Talk:Agnatha

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WikiProject Animals (Rated Start-class, Low-importance)
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Rewrite[edit]

My apologies for rewriting the page. There was nothing wrong with it, but it was difficult to fit in all the material I wanted to add without some reorganization. Feel free to hack up whatever I did if it is unsatisfactory - DJK 22:53, 18 May 2003 (UTC)

I'm sorry, but[edit]

Agnatha are not fishes. They have completely different skeleton, and their notochord lasts unchanged for their whole life. — Preceding unsigned comment added by 213.199.221.98 (talk) 14:41, 21 October 2004 (UTC)

What are hermaphites? — Preceding unsigned comment added by 67.169.11.202 (talk) 18:28, 7 July 2009 (UTC)

Hagfish[edit]

Hagfishes aren't really agnathans. All agnathans are jawless vertebrates who's mouths are fixed open. A hagfish's mouth is not fixed open, they have horizontally articulating "jaws", while agnathans just have a mouth fixed open. Giant Blue Anteater 05:17, 9 September 2006 (UTC)

Cyclostomes[edit]

Hagfishes are considered agnathans because they are cyclostomes. Hagfishes belong in the Myxinidae family under the class Agnatha. Information cited from http://www.gma.org/fogm/Hagfish_Lamprey.htm Qwertyloo —Preceding undated comment added 02:44, 10 October 2006 (UTC).

Old terminology[edit]

Agnatha is a dated term; it is being used less and less because the group is paraphyletic. This should be mentioned somewhere in the article. Fuzzform 21:42, 22 March 2007 (UTC)

Where does this one belong then? Bob the Wikipedian (talk) 23:12, 13 May 2008 (UTC)
We could describe it simply as an early craniate or chordate. —Preceding unsigned comment added by Cephal-odd (talkcontribs) 05:50, 14 May 2008 (UTC)

POV[edit]

The statement that Agnatha are limited in their ability to evolve seems POV. There are numerous sucessful species and as another contributer accidentally pointed out, lack of jaw has not prevented the development of an opening and closing mouth. JDN —Preceding unsigned comment added by 62.6.149.17 (talk) 14:06, 28 July 2009 (UTC)

I'd go one further to say I'm not happy with the comment that "Agnathan feeding habits have limited their ability to advance evolutionarily"... pretty sure that's not how evolution works, there's no "advancement". Nor can I see their feeding habits being limiting. Quite the reverse, lamprey feeding habits are rather specialised, which tends to be derived traits, as well as they show two different feeding habits during their life-cycle. Hagfish are generalist scavengers, not exactly a "limiting" lifestyle.

That section needs re-writing, which I may do later (once I've dug up some references... something else it lacks). —Preceding unsigned comment added by 86.140.234.117 (talk) 12:40, 25 March 2011 (UTC)

agnathan paraphyly[edit]

The article says "Many recent textbooks regard the group as paraphyletic[2] but recent molecular data, both from rRNA[3] and from mtDNA[4] strongly supports living agnathans as monophyletic."

I think we should draw a distinction between agnathans (all jawless vertebrates) and the possible lamprey-hagfish clade (usually called cyclostomes). I don't think anyone has argued that all jawless fishes, including all ostracoderms, belong to a clade that excludes gnathostomes. On the other hand, molecular phylogenies have suggested that cyclostomes form such a clade, although morphological evidence tends to suggest that they do not. We should be clear which of those two taxa we're referring to: Agnatha or Cyclostomata. Cephal-odd (talk) 13:58, 18 August 2009 (UTC)

I hate to spoil plans to revamp the system, but Wikipedia wouldn't allow us to make the change based on our own original research. You can publish your own paper on it, though. Post the link here and if we like it, we'll fix the article. Bob the Wikipedian (talkcontribs) 17:32, 18 August 2009 (UTC)
Fortunately there's no need to invoke any original research! The distinction between Agnatha and Cyclostomata has been in the literature for decades. To conflate the two would be somewhat like writing an article about dinosaurs that only discussed modern birds. Cyclostomes are an important part of the agnathan story but not the only one.
As suggested, I've included some references that show that most fossil agnathans, such as galeaspids, thelodonts, and osteostracans, are not closely related to cyclostomes but are stem gnathostomes. Cyclostomes seem to have split off before the evolution of dentine and bone, which are present in many fossil agnathans, including conodonts. There are more details at the Cyclostomata article.
Cheers, Cephal-odd (talk) 19:58, 2 September 2009 (UTC)

Vertebrates[edit]

According to another article, Hagfishes are not vertebrates, but another group of Craniates because they don't have a backbone. --121.218.219.122 (talk) 08:05, 25 September 2009 (UTC)

The name Craniata usually appears when hagfishes are thought to be outside the clade comprising lampreys and gnathostomes (which is then called Vertebrata). In that case, Agnatha usually includes hagfishes anyway, because it's then defined as non-gnathostome craniates. Lampreys and hagfishes are pretty much the canonical extant agnathans.
Cephal-odd (talk) 03:10, 27 September 2009 (UTC)

Fertilization[edit]

The statement that fertilization is external in lampreys and hagfishes needs to be corrected. Fertilization in lampreys is just barely external-- males and females release sperm and egg into a cavity formed between their bellies as the press against each other during mating. Fertilization in hagfishes never has been observed, but given the kind of egg they produce (large, yolky and 'shark-like') internal fertilization seems most likely. I'll make the change as soon as I dig up the references. Struvite (talk) 05:16, 29 December 2010 (UTC)

Name is Greek[edit]

You are sadly mistaken if you think a word like 'Agnatha' has a Latin origin. It is of course Greek in origin, as are most of the taxonomic names in biology. It is derived from the Greek negative prefix a + gnathos = having no jaws. If you doubt this, use a dictionary with etymological derivations. Macdonald-ross (talk) 08:46, 8 October 2012 (UTC)