protostome

File:Protovsdeuterostomes.svg, the first opening becomes the embryos' mouth while the anus is formed later. Also, the secondary body cavity (shown in blue) forms from tissue that splits away from the rest, instead of by folding in from the gut walls.]]

{{See also|Embryological origins of the mouth and anus}}

In animals at least as complex as earthworms, the first phase in gut development involves the embryo forming a dent on one side (the blastopore) which deepens to become its digestive tube (the archenteron). In the sister-clade, the deuterostomes ({{lit|second-mouth}}), the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes (from Greek {{lang|grc|πρωτο-}} {{Transliteration|grc|prōto-}} 'first' + {{lang|grc|στόμα}} {{Transliteration|grc|stóma}} 'mouth') were so named because it was once believed that in all cases the embryological dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut.{{cite book |last1=Peters |first1=Kenneth E. |last2=Walters |first2=Clifford C. |last3=Moldowan |first3=J. Michael |title=The Biomarker Guide: Biomarkers and isotopes in petroleum systems and Earth history |volume=2 |year=2005 |publisher=Cambridge University Press |isbn=978-0-521-83762-0 |page=717}}

It is now known that the fate of the blastopore among protostomes is extremely variable; while the evolutionary distinction between deuterostomes and protostomes remains valid, the descriptive accuracy of the name protostome is disputable.

Protostome and deuterostome embryos differ in several other ways. Secondary body cavities (coeloms) generally form by schizocoely, where the coelom forms out of a solid mass of embryonic tissue splitting away from the rest, instead of by enterocoelic pouching, where the coelom would otherwise form out of in-folded gut walls.{{cite book |last=Safra |first=Jacob E. |title=The New Encyclopædia Britannica, Volume 1; Volume 3 |year=2003 |publisher=Encyclopædia Britannica |isbn=978-0-85229-961-6 |page=767}}

The common ancestor of protostomes and deuterostomes was evidently a worm-like aquatic animal of the Ediacaran. The two clades diverged about 600 million years ago. Protostomes evolved into over a million species alive today, compared to ca. 73,000 deuterostome species.The Invertebrate tree of life, Giribet & Edgecombe, 2020; p.155

Protostomes are divided into the Ecdysozoa (e.g. arthropods, nematodes) and the Spiralia (e.g. molluscs, annelids, platyhelminths, and rotifers). A modern consensus phylogenetic tree for the protostomes is shown below.{{cite journal |first1=Gregory D. |last1=Edgecombe |first2=Gonzalo |last2=Giribet |first3=Casey W. |last3=Dunn |first4=Andreas |last4=Hejnol |first5=Reinhardt M. |last5=Kristensen |first6=Ricardo C. |last6=Neves |first7=Greg W. |last7=Rouse |first8=Katrine |last8=Worsaae |first9=Martin V. |last9=Sørensen |doi=10.1007/s13127-011-0044-4 |title=Higher-level metazoan relationships: recent progress and remaining questions |date=June 2011 |journal=Organisms, Diversity & Evolution |volume=11 |issue=2 |pages=151–172 |s2cid=32169826 |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:27755241 |url-access=subscription }}{{Cite journal |last1=Fröbius |first1=Andreas C. |last2=Funch |first2=Peter |date=2017-04-04 |title=Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans |journal=Nature Communications |volume=8 |issue=1 |pages=9 |doi=10.1038/s41467-017-00020-w|pmid=28377584 |bibcode=2017NatCo...8....9F |pmc=5431905 }}{{Cite journal |last1=Smith |first1=Martin R.|last2=Ortega-Hernández|first2=Javier |title=Hallucigenia's onychophoran-like claws and the case for Tactopoda |journal=Nature |volume=514|issue=7522 |pages=363–366 |doi=10.1038/nature13576 |pmid=25132546|year=2014|bibcode=2014Natur.514..363S|s2cid=205239797|url=http://dro.dur.ac.uk/19108/1/19108.pdf}}{{Cite web |url=http://palaeos.com/metazoa/ecdysozoa/ecdysozoa.html |title=Palaeos Metazoa: Ecdysozoa |website=palaeos.com |access-date=2017-09-02}}{{Cite journal |last1=Yamasaki |first1=Hiroshi |last2=Fujimoto |first2=Shinta |last3=Miyazaki |first3=Katsumi |date=June 2015 |title=Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences |journal=Zoological Letters |volume=1 |pages=18 |doi=10.1186/s40851-015-0017-0|pmid=26605063 |pmc=4657359 |doi-access=free }}

The timing of clades radiating into newer clades is given in mya (millions of years ago); less certain placements are indicated with dashed lines.{{Cite journal |last1=Peterson |first1=Kevin J.|last2=Cotton|first2=James A.|last3=Gehling |first3=James G. |last4=Pisani |first4=Davide |date=2008-04-27 |title=The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records |journal=Philosophical Transactions of the Royal Society of London B: Biological Sciences |volume=363 |issue=1496 |pages=1435–1443 |doi=10.1098/rstb.2007.2233 |pmid=18192191 |pmc=2614224}}

{{clade|{{clade

|1=Xenacoelomorpha 60 px

|label2=Nephrozoa |sublabel3=650 mya

|2={{clade

|label1=Deuterostomia

|1={{clade

|1=Ambulacraria 60 px

|2=Chordata 60 px

}}

|label2=Protostomia |sublabel2=610 mya

|2={{clade

|3=†Kimberella60 px

|label1=Ecdysozoa

|1={{clade

|label1=Scalidophora

|1={{clade

|1=Priapulida 45 px

|2=Kinorhyncha 35 px

}}

|2={{clade

|label1=Nematoida

|1={{clade

|1=Nematoda 60 px

|2=Nematomorpha 60 px

}}

|2={{clade|state1=dashed

|1=Loricifera 55 px

|label2=Panarthropoda

|2={{clade

|1=Onychophora 60 px

|label2=Tactopoda

|2={{clade

|1=Tardigrada 60 px

|2=Arthropoda 60 px

}}

}}

}}

}}

}}

|label2=Spiralia

|2={{Clade

|label1=Gnathifera

|1={{Clade

|1=Rotifera and allies 50 px

|2=Chaetognatha 80 px

}}

|label2=Platytrochozoa |sublabel2=580 mya

|2={{Clade

|1=Platyhelminthes and allies 80 px

|label2=Lophotrochozoa |sublabel2=550 mya

|2={{Clade

|1=Mollusca 60 px

|2=Annelida and allies 75 px

}}

}}

}}

}}

}}

}}|style=font-size:85%;line-height:85%|label1=Bilateria}}

• Embryological origins of the mouth and anus
• Urbilaterian, a hypothethical common ancestor to Protostomes and Deuterostomes

{{Reflist}}

{{Wikispecies|Protostomia}}

• [http://www.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=198701 The Taxonomicon] for Karl Grobben
• {{Commons category-inline|Protostomia}}

{{Animalia}}

{{Taxonbar|from=Q5171}}

{{Authority control}}

Category:Ediacaran first appearances

Category:Infrakingdoms

Category:Taxa named by Karl Grobben