and Phlogites is not considered here. Maybe it was ambulacraria.
d : There are no fossils of lancetfish (Leptocardia). Although four fossil genera had already been assigned to the class, all four could not keep this assignment for different reasons.
e : The genus Skeemella may also belong to the Vetulicolia.

Body shapes and types of movement

The millimeter-sized representatives of the genus Saccorhytus could represent the oldest fossilized new mouth animals. The bag-like organisms were taxonomically placed in the vicinity of the Vetulicolia and Vetulocystida and found in the 535 million year old Kuanchuanpu schist in southern China. Presumably the tiny animals showed a very simplified blueprint. In contrast to Saccorhytus , the last common ancestors of all new mouths were probably worm-shaped. It has not been clarified whether the animals were stuck on the sea floor (or the like) ( benthic-sessile movement type ), crawled over the sea floor or bored through it ( benthic-vagile movement type or subbenthic-vagile movement type ) or even moved freely swimming ( pelagic -vagile movement type ), although the latter is currently considered rather unlikely.

The majority of the Ambulacraria retained the benthic way of life. The first echinoderms (Echinodermata) were built bilaterally symmetrically and moved crawling or jumping over the sea floor. But even in the Lower Cambrian, many lost their mirror symmetry in favor of asymmetrical or radially symmetrical bodies. The exchange of bilateral symmetry with radial symmetry went hand in hand with the exchange of the benthic-vagile movement type with the benthic-sessile movement type. Permanently stuck animals no longer need a body structure that is designed for one main direction of movement. All recent forms are derived from such sessile and pentaradial echinoderms; they may have emerged from the fossil genus Camptostroma . Only the larvae retained a bilaterally symmetrical structure. Besides the still sessile sea lilies, the other echinoderms groups later returned to the benthic-vagile movement type. This applies to the closely related hairy stars as well as to the entirety of the Eleutherozoa, i.e. sea cucumbers (Holothuroidea), sea urchins (Echinoidea), starfish (Asteroidea) and brittle stars (Ophiuroidea). Almost half of all today's sea urchin species (“ irregularia ”) show signs of a secondary bilateral symmetrical body shape, which was fully developed again in the sea rollers.

The other ambulacraria, the hemichordata, also settled on benthic types of movement. Acorn worms (Enteropneusta) burrow through the upper seabed, wing gills (Pterobranchia) stay in fixed tubes most of the time, which they sometimes leave by crawling. Animals from the wing-gill family of the Cephalodiscidae move around on the sea floor without ever building living tubes.

The back string animals (Chordata) on the other hand went over to a free-swimming way of life. They developed elongated and laterally flattened bodies that were stabilized with a chorda dorsalis . Today's lancet fish (Leptocardia) rarely move in open water. Instead, they bury their tail end first in coarse sand or lie flat on their side on a firmer seabed. The first olfactores probably also led a pelagic life. The early Cristozoa did not deviate from this, as can be seen from the fossils of the Myllokunmingiida, Pikaiidae and Conodontophora. The other olfactores, the tunicata, switched to the benthic-sessile movement type as early as the Lower Cambrian, but retained pelagic larval stages. The adult animals lost their bilaterally symmetrical physique. Later, the tuniculate groups of the Salps ( Thaliacea ) and the Appendicularia ( Copelata ) returned to the open water for adult life. In addition, the appendicularia remained in their bilaterally symmetrical larval shape for adulthood.

The body shapes of the extinct Vetulocystida and Vetulicolia can only be traced using fossils from the Cambrian. Vetulocystida were built bilaterally symmetrically. Their bodies were divided into two parts with flattened, wide fore bodies and tails, which were centered at the back of the fore bodies and were about a third of their width. Most of the time, Vetulocystida presumably rested in one place on the sea floor. They found support by burying their tails underground so that only the front part of the body peeked out. Occasionally they changed their location by creating propulsion with the help of their tails, which they swung sideways to and fro.

The physique of the Vetulicolia was in a way similar to that of the Vetulocystida. They too had bilaterally symmetrical shapes with broad front bodies and tails. However, the front bodies were not flattened, but flattened on the sides. Furthermore, the tails do not start in the middle, but near the upper rear ends of the body ( dorsal-posterior ). Vetulicolia probably spent most of the time on the seabed and could simply swim away in case of danger. Two species differed from this way of life. Banffia went on to a digging existence. In contrast, Vetulicola developed into pure swimmers with a very streamlined physique.

Web links

Commons : Deuterostomia  - collection of images, videos and audio files

Individual evidence

  1. ^ Hynek Burda: General Zoology. Verlag Eugen Ulmer, Stuttgart, 2005, ISBN 3-8001-2838-1 , p. 55.
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  3. ↑ Karl Ernst von Baer: About the history of the development of animals • First part . Publishing house Gebrüder Bornträger, Königsberg, 1828.
  4. ↑ Ernst Haeckel: The biology of the lime sponges . Georg Reimer Verlag, Berlin, 1872, pp. 328–339 ( digitized version ).
  5. ^ Thomas Henry Huxley: On the classification of the animal kingdom . In: The Journal of the Linnean Society. Zoology . Volume 12, 1875, doi : 10.1111 / j.1096-3642.1875.tb02582.x , pp. 199-226.
  6. ^ Thomas Henry Huxley: On the classification of the animal kingdom . In: The American Naturalist . Volume 09, 1875, doi : 10.1086 / 271442 , pp. 65-70.
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  8. ^ Thomas Henry Huxley: On the classification of the animal kingdom . In: The American Naturalist . Volume 09, 1875, doi : 10.1086 / 271442 , p. 67.
  9. ↑ Alexander MacAlister: An Introduction to Animal Morphology and Systematic Zoology • Part I . Publishers Longmans, Green and Co., London, 1876. p. 48 ( digitized ).
  10. ↑ Berthold Hatschek: Textbook of Zoology • First delivery . Gustav Fischer Verlag, Jena, 1888, p. 41.
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  33. ↑ John A. Cunningham, Alexander G. Liu, Stefan Bengtson and Philip CJ Donoghue: The origin of animals: Can molecular clocks and the fossil record be reconciled? In: Bioessays . Volume 39, 2016, doi : 10.1002 / bies.201600120 , pp. 1–12.
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  36. ↑ JinShu Li, JianNi Liu, Qiang Ou: New observations on Vetulicola longbaoshanensis from the Lower Cambrian Guanshan Biota (Series 2, Stage 4), South China . In: Science China Earth Sciences . Volume 60, 2017, doi : 10.1007 / s11430-017-9088-y , p. 1798.
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