cuttlegirl said:But they have radial symmetry instead of bilateral...I have often thought, as a mom, that a third arm would be useful.
cuttlegirl said:Great, now I am going to have to dig out my development books... I know that echinoderm larva have bilateral symmetry, but doesn't the adult stage develop inside of the larvae? Off to do some reading...
Echinoderms evolved from bilaterally symmetric creatures. Later forms were lopsided. Echinoderms' larvae are ciliated free-swimming organisms that organize in a bilaterally symmetric fashion that makes them look like embryonic chordates. Later, the left side of the body grows at the expense of the right side, which is eventually absorbed. The left side then grows in a pentaradially symmetric fashion, in which the body is arranged in five parts around a central axis.
cuttlegirl said:Some more thoughts... maybe it helps the octopus go forwards, backwards and sideways. Crabs can walk sideways (they have ten legs).