The Joy — and Pain — of Marine Census Taking

If you looked at the abyssal plain from afar, you might think it was one giant, boring mud flat. Ahhh, not so. The plain is alive . . . and scientists are busy sifting it to see what’s there . . .

To get to be the one to sit down in front of that microscope would be both blessing and curse. Can you imagine the excitement of looking into the eyepieces and not knowing if you’ll see something completely new to science? And getting to do this for your job? It’s like Christmas every day . . . interspersed by long periods of soul-crushing tedium as you see predominantly the same species you looked at in the last 15 samples, I’d imagine. 20 samples with 50 to 100 species each? You can do the math on that.

In spite of what they say in the film, nematodes — tiny roundworms found in great abundance in soil and water all over the planet — are actually not very closely related to earthworms (annelids), at least according to studies of their DNA and RNA. Though they’re both protostomes — a major division of the bilaterally symmetrical animals characterized by embryos in which the first dent that forms in the embryonic ball becomes a mouth — nematodes are in the ecdysozoa, or the exoskeleton-shedding invertebrates like insects and arthropods.

Annelids(including earthworms), on the other hand, are in the other great protostome division, the lophotrochozoa. This division notably include the moss-animals (remember them?) and the molluscs (snails, octopuses, squid, chitons, bivalves, etc.). Members of this group either have trochophore larvae with bands of cilia around their middles, or a lophophore, a crown of fan-shaped cilia surrounding — and provisioning — the mouth.

In any case, the take-away point here is that although nematodes and annelids are both worms — a perfectly good informal term for a long, legless creature that has only to do with the way a creature looks, not its evolution-based taxonomy — that doesn’t make them closely related. Evolution, in its directionless wandering, often fools us that way. Have a look at the tree here.