Talk:Echinoderm

Can somebody tell more about the evolution of Echinoderms?

I was slightly amazed there was so little information about the evolution of Echinoderms. When I did my first-year course on invertebrates I'm sure I was told more than given here, so there must be a lot more info on this with the specialists (they were well studied). Just looking at plate 95 of Haeckels Kustformen der Natur I see weird bilateral forms from the lower Silurian period, so plenty to tell I would imagine. And also I would expect molecular biologists have more to tell. Codiv (talk) 23:08, 16 July 2022 (UTC)

Well, this is a general article and it certainly covers "the main points". The 'Fossil history' illustrates eight forms including several that are distinctly oddly shaped by modern standards, and including near-spherical, blastoid, and bilaterally-symmetric forms, so it clearly gives a clue that early forms did not much resemble the five-star form that readers will recognize. By the way, Haeckel's illustrations are often imaginative and sometimes definitely wrong, so they are unreliable guides to ancient anatomy. It might well be desirable to have an article on the Early echinoderms or indeed on the Evolution of echinoderms, but those and the more specialized detail that they might contain would naturally form subsidiary articles with "main" links from here. For comparison, Arthropod contains images of just two fossils, and it is a well-balanced article; Mollusca similarly pictures two fossils in its phylum. All the best, Chiswick Chap (talk) 08:42, 17 July 2022 (UTC)

@Codiv I had the same reaction as you did to this article, which sent me down a very deep rabbit-hole of research. The reason the information is not present is simple: There is no agreement whatsoever on the relationships among fossil taxa. After a great deal of searching, I am convinced that no-one has even published a full cladogram that accounts for all of the groups in the traditional Linnaean taxonomies. In fact, the Linnaean taxonomies still form the basis for most discussion, as no alternative group names have been proposed to replace the various groups thought to be paraphyletic and/or polyphyletic.

A further problem is that many of the articles on major groups are barely stubs, or have been redirected to other groups in ways that are not consistent among the various pages. These things are never entirely settled, but I have not encountered phylum where attempting to walk the page tree is quite so bewildering.

@Chiswick Chap thanks for the suggestion to look at Arthropod and Mollusca — it's helpful to have a point of reference for improving this article. I notice that both of those pages have a roughly five-part organization (approximate categories, not exact section names):

• Etymology (not present for Echinoderms)
• Description (including Diversity followed by various anatomy-ish sections)
• Ecology (not present for Mollusca, but has analogues in the sections on this page)
• Classification (includes fossil history)
• Interaction with Humans

I'm going to do a bit of re-organization to align with this, mostly moving Diversity up to the top above Anatomy (like Mollusca, and similar-ish to Arthropoda), and moving the rest of the Taxonomy and Evolution section down to just before Use By Humans (like both Mollusca and Arthropoda). That will keep an expanded Taxonomy and Evolution section from clogging up the page before you get to the information about living echinoderms.

I noticed that both pages have multiple cladograms plus tables and illustrations. I intend to expand this section for Echinoderms based on my research, showing phylogeny down to the class level. It will probably be a little longer than the corresponding material for Mollusca, as the situation with Echinoderms is absurdly complex and contentious and requires historical context. But it should be noticeably shorter than the Evolutionary History section for Arthropods. I figure if I stay in that range it should be fine.

I probably won't change the contents of other sections unless I noticed inconsistencies.

I'm happy to discuss alternatives for any of this, but I'm going to go ahead and get started as this will be done in several stages.

Ixat totep (talk) 02:25, 29 October 2024 (UTC)

I've done the section moves and added some references to cite later. Looking at the existing taxonomy section, I think we can banish the details of Asterozoa vs Cryptosyringida to Eleutherozoa, where it is already covered in similar detail. Asterozoa has been pretty firmly established as the winner for a while now.

This page should cover the consensus for extant classes (which is pretty solid) and the history and controversy around the extinct classes. For the extinct classes, we will need to show several alternatives and the historical context.

The "Fossil history" section will need a bit of rework to acknowledge the disagreements over pentamery-first (Arkarua) vs stereom-first (Ctenoimbricata and Helicocystis) theories, but I'd rather change it as little as possible.

However, I can't figure out what "Further information: Dibrachicystis" is doing there as the brief article is a seemingly random one about a particular genera of unclear significance, except perhaps that it has an Eocrinoid cladogram... which would be better referenced on the Eocrinoidea page if we need to do so (I have ambitious of improving that page as it's one of the most confusing taxa / grades in the phylum, and will put a few cladograms there when I do).

Ixat totep (talk) 03:14, 29 October 2024 (UTC)

Many thanks. The reason for the lack of cladograms in the literature (and therefore here) is that genes seem to get passed around between even distantly-related echinoderms like, hm, fun things at a party. Attempts at trees have always ended up in a mess. I expect eventually someone will work out a clever way of tracing the exchanges..... Chiswick Chap (talk) 08:01, 29 October 2024 (UTC)

@Chiswick Chap yeah it's not that any particular article is wrong, it's that what we know is confusing and hard to capture! But I'm enjoying the challenge, and there's a 2024 overview paper that has at least narrowed it down to two general hypotheses worth capturing. I'll hopefully get that part written up later today.

Ixat totep (talk) 15:36, 29 October 2024 (UTC)

Fixing the "Pentaradiality as a plesiomorphy" cladogram

@Davemck Thanks for trying to fix the cladogram! I went back to the source and neither what I had originally (which is what you changed it back to) nor what I had changed it to are correct. After the first "some Eocrinoids" there should be a four-way polytomy, like this:

1. Lepidocystoids [Eocrinoidea begins]
2. (unnamed group)
   1. some Eocrinoids
   2. Blastozoa
      1. some Eocrinoids
      2. (unnamed group)
         1. some Eocrinoids [Eocrinoidea ends]
         2. (unnamed group)
            1. Ctenocystoids
            2. Homosteleans (Cinctans)
      3. Homoiosteleans (Solutes)
      4. (unnamed group)
         1. Diploporita [Cystoids start]
         2. (unnamed group)
            1. Rhombifera [Cystoids end]
            2. Blastoidea

My apologies for the confusing commit message, thanks again for attempting to parse it. I'm going to put in this version, but if you think the resulting cladogram still doesn't match the above, feel free to fix further with my thanks! If you disagree with the above interpretation of the source, please comment here and we can discuss the correct topology.

Ixat totep (talk) 23:16, 6 November 2024 (UTC)

Aslo, I had Blastozoa in the wrong place... cladogram markup is easy to get lost in...

Ixat totep (talk) 23:34, 6 November 2024 (UTC)

Or maybe I didn't... I'm going to study this thing a bit more.

Ixat totep (talk) 23:35, 6 November 2024 (UTC)

Sounds good. I got involved because it appeared on Category:Articles using duplicate arguments in template calls, which is what I work from. It's useful to do "Show preview" & check for errors as a last step before "Publish changes". And you're right: cladograms can make you pull your hair out :-)

Davemck (talk) 23:55, 6 November 2024 (UTC)