Extraterrestrial Snail

The large round shells of moon snails (Polinices lewisii) are one of the more memorable features of a walk on North Coast tidelands. Their sheer size – some reach softball proportions – is remarkable, in a region otherwise bereft of large gastropods. But the casual tourist may miss the fact that the animal itself was even two or three times larger than that.

In echo of their spacey name, moon snails are great sci-fi doomsday machines, implacably bulldozing the mud in quest of anything that can't run. Just under the surface, the animal expands to dinner plate size, squishing and undulating through the substrate, leaving just a quarter-sized bit of shell visible from above.

All shellfish it encounters are engulfed in that big gluey mantle, after which the snail's abrasive tongue rasps… rasps… rasps… until it's drilled a neat hole in the victim's shell. The attacker then pumps it full of digestive juices, which dissolve the flesh. Finally, it sucks the slurry back out and moves on, leaving behind a half-digested husk.

Thus, the presence of Polinices can be readily divined, not just by the vacated shells of past generations, but also the many clam and cockle shells littering the beach, each with a distinctive round hole near the hinge, as if pierced by a Native pump drill. Rubbery grey sand collars – its equally extraterrestrial egg cases – are another clue.

When I was a kid, oystermen and clam diggers threw moon snails up the bank to stop them damaging their beds. The law is not so dumb as to allow that now, but I used to eat this mega-escargot regularly before a decade or so, when that too became illegal. I'm not sure why; they're certainly not endangered, and the only people I ever knew who gathered them as food were me and a handful of elderly tribal members.

Any road, the only creatures that benefit materially from these Dr. Who villains today are the similarly B-movie giant black-eyed hermit crabs (Pagurus armata) that inhabit their empty shells.

Those guys are, if anything, even more memorable.