Water Fleas

Great fleas have little fleas upon their backs to bite 'em,
And little fleas have lesser fleas, and so ad infinitum. 
                              -Nursery rhyme 

The WOLF school has been exploring life in a few drops of pond water.  While trying to photograph some tiny pond pygmy backswimmers flitting around in a single drop, I came across these indistinct creatures.  I could tell they were alive by the motion in their body in the video, but I could not make out any distinct features with my crude equipment.  I sent the video to Dr. David Bowles who identified them as water fleas of the Cladocera order of crustaceans.

Dorsal view - Click to enlarge

There is nothing to see at first glance to suggest that this is related to the noble order that includes lobsters, shrimp and crayfish.  There are over 600 species plus many more that haven't been identified for reasons I can understand, looking at our specimen.  The first evidence of life I saw was when it defecated in this video.  Be watching carefully at the 20 second mark.

It has a translucent carapace covering all but the small head, showing all the internal organs.  The green dots are eggs, something it produces usually on its own (parthenogenesis) except when under harsh conditions when it reverts to sexual reproduction as described in the Kansas Naturalist.  I can make out its single compound eye, mounted above the beak-like rostrum like a early prototype of a Cyclops.

From the Kansas Naturalist

Aside from its monocular vision, water fleas have several other interesting features.  It has two pair of antennae, the first having tiny olfactory hairs.  The second pair are well muscled and are used for swimming, its sole method of propulsion.  Its legs are covered with fine hairs which strain food particles such as phytoplankton, bacteria and organic detritus. 

As a herbivore, water fleas are at the very base of the food chain, the first consumers as well as some of the smallest prey of the tiny pygmy back swimmers we have been studying.  ..... and so ad infinitum.