Gastropodlike U-shaped guts are known from elsehwere, like
Crinoids
Lophophorates (brachiopods, bryozoans, phoronids)
There are other examples of such kludgy designs.
Amniote early embryos have gill bars, gill pouches, and a fishlike circulation (heart - ventral aorta - gill arches - dorsal aortas). Several of these structures are then used for other purposes; the remainder is resorbed. Birds and mammals resorb one of a pair of arches, the systemic arches; birds resorb the left one and mammals the right one.
Some land vertebrates have extra digits with little or no functionality.
(per-foot, not per-animal):
* Dogs and cats have four functional digits and one dewclaw.
* Cows, pigs, etc. have two extra digits, one on each side of their two functional digits.
* Horses are sometimes born with extra digits on each side of their one functional digit.
And extinct equines form a nice intermediate state -- they grow all three digits, though in the later ones, the side digits are much smaller than the middle one.
Plants alternate between a haploid gametophyte stage and a diploid sporophyte stage. These are distinct individuals among the more primitive plants, but among seed plants, the gametophytes are microscopic and typically only a few cells. Nearly all of a seed plant is sporophyte. It is as if seed plants were trying to converge on the animal situation of only the gametes being haploid, but could not quite make it.
[This message has been edited by lpetrich, 02-27-2004]