Post by Carl Fink Post by James Nicoll
The Arm of the Starfish (Poly O'Keefe, book 1) by Madeleine L'Engle
I also found this in the library as a young teen. And I couldn't get through it.
Bounced right off--it was surprisingly boring.
Yeah, echinoderms are as closely related to us (to the extent that's meaningful)
as a squid is to a tubeworm.
In context, it goes deeper than that.
If you've already seen my rant on protostomes vs. deuterostomes
Doctir Who, and the Urbilatarian, hit 'n' now.
Every multicellular animal begins as a single cell, a fertilized
ovum. That cell divides again and again, till it becomes a lump
of many cells. It then hollows out into an empty sphere whose
wall is one cell thick.
Then the cells on one spot of its surface start dividing faster
than the rest of it, and those cells don't turn into an
additional lump, but grow inward till the embryo resembles a cup,
with a wall two cells thick. If the animal is going to grow
into a sponge, it takes it from there; more complex animals grow
a third cell layer between the first two, and the three layers
develop into different tissues, but I won't go into that here.
Here's the very young animal, with an opening into its interior
(technically called a _stoma_, Greek for "mouth"). The animal is
now going to develop another opening at its opposite end, so it
can have a gut that takes in food at one end and gets rid of
waste at the other.
Most phyla of animals, called protostomes ("mouth first"), turn the
first opening into the mouth and the second opening into the anus.
Another group, called deuterostomes "mouth second") do the other
The deuterostomes consist of the chordates and the echinoderms.
All the others, from worms to arthropods, are protostomes.
So, in the context of all those phyla of protostomes, starfish
really *are* closely related to humans.
Which is why I mutter imprecations at the computer whenever I
watch one of my favorite episodes of Doctor Who, "The Lazarus
Experiment." In which a mad scientist messes with his own DNA to
become younger, and instead turns into a ravenous monster, half
human, half scorpion. "He's regressed to some primitive
ancestor," says the Doctor.
"No!" I say each time, "humans are deuterostomes, scorpions are
protostomes; he would have to regress to the Urbilatarian, the
ancestor of both protostomes and deuterostomes, whose existence
we assume but we've never found any fossil evidence for it."
And then I say to myself, "This isn't science. This is Doctor
Dorothy J. Heydt
djheydt at gmail dot com