Ostracods in a Fountain

Ostracod grazing on filamentous green algae - Micrographia.com

You, like me,  probably haven't spent much time thinking about ostracods.  Larry Wegmann introduced me to some he found in the top dish of a little yard fountain.  They are seen browsing around the resident algae in his video.  As the fountain runs on processed city water, the question is how they got there.  They are known to occur in almost any kind of water including small pools of water in bromeliads growing on trees, so Larry's finding is not surprising.  How they got there remains a question.  The eggs are tiny so they could stick to a birds feet are even be blown in the wind.

Empty shell - Micrographia.com

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 detritis) 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.

Linda Bower has a fantastic video of ostracods feeding on Youtube.  A second video shows Fragile Forktail Damselfly larvae feeding on ostracods starting at 1:47.  Its a tough world out there!

*  Amazing Facts about Ostracods.