at the Lake Biwa Museum, Japan

Robin James Smith

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Genus Metacypris Brady & Robertson, 1870

Superfamily: Cytheroidea Baird, 1850
Family: Limnocytheridae Klie, 1938
Subfamily: Timiriaseviinae Mandelstam, 1960

One species has been reported from Japan:

1. Metacypris digitiformis Smith & Hiruta, 2004

Dorsal view of a female Metacypris digitiformis, anterior to the bottom, length about 0.5 mm. Two large brood pouches, one in the posterior part of each valve, gives the female of this species a very distinctive heart shape in dorsal view.

External view of a female left valve of Metacypris digitiformis, length 491 microns.

External view of a female right valve of Metacypris digitiformis, length 481 microns.

Additional figures in: Smith & Hiruta 2004 (carapace and appendages); Smith & Janz 2009 (carapace); Sidorov & Semenchenko 2012 (carapace).
Habitat: Littoral zones of a lake (Smith & Janz 2009); marshes (Smith & Hiruta 2004; Hiruta & Mawatari 2013); swampy ox-bow lake (Sidorov & Semenchenko 2012).
Mode of life: Benthic.
Reproductive mode: Sexual.
Known distribution: Shiga Prefecture (Smith & Janz 2009); Hokkaido (Smith & Hiruta 2004; Hiruta & Mawatari 2013). Elsewhere, far east of Russia (Sidorov & Semenchenko 2012).

Hiruta, S. F. & Mawatari, S. F. 2013. Ostracods (Crustacea) from Sarobetsu Marsh, northern Hokkaido, Japan: taxonomy and phenology with description of Pseudocandona tenuirostris sp. nov. Species Diversity, 18, 57-74.

Sidorov, D. A. & Semenchenko, K. A. 2012. New records of freshwater ostracods (Crustacea) from the Far East of Russia, with a checklist of recent freshwater ostracods of the region. Arthropoda Selecta, 21, 227-234.

Smith, R. J. & Hiruta, S. 2004. A new species of Metacypris (Limnocytherinae, Cytheroidea, Ostracoda, Crustacea) from Hokkaido, Japan. Species Diversity, 9, 37-46.

Smith, R. J. & Janz, H. 2009. Recent ostracods of the superfamilies Cytheroidea and Darwinuloidea (Crustacea) from Lake Biwa, a Japanese ancient lake. Species Diversity, 14, 217-241.

Key characters Metacypris digitiformis
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 visible
Carapace - lateral view - ventral marginVentral margin convex
Carapace - lateral view - valve heightLeft and right valves similar height
Carapace - internal viewAnterior calcified inner lamella wider than posterior one
Carapace - ornamentation - denticlesNo denticles near ventral margin
Carapace - ornamentation - sulcusNo sulcus
Carapace - ornamentation - surfaceSurface pitted
Carapace - width/length ratio (w/l)Greater than 0.7 (rounded species)
Antennule - segmentsFive moveable segments
Antennule - Rome organRome organ absent
Antenna - exopoditeExopodite a spinneret seta
Antenna - swimming setaeNo swimming setae present
Fifth limb - morphologyWalking leg
Sixth limb - segmentsFour segments
Sixth limb - setae on first segmentFour setae
Sixth limb - h3 seta on final segmentNo h3 seta
Seventh LimbWalking leg, larger than sixth limb
Seventh Limb - segmentsFour segments
Seventh Limb - first segmentFour setae
Caudal ramusReduced to only one or two setae or absent
Caudal ramus - attachmentWith no caudal ramus attachment