at the Lake Biwa Museum, Japan

Robin James Smith

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Genus Microdarwinula Danielopol, 1968

Superfamily: Darwinuloidea Brady & Robertson, 1885
Family: Darwinulidae Brady & Robertson, 1885

One species has been reported from Japan:

1. Microdarwinula zimmeri (Menzel, 1916)

Left side view (on the left) and dorsal view of female Microdarwinula zimmeri, length about 0.3 mm.

External view of a female left valve of Microdarwinula zimmeri, length 350 microns.

External view of a female left right of Microdarwinula zimmeri, length 337 microns.

Additional figures in: Danielopol 1968 (carapace and appendages); Rossetti & Martens 1998 (carapace and appendages); Smith 2011 (carapace).
Habitat: Seeps and gravel banks of rivers.
Mode of life: Benthic and interstitial.
Reproductive mode: Asexual, males unknown.
Known distribution: Shiga Prefecture (Smith 2011). Elsewhere, known from Europe, Western Africa, North America, the Caribbean, Madagascar, the Middle East and Indonesia (see review of the distribution in Rossetti & Martens 1998).

Danielpol, D. L. 1968. Microdarwinula N. G. et quelques remarques sur la Répartition de la famille Darwinulidae Br. et Norm. [Crustacea, Ostracoda]. Annales de Limnologie, 4, 153-174.

Rossetti G. & Martens, K. 1998. Taxonomic revision of the Recent and Holocene representatives of the Family Darwinulidae (Crustacea, Ostracoda), with a description of three new genera. Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Biologie, 68, 55-110.

Smith, R. J. 2011. Groundwater, spring and interstitial Ostracoda (Crustacea) from Shiga Prefecture, Japan, including descriptions of three new species and one new genus. Zootaxa, 3140, 15-37.

Key characters Microdarwinula zimmeri
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 viewNo calcified inner lamella
Carapace - ornamentation - denticlesNo denticles near ventral margin
Carapace - ornamentation - sulcusNo sulcus
Carapace - ornamentation - surfaceSurface smooth
Carapace - width/length ratio (w/l)Between 0.4 and 0.7 (medium species)
Antennule - segmentsFive moveable segments
Antennule - Rome organRome organ absent
Antenna - exopoditeExopodite reduced to small segment
Antenna - swimming setaeNo swimming setae present
Fifth limb - morphologyWalking leg
Sixth limb - segmentsFive segments
Sixth limb - setae on first segmentThree setae
Sixth limb - h3 seta on final segmentH3 seta short; much shorter than half length of claw
Seventh LimbWalking leg, larger than sixth limb
Seventh Limb - segmentsFive segments
Seventh Limb - first segmentTwo setae
Caudal ramusReduced to only one or two setae or absent
Caudal ramus - attachmentWith no caudal ramus attachment