Aliens

Via NewSuperstitionist: Adult starfish are not bilateral because they don’t have a body. A starfish is just a “head walking about the seafloor on its lips”.

The larva is bilateral and looks like other simple invertebrates, a worm with head and tail. When it morphs into an adult, it stops expressing the genes for body and just expresses the head purpose.

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To the team’s surprise, the genes that determine the head end in bilaterians were expressed in a line running down the middle of each arm on the underside of the starfish. The next head-most genes were expressed on either side of this line, and so on.

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Super-weird, and an interesting case study in topology. But it does make sense.

Question: Does the default head have pentagonal symmetry? You can see a pentagon in insects. Two antennas then two eyes then mouth. Mammals, two ears then two eyes then mouth. In both, the mouth itself is bilateral, so the form is really a sort of hexagon. The generic insect has two mouth parts side by side. In mammals the upper and lower jaws are separate left and right halves in early embryo stages then partly fuse. Most mammals keep a split upper lip, and the split remains in some humans as cleft lip/cleft palate.

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Martian and Happystar wish to interrupt this program with a special message to their author.