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From: dorettas@iddic.UUCP (Doretta Schrock)
Newsgroups: net.bio
Subject: Re: Morphological Asymmetry: the octopus as a candidate
Message-ID: <2190@iddic.UUCP>
Date: Thu, 19-Sep-85 13:44:13 EDT
Article-I.D.: iddic.2190
Posted: Thu Sep 19 13:44:13 1985
Date-Received: Sat, 21-Sep-85 06:13:25 EDT
References: <295@ihnet.UUCP> <462@scirtp.UUCP>
Distribution: net
Organization: Tektronix, Beaverton OR
Lines: 39

> > 
> > 	What is the earliest animal (on the evolutionary scale)
> > that exhibits morphological asymmetry against a backdrop of
> > bilateral symmetry?
> > A friend nominated a particular crab
> > possessing one large claw, for fighting.
> 
> I may be totally off (if so, flame), but I recall that
> Paramecia are basically asymmetrical except for their
> gullet. Surely a creature such as this existed, in some
> form, before the crustacean mentioned.
> 
> -todd jones

  Todd's comment may be correct, but I thought that only *multi*-cellular
animals were described using symmetry (as otherwise you are describing
the organelles, not cellular structures).  Without consulting my
Larousse Encyclopaedia of Animal Life (this is what Noah used to make
sure he didn't forget anyone :-), I nominate the humble octopus.
Now, wait.  Believe it or not, these animals *are* bilaterally symmetrical.
What appears to be their "head" is actually a sac containing the visceral
organs; their legs are a modified molluscal foot, and their brains are
arranged in five lobes organized around the esophagus (!).  Despite these
apparent asymmetries (since the head is really the body, they don't qualify
for radial symmetry either), they are classified as being bilaterally
symmetrical, as is apparent upon internal examination.  So they do fulfill
the criteria of morphological asymmetry against a background of bilateral
symmetry.  Whether or not they are the "lowest" on the evolutionary scale
is another question.  These beasts are in many ways more evolved than we
are, though in other ways are pretty primitive.

Other nominations?


			Happy metabolizing.
				Mike Sellers

P.S. How, you may ask, do I possess such arcane knowledge of the bizarre
octopus vulgaris? Elementary.  I wrote a paper on it in college!


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