Eucyclops, Claus, 1893

Ding, Ruirui, Chen, Feizhou & Alekseev, Victor R., 2022, A redescription of the rare eucyclopine copepod Eucyclops productus Kiefer, 1939 (Multicrustacea: Copepoda: Cyclopoida: Cyclopidae) and a keу to Eucyclops subgenera and species of China and adjacent areas, Zootaxa 5182 (4), pp. 377-388 : 386-387

Keу to Eucyclops subgenera and species of China and adjacent areas

The key includes also subgenera still not found in this area but possible after more profound faunistic research.

1. Antennule 11–segmented.......................................................... Subgenus Мrazekicyclops (Not found in this area but possible in underground water)

– Antennule12–segmented............................................................................... 2

2. Caudal rami with denticles on dorsal surface or hair–setae at inner margin...................... Subgenus Ciliocyclops E. (C.) permixtus Kiefer, 1928 [Kangra Valley, Western Himalayas, India]

– Caudal rami without hairs on inner margin or denticles on dorsal surface......................................... 3

3. Caudal rami very short (L/W <2.7)................................................ Subgenus Breviramocyclops (Not found in this area but possible in underground water)

– Caudal rami longer (L/W> 2.7, usually more than 3)........................................................ 4

4. Distal setae of P4enp3 long, extending above tips of nearest spines..................... Subgenus Subterrocyclops (5)

– Distal setae of P4enp3 short, usually shorter than nearest spine or sometime only outer seta can reach distal end of adjacent spine, but never longer than it........................................................................... 7

5. Caudal rami with much reduced serra, there are only 3–4 spinules above lateral set............................................................... E. (Sub.) chivahensis Lindberg, 1960 [Lake Shiva, Badakhshan Province, Afghanistan]

– Caudal rami with developed serra ....................................................................... 6

6. Caudal rami with serra of small equal spinules; L/W about 4. P4enp3 distal spines not less than segment length. Female body size without caudal setae more than 1 mm ............................. E. (Sub.) nagasaki Ueno, 1934 [Cave, Japan]

– Distal spinules of caudal rami serra noticeably larger than proximal ones; L/W ratio of caudal rami about 3. P4enp3 distal spines noticeably shorter than segment length. Female body size without caudal setae less than 1 mm .................................................. E. (Sub.) bryophilus Lindberg, 1950 [moss near the waterfall, Shillong, Assam, India]

7. Caudal rami smooth with only few spinules above lateral seta.......................... Subgenus Мacrurocyclops (8)

– Caudal rami with more or less developed serra extending along outer edge....................................... 9

8. Caudal rami very long, L/W 8–10. Caudal dorsal seta shorter than outermost seta................................................................................................ E. (M.) macrurus (Sars G.O., 1863) [Palearctic]

– Caudal rami much shorter, L/W about 5. Caudal dorsal seta longer than outermost seta................................................................................... E. (M.) defectus Lindberg, 1937 [Pachmarhi, Central India]

9. Leg 5 with very small inner spine shorter than leg segment.................................. Subgenus Sarsicyclops [Not found in this area but possible in underground water]

– Leg 5 with larger inner spine longer than leg segment....................................................... 10

10. Antennule with denticulate hyaline membrane at distal segments (10th and/or 11th and/or 12th).................................................................................................... Subgenus Denticyclops (11)

– Antennule with smooth/finely–serrated hyaline membrane or without it......................................... 15

11. The 10th and 11th segments of antennule with denticulate hyaline membrane, the 12th segment with smooth hyaline membrane......................... E. (D.) taiwanensis Sukhikh, Alekseev, 2015 [Abvil Lake, Taiwan Province, China]

– All three distal segments of antennule with denticulate hyaline membrane....................................... 12

12. Caudal rami long, L/ W 5.5 and more................................................................... .. 13

– Caudal rami shorter, L/W less than 5.5. Spines of swimming legs wide, conspicuously spatulate...................... 14

13. Hyaline membrane of the 12th segment of antennule with small denticles of the same size....................................................................................... E. (D.) macruroides (Lilljeborg, 1901) [Palearctic]

– Proximal part of hyaline membrane of the 12th segment of antennule with 8–12 large denticles, distal part of the membrane with much smaller denticles....................................... E. (D.) denticulatus (Graeter, 1903) [Palearctic]

14. Distal segments of antennule with hyaline membrane reduced to tiny separate teeth (sometimes visible only as small dots). Caudal rami with lateral serra of spinules significantly increasing distally. Innermost caudal seta usually bare, sometimes with rare hairs. Inner spine of P5 short, nearly equal to segment length; this spine thin, not more than 2 times wider than adjacent setae.............................................. E. (D.) euacanthus (Sars G.O., 1909) [Africa, Asia, Australia]

– Distal segments of antennule with wide serrated hyaline membrane. Caudal rami with lateral serra of small spinules. Innermost caudal seta densely plumose. Inner spine of P5 noticeably longer than segment; this spine very thick, 3–4 times wider than adjacent setae.......................................................................................... E. (D.) microdenticulatus Lindberg, 1940 [Small ponds and streams, Gujarat, Maharashtra, Tamil Nadu, South West India]

15. Antenna basipodite with hair–setae near distal border (groups N1, N2)..................... Subgenus Eucyclops (16)

– Antenna basipodite without groups N1, N2 of hair–setae.............................. Subgenus Speratocyclops (17)

16. P4 coxal spine homogenously plumose on both sides...................................... Eucyclops (E.) agiloides (Sars G.O., 1909) s. lat. [Africa, Asia]

– P4 coxal spine inner margin with continuous hairs, while outer margin with “gap” (hairs/denticles missing at the middle of margin).............................................. Eucyclops (E.) serrulatus (Fischer, 1851) s. lat. [Palearctic]

17. In caudal rami innermost seta shorter than outermost seta..................................................................................... E. (S.) leschermoutouae Alekseev et Defaye, 2004 [well in Balearic Islands, Europe]

– Innermost caudal seta longer than or subequal to outermost seta............................................... 18

18. Caudal rami long, L/W> 5............................................................................. 19

– Caudal rami shorter, L/W <5........................................................................... 20

19. Inner spine of leg 5 very strong, knife-like, L/W> 6......................................................... 19

– Inner spine of leg 5 weak, seta-like, L/W about 5..................... E. (S.) biwensis Ishida, 1998 [Lake Biwa, Japan]

20. Caudal rami L/W 6–8. P4 coxal spine homogenously covered with long thin hairs; P4 intercoxal plate with long dense hairs on distal edge....................................................... E. (S.) speratus (Lilljeborg, 1901) [Palearctic]

– Caudal rami L/W> 8. P4 coxal spine with short denticles distally and long hairs proximally; P4 intercoxal plate with few rare hairs on distal edge.................................... E. (S.) productus Kiefer, 1939 [North India, Western China]

21. Inner outgrowth of P4 basipodite hairless..... E. (S.) dumonti Alekseev, 2000 [Eastern Siberia, Mongolia, China, Thailand]

– Inner outgrowth of P4 basipodite with hairs............................................................... 22

22. Caudal rami L/W <4. Innermost caudal seta subequal to outermost seta (1.1–1.2: 1)........................................................................ E. (S.) arcanus Alekseev, 1990 [Eastern Siberia, Mongolia, Northern China]

– Caudal rami longer, L/W> 4.2. Innermost caudal seta noticeably longer than outermost seta (1.4–1.8:1)............... 23

23. P4 intercoxal plate with hairless distal margin........................................................................................... E. (S.) troposperatus Alekseev et Yusoff, 2013 [City ponds in Dumen, Sumatra, Indonesia]

– P4 intercoxal plate with setules at its distal margin.......................................................... 24

24. P4 intercoxal plate with long-hair setules at its distal margin............................................................................................ E. (S.) azonrensis Defaye & Dussart, 1991 [Azores, Madeira, North Africa]

– P4 intercoxal plate with short stiff setules at its distal margin.......................................................................................... E. (S.) delongi Alekseev, Abramova, Chaban, 2019 [Eastern Siberia, China?]