Pterobranchia

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Pterobranchia
Temporal range:
Recent
Cephalodiscus nigrescens (collected from the Weddell Sea)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Hemichordata
Class: Pterobranchia
Lankester 1877
Orders
Synonyms
  • Graptolithoidea Lapworth sensu Beklemishev, 1951

Pterobranchia, members of which are often called pterobranchs, is a

Cambrian Period
.

The class Pterobranchia was established by

Enteropneusta
.

Electron microscope studies have suggested that pterobranchs belong to the same clade as the extinct graptolites,[1][2] and phylogenetic analysis suggests that the pterobranchs are living members of the graptolite clade.[3][4]

Biology

Pterobranchs are small worm-like

Atubaria has been regarded as a questionable species by Tassia et al. (2016) and is no longer considered valid.[7]

The collar bears a number of large arms, each of which includes a row of tentacles along one side. The number of arms varies between species, with anything from one to nine pairs. The tentacles are covered in cilia and aid in filtering food from the water. The trunk includes a simple tubular gut, and is curved over so that the

Atubaria have a single pair of gill slits in the pharynx, although Rhabdopleura has none.[5]

Development of pterobranchs have been studied only in

dioecious, with the fertilised egg hatching to produce a free-swimming ciliated larva. Despite the close relationship between the two groups, the larva does not resemble that of the acorn worms; they are "planula-like",[12] and do not feed (lecithotrophic).[13] Eventually, the larva settles onto the substrate and metamorphoses to an adult. Alternatively, they also reproduce asexually by budding to create a new colony.[5]

Evolution

Paleontology

The earliest pterobranchs, including

small carbonaceous fossils are known from the Buen Formation.[16]

Taxonomy

Comparison of 18S ribosomal RNA sequences indicated that pterobranchs are closely related to enteropneust hemichordates.[17]

Phylogeny of Pterobranchia[4]
Pterobranchia

Cephalodiscida

Graptolithina

Rhabdopleurida

Eugraptolithina

Dendroidea

Graptoloidea

Class Pterobranchia Lankester 1877[4]

  • Subclass Cephalodiscida Fowler 1892 stat. nov.
  • Subclass
    Graptolithina
     Bronn 1849
    • Order ?†
      Camaroidea
      Kozlowski 1928 sensu Kozlowski 1949
    • Order ?†
      Crustoidea
      Bulman 1970
    • Order ?†
      Dithecoidea
      Obut, 1960
    • Order ?†
      Tuboidea
      Kozlowski 1938 sensu Kozlowsk 1949
    • Order Rhabdopleurida Fowler 1892 sensu Beklemishev 1951
    • Clade †Eugraptolithina Mitchell et al., 2013
      • Order †
        Dendroidea
        Nicholson 1872
      • Order †
        Graptoloidea
        Maletz, Carlucci and Mitchell 2009

Genomics

Genetic code

The two pterobranch taxa

mitochondrial genome.[18][19]

Table of alternative codons in pterobranchs and comparison with the standard genetic code
Genetic code Translation
table		 DNA codon RNA codon Translation
with this code		 Standard translation
Pterobranchia mitochondrial 24 AGA AGA Ser (S) Arg (R)
AGG AGG Lys (K) Arg (R)
TGA UGA Trp (W) STOP = Ter (*)
Cephalodiscidae mitochondrial 33 AGA AGA Ser (S) Arg (R)
AGG AGG Lys (K) Arg (R)
TGA UGA Trp (W) STOP = Ter (*)
TAA UAA Tyr (Y) STOP = Ter (*)
Amino acids
 biochemical properties 		nonpolar polar basic acidic Termination: stop codon

References

  1. doi:10.1111/j.1502-3931.2008.00123.x
    .
  2. ISBN 978-0-375-40119-0
    .
  3. doi:10.1111/j.1502-3931.2012.00319.x
    .
  4. ^
    ISSN 1214-1119
    .
  5. ^
    ISBN 978-0-03-056747-6
    .
  6. ISBN 9781118515617
    .
  7. PMID 27701429
    .
  8. S2CID 84014156
    .
  9. S2CID 86563917
    .
  10. doi:10.1111/j.1463-6395.1988.tb00907.x
    .
  11. doi:10.1111/j.1463-6395.1988.tb00906.x
    .
  12. PMID 18798243
    .
  13. ^ Hemichordate Nervous System
  14. doi:10.1017/jpa.2014.7
    .
  15. PMID 21439828
    .
  16. doi:10.1130/G39788.1
    .
  17. PMID 7620637
    .
  18. PMID 21599892
    .
  19. PMID 30476024
    .

External links

Wikimedia Commons has media related to Pterobranchia.
Wikispecies has information related to Pterobranchia.
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