dorettas@iddic.UUCP (Doretta Schrock) (09/19/85)
> > > > 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!
peter@graffiti.UUCP (Peter da Silva) (09/22/85)
OK. You've shown it's bilaterally symmetrical. Now how is it morphologically assymetrical? Nothing you described tells me that. See: __ / \ ( ) O O /||\ _/||||\_ //||\\ / \ Even the 5 brains can be arranged symmetrically: 1 2 3 4 5
buchbind@agrigene.UUCP (09/24/85)
> OK. You've shown it's bilaterally symmetrical. Now how is it morphologically > assymetrical? Nothing you described tells me that. > > > See: > __ > / \ > ( ) > O O > /||\ > _/||||\_ > //||\\ > / \ > > Even the 5 brains can be arranged symmetrically: > > > 1 > 2 3 > 4 5 One of the back two arms in the male is specialized for a sexual function (transport of sperm). I don't know about the female. (Are there seperate genders?) In any case, that makes the octopus asymmetical. -- Barry Buchbinder (608)221-5000 Agrigenetics Corp.; 5649 E. Buckeye Rd.; Madison WI 53716 USA {seismo!uwvax!|decvax|ihnp4}!nicmad!agrigene!buchbind