Ostracod or Ostracode

Gigantocypris sp. the gigantic ostracod.

Unfortunately, this is not my photo. I only wish I could see one of these up close like that! This is from the blog of José Xavier, a Portuguese researcher who participated in an IPY cruise earlier this year. Some of the creatures they sampled were deep sea ostracods, along with a menagerie of other treasures, such as a trio of squid: Bathyteuthis abyssicola , Galiteuthis glacialis and Slosarczykovia circumantarctica, but back to the ostracods...

The life photo meme said, "Hard". Hmmm... so many possible interpretations, but then I remembered the ostracods. This crustacean looks like a clam or mussel externally with its bivalved carapace. The morphology of the carapace is the main characteristic that taxonomic and phylogenetic studies have been based on, and the heavily calcified valves of benthic species are well represented in the fossil record from the Ordovician period onwards. Inside that carapace is mostly head and gonads, with 6 to 7 pairs of appendages (antennules, antennae, mandibles and maxillae and 2-3 pairs of thoracic appendages). These appendage can be extended through the valve gape.

As a related side note, the ostracods have the largest sperm, both absolute size and size relative to body. In many species the males need a special organ called a "Zenker's organ" to help expel the sperm.

Ostracods are a diverse group, with 6,000 described living species making them one of the largest crustacean taxa. There are also about 10,000 fossil species described, including Colymbosathon ecplecticos, the current record holder for the oldest fossilized penis at 425 mya.

Modern ostracods are found mainly in the marine realm, but also in fresh water, salt lakes, hot springs, and more rarely, terrestrially in the damp forest soils of Australia, New Zealand, and Brazil. There are ostracods as small as 0.2mm and as large as 30mm. Most are benthic animals living on and in the sediments as adults, but a few are planktonic for all of their life. Ostracods employ most of the possible feeding strategies available: filter feeding, detritivore, herbivore, planktivore, scavenging carnivore, a few are parasitic to other crustaceans and echinoderms, and a few, such as Gigantocypris sp., are predatory carnivores.

I have some fresh water ostracods in an aquarium, which we needed to view under the microscope to identify. They were barely visible in the aquarium, about .5mm to .75mm in total size, and a pale translucent white. Somewhere I have some pictures of them, but they pale in comparison to the up to 30mm giant above, in its deep sea camouflaging orange pigment.

Part of why I thought about the ostracods is that Todd Oakly, of Evolutionary Novelties, recently began a series of posts on ostracods he calls Ostra-Blog. Giantocypris was the inaugural post. In the past he has covered evolution of the ostracod eye, which was central to his Ph.D thesis and his current work. Of the Gigantocypris sp. he says:

Perhaps the most amazing feature of Gigantocypris is their eyes. In most animals' eyes, light is bent and focused with lenses. But a select few bend light with mirrors. Gigantocypris is one of the few, bearing a huge pair of parabolic reflectors behind light sensitive patches.

Such an interesting group of crustaceans, capped off by the giant of them all complete with mirrored satellite dishes in its eyes.

Of course this still leaves open the question: Is it "ostracod" or "ostracode"?

Classification for Gigantocypris agassizii

Kingdom

Animalia

Phylum

Arthropoda

Class

Ostrocoda

Order

Myodocopida

Family

Cypridinidae

Genus

Gigantocypris

Species

Gigantocypris agassizii (G.W.Miller 1895)

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Ruppert, E.E., Fox, R.S. & Barnes, R.D. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole.: 687-690.

Chapman, A. (1960) Terrestrial Ostracods of New Zealand. Nature (1960) vol. 185 (4706) pp. 121-121 doi:10.1038/185121a0

Pinto, L.L. (2005) On new terrestrial ostracods (Crustacea, Ostracoda) from Brazil, primarily from São Paulo State. Zoological Journal of the Linnean Society vol. 145 (2) pp. 145-173 doi:10.1111/j.1096-3642.2005.00185.x