They drift. They hang in the water, not moving, holding onto a blade of seaweed. They let go, and drift slowly in the current. Sideways, upwards, backwards, forward; it makes no difference to them which way they're facing.
Then, suddenly, they discover modern physics and execute a quantum leap. You were looking straight at one, and then, without any intervening movement, it was 'way over on the far side of the tank or tidepool. You never saw it go; it was just gone.
It doesn't help that as often as not, it was transparent, or nearly so, to begin with.
Four shrimp came home with me last week. Three are tiny, 1/4 to 1/2 inch long, and transparent, except for the eyes. If the light is right, they're like shards of greenish glass.
The larger one is visible, mostly because she's been eating well. And because she's carrying a load of eggs. At least they're a decent colour.
|Sitka shrimp, 1 inch long, with babies. Colour saturated and darkened.|
The green and brown solid mass in her cephalothorax and along her spine is mostly her digestive system. When food is scarce, it shrinks. When the food is digested, it moves along the spine and out the anus, visible all the way.
The eggs are held under her abdomen with her pleopods (aka swimming legs); she is constantly tending them with her walking legs.
Click on the photo to see it full size; now you can see the pattern of red and blue dots on her carapace, and the long, sawtoothed blade (the rostrum) stretching out from the top of her head.
|Top view, in a white tray, with no place for her to go. The eggs are visible through the whole thickness of her body. (Saturated and darkened again.)|