Sunday, January 16, 2011

A confusion of pointy bits

"All decapods have ten legs..." (Wikipedia) Sounds so simple. And when the decapod in question is a crab, it is: five legs on either side, and a bunch of appendages around the face for eating, seeing, and smelling.

When it's a shrimp, however, things get confusing. The "walking legs" include the chelipeds, or pincers (two sets), which are right next to the maxillipeds, which Wikipedia counts among the five, but which would make up six on the shrimp. They also count as mouthparts. Then there are the 5 pairs of swimmerets; in diagrams, they look like legs. Luckily, in real life they're small, and mostly hidden under the tail segments.

I've been trying to count the legs on the largest of my shrimp, now that he's got a bit of colour. It's difficult. Maybe if he would just stop moving for a moment ...

Counting from the rear; 1 2 3 4 ... Aaargh!

Some things are easy; he has two sets of antennae, one long and one short. The long ones are very fine, transparent, always flicking about, and maybe twice his length. Can you see them here?

Photo cropped at tips of antennae.

5 legs countable. And with the chin up, separated from all those sharps on the head.

Let's name them.

Diagram from Louisiana Fisheries

So we've got 5 walking legs, the front two of which are also chelipeds, because they have pincers on the tips. Small ones, only visible in a few photos. If you look closely at the centre of the first clump of feet on the photo above, you can see one in the background.

Then there are the maxillipeds, which would correspond to our jaws (Maxilla): they would be the two straight blades sticking forward at the mouth.

Along the top, toothed like a saw blade, sharp as a spear, is the rostrum.  On either side of it are the two stalked eyes (another set of appendages), and the shorter antennae. (So far, so good.)

But then, what are the two flags he waves above his head? And what do they do?

Top view. Look at it full size (left click - open new tab) to see the various tools he's carrying.

The little shrimp, half the black one's size, are just beginning to show their stripes, and pick up a bit of colour. They wave tiny flags, too.

1/2 inch long shrimp. His innards are easier to see than his head accroutements.


  1. It's like a little, living swiss army knife. Thanks!

  2. Anonymous7:12 pm

    I really like the pictures taken with your new camera. I've got a Sony as well, different model. Your pictures have always been fantastic, but now they're unbelievably good.
    Can you attach lenses to that one? If so, imagine what adding a macro conversion lens would produce with that one.

  3. wow, that's a lot of parts :O)

  4. I've seen a lot of shrimp, but never looked at one this closely. Thanks for the education.

  5. Anonymous,
    The camera isn't made for additional lenses. But long ago, with my first digital, I made myself a DIY macro lens with pirated lenses from binoculars and an old projector. It didn't work with the next cameras I got (Canon and Olympus) but on this one, it does. It adds a bit of magnification, not a lot, but every bit helps.

    I'm going to try out a couple of other combinations; I still have the makings.


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