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==Taxonomic table== ==Taxonomic table==


Revision as of 16:50, 13 November 2006

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Taxonomic table

Setting up the table has already caused one fair comment to be raised about what happens to the taxon Uniramia. My visits to various sites on the Net has taught me that the situation about the higher classification of the arthropods is chaotic. Valid arguments could be made for any of many of these schemes. The disturbing thing is that many of these different schemes appear on "dot edu" where they are presented as a professor's gospel to his class.

I've probably already left the impression that, right or wrong, I have a preference to the ITIS scheme, and by extension (since ITIS is focused on North America) looking at the "Species 2000" where applicable. I tend to use these on a "without prejudice" basis that recognizes the difficulties inherent in having bureaucrats control the science. This view treats ITIS as a reference point, and nothing more. If a person B's particular scheme differs from ITIS in a defined way it is 1 generation removed from ITIS. A similar situation applies if C's scheme differs in defined way from ITIS. However, if C defines his scheme with reference to B's then he is 2 generations removed from the reference point. String a few schemes in a row, and you begin to lose perspective on the subject.

Cladists have a stated vision of some day being rid of Linnean ranks altogether. Given the uncertainty that often arises from guessing whether a particular taxon is a class or an order, I can sympathize with that view. But without ranks the cladist's tree sometimes lacks good climbing branches where you can place your feet as you go up.

I think that if we can maintain some consistency in using the primary KPCOFGS rankings, we can have more flexibility with the secondary rankings. There is already some degree of acceptance that in most cases only primary ranks will appear in what was the "Placement" list, and what is now the top part of the tables. That doesn't mean that there can be no exceptions to this rule. (Cf. Misplaced Pages:Ignore all rules)

So, to get back on topic, higher arthropod classification is confused! But there remains that if we want anything about the subject on Misplaced Pages, we absolutely need to deal with the confusion. Here then is where I see things as standing between phylum and class in the Arthropoda:

  1. The trilobites (not listed in ITIS) are a phylum with a single class, and that fact appears generally accepted - no problem.
"Generally accepted"? Granted, I'm no expert (I've read a book about trilobytes, is all), but a quick google on "trilobite phylum" got me lots of assertions that trilobites are part of arthropoda. And trying "trilobyte classification" got me a claim that there are eight classes of trilobytes. Vicki Rosenzweig
Yes - were is it generally accepted? I was taught that trilobites were a class of Arthropods and my animal biology text from 1996 confirms this. Has something changed since my freshman year of college? --maveric149
This is a woops -- it should have read subphylum trilobitomorpha with a single class Trilobita. I tried "trilobite classificatio" and it said 8 orders not 8 classes.
  1. Chelicerata seems to be the generally accepted name for that sub-phylum; there may very well have been some reason to distinguish this term from Chelliceriformes in the past, but those reasons seem to be fading.
  2. I have yet to examine issues in the Crustacea, but at least there appears to be general acceptance that is is properly a subphylum.
  3. In text of the article as it has been the Hexapoda has been treated as a class in Uniramia equivalent with the each of the four classes in Myriapoda. Myriapoda was nowhere to be seen; I was ready to throw out Uniramia (not in ITIS) while restoring Myriapoda. Some of the sites that I have seen which treat Uniramia as a subphyllum also show it as containing two Superclasses: Myriapoda and Hexapoda. This may present the most workable solution to this problem because it allows Insecta to remain as a class.
  4. ITIS does not assign a class to the three primitive hexapod orders. We can leave it like that or we can apply a class name from another source. In the latter case some sites have opted for a separate class name for each, some have used Endognatha for all three together, and one has limited Endognatha to the Diplura while assigning the class name Parainsecta to the combined Collembola and Protura. I'm open on this point but will leave it as is in the absence of arguments. Eclecticology, Tuesday, July 16, 2002

The schemes vary, to be sure, but that doesn't mean that the one we choose doesn't matter! The division given on the page was from Brusca & Brusca, about a decade old but still considered a standard reference point. ITIS is quirky on several points, and if this is one of them, I say we should follow something else. To use the extreme example, there is nothing wrong with showing prejudice against their four-kingdom system.

This comes down to a question of what is an authoratative site. http://www.for.gov.bc.ca/hfd/pubs/Docs/Wp/Wp09.pdf uses it but so do several other sites that I called up on google. Tree of life, which is cladistics based and does not use ranks does show hexapoda and myriapoda to have a common source within the arthropoda, but distinct from the rest; it does not use the term Uniramia. The introduction of the super-class seems to be more linked with those sites that accept Uniramia as a subphylum. As I said before, the subphylum/supeclass approach seems like a workable solution.
The mention of Brusca & Brusca raises some interesting questions about doing science on the Internet. Brusca may very well be an important authority who presumably gives reasons for his classification in his book, but that isn't on the net. Buying a copy of his book (1997 edition) on the net would cost me US$60.00 through Barnes & Noble, and I doubt that I could find it on the shelf of a local bookstore. The public library may have it, but it could just as easily have a work on the subject by another author with a totally different point of view. I see Misplaced Pages as a project about the democratization of knowledge with open codes and data, and one where the sources of data cannot remain in protected fiefdoms. Printed sources that are not easily accessible to the bulk of our readers can have the unfortunate effect of creating knowledge elites.

Can you give something reasonably prominent (i.e. not a prof's page), other than ITIS, that ranks Myriapoda and Hexapoda as subphyla? I've seen various things on arthropods, but can't recall any instances of this, except perhaps in older schemes where the Arthropoda are split into several phyla.

I have seen, in schemes keeping the Hexapoda as a class, the Protura, Collembola, and Diplura made into subclasses. I doubt anyone would go so far as to make them classes, though, so if we want the Insecta as a class we may have to just leave them. The Endognatha used to be use a fair bit, but don't seem to be a natural group and so have lost popularity.

On this point I am quite content to leave the lower hexapods without classes, (even if parainsecta has a certain ring to it).

I'd rather have Hexapoda as a class, which is the way the taxoboxes are set up so far, than have three orders that don't belong to a class. I'm not convinced that those three orders aren't insects - I've seen collemboles, and they look insect enough to me. Why are they classified outside the insects? -phma

Well, as they're the first insects to have diverged from the others, whether they should be included or not is academic, but usually they get separated because of a few key differences. Most notable is that all three have an endognathous jaw structure, whereas true insects have an ectognaths. Also, insects have 11 abdominal segments, while proturans have 12 and springtails have 4-6, and insects have two antennae, whereas the proturans have none.

What a surprise, I'm siding with Josh on this one! I quickly looked through the insect articles, but the only one that I could find with a box set up was the fireflies; that's not a difficult change to make. Sure, Class Hexapoda appears on some old format pages but they need changing anyway. If we accept that collembola "look insect enough" we also have to accept that to some people spiders look insect enough. For a significant majority of people "insect" is a far more familiar term than "hexapod", and there are more different insects than anything else. It would be nice if these primitives had, but I can make do as long as they have order. Eclecticology

If I may, I'd like to reverse my decision on this point. Someone added information to the Collembola page about a study indicating they are not, in fact, closely related to the other Hexapoda. This is, if exciting and ipotentially mportant, still new and I don't think we should remove the Collembola just yet. However. The study porn is sexapoda are closer to the Crustacea than to the Myriapoda. This appears better established, and changes things considerably. A while ago the Uniramia were considered monophyletic and it was unclear whether or not the Myriapoda were. Since then, the monophyly of the Myriapoda became generally accepted (though it still seems mysterious to me) and now the monophyly of the Uniramia is being doubted. As such, the ITIS system of separate subphyla, though less common, is now more generally acceptable, and since I was the one who balked at it at the first place, I'm taking the liberty of restoring it. Please feel free to reverse the change if you have any objections; otherwise I'll clean up the related pages, some of which need cleaning anyways, in the next little while.

Thanks, user:Josh Grosse

-

I'm taking the main classification course on biodiversity for insects for Entomology majors at Texas A&M and the way they break it down is (for class, we probably are only covering what is important to the prof):
Subphylum Trilobitomorpha
Class Trilobita
Subphylum Chelicerata
Class Merostomata
Class Arachnida
Class Pycnogonida
Subphylum Crustacea
Class Cephalocarida
Class Branchopoda
-many more-
Subphylum Atelocerata
Class Diplopoda
Class Chilopoda
Class Symphyla
Class Pauropoda
Class Hexapoda
Just my two cents - Kugamazog

"Maxillipoda" problem

I've had a chance to look at the crustacea. Four of the five seem well behaved at this level. Only what the article previously showed as "Maxillipoda" gives any problem. ITIS has them as the table temporarily shown with 2 of the 6 as independent sub-classes, Mystocaridae as an order in Ostracoda which is itself treated as a class, Tantulocarida missing entirely, and only Copepoda remaining as a subclass of Maxillopoda. Others choose different combinations to be in or out of Maxillopda. My tendency is to treat all these "sub-classes" as direct classes, and effectively eliminating Maxilopoda since it is left with a single sub-class. I suppose that eventually somebody will come along with more certain material, or lloking more deeply will give us better insights as we move along. Eclecticology, Wednesday, July 17, 2002

Redundant "tripoblastic"?

Several biology articles contain the phrase "tripoblastic protostomes". Is my understanding correct that here the word "tripoblastic" is redundant, since it describes precisely the Bilateria, to which the protostomes belong? AxelBoldt 19:55 Dec 3, 2002 (UTC)

Entirely so. If memory serves, the phrase was there only as a way to indicate two levels of classification at once.

Where to discuss taxonomy?

Question: Where is the proper place to discuss scientic names and taxonomy on the wikipedias of animal names and such. I have more questions, but also some ideas...Please answer on my page! Dan Koehl

Pararthropoda

Someone had added to this article that the arthropods, tardigrades, and onychophorans make up the taxon Pararthropoda. This name has been applied to the group, but does not seem to be very common, and it is not used in most classification systems - including essentially all that do not recognise the Ecdysozoa. As such, I think mentioning it on that page and treating it in its own article should be more than sufficient. If we try mentioning every group that has been connected with the arthropods, any content we might try adding to the article will be swamped in terminology; we should restrict ourselves to the important ones.

Regarding

NCBI's high-level arthropod taxonomy.

Just for reference, here is how NCBI's taxonomy site deals with the arthropods. 

 PANARTHROPODA (NR)
   ARTHROPODA (P)
     CHELICERATA (SubP)
     MANDIBULATA (NR)
       MYRIAPODA (SubP)
       PANCRUSTACEA (NR)
         CRUSTACEA (SubP)
         HEXAPODA (SupC)
           DIPLURA (O)
           ELLIPLURA (NR)
           INSECTA (C)
   ONYCHOPHORA (P)
   TARDIGRADA (P)

Let's not get confused between taxonomy (the branching structure of the tree, which can hopefully be established empirically) and metataxonomy (the rankings of the nodes of the tree as phyla, classes, and so on). There is no real empirical basis for metataxonomy: it is a matter of tradition and taste. NCBI has a sane policy here: they preserve traditional taxonomic levels wherever possible. For example, when new genetic results motivate a new clade, they typically assign it "No Rank"; an example is the newish Pancrustacea group based on recent evidence that crustaceans and hexapods are allied. The metaclassification of the Crustacea as a subphylum, the hexapods as a superclass, and so on, are all fairly traditional and NCBI tends not to muck with them.

We might consider the following NPOV approach: present a consensus branching order as fact, and then have a separate section devoted to more controversial super- and sub-groupings. For example, we might say: 

 ARTHROPODA (P)
   CHELICERATA (SubP)
   MYRIAPODA (SubP)
   CRUSTACEA (SubP)
   HEXAPODA (SupC)

and then later say that some recent researchers favor grouping crustaceans and hexapods into a new group, the Pancrustacea, and so on.

Arthropod growth confusion

The current paragraph on arthropod cuticles and growth is confusing to someone who is reading this article to learn (e.g., me), as opposed to someone who already knows the subject (e.g., the editors). It makes three apparently different statements about arthropods and their cuticles:

  1. Cuticles are shed in order to grow.
  2. Hardened cuticles prevent further growth.
  3. Cuticles are digested when arthropods need to grow.

I suspect that there is truth in all of these, but there is no flow to this text that suggests what the complete truth might be. (Are these aspects of different arthropods? Are they each part of a different growth cycle in all arthropods? Are there other possibilities?) The wording suggests at least two editors for this text with entirely different writing styles that did not attempt to connect the two sections. Could someone knowledgeable about this topic fix that paragraph? Thanks. — Jeff Q 03:09, 10 Feb 2005 (UTC)


Other confusion

A minor note, but the opening paragraph states that "over eighty percent extant (living today) animal species are arthropods" and the following paragraph contradicts that with "75% of all animals on Earth are arthropods". That second paragraph could be removed altogether, however I am not sure which is correct >80% or 75%.

Taxonomy again: sources needed

The list of Crustacean classes in the taxobox is missing some groups of animals: in particular, non-cirripedian thecostracans and pentastomids. Why is this? Whose classification are we using? There's no reference in the article, and the classification doesn't follow ITIS, or SN2000, or Martin & Davis, all of which have a class Maxillopoda containing these missing groups.

The article says only:

Here we have followed a "splitting" taxonomy, containing only generally accepted groups and assigning them higher ranks

It's not a problem to have different classifications in different articles as long as we have a good justification, ideally a reference to a reasonably authoritative source. (And for the moment I'll update the taxonomy to include the missing groups). Gdr 22:02, 3 January 2006 (UTC)

Possible Classification

On most points, this agrees with what we have. Most of the stuff it adds are not common and don't add much to the article (things like "subdomain Opisthokonta") or are generally considered obsolete (things like class Trilobitoidea). The main exceptions are the use of Maxillopoda and Uniramia; as discussed above, things can go either way on these.

Whose classification is this? Gdr 10:45, 10 March 2006 (UTC)

Why is breathing by trachea difficult?

It is not clear why breathing by trachea raises a difficulty for creatures with an exoskeleton. Dan Gluck 19:48, 26 August 2006 (UTC)

Confused, legs/segment?

Quote: "The common ancestral arthropod, though, apparently happened to be one who had evolved not just chitinous mouthparts like other segmented worms, but also a chitinous structure all over its body; with all arthropods, the segments have become distinct (at least in larvae), each covered with one or more plate, and with legs, or limbs, one pair per segment."

Am I just reading it wrong if I think it sais that all arthropods are restricted to one pair of legs / segment? If not, diplopoda are defined by them having two pairs of legs on each segment excluding head, rear and the four segments following the head. Fjejsing 06:08, 18 September 2006 (UTC)

  • Rats. Just found out that diplopoda has merged two segments, hence the dual pairs of legs. Nm my previous post, sorry for the lack of research, move to delete. Fjejsing 06:15, 18 September 2006 (UTC)
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