at the Lake Biwa Museum, Japan

Robin James Smith

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By R. J. Smith

This is an online key to the freshwater ostracod genera found in Japan (version 1.1).
Comments are welcome:

Tick the boxes of the characters that apply and click the submit button at the bottom. If you are unsure about a particular character, you can leave it blank. Additionally, if you are only partially sure of a character (i.e. your specimen has swimming setae, but you are not sure of their length), you can tick two or more states. Results are displayed below. Click the corresponding [?] to find out more about each character (opens in a new window).


1. Carapace - ventral valve overlap [?]
Left valve overlaps right along ventral margin (34 genera)
Right valve overlaps left along ventral margin (7 genera)

2. Carapace - margin structure - septa [?]
Septa present along all free margins (1 genus)
Septa present only along anterior margin (1 genus)
No septa present (39 genera)

3. Carapace - margin structure - ridges on inner calcified lamella [?]
On right valve (8 genera)
On left valve (10 genera)
No ridges (27 genera)

4. Carapace - dorsal view - female with brood pouch [?]
Brood pouch visible (3 genera)
Brood pouch not visible (38 genera)

5. Carapace - lateral view - ventral margin [?]
Ventral margin convex (3 genera)
Ventral margin approximately straight to concave (38 genera)

6. Carapace - lateral view - valve height [?]
Left and right valves similar height (40 genera)
Right valve noticeably higher than left (1 genus)

7. Carapace - internal view [?]
Anterior calcified inner lamella wider than posterior one (33 genera)
Anterior calcified inner lamella about as wide as posterior one (4 genera)
No calcified inner lamella (4 genera)

8. Carapace - ornamentation - denticles [?]
Small denticles near ventral margin of valves (5 genera)
No denticles near ventral margin (36 genera)

9. Carapace - ornamentation - sulcus [?]
Sulcus present near dorsal margin (2 genera)
No sulcus (39 genera)

10. Carapace - ornamentation - surface [?]
Surface smooth (28 genera)
Surface striated (4 genera)
Surface pitted (10 genera)

11. Carapace - width/length ratio (w/l) [?]
Less than 0.4 (slender species) (21 genera)
Between 0.4 and 0.7 (medium species) (18 genera)
Greater than 0.7 (rounded species) (4 genera)


12. Antennule - segments [?]
Seven moveable segments (34 genera)
Six moveable segments (3 genera)
Five moveable segments (4 genera)

13. Antennule - Rome organ [?]
Rome organ present (25 genera)
No Rome organ (16 genera)


14. Antenna - exopodite [?]
Exopodite a spinneret seta (4 genera)
Exopodite reduced to small segment (37 genera)

15. Antenna - swimming setae [?]
Swimming setae very long, reaching well beyond end of claws (4 genera)
Swimming setae long, reaching to about end of claws (19 genera)
Swimming setae reduced, not reaching to end of claws (7 genera)
No swimming setae present (14 genera)

Fifth Limb

16. Fifth limb - morphology [?]
Walking leg (4 genera)
Maxilliped (37 genera)
      Male palps with moveable terminal hooks (11 genera)
      Male palps one fused mass (5 genera)
     N.B. for some genera males are unknown.

Sixth Limb

17. Sixth limb - segments [?]
Four segments (6 genera)
Five segments (35 genera)

18. Sixth limb - setae on first segment [?]
Four setae (3 genera)
Three setae (3 genera)
Two setae (14 genera)
One seta (17 genera)
No setae (4 genera)

19. Sixth limb - h3 seta on final segment [?]
H3 seta very long; approximately half length of claw (3 genus)
H3 seta short; much shorter than half length of claw (34 genera)
No h3 seta (4 genera)

Seventh limb

20. Seventh Limb [?]
Walking leg, smaller than sixth limb (1 genus)
Walking leg, larger than sixth limb (6 genera)
Cleaning limb, with a pincer at end (20 genera)
Cleaning limb, with three setae at end (14 genera)

21. Seventh limb - segments [?]
Three segments (20 genera)
Four segments (16 genera)
Five segments (7 genera)

22. Seventh Limb - first segment [?]
Four setae (3 genera)
Three setae (30 genera)
Two setae (6 genera)
One seta (2 genus)

Caudal ramus

23. Caudal ramus [?]
Elongate ramus with two claws and three setae (2 genera)
Elongate ramus with two claws and two setae (27 genera)
Elongate ramus with two claws and one seta (3 genera)
Reduced ramus with two setae (3 genera)
Reduced ramus with one seta (1 genus)
Reduced to only one or two setae or absent (6 genera)

24. Caudal ramus - attachment [?]
Loop at dorsal end (3 genera)
Triangular loop at ventral end (5 genera)
With no loops (24 genera)
With no caudal ramus attachment (10 genera)

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Results link to pages about each genus. No results? No species so far reported from Japan matches your species.