Ostracod Diner

Linda Bower has produced one of her finest water macro videos, matching action with music in a way that Beethoven would be proud of.  This one is of the larvae of a predaceous diving beetle that seems built to feed on ostracods.  For those of us unfamiliar with these species, this will take a lot of explaining.  First I am taking this directly from our 2017 blog posting about ostracods in a fountain.

Ostracods, a.k.a. seed shrimp, are tiny crustaceans that live in water.  They are an ancient species with 70,000 species identified but "only" 13,000 that have survived extinction.  They are common in fresh water, frequently in temporary pools and ponds.  Their eggs resist dehydration and can wait for months or many years before hatching with their next hydration.

Click to enlarge - Pionocypris vidua, - bumblebee.org

Their flattened bodies lie within a bivalve structure similar to a mollusc.  They swim with their legs extended but can contract them and close their "shell" to protect themselves.  They lack a distinct abdomen and circulatory system but have antennae to seek out food (diatoms, bacteria and detritus) and mandibles and maxilla to obtain it.  I will leave the anatomical details to Wikipedia.


Here are what 5th grade WOLF students would call "Fun Facts"* although some might be R-rated.

• Although fish eat ostracods, some may survive the passage through the gut.  One study showed that 26% of those eaten by a bluegill passed out the rectum alive. Who counts these things?
• Many species reproduce parthenogenetically, i.e. without male fertilization, but some species have the largest sperm in the animal kingdom, up to 3.6 times longer that the adult's body.
• Ostracods are the most abundantly preserved arthropod in the fossil record (500 million years) and boast the oldest known example of a fossilized penis, 425 million years ago.
• Some species are bioluminescent, a defense mechanism seen in this video.  During WWII, Japanese troops collected and dried specimens, then rehydrated them to provide a dim light for map reading without giving away their location.

We described predaceous diving beetles back in 2013 when we were young(er) and innocent (sorta) in this blog.  We were describing large and menacing beetles with 2" larvae that can put a major hurt on a naive naturalist's finger.  At that time I impulsively grabbed a larva and had throbbing finger and swelling to remember it by.  These in Linda's video belong to a genus of 1-3 mm beetles that probably couldn't penetrate my skin but are genuinely ferocious under Linda's microscope.

Desmopachria beetle larva

It is hard remember that these larvae, resembling alligators are actually tiny.  In the video you will see them grabbing the ostracods and opening the bivalve "shell" like an oyster.   Once open they pull out the "meat" with the panache of a seafood gourmet at an oyster festival.  I almost expected to see it wipe its mandibles with a bib napkin.  The Desmopachria larva looks like it was designed to prey on ostracods.

 Desmopachria dispersa - Mike Quinn CC

Linda has identified these tiny beetle larvae as being in the genus Desmopachria.*  There are way over 100 species in this genus with more identified each year.  They can be collected by their attraction to black lights and mercury vapor lamps.  Only the adult beetles can be identified by species, the larvae are all just Desmopachria sp.


Her video features guest appearances by flatworms (they look blue under the LED lights) and a Nematode in the last clip.  For the big show you are now ready to see Desmopachria and the Ostracods!
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Much more on fascinating ostracods 30 Interesting Ostracod Facts.
 * For more details on Desmopachria, download Water Beetles of Florida  5.53 This is a large comprehensive PDF.  For the Desmopachria basics, see this page 5.53.
Photographs are taken from Linda Bower's video.