Monday, June 8, 2015

Nature Study at the Beach :: Crabs!

Like I said last week, this particular beach is one of the most touristy beaches we frequent, but we always seem to find the strangest things there anyway.

Case in point: this frisbee-sized chiton my daughter pulled out of the wrack on a prior visit.

This time we had a similar experience--but more on that in a minute.

Since it was ultra-low tide when we went, we had the opportunity to watch lots and lots of shore crabs wriggling among the rocks, in and out of the mussels and barnacles.

see that little guy at the bottom?  they sure are good at blending in!

We brought home two perfectly-in-tact crab shells, one dead and one exoskeleton, for further study.  (The one on the left is about four inches across, the exoskeleton on the right about an an inch and a half.)  

They had just washed on shore and were still waterlogged, legs dangling loose and flexible from their bodies.  In a couple days, they had stiffened up and, in the case of the tiny one, the top piece of its body had delicately detached on its own, exposing the dried-out inner membranes.

I wasn't sure how much longer the big guy was going to last without smelling up the place (the crab shells we usually find are smelly, and considering how fleshy this one still was, I thought it would be even worse), so I took the opportunity to draw it as soon as I could:

...and painted
The kids included it in their journals as well.  I love this version by my 5yo son:

But the most exciting find of the day was something we did not bring home.

Gianna pulled this cracked shell out of the water, about twelve inches long, blue-tinged and bumpy.

Based on its size and on the fleshy bits, I decided it was best to leave him at the beach for another family to find and observe, but I took lots of photos so that we could identify it at home because I hadn't a clue what it was.  Definitely some kind of crustacean, likely a crab, but the shell was vertically-ordered rather than horizontally.  I pulled out the field guides we had along but drew a blank.

When we got home, I started googling.  I think my magic combination was "pacific large shell bumpy blue crab."  Turns out it's a sheepcrab, also called a spider crab.  Based on the photos I saw, the latter name seems most fitting, and I was pretty glad the whole thing hadn't washed ashore, legs and all.

Because, I mean, is it just me, or does this thing not look pretty darn creepy?

photo NOT BY ME -- I would never get close enough to take a picture like that!  (more here)

And as you might guess, that guy was the very first discovery from the trip that my oldest son put in his nature journal!  Nature study: a little something for everybody. ;)

ETA: Dawn at Mud to Meteors keyed me in to some fascinating information about exoskeletons, including this time-lapse video of a spider crab molting.  Amazing!