at the Lake Biwa Museum, Japan

Robin James Smith

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Genus Ilyodromus Sars, 1894

Superfamily: Cypridoidea Baird, 1845
Family: Cyprididae Baird, 1845
Subfamily: Herpetocypridinae Kaufmann, 1900

One species has been reported from Japan:

1. Ilyodromus intermedius Okubo, 2011 in Smith et al. 2011

Left side view of a female Ilyodromus intermedius, length 1.1mm.

External view of a female left valve of Ilyodromus intermedius, length 1153 microns.

External view of a female right valve of Ilyodromus intermedius, length 1115 microns.

Additional figures in: Okubo & Ida 1989 (carapace), Okubo 1990 (carapace, caudal ramus), Okubo 2004 (carapace and caudal ramus), Smith et al. 2011 (carapace and appendages).
Habitat: Rice fields, and Lake Biwa, along the lakeshore and down to a depth of 4.6 m.
Mode of life: Benthic.
Reproduction mode: Asexual, males unknown.
Known distribution: Shiga Prefecture (Okubo 2004; Smith et al. 2011); Gumma Prefecture (Okubo & Ida 1989, as Ilyodromus smaragdinus); Okayama (Okubo 1990 as Ilyodromus smaragdinus).

Okubo, I. 1990. Sixteen species of freshwater Ostracoda from Japan. Bulletin of the Biogeographical Society of Japan, 45, 39-50.

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

Okubo, I. & Ida, K. 1989. Freshwater Ostracoda from Gunma Prefecture, Japan. Bulletin of the Biogeographical Society of Japan, 44, 105-107. [In Japanese]

Smith, R. J., Janz, H. & Okubo, I. 2011. Recent Cyprididae and Ilyocyprididae (Crustacea: Ostracoda) from Lake Biwa, Japan, including a summary of the lake's ostracod fauna. Zootaxa, 2874, 1-37.

Key characters Ilyodromus intermedius
Carapace - ventral valve overlapLeft valve overlaps right along ventral margin
Carapace - margin structure - septaNo septa present
Carapace - margin structure - ridges on inner calcified lamellaOn left valve AND on right valve*
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 - denticlesNo denticles near ventral margin
Carapace - ornamentation - sulcusNo sulcus
Carapace - ornamentation - surfaceSurface smooth
Carapace - width/length ratio (w/l)Less than 0.4 (slender species)
Antennule - segmentsSeven moveable segments
Antennule - Rome organRome organ present
Antenna - exopoditeExopodite reduced to small segment
Antenna - swimming setae Swimming setae reduced, not reaching to end of claws
Fifth limb - morphologyMaxilliped
Sixth limb - segmentsFive segments
Sixth limb - setae on first segmentTwo setae
Sixth limb - h3 seta on final segmentH3 seta short; much shorter than half length of claw
Seventh LimbCleaning limb, with a pincer at end
Seventh Limb - segmentsThree segments
Seventh Limb - first segmentThree setae
Caudal ramusElongate ramus with two claws and two setae
Caudal ramus - attachmentTriangular loop at ventral end
* Not easy to see with light microscopy, but visible with scanning electron microscopy.