OSTRACOD RESEARCH

at the Lake Biwa Museum, Japan


Robin James Smith

Freshwater Ostracods

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<i>Candona candida</i>, female, left side view, length 1 mm. This is a common species in the cooler parts of the northern hemisphere. It was one of the earliest ostracod species to be named, in 1776.
<i>Cypretta seurati</i>, females, dorsal views, length 0.6 mm. This species is common in rice fields in Japan. The black rectangular areas are the eyes. This group of ostracods only have one eye located inside the transparent carapace.
<i>Cyprinotus uenoi</i>, side views, length male (top) 1.5 mm, female 1.9 mm. This species is abundant in the early rice-growing season in Japan. Elsewhere, it has been reported from China, the Philippines and Korea.
<i>Dolerocypris sinensis</i>, female, left side view, length 1.9 mm. This species is common in rice fields in Japan. It was first described from China, but is widespread in Eurasia. It is a fast swimmer, aided by its thin, elongate shape.
<i>Dolerocypris ikeyai</i>, female, left side view, length 1.1 mm. This species lives in the runoff of springs and seeps throughout most of Japan, and South Korea. It has lost the ability to swim, like many spring-dwelling ostracods.
<i>Scottia birigida</i>, male, left side (top) and dorsal view, length 0.65 mm. This species is found in wet leaf litter and on the soil surface around small, shallow channels. Because it doesn't live in free-standing water it is sometimes called a 'semi-terrestrial' species.
<i>Eucypris pigra</i>, female, left side (top) and dorsal view, length 1 mm. This species is usually associated with discharge of groundwaters at the surface. It is found in Europe, central Asia, Japan and Korea.
<i>Undulacandona spinula</i>, left side views male (top) and female, length 0.7 mm. It lives in the groundwater below Otsu City and was discovered in a domestic well in 2007. The groundwater ostracods of most parts of the world remain very poorly studied.
<i>Cavernocypris danielopoli</i>, female, left side view, length 0.56 mm. This species is only known from two caves in South Korea. Its triangular shape is a feature shared by other groundwater ostracods.
<i> Limnocythere cyphoma</i>, left side views, male (right) and female, length 0.4 mm. This is one of the smallest freshwater ostracods in Japan, found in Lake Biwa living in the spaces between sand grains.
<i>Heterocypris incongruens</i>, female, left side view, length 1.8 mm. This is one of the few truly cosmopolitan species of freshwater ostracods, found in most places of the world.
<i>Heterocypris incongruens</i>, female, right side view, length 1.6 mm. This is a scanning electron microscope photograph of a specimen with the right valve removed, revealing the complex body inside.
<i>Notodromas trulla</i>, left side views, length female (top) 0.8 mm, male 0.9 mm. This group is neustonic, hanging upside down from the water surface to feed. This particular species is probably endemic to Japan.
<i>Fabaeformiscandona nishinoae</i>, left side views, length male (top) 1.2 mm, female 1 mm. This species is endemic to the deep parts of Lake Biwa below 60m. The four curved stripes on the male carapace are the testes.
<i>Fabaeformiscandona okuboi</i>, left side views, male (top) and female, length 0.8 mm. This species is another example of a Lake Biwa endemic. There are 12 described <i>Fabaeformiscandona</i> in Lake Biwa, and so far nine are only known from the lake. There are also others living in the lake not yet described.
<i>Fabaeformiscandona myllaina</i>, left side views, male (top) and female, length 1.3 mm. Although found in Lake Biwa, this species is not endemic to the lake, also being found in other parts of Japan and China. In this groups the males are generally larger than the females.
<i>Heterocypris rotundata</i>, male, left side view, length 1.1 mm. The looping lines on the carapace are the testes. This group produces giant sperms.
The giant sperm of <i>Heterocypris rotundata</i> photographed with phase contrast. The average length of a sperm for this species is 1.3 mm, longer than the male (1.1 mm). In this superfamily sperm ranges from 268 microns through to 11,787 microns (= 1.17 cm) in length.
A diagram showing the structure of the posterior region of an ostracod's giant sperm. Ostracod sperm have no flagellum. The sperms consist of an extremely elongated nucleus that stretches almost the entire length, wrapped by two giant mitochondria in the posterior region.
The male sexual organ of <i>Heterocypris rotundata</i>. Ostracods have two sets of sexual organs, one each side of the body, which are used simultaneously during copulation. The shape of the male sexual organ is useful for identifying species.
<i>Darwinula stevensoni</i>, female, ventral view anterior to right, length 0.8 mm. Scanning electron microscope photograph. Many species of freshwater ostracod, like this one, reproduce without sex, with females cloning themselves via parthenogenesis. Populations are therefore entirely females.
<i>Cypris granulata</i>, female, dorsal view, length 1.3 mm.  It has a global circum-tropical distribution and in Japan it has been reported from rice fields, ponds and the shoreline of Lake Biwa.
<i>Tanycypris alfonsi</i>, female,left side view (top) and dorsal view, length 1.3 mm. This species lives in Korea and Japan, but has also be found in a greenhouse in the botanical gardens of Munich, Germany, where it is considered to be an alien species.
<i>Tanycypris centa</i>, female, left side view, length 1.1 mm. Like the previous <i>Tanycypris</i> species, this species can jump by flicking its powerful caudal ramus downwards, a bit similar to a springtail.
<i>Ilyodromus intermedius</i>, female, left side view, length 1.1mm. This species is currently only known from Japan, reported from rice fields and the southern basin of Lake Biwa.
<i>Ilyocypris japonica</i>, female, right side view. length 0.85 mm.  This species is very common in rice fields in Japan, found living in the top few mm of the muddy substrate.
<i>Physocypria biwaensis</i>, female, left side view, length 0.6 mm. This specimen is from Lake Biwa at 36 m depth; specimens from the deeper parts of the lake tend to be paler than those from shallower depths.
<i>Pseudocandona atmeta</i>, male, left side view, length 1.2 mm. This species was discovered living in a bog in the northern part of Honshu, Japan. There are still many species of freshwater ostracods yet to be discovered and described, including in Japan.
<i>Herpetocypris chevreuxi</i>, female, right side view, length 1.9 mm. As well as Japan, this species has been found in Europe, Central Asia, North and South Africa, and South America.
<i>Dolerocypris mukaishimensis</i>, male, left side view, length 0.65 mm. This is a brackish water species found in estuaries, rockpools and salt marshes along the coasts of Japan and Korea, but it can tolerate near freshwaters as well.

Lake Biwa

Video

All photography and artwork by R.J. Smith.