Unraveling Arthropoda

This post was chosen as an Editor's Selection for ResearchBlogging.orgA new paper, published online in Nature this week, aims to resolve long-standing disputes within Arthropod phylogenetics. This work offers strong evidence for, and opens new, perplexing questions about, the deep evolutionary history of arthropods.

The phylum Arthropoda consists of four major subphyla:

  • Chelicerata – Arachnids, horseshoe crabs, sea spiders.
  • Myriapoda – Centipedes, millipedes.
  • Crustacea – Crabs, lobsters, shrimp, copepods, ostracods, barnacles, pill bugs, brine shrimp, water fleas, remipedes, ect.
  • Hexapoda – Insects, silverfish, springtails.

All known arthropods are included in these subphyla. However, the interrelation of the subphyla has long been in contention. Up to now, a series of morphological and molecular-based classification paradigms have been employed to parsimoniously resolve the deep phylogeny of arthropods; with mixed results. Two of the competing hypotheses of deep arthropod phylogenetics are the Paradoxopoda and Mandibulata models.

Both Mandibulata and Paradoxopoda propose a Pancrustacean clade consisting of Hexapods and Crustaceans as closely related sister groups. They differ in their treatment of the Myriapods and Chelicerates. Paradoxopoda has Myriapods and Chelicerates as closely related sister groups. Mandibulata, on the other hand, has Myriapods as a sister group to Pancrustaceans, and Chelicerates as a distant, early-branching clade of arthropods. While Mandibulata is supported by taxonomy (Crustaceans, Hexapods, and Myriapods all have mandibles, where as Chelicerates have chelicerae for mouthparts), Paradoxopoda is primarily supported by recent mitochondrial molecular pylogenetics.

Also under contention is the relationship between Crustaceans and Hexapods within the increasingly well supported Pancrustacean clade. It has not yet been settled if the two are distinct sister groups, or if the Hexapods are nested within the Crustaceans. If the latter is true, researchers have not been able to determine which branch of the Crustaceans gave rise to the Hexapods.

In the present study, researchers at University of Maryland, Duke, and the Natural History Museum of LA have dramatically improved on previous molecular approaches for inferring deep arthropod phylogenetics. They did this by increasing the number and diversity of arthropod species included, as well as the type and amount of genetic sequence characters used. Whereas previous approaches used mitochondrial genetic sequences, resulting in the morphologically perplexing Paradoxopoda model; the researchers in this study instead used nuclear protein-coding genes. Nuclear genes have been increasingly used to resolve deep evolutionary relationships in animals.

The researchers included in their molecular phylogenetic analysis 75 arthropod species. The 75 arthropod taxa were chosen to encompass the broadest spectrum of known arthropod groups. From each of these species, they sequenced 62 nuclear genes; totaling 41 thousand bases of DNA sequence per species. These sequence data sets from the 75 different arthropods were compared to one another, producing this phylogenetic tree:

Maximum likelihood phylogenetic tree of arthropods. Adapted from Regier et al., 2010.

This tree further supports a Pancrustacean clade consisting of Hexapods and Crustaceans. In addition, this work supports the Mandibulata model of deep evolutionary relationships within Arthropoda. Pancrustacea is sister to the Myriapods, forming the Mandibulata clade; which is then sister to the early-branching Chelicerates. This reconstruction strongly refutes the mitochondrial Paradoxopoda model.

The most notable results of this study are in regard to the internal structure of the Pancrustacean clade. Instead of a distinct separation between Crustaceans and Hexapods, we see four resolved clades within Pancrustacea. The Hexapod clade is upheld and nested completely within Crustacea. In addition Crustaceans are split into three paraphyletic clades; Vericrustacea, Oligostraca, and Xenocarida. Vericrustacea (‘true crustaceans’) includes the decapods (crabs and lobsters), mantis shrimp, barnacles, copepods, and branchiopods; most of the critters commonly thought of as crustaceans. Oligostraca is a strange and early branching crustacean group that includes ostracods, tongue worms, and branchiurans. Xenocarida (‘strange shrimps’) includes remipedes and cephalocarids.

It turns out that, according to this analysis, the Xenocarids are the long sought-after sister group to Hexapods. Together they form the new clade Miracrustacea (‘surprising crustacean’). The Miracrustaceans are sister to the Vericrustaceans, forming a clade that is in turn sister to the Oligostraca, rounding out Pancrustacea.

This study causes some serious upheavals in the Pancrustacean clade; breaking Crustaceans into three paraphyletic clades, placing remipedes as close sister taxa to Hexapods, and nesting the Hexapods completely within the Crustaceans. At the same time it presents new and exciting questions to morphologists and evolutionary-developmental biologists.

Further morphological, genetic, and evolutionary study is required in order to understand the full implications of these newly resolved arthropod relationships. However, this research represents a robust step forward towards unraveling Arthropoda.


  • Regier, J., Shultz, J., Zwick, A., Hussey, A., Ball, B., Wetzer, R., Martin, J., & Cunningham, C. (2010). Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences Nature DOI: 10.1038/nature08742


23 Responses to “Unraveling Arthropoda”

  1. 1 Cliff Cunningham February 12, 2010 at 10:01 am

    Dear Dr. Bok,
    This is the best write-up of our paper! Thanks so much.

  2. 2 Mike Bok February 12, 2010 at 10:11 am

    Dr. Cunningham,

    I’m glad you liked my writeup!

    It’s a great paper and an impressive effort. I can really appreciate the amount of sequencing and compiling your team had to do. The implications of this are really exciting, even for people who study arthropod visual pigment evolution like me.

    I’m still a few years, and a bit of luck, away from being “Dr.” Bok, by the way.

  3. 3 jaredcormier February 16, 2010 at 7:00 am

    Holy crap, that’s a lot of data to crunch for a single phylogeny. This was quite an impressive study. ~4,650 runs on a sequencer just to get the data and then to crunch and compare all of those data…

  4. 4 Thomas R September 19, 2010 at 5:47 pm

    Thank you for a fascinating article!

    I am curious about the timescale; does the number 0.03 in the picture represent 30 million years (0.03 billion), thus placing Arthropda in the Devonian time period (360-400 million years ago)?

    • 5 Mike Bok September 20, 2010 at 4:53 pm


      The scale bar is in nucleotide changes per site. There are no divergence time estimates associated with this phylogeny.

      Arthropoda was already a well established and diverse phylum in the Devonian. The earliest arthropod fossils are from the early Cambrian, well over 500 MYA.

  5. 6 new games in june 2014 August 26, 2014 at 3:03 am

    Definitely believe that which you said. Your favourite justification seemed to be at
    the internet the easiest factor to have in mind of.
    I say to you, I certainly get annoyed even as other
    folks think about worries that they just do not recognise about.
    You controlled to hit the nail upon the highest and also defined out
    the whole thing without having side-effects , folks can take a
    signal. Will likely be again to get more. Thank you

  6. 7 กระดูกทับเส้นประสาท September 13, 2014 at 12:07 pm

    In order to avoid back pain, avoid sitting for extended periods of time.
    A bed board may be necessary to create the firmness necessary
    to keep the back free from pain. Yoga is the most effective way as it assists to regulate all
    the body functions perfectly and relieves back pain considerably.

  7. 8 tenso September 17, 2014 at 12:49 pm

    Hi there, yeah this paragraph is in fact nice and I have learned lot of things from it concerning blogging.


  8. 9 Blank Calendar 2016 November 12, 2015 at 6:02 am

    Pretty! This has been a really wonderful post. Thank
    you for providing these details.

  9. 10 Printable calendar January 14, 2016 at 3:20 am

    Hi there it’s me, I am also visiting this web site on a regular basis, this site is genuinely pleasant and the viewers are actually sharing good thoughts.

  10. 11 February 2016 Printable Calendar January 25, 2016 at 2:32 am

    Hello, this weekend is pleasant in favor of me, for the reason that this moment i am reading this great
    informative post here at my residence.

  11. 12 remove viruswin32virut April 9, 2017 at 5:49 am

    Hi mates, how iis everything, and what you want to ssay regarding this paragraph,
    in my view its tduly awesome designed for me.

  1. 1 Scientia Pro Publica 21 « Mors dei Trackback on February 16, 2010 at 9:41 pm
  2. 2 ResearchBlogging.org News » Blog Archive » Editor’s Selections: Never Asking for Directions, Food, or The Identity of Your Uncle Trackback on February 18, 2010 at 2:43 pm
  3. 3 Arthropods in pop culture: Tongue replacing isopods « Arthropoda Trackback on February 24, 2010 at 2:16 pm
  4. 4 Is the Drosophila actually Drosophila? « Arthropoda Trackback on April 9, 2010 at 1:37 am
  5. 5 Arthropods in pop culture: Attack of the Camel Spiders « Arthropoda Trackback on June 30, 2010 at 3:28 pm
  6. 6 Is ‘the Drosophila‘ actually Drosophila? or: Drosoph-Apocalypse Now « Arthropoda Trackback on September 15, 2010 at 4:40 pm
  7. 7 Scientia Pro Publica 21: Darwin's 201st Birthday Edition | This Scientific Life Trackback on July 24, 2014 at 3:34 pm
  8. 8 play free Trackback on November 22, 2014 at 12:00 pm
  9. 9 http://scritter.Guldhammer.Info Trackback on April 19, 2020 at 1:07 pm
  10. 10 절지동물의 분류 – 전국과학교사협회 Trackback on December 20, 2020 at 9:51 am
  11. 11 [강의자료] 절지동물 분류 그림 - 자바실험실 Trackback on December 27, 2020 at 12:51 am

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

I have moved.
Arthropoda can now be found here.

Michael Bok is a graduate student studying the visual system of mantis shrimp.

Flickr Photos

%d bloggers like this: