at the Lake Biwa Museum, Japan
Robin James Smith
2. Some marine species produce a bright, blue light (bioluminescence). More....
3. With a fossil record stretching back almost 500 million years, ostracods are the most abundantly preserved arthropod in the fossil record. More....
4. The oldest known fossil penis belongs to an ostracod 425 million years old. More....
5. Many species reproduce without sex by cloning themselves. More....
6. Some species live on the gills of other crustaceans, such as crayfish. More....
7. Their eggs can survive complete drying and be viable many years later. More....
8. The wind, birds and toads all help ostracods get around. More....
9. They can survive being eaten by fish. More....
10. Some species can survive out of water by taking a small supply of water with them in their shells. More....
11. By attacking in groups, ostracods can prey on animals much larger than themselves. More....
Giant sperms of Australocypris robusta. |
The male stores the sperms by coiling them into a ring.
1. Ostracod sperms of the group Cypridoidea are massive, at least one-third the length of the corresponding males, and often much longer. The longest belongs to the Australian species Australocypris robusta, reaching 11.7 mm in length, 3.6 times the length of the male.
Some insects have longer sperms, notably the fruit fly Drosophila bifurca, the sperms of which can reach 58 mm in length. But ostracod sperms are much thicker, so the corresponding volumes are much greater; the volume of a single sperm of the ostracod Australocypris robusta is nearly six times greater than that of the fruit fly Drosophila bifurca. Additionally, while the sperms of Drosophila bifurca consists almost entirely of very long flagella, ostracod sperms have no flagella at all. Each sperm consists of an extremely stretched out nucleus, wrapped for a lot of its length by two giant mitochondria.
|Ostracods mating (male on left)|
Matzke-Karasz, R. 2005. Giant spermatozoon coiled in small egg: fertilization mechanisms and their implications for evolutionary studies on Ostracoda (Crustacea). Journal of Experimental Zoology, 304B, 129 - 149.
Smith, R. J., Matzke-Karasz, R. & Kamiya, T. 2016. Sperm length variations in five species of cypridoidean non-marine ostracods (Crustacea). Cell and Tissue Research, 366, 483-497. DOI 10.1007/s00441-016-2459-x.
|A female Vargula, length about 2.4 mm||Bioluminescent Vargula in a small petri dish|
Cohen, A. C. and J. Morin 2003. Sexual morphology, reproduction and bioluminescence in Ostracoda. In: L. E. Park and A.J. Smith (eds.) Bridging the Gap: Trends in the Ostracode Biological and Geological Sciences. The Paleontological Society Papers 9:37-70. New Haven: Yale University Press.
Morin, J. G. and Cohen, A. C. 1991. Bioluminescent displays, courtship, and reproduction in ostracodes. In R. Bauer and Martin, J. (Eds.), Crustacean Sexual Biology:1 16. New York:Columbia University Press.
Whatley, R. C., Siveter, D. J. and Boomer, I. D. 1993. Arthropoda (Crustacea: Ostracoda). 343-356. In Benton, M. J. (ed.) The Fossil Record 2. Chapman and Hall, London, 827pp.
Siveter, D. J., Sutton, M. D., Briggs, D. E. G. & Siveter, D. J. 2003. An ostracod crustacean with soft parts from the Lower Silurian. Science, 302, 1749 - 1751.
|A ventral view of Darwinula stevensoni, an 'ancient asexual'|
There are some short term advantages to asexual reproduction, for example, no time or energy is wasted producing males or searching for a mate and only one individual is needed to start a new population, so such species can spread quicker than their sexual counterparts. However, in the long term reproduction without sex can cause genetic mutations to build up and asexual populations are condemned to extinction.
There is one puzzling exception to this, a family of freshwater ostracods called the Darwinulidae. Fossil evidence has shown that there has been no males in this group for millions of years, maybe as long as 200 million years. Today the Darwinulidae are still thriving all over the world and new species are still being discovered, but all are asexual populations consisting of only females. Such groups are called 'ancient asexuals' and some recent research has been trying to unravel the mysteries to their survival and evolution.
UPDATE: Live male Darwinulidae have been found! On the mountainous island of Yakushima in southern Japan, we found three Darwinulidae males amongst over 400 females. The males are smaller than the females, and a similar size to juvenile females, making them difficult to spot. Are all Darwinulidae species really 'ancient asexuals' or have rare diminutive males just been missed in other species and the fossil record? Further research will tell.
Martens, K. (ed.). 1998. Sex & parthenogenesis. Backhuys Publishers, Leiden, 335 pp.
Martens, K., Rossetti, G. & Horne, D. J. 2003. How ancient are ancient asexuals? Proceedings of the Royal Society, B, 270, 723 - 729.
Smith, R. J., Kamiya, T. & Horne, D. J. 2006. Living males of the 'ancient' asexual Darwinulidae (Ostracoda, Crustacea). Proceedings of the Royal Society, B, 273, 1569 - 1578.
|A mating couple of entocytherid ostracods, male on top.|
6. Consisting of about 220 species, the family Entocytheridea is a diverse group which lives on other crustaceans. With their tiny size and narrow shells, they are ideally suited to living in the tiny spaces on the gills and thoraxes of crayfish, amphipods and crabs. They have specially adapted thoracic limbs and antennae to grab hold of their hosts. Although the exact relationship between the entocytherids and their hosts is not clear, it is thought that in return for a safe place to live, the ostracods help to keep the bodies of their hosts clean.
Hart, D. G. & C. W. Hart, Jr, 1974. The ostracod family Entocytheridae. Natul. Nat. Acad. Nat. Sci. Philadelphia, Monograph 18: 1- 239.
|Eggs of Heterocypris rotundata stuck to algae. Size of eggs = 0.13 mm.|
7. Many freshwater ostracods can be found in temporary water bodies, such as puddles and rice fields. The secret to their survival in such temporary habitats is because their eggs can be viable many years after being dried. When water is available the eggs start to develop and hatch.
Georg Ossian Sars (1837 - 1927), a famous Norwegian crustacean worker, used this ability to study ostracods from the other side of the globe. People in South Africa and Australia sent him dried sediment that they had collected from dried up ponds or rivers. By adding water to the dried sediment and waiting for a few weeks, Sars raised ostracods, many of them new species that he later named and described.
Sars, G. O. 1895. On some South-African Entomostraca raised from dried mud. Skrifter i Videnskabs-selskabet. I. Mathematisk-Naturvidenskabs Klasse 1895 (8): 1-56.
Sars, G. O. 1896. On some west Australian Entomostraca raised from dried sand. Arch. Math. Naturv. 18, 1-35.
|"All aboard the tern. Next stop Scotland!" An arctic tern. (Image from Wikimedia Commons.)|
Horne, D. J. & Smith, R. J. 2004. First British record of Potamocypris humilis (Sars, 1924), a freshwater ostracod with a disjunct distribution in northern Europe and southern Africa. Bollettino della Societe Paleontologica Italiana, 43 (1-2), 297-306.
Laessle, A. M. 1961. A micro-limnological study of Jamaican Bromeliads. Ecology, 42, 499-517.
Seidel, B. 1989. Phoresis of Cyclocypris ovum (Jurine) (Ostracoda, Podocopida, Cyprididae) on Bombina variegata (L.) (Anura, Amphibia) and Triruris vulgaris (L.) (Urodela, Amphibia). Crustaceana 57, 171-176.
|"Whoa! That was a journey I don't want to repeat!" Cypridopsis vidua|
9. Fish eat ostracods, sometimes in great numbers. However, the fish don't get it all their own way. Experiments with the ostracod Cypridopsis vidua showed that 26% of specimens eaten by small bluegill sunfish came out the other end alive and unharmed. By tightly closing their shells and waiting they survived passage through the gut of the fish.
Vinyard, G. 1979. An ostracod (Cypridopsis vidua) can reduce predation from fish by resisting digestion. American Midland Naturalist, 102, 108 - 190.
|Terrestricythere elisabethae walking towards you.|
10. All ostracods respire by extracting oxygen from water, but this hasn't stopped one group from venturing out onto dry land. The Terrestricytheroidea can walk over a dry surface by taking a small supply of water with them, in and around their shells. Special hairs on the shells help to retain the water and drag it along with them. However, if the ostracods are unable to replenish this water before it evaporates they perish.
Horne, D. J., Smith, R. J., Whittaker, J. E. & Murray, J. W. 2004. The first British record and a new species of the superfamily Terrestricytheroidea (Crustacea, Ostracoda): morphology, ontogeny, lifestyle and phylogeny. Zoological Journal of the Linnean Society, 142, 253 - 288.
There is even a report of myodocopid ostracods attacking a diver; during a night dive in Panama, the diver's ears, hair and beard were covered with ostracods, forcing him out of the water.
Cohen, A. C. 1983. Rearing and postembryonic development of the myodocopid ostracode Skogsbergia lerneri from coral reefs of Belize and the Bahamas. Journal of Crustacean Biology, 3, 235 - 256.Back