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Home Q & A Board Biology-Related Homework Help Genetics and Developmental Biology
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lglick01 lglick01
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12 years ago
animal Y has 3 germ layers, bilateral symmetry, and no coelom. animal Y is an..

a) sponge
b)arthropod
c)flatworm
d)mollusk

and why?  


thank you so much!
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Replies
wrote...
#1
12 years ago
Me personally, I'd list the choices in order of novel evolutionary traits... starting with the least complex to the most complex.  That could help you.
Sponge -> Flatworm -> Mollusk -> Arthropod

Let's go through each requirements... 3 germ layers?
Sponges, in the phylum Porifera, are parazoans, meaning they have NO tissue layers.  Arthropods, Flatworms, and Mollusks all have 3 germ layers.  This eliminates choice A.

Bilateral symmetry?
The only choice without bilateral symmetry is Sponge, and we've already eliminated that.  Arthropods, Flatworms, and Mollusks all have bilateral symmetry.

No coelom?
Flatworms, of the phylum Platyhelminthes, do NOT have a coelom.  Arthropods and Mollusks do.  This eliminates choice C.

And... that's it.  Either the question didn't give enough information, you typed it incorrectly, or... something.  It's probably a 50/50 chance, but I'd personally choose B, Arthropod because the questions says "animal Y is !!an!!...""Animal Y is an arthropod" would makes sense but "Animal Y is an mollusk" wouldn't make sense; "Animal Y is a mollusk" would... but really, at this point, I have no idea.

But hopefully I helped you on how to eliminate choices on this kinds of questions?
wrote...
#2
12 years ago
Good answer above, I agree completely and I think arthropod is the answer too because not all mollusks have bilateral symmetry -some gastropods (snails) have twisted their bodies around in a process called TORSION and have lost that bilateralism!!
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bio_manbio_man
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7 years ago
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