OSTRACOD RESEARCH

at the Lake Biwa Museum, Japan


Robin James Smith

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Genus Physocypria Vavra, 1897

Superfamily: Cypridoidea Baird, 1845
Family: Candonidae Kaufmann, 1900
Subfamily: Cyclocypridinae Kaufmann, 1900

Two species have been reported from Japan:

1. Physocypria nipponica Okubo, 1990


External view of a female left valve of Physocypria nipponica, length 586 microns.



External view of a female right valve of Physocypria nipponica, length 575 microns.



The male sexual organ of Physocypria nipponica, length 162 microns.

Additional figures in: Okubo 1990 (carapace, caudal ramus and male sexual organ); Okubo 2004 (carapace); Smith & Janz 2008 (carapace, male fifth limbs, and male sexual organ); Chang et al. 2012 (carapace, male fifth limbs, and male sexual organ).
Habitat: Rice fields, and shallow areas of Lake Biwa.
Mode of life: Nektobenthic.
Reproductive mode: Sexual.
Known distribution: Japan and Korea (Chang et al. 2012).

References:
Chang, C. Y., Lee, J. & Smith, R. J. 2012. Nonmarine ostracods (Crustacea) from South Korea, including a description of a new species of Tanycypris Triebel (Cyprididae, Cypricercinae). Zootaxa, 3161, 1-19.

Okubo, I. 1990. Seven new species of freshwater Ostracoda from Japan. Researches on Crustacea, 19, 1-12.

Okubo, I. 2004. Nihon tansui san kaimijinko rui ni tsuite. Kabushikigaisha Sanmon Insatsusho, Okayama, Japan, 72pp. [In Japanese, privately published].

Smith, R. J. & Janz, H. 2008. Recent species of the Family Candonidae (Ostracoda, Crustacea) from the ancient Lake Biwa, Central Japan. Journal of Natural History, 42, 2865-2922.


2. Physocypria biwaensis (Okubo, 1990)


Left side view of a female Physocypria biwaensis, length about 0.6 mm.



External view of a female left valve of Physocypria biwaensis, length 580 microns.



External view of a female right valve of Physocypria biwaensis , length 568 microns.



The male sexual organ of Physocypria biwaensis, length 134 microns.

Additional figures in: Okubo 1990 (carapace, caudal ramus and male sexual organ); Okubo 2004 (carapace); Smith & Janz 2008 (carapace and male sexual organ)
Habitat: Found at all depths of Lake Biwa.
Mode of life: Nektobenthic.
Reproductive mode: Sexual.
Known distribution: Currently only known from Lake Biwa.

References:
Okubo, I. 1990. Seven new species of freshwater Ostracoda from Japan. Researches on Crustacea, 19, 1-12.

Okubo, I. 2004. Nihon tansui san kaimijinko rui ni tsuite. Kabushikigaisha Sanmon Insatsusho, Okayama, Japan, 72pp. [In Japanese, privately published].

Smith, R. J. & Janz, H. 2008. Recent species of the Family Candonidae (Ostracoda, Crustacea) from the ancient Lake Biwa, Central Japan. Journal of Natural History, 42, 2865 - 2922.


These two species are difficult to distinguish. Differences include the following:

Key characters Phyocypria biwaensis & Phyocypria nipponica
Carapace - ventral valve overlapLeft valve overlaps right along ventral margin
Carapace - margin structure - septaNo septa present
Carapace - margin structure - ridges on inner calcified lamellaNo ridges
Carapace - dorsal view - female with brood pouchBrood pouch not visible
Carapace - lateral view - ventral marginVentral margin approximately straight to concave
Carapace - lateral view - valve heightLeft and right valves similar height
Carapace - internal viewAnterior calcified inner lamella wider than posterior one
Carapace - ornamentation - denticlesSmall denticles near ventral margin of valves
Carapace - ornamentation - sulcusNo sulcus
Carapace - ornamentation - surfaceSurface smooth
Carapace - width/length ratio (w/l)Between 0.4 and 0.7 (medium species)
Antennule - segmentsSeven moveable segments
Antennule - Rome organRome organ present
Antenna - exopoditeExopodite reduced to small segment
Antenna - swimming setaeSwimming setae very long, reaching well beyond end of claws
Fifth limb - morphologyMaxilliped; Male palps with moveable terminal hooks
Sixth limb - segmentsFive segments
Sixth limb - setae on first segmentNo setae
Sixth limb - h3 seta on final segmentH3 seta short; much shorter than half length of claw
Seventh LimbCleaning limb, with three setae at end
Seventh Limb - segmentsFour segments
Seventh Limb - first segmentThree setae
Caudal ramusElongate ramus with two claws and two setae
Caudal ramus - attachmentWith no loops