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Does a phylum have anything to do with size?; If so, then Arthropods...
Topic Started: Jun 15 2017, 11:26 AM (633 Views)
Inceptis
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I saw a definition for phylum the other day:

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The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group.

What counts as more closely related? And as a phylum grows in size and more data becomes available, should it be split at a certain point if it gets exceptionally large and relations grow farther apart?

The most relevance this question has is in the matter of arthropoda. If yes, then Hexapoda alone might be too large to count as a phylum, let alone a subphylum.
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Tartarus
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As Linnaean taxonomic ranks are somewhat arbitrary it is tricky to say with any certainty at just what point a clade gets the phylum rank.
As for how big a phylum is though I don't think that should matter too much. I for one have no problem with phyla ranging from having as few as one member species (e.g. Placozoa) to as many as millions of member species (e.g. Arthropoda).
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Inceptis
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Darn. Now that I think about it, we're in the same phylum as lancelets, and those are pretty far relatives. Meanwhile, a child could make the connection between a spider and an ant, even though they're as different as mouse and fish. I guess I'm just jealous of Arthropoda's quantity.
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IIGSY
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This is just my two cents, but I think tunicates and lancelets should be seperate phyla.
Projects
Punga: A terraformed world with no vertebrates
Last one crawling: The last arthropod

ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess)

Potential ideas-
Swamp world: A world covered in lakes, with the largest being caspian sized.
Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

Quotes


Phylogeny of the arthropods and some related groups


In honor of the greatest clade of all time


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Inceptis
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Well, so far, the definition of Chordata is more or less that the organism has a notochord at some point in it's development, which is true for lancelets and tunicates.
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IIGSY
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Inceptis
Jun 23 2017, 10:09 PM
Well, so far, the definition of Chordata is more or less that the organism has a notochord at some point in it's development, which is true for lancelets and tunicates.
Yeah, but tunicates and lancelets differ from vertebrates in fundamental ways. It would be like putting tardigrades and onychophores in the same phylum as arthropods.
Projects
Punga: A terraformed world with no vertebrates
Last one crawling: The last arthropod

ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess)

Potential ideas-
Swamp world: A world covered in lakes, with the largest being caspian sized.
Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

Quotes


Phylogeny of the arthropods and some related groups


In honor of the greatest clade of all time


More pictures


Other cool things


All African countries can fit into Brazil
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Inceptis
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I'm not sure it's that severe. Besides, tunicates are sessile filter feeders distantly related to Tetrapods. Barnacles are sessile filter feeders distantly related to spiders. To each their own, I guess.
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IIGSY
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Inceptis
Jun 24 2017, 05:09 PM
I'm not sure it's that severe. Besides, tunicates are sessile filter feeders distantly related to Tetrapods. Barnacles are sessile filter feeders distantly related to spiders. To each their own, I guess.
It is. A tunicate is a distant to a tetrapod as a velvet worm is too a spider.
Projects
Punga: A terraformed world with no vertebrates
Last one crawling: The last arthropod

ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess)

Potential ideas-
Swamp world: A world covered in lakes, with the largest being caspian sized.
Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

Quotes


Phylogeny of the arthropods and some related groups


In honor of the greatest clade of all time


More pictures


Other cool things


All African countries can fit into Brazil
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Tartarus
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Insect Illuminati Get Shrekt
Jun 24 2017, 06:42 PM
A tunicate is a distant to a tetrapod as a velvet worm is too a spider.
What are you basing this on?
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Datura
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Tartarus
Jun 24 2017, 06:59 PM
Insect Illuminati Get Shrekt
Jun 24 2017, 06:42 PM
A tunicate is a distant to a tetrapod as a velvet worm is too a spider.
What are you basing this on?
It's IIGS. He's probably not basing it on anything. He's a bug fetishist.
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LittleLazyLass
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No need to be rude, Datura.

Both divergences go back to the early Cambrian, so he's probably not to far off.
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Inceptis
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In my opinion, it seems to make more sense to define the hierarchy of clades based on when they diverged in evolutionary time, at least in some cases. However, this causes some obvious issues, especially with the phylums that have no history until well after the Cambrian.
This was getting fairly big.
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IIGSY
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A huntsman spider that wastes time on the internet because it has nothing better to do
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Datura
Jun 24 2017, 07:22 PM
Tartarus
Jun 24 2017, 06:59 PM
Insect Illuminati Get Shrekt
Jun 24 2017, 06:42 PM
A tunicate is a distant to a tetrapod as a velvet worm is too a spider.
What are you basing this on?
It's IIGS. He's probably not basing it on anything. He's a bug fetishist.
Dude. Stop that. I mean it.

Anyway, my claim isn't entirely baseless. Look at like this.

Tunicates and lancelets are related to vertebrates, as they have a notochord, but they lack a cartilage/bone endoskeleton

Velvet worms and tardigrades are related to arthropods as they have paired legs with claws, but they lack a sclerotized exoskeleton.

Plus, both vertebrates and arthropods diverged from tunicates/velvet worms in the early cambrian, possibly in the late neoproterozoic.
Projects
Punga: A terraformed world with no vertebrates
Last one crawling: The last arthropod

ARTH-6810: A world without vertebrates (It's ded, but you can still read I guess)

Potential ideas-
Swamp world: A world covered in lakes, with the largest being caspian sized.
Nematozoic: After a mass extinction of ultimate proportions, a single species of nematode is the only surviving animal.
Tri-devonian: A devonian like ecosystem with holocene species on three different continents.

Quotes


Phylogeny of the arthropods and some related groups


In honor of the greatest clade of all time


More pictures


Other cool things


All African countries can fit into Brazil
Offline Profile Quote Post Goto Top
 
Tartarus
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Prime Specimen
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Inceptis
Jun 24 2017, 11:04 PM
In my opinion, it seems to make more sense to define the hierarchy of clades based on when they diverged in evolutionary time, at least in some cases. However, this causes some obvious issues, especially with the phylums that have no history until well after the Cambrian.
The problem here is that divergence times will vary depending on which groups we're talking about and how much a group diversifies varies immensely, with some remaining fairly conservative and close to an ancestral form and others branching into numerous hugely different descendant lineages. So having a phylum as all creatures from after a certain divergence point in the distant past probably wouldn't work all that well.
In any case, as I said before, "phylum" is a somewhat arbitrary term anyway so it shouldn't be too huge of a deal which groups we consider phyla.
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