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Freshwater Ostracod

Freshwater Ostracod
Portland/ Crystal Springs Rhododendron Gardens, Multnomah County, Oregon, USA
November 28, 2014
Size: About .8 mm
As far as I can figure out, this fellow belongs in the sub-class Podocopa, the order Podocopida, the sub-order Cypridocopina, the super-family Cypridoidea, and a few things below that that I'm having difficulty figuring out. Podocopa contains the only freshwater ostracods, as does Podocopida. I really don't think that this belongs in the sub-order Darwinulocopina (there's only one species option in the United States, but it's much more rectangular and lacks the striping and coloration of this ostracod), and my only other freshwater option is Cypridocopina. Cypridoidea is the only freshwater option in Cypridocopina, which makes me really appreciate how many marine ostracods there are. After that it gets tricky, and I would want to dissect a specimen before going further.

It really looks like one of the most common species of ostracoda on the planet, Cypridopsis vidua, but I don't feel safe calling it that yet. One clue was that it crawled along the bottom like a burrower, which I think is something Cypridopsis vidua does. I know that one species, Potamocypris pallida, looks a lot like Cypridopsis vidua, but it seems to lack the two yellow spots on either side of the eye (the small rectangular black spot near the front).

What source would you use for information about North American ostracods?

North American Ostracod Literature
As far as I know, there hasn't been a comprehensive recent North American ostracod identification book published. The book Fresh-water Biology by Ward and Whipple (1957 second edition) has a chapter written by Willis L. Tressler (with identification keys) for North American ostracods. Fresh-water Biology is a book full of identification keys for everything you could possible find under a microscope in fresh water in North America. Even though some of the groups are outdated, I highly recommend it. The first edition (1918) also has an ostracod section (it's completely different from Tressler's) that is really more interesting historically than useful taxonomically. Both books are available online.

A more recent (c. 1970) and heavily illustrated (black and white) resource for Canadian ostracods is L. D. Delorme's Freshwater Ostracodes of Canada Parts 1-5. These articles have full species descriptions for each species, and include photographs of dissected appendages and shell shapes. They were published in the Canadian Journal of Zoology, and they are available (for a price) on the Journal's website: I was able to get the articles through an Interlibrary loan at my local library.

If you like spending money, then I would recommend Freshwater Ostracods of the World by Ivana Karanovic. This was published in 2012, has keys for all species of freshwater ostracods on the planet, and has nearly 90 pages of information about their biology. For a definite identification, dissection is generally required (if you want to try dissection, I would recommend a #11 surgical blade with a #3 handle for .5mm cutting, and this pdf: I think this book is worth the $175 price, and the 90 page biology section at the beginning will improve the value of Delorme's articles and Tressler's chapter.

Karanovic also wrote a comprehensive book in 2006 about the subfamily Candoninae in North America. It's called: Recent Candoninae (Crustacea, Ostracoda) of North America. I wish you luck finding a copy for purchase; I got to read a copy through Interlibrary Loan. There is also a set of keys in this book: How to Know the Freshwater Crustacea. They aren't as detailed, but they are definitely worth using. As a side note, the 'How to Know' or 'Pictured Key Nature Series' is a fantastic series that covers many of the groups of creatures nobody else covers (like protozoa, tapeworms, true slime molds, mites and ticks, eastern land snails, etc.) and the series: 'Synopsis of the British Fauna' is more recent, has even better creature id coverage, and has three books dedicated to British ostracods, many of which occur in North America.

And lastly, two websites; NANODe ( and Ostracode Diversity ( NANODe has black-and-white pictures of shells of many North American Ostracods, and Ostracode Diversity has color pictures of many "live" North American ostracods. There are many other books/articles/chapters that are older or cover smaller ostracod groups, but these are the main ones.

Have fun looking through these!

Thank you so much!
I started looking at these as soon as I saw your comment; they are quite helpful! I've done my best with the web sources, and requested Fresh-water Biology from a local library--libraries seem to be the best option.

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