Redescription of Diaphanosoma dubium Manuilova, 1964 (Branchiopoda: Ctenopoda: Sididae), and description of a new, related species

Hydrobiologia 441: 73–92, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.

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Redescription of Diaphanosoma dubium Manuilova, 1964 (Branchiopoda: Ctenopoda: Sididae), and description of a new, related species N. M. Korovchinsky A.N.Severtsov Institute of Ecology and Evolution of Russian Academy of Sciences, Leninsky prospect 33, 117071 Moscow, Russia Received 1 August 1998; in revised form 1 February 2000; accepted 20 August 2000

Key words: Diaphanosoma dubium,D. pseudodubium sp.nov., morphology, taxonomy, geographical distribution

Abstract The poorly known D. dubium Manuilova is redescribed on extensive material from more than 80 populations from the Russian Far East, Central Asia, Mongolia, China, Japan, Vietnam, the Philippines, Thailand, Malaysia, Bangladesh, India and Sri Lanka. Its morphological variability and geographical distribution are analysed and supplemented by notes on biology. The conspecificity of morphologically different distant populations is discussed. In the northern part of its range, D. dubium was long confused with D. brachyurum or D. leuchtenbergianum, and in the south with D. modigliani. It seems that the recent appearance of D. dubium in fish ponds of Uzbekistan and Kazakhstan was an introduction, together with Far Eastern fish. D. pseudodubium sp.nov., close to but markedly different, is described from two lakes in the lower Amur river system. D. dubium, D. pseudodubium, D. tropicum and D. modigliani s. str. form a group of related species, widely distributed in Eastern and Southern Asia. Abbreviations: ad – adult parthenogenetic females; juv – juvenile parthenogenetic females Introduction Diaphanosoma dubium was described from some large lakes along the lower Amur river, Russian Far East (Manuilova, 1964), though it had been recorded from Japan and China before under the names D. brachyurum var. leuchtenbergianum, D. brachyurum frontosa and D. leuchtenbergianum (Ueno, 1927, 1932, 1937a,b, 1938, 1940; Borutsky, 1952; Yen Hsi-chu, 1956). Occasional drawings of the characteristically large, dorsally protruding head of the species (e.g. Ueno, 1927, 1937a,b) support this suggestion. In spite of this and other pronounced features, this species was not recognized for about 40 years after its probable first record (Ueno, 1927). Even after Manuilova’s (1964) description, authors continued to call the species D. leuchtenbergianum (Chiang & Du, 1979; Thanh, 1980), until its description from India (Kanduru, 1981) and Bangladesh (Hossain, 1982), and record in India (Fernando & Kanduru, 1984). Later on, some authors further spe-

cified its description (Korinek, 1987; Korovchinsky, 1992) based on type and other material, and emended the name of the taxon (International Code of Zoological nomenclature, articles 30a, 31c and 32d) (Korovchinsky & Mirabdullaev, 1994). The examination of additional zooplankton material from East, South-East and South Asia made it possible to document the presence of D. dubium in the tropical zone (Korovchinsky, 1998), where it co-occurs with D. tropicum. The present study attempts to complete the revision of the D. modigliani – D. dubium species group, supplemented by the description of a new species from the Amur river system.

Materials and methods Material was borrowed from the collections of Zoological Museum of Moscow State University (ZMU), Zoological Institute in St-Peterburg (ZIN), as well as

74 from the extensive zooplankton collections of Prof. H.J. Dumont (University of Ghent, Belgium) (HJD), Prof. C. H. Fernando (University of Waterloo, Canada) (CHF), Prof. D. G. Frey (Indiana University, U.S.A.) (DGF), and others indicated in the list of material. Most of the material examined was in formalin. Diaphanosoma dubium Russian Far East, Amur river system: 1) Lake Bolon’, 1934, 4 ad ZIN (syntypes, N 1/43534); 5.8.1933, 5 ad; 2.9.1933, 24 ad, 4 ad males (ZIN 260-934); 2) Amur river near Tcheltsy, 11.9.1933, 9 ad, 5 ad males (ZIN 260-934; 3) Canal Verhne-Olinskaja near Amur river, 17.9.1933, 20 ad, 11 ad males (ZIN 260-934); 4) Floodplane of Kisui river, 24.7.1911, 1 juv (ZIN 508-1911); 5) Lake Sinda, 10.7.1930, 9 juv (ZMU); 6) Lake Petropavlovskoje, 9.6.1930, 1 ad (ZMU); 7) Lake Padalinskoje, 10.8.1933, 3 ad, 9 juv (ZIN 260934); 8) Lake Gassi, July 1930, 25 ad (ZMU); 9) Lake Boulen, August 1930, 7 ad, 3 juv (ZMU); 10) Lake Udyl’, 13.9.1930, 5 ad, 1 ad male (ZMU); 11) Lake Orel’, 20.9.1930, 1 juv male; 12) Amur river near Leninskoje, 10.6.1950, 1 ad (ZMU). Primorsky Territory: 13) Lake Khanka, 7.9.1932, numerous ad (ZIN); 14) Lake Khasan, 2.9.1956, 10 ad, 2 ad males, 2 juv (ZMU); 15) Fish pond, Tchernigovsky distr., 5 ad (leg. T.Britayev). Kazakhstan: 16) Tchiliksky fish-factory, AlmaAtinskaja region, August 1992, 22 ad, 5 juv (leg. I.Mirabdullaev); 17) Almaty City, pond, fall of 1997, 2 ad (leg. E. Krupa). Uzbekistan: 18) Kashkadarjinsky fish-factory, July 1990, 21 ad, 2 juv (leg. I.Mirabdullaev); 19) Fish station UzNIIRH near Tashkent City, 20.9.1991, numerous adults and juv (leg. I.Mirabdullaev). Mongolia: 20) Lake Buir-nor, 19.8.1950, numerous ad (ZMU); 19.7.1966, 1 ad(leg. D.Aujur). China, Inner Mongolia (leg. Su Rong, HJD): 21) Qianqishuiku reservoir, August 1987, about 50 ad; 22) Lake Xianquang, August 1984, 4 ad, 1 juv male; 23) Shanghao reservoir, September 1984, 3 ad; 24) Lake Qoujinlang, September 1984, numerous ad and some juv; 25) Shuangshan reservoir, June 1985, 1 ad; 26) Denkou, Yellow river, 21.9.1986, 3 ad; 27) Zhongqishuiku, September 1986, 1 ad; 28) Dashuwan reservoir, September 1986, 2 ad, 4 juv, 1 juv male; 29)

Lake Shengli, 1.9.1984, 1 ad; 30) Zhagestai reservoir, August 1983, 11 ad; 31) Sifestan pond, August 1984, 1 juv; 32) Lake Muanghai, August 1984, 5 ad; 33) Fisheries Institute pond, Huhhoto City, 17.7.1987, 1 ad, 1 juv. Heilongjiang Province (leg. Wong Quangxi): 34) Lake Jaoquan, Wudalianchi, July 1990, 1 ad, 3 ad males; 35) Lake Wudalianchi, September 1990, 3 ad, 2 ad males; 36) Fishpond, Harbin City, 15.9.1994, 17 ad, 5 juv, 1 juv male; 37) Harbin City, Taiyangdao, 3.10.1994, 1 ad, 2 juv, 3 ad males. Jilin Province (leg. Wong Quangxi): 38) Jilinshi (Kilin), 31.8.1991, some deformed ad; 39) Pool, Taonan, 28.8.1986, 5 ad, 4 juv; Liaoning Province (leg. Wong Quangxi): 40) Kaiyuan, 1.7.1987, numerous ad and juv. Hebei Province (HJD): 41) Canal Yufu near Chengde City, 31.7.1989, 24 ad, 2 juv; 42) Chengde City, 4.8.1989, 26 ad, 6 juv. Shanxi Province (HJD): 43) Karp pond, Sian City, 2.8.1989, 4 ad. Sichuan Province (DGF, N6310): 44) Pool on campus of Sichuan University, 3 ad. Hubei Province (ZMU): 45) Lupidatan, small reservoir, 3.10.1958, 1 ad; 46) Czinpiertan, 5.10.1958, 13 juv; 47) Lanpin reservoir, 22.10.1958, some deformed ad; 48) Chanshou, 26.10.1958, 2 ad; 49) Lao-mauya, Kaisan, 31.10.1958, 1 ad; 50) Xujiahe reservoir, 18.10.1997, some ad. Jiangsu Province: 51) Lake Tai near Nanjing City, May 1987, 1 juv (CHF); 52) Lake Tai in Wuxi City, July 1996, 2 ad (HJD); 53) Lake Shuan-wuhu Nanjing City, 1.10.1996, 4 ad, 3 juv (leg. Chen Yuan-Gao); 54) Pond Gian Hu, Nanjing City, 1.10.1996, 24 ad and many juv (leg. Chen YuanGao). Guangdong Province (DGF, NN 6314, 6316): 55) Lotus pond, Jivjiang Co., 9.10.1956, 2 juv; 56) Pond, Junan Town, Shunde Co., 11.6.1956, 33 ad and many juv. Guangxi Province: 57) Lotus pond, Gui Co, 24.7.1956, 2 deformed ad (DGF, N 6311); 58) Large pond, Yuang-shua, Guilin City, 20.7.1989, 34 ad, 27 juv (HJD); 59) Li river, Guilin City, 20.7.1989, 44 ad, 4 juv (HJD). Yunnan Province: 60) Lake Daguanlou, Kunming City, 28.9.1957, 1 juv (DGF); 61) Pond at edge of Lake Erhhai, Dali Co., 23.7.1989, 35 ad, 5 juv (HJD). Japan: 62) Pond, Kyoto City, 25.8.1980, 2 juv (HJD); 63) Lake Biwa, littoral zone, some ad (leg. O. Timoshkin & N. Sheveljeva). Vietnam (North) (HJD): 64) Hoan Kiom, Hanoi City, 15.10.1993, 37 ad, 7 juv; 65) West Lake, Hanoi City, 15.10.1993, 2 ad; 66) Fish pond E5, 15.7.1995, numerous ad; 67) Hoa Binh reservoir, 30.8.1995, 2 ad.

75 Thailand Khon-Kaen Province (leg. Renu Sirimongkonthaworn): 68) Thung Sang swamp,Muang distr., 23.9.1996, numerous ad; 69) Ubolpatiana Reservoir, 25.5.1994, 14 ad; 70) Pond, Summakorn vill., Bangkok Co., 25.10.1994, 1 ad (leg. Janewit Wongsanoon). Philippines: 71) Illaguen River, Ixabila, North-Eastern Luzon, 1.8.1994, 1 ad (HJD). Malaysia: 72) Fish-pond, Kuala Kangsar, Perak State, 11.10.1974, numerous ad (CHF, N II-213); 73) Reservoir in Malacca City, 6.4.1993, 43 ad and juv (HJD). Bangladesh (CHF): Mymensingh: 74) 27.11.1979, numerous ad (N9-94.5); 75) Bau, Brammaputra river, 3.11.1979, 1 juv (N4-47); 76) The same, 3.12.1979, 6 juv (N4-402); 77) Harchaki, Beltali, 29.10.1979, 5 ad, 2 juv (N9-907); 78) Bau farm, ricefield, 23.10.1979, 33 ad (N5-57); 79) Kalibari, Shanbungang, 9.10.1979, 1 ad, 3 juv (N9-912); 80) Sattrapur, Bang, derelict marsh, 22.12.1979, 2 juv (N8-802); 81) Hindupara, Reltali, derelict pond, 29.10.1979, 3 juv (N1-105); 82) Harchaki Beel, 4.12.1979, 3 ad (total mount, leg. V.Korinek); Fatikjani: 83) Tangail river/stream, 30.10.1979, 4 juv (N4-407). Sri Lanka (CHF): 84) Parakrama Samudra reservoir, 25.4.1981, 58 ad (N4-409); 85) Small lake Tissa Maharama, Yodawewa, 12.1.1980, 13 ad, 2 juv (N5584.2); 86) Small reservoir Mahawewa near Agunakopalana, 24.10.1981, 1 ad (N5-548.2); 87) Ridiyagama reservoir, 4.1.1980, 3 ad (N4-412). India: 88) Unnamed reservoir, Delhi Co., 1 ad (leg.P.Kaur). Diaphanosoma pseudodubium Russian Far East, Amur river system (ZMU): 1) Lake Dabanda, 28.6.1930; 2 ad; 2) Lake Pir, 13.7.1930, 8 ad, 3 juv. Figures were made by means of an RA-4 drawing apparatus. To count the number of ommatidia, the eye pigment was dissolved by KOH. The size-frequency distribution in two populations of D. dubium was counted by means of random measurements of more than 400 specimens from each of them.

Redescriptions, descriptions and remarks Diaphanosoma dubium Manuilova, 1964 Ueno, 1927: 273-274, Pl.21, Figs 2a–f (D. brachyurum var. leuchtenbergianum); 1937a: 200, Fig.1 (D. brachyurum, partim); 1937b: 41–42 Fig.2 (D. brachyurum, partim); Yeh Hsi-chu, 1956: 46, T.1, 3, 3a (D. leuchtenbergianum); Manuilova, 1964: 110–112, Fig. 28 (D. dubia); Chiang & Du, 1979: 90–91, Fig.60, A, B (D. leuchtenbergianum); Thanh, 1980:193–194, Fig. 106 (D. leuchtenbergianum); Korinek, 1987: 38– 42, Figs15-34 (D. dubia); Korovchinsky, 1992: 42, Figs 198–202; Korovchinsky & Mirabdullaev, 1994: 8–9, Fig.1 (D. dubium). Diagnosis: Head very large, its dorsum greatly protruding. Apical end of antennal basipodite with long thin outer seta. Proximal segment of upper, 2segmented antennal branch with small apical spine. Upper Posterior corner of valves often protruding upward. Their posterior and postero-ventral margins low and usually oblique, bearing 8–40 (usually 12–29) small, slightly curved, rather sparse denticles with thin setules between them. No dorsal inner spine near posterior valve margins. Postabdomen usually much prominent dorsally. Copulatory appendages of males sole-like, enlarging distally. Parthenogenetic female: Measurements of body parts of specimens from different populations are shown in Table 1. Head (e.g. Figs 1, 18 and 19) very large, its massive dorsum greatly protruding; general shape of anterior body part cone-shaped. Ventrally, anterior part of head usually with rounded bulge under the eye. Form of head may be rather different (Figs 1, 19, 27 and 38). Antennules with long flagellum covered by fine setules (Fig. 29). Eye of average size, sometimes large, usually closer to ventral side of head, consisting of 40–42 ommatidia (Vietnamese specimens from fish pond E5). Swimming antennae powerful and of different relative length; their apical ends usually reach the postero-dorsal corner of valves or exceed it, rarely rather short as in specimen from the Philippines (61.4% of body length). At apical end of basipodite (Fig. 10), one small dorsal outgrowth; another one at base of upper antennal branch; on middle of outer side a comparatively long thin, sometimes rather robust seta, tapering distally; two small outgrowths in front of lower antennal branch. Proximal segment of 2-segmented upper branch usually widened (Fig. 20), rarely narrow (Fig. 39) with small spine on the apical

76 Table 1. Measurements of soft body parts of Diaphanosoma dubium from 9 populations (n=15) Body length, mm

Head length: Head height: Diameter of eye: body length,% body length,% body length,%

Length of Length of upper Length of lower Length of setae Number of swimming antennal branch: antennal branch: natatoriae: denticles on antennae: body length of: length of: body length,% postero-ventral length,% basipodite, % basipodite,% valve margin

1. Lake Khanka, Russian Far East 0.98–1.12. 45.5–49.3 24.7–28.2 1.04 47.5 26.5 0.044 1.20 1.20 4.25 2.52 4.54

7.1–9.7 8.2 0.60 7.3

67.1–78.6 71.7 3.16 4.41

69.3–81.9 75.8 4.0 5.26

44.3–58.8 49.0 2.56 5.22

71.4–79.2 74.7 2.26 3.03

13–29 19.4

2. Lake Buir-nor, Mongolia 0.99–1.26 47.8–50.7 1.12 49.5 0.09 0.93 7.99 1.88

6.9–8.5 7.7 0.49 6.35

65.9–73.6 70.0 2.13 3.04

57.1–70.4 63.2 4.20 6.65

38.1–48.8 43.1 3.03 7.02

57.7–69.9 64.8 5.95 9.18

19–40 29.4

3. Qianqishuiku Reservoir, Inner Mongolia, China 0.98–1.36 48.8–52.1 27.2–31.8 1.15 50.7 29.9 0.11 1.13 1.44 10.0 2.23 4.82

7.1–8.6 7.9 0.49 6.20

61.0–69.5 65.0 2.36 3.64

56.1–70.4 63.9 4.22 6.64

35.9–45.7 41.0 2.67 6.51

57.1–71.6 65.1 4.58 7.04

16–34 26.0

4. Hoan Kiom, Hanoi City, North Vietnam 0.78–0.95 51.7–58.5 28.3–32.3 0.85 55.0 30.7 0.049 1.97 1.01 5.80 3.59 3.28

9.5–10.8 10.0 0.37 3.66

70.5–78.3 74.2 2.22 2.99

56.6–68.0 60.2 2.80 4.65

38.6–45.3 40.4 1.73 4.28

60.6–72.6 68.4 2.60 3.80

17–27 21.4

5. Fish pond E5, North Vietnam 1.08–1.37 47.9–55.7 1.23 51.2 0.11 2.37 9.08 4.64

25.3–31.9 28.8 1.80 6.27

7.0–8.4 7.7 0.37 4.81

64.5–75.3 69.8 2.81 4.03

60.2–66.7 63.0 2.27 3.61

37.9–45.2 41.6 2.15 5.18

54.1–66.3 60.8 3.71 6.10

18–35 27.9

6. Mymensingh, Bangladesh (9–94.5) 0.80–1.16 49.1–52.1 28.4–33.3 0.99 50.5 30.5 0.11 1.07 1.11 10.9 2.12 3.64

8.3–10.3 9.1 0.77 8.46

65.2–78.3 70.5 2.87 4.06

55.6–67.1 60.0 2.78 4.63

37.1–44.3 39.6 1.89 4.75

51.9–73.7 62.8 5.33 8.48

10–23 15.6

7. Fish pond, Kuala Kangsar, Perak State, Malaysia 0.78–1.12 44.1–50.6 25.7–28.4 0.94 47.8 27.2 0.11 1.77 0.85 11.7 3.71 3.12

7.4–9.7 8.7 0.50 5.80

68.1–76.9 72.3 2.65 3.66

61.0–71.2 64.0 1.41 2.20

38.2–47.9 41.9 3.25 7.76

61.8–79.4 71.5 3.80 5.32

13–27 20.8

8. Parakrama Samudra Reservoir, Sri Lanka 0.77–1.06 46.2–50.0 25.5–31.0 0.90 48.3 29.2 0.079 1.15 1.68 8.78 2.37 5.76

7.9–9.3 8.6 0.37 4.26

66.2–72.7 69.6 1.88 2.70

55.7–65.3 62.1 2.73 4.40

34.2–44.0 40.1 2.58 6.44

64.5–73.8 69.2 2.68 3.87

15–28 19.3

9. Thang Sang swamp, Khon-Kaen Province, Thailand 0.76–0.95 45.5–49.1 25.4–29.6 8.6–11.1 0.83 46.8 27.4 10.1 0.046 1.03 1.23 0.76 5.49 2.20 4.49 7.53

65.6–74.6 68.9 2.40 3.49

64.0–73.9 68.9 3.01 4.36

44.0–53.6 46.9 1.90 4.05

67.2–76.7 71.6 3.25 4.54

8–16 11.7

26.8–31.7 29.2 1.46 5.01

From top to down: Limits of variation, mean, SD,CV.

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Figures 1–8. Diaphanosoma dubium (Amur river, Russian Far East: 1–4, 8 – lake Bolon’ (1, 3, 8 – lectotype), 5 – lake Padalinskoje, 6 – lake Gassi, 7 – lake Petropavlovskoje). Female: 1. lateral view; 3. distal end of first segment of upper antennal branch; 4–7. distal end of second segment of upper antennal branch; 8. postabdomen, lateral view. Male: 2. lateral view.

78

Figures 9–17. Diaphanosoma dubium (9–11, 13, 17 – lake Khanka, Primorsky Territory, Russian Far East; 14–16 – lake Bolon’, Amur river system (14, 16 right - lectotype, 12 – lake Buir-nor, Mongolia). 9. distal end of second segment of lower antennal branch; 10. distal outer part of antennal basipodite; 11, 12. distal end of first segment of upper antennal branch; 13. distal end of second segment of upper antennal branch; 14. shell, lateral view; 15. ventral valve margin; 16, 17. armament of postero-ventral valve margin.

79

Figures 18–26. Diaphanosoma dubium (18 – lake Khanka, Primorsky Territory, Russian Far East, 19 – lake Buir-nor, Mongolia; China: 20 – pond Gian Hu, Nanjing City; 21 – lake Muanghai, Inner Mongolia; 22 – canal Yufu near Chengde City, 23 Lotus pond, Gui Co., Guangxi Prov.; 24–26. Harin City, Heilongjiang Prov.) Female: 18, 19. general lateral view; 20. first segment of upper antennal branch; 21–23. distal end of second segment of upper antennal branch. Male: 24. distal outer part of antennal basipodite; 25. hook on distal endital end of first thoracic limb; 26. copulatory appendages (left – lateral view, right – frontal view).

80 end varied in size and situated in different position in relation to apical dorsal corner (Figs 3, 11, 12 and 39). A small outgrowth of different shape below this spine. End of distal segment with comparatively large spine of different shape, pointed inner outgrowth near it (sometimes absent), and rounded outer outgrowth (Figs 4–7, 13, 21, 22, 30–32 and 40–42). Antennal setal formula 4-8/0-1-4. Pattern of setal setation as described in D. modigliani s.str. (Korovchinsky, 1991a). Valves oblong-oval, upper posterior corner often protruding upward (Figs 14, 17 and 35). In general, posterior and postero-ventral valve margins low, usually oblique (Figs 18 and 37), or more straight (Figs 1, 19 and 27). Posterior margin comparatively short, its upper part often slightly protruding (Figs 16, 17, 33 and 35), then rapidly passing into postero-ventral margin which smoothly connects with ventral margin. The latter with rather large narrow ventral inflexion (Figs 14, 15 and 43), not shifted proximally, or more or less shifted if posterior margin more oblique, bearing 9–12 (up to 15 after Korinek, 1987) long feathered setae, the proximal of which is shorter and passes on the internal side of the inflexion. Some similar long setae usually on the lower part of postero-ventral margin (Fig. 43). The latter with a row of 8–40 (in one female up to 45) (usually 12–29) slightly curved denticles (Figs 16, 17, 33, 36 and 44–48), the 10–15 lowermost of which noticeable larger than uppermost, their number usually differing on both valves: 20/18 (lectotype), 17/19, 26/29, 36/31, 15/11, etc.. Number of denticles increasing with body size. The row of denticles usually subdivided into poorly delineated groups of 1–3 denticles, sometimes by 4– 9, in the case of small ones with thin setules between them. A row of minute supramarginal spinules along inner side of postero-ventral margin (Fig. 36). No dorsal spine at posterior valve margins. Postabdomen usually prominent dorsally (Fig. 8), but sometimes less prominent (Fig. 49) with comparatively small and strongly curved claws, having three rather short basal spines and a distal row of lateral spinules. Lateral armament of postabdomen inconspicuous. Setae natatoriae long . Body length: 0.56 – 1.54 mm. Males (Fig. 2) with slender body, less massive and protruding dorsal part of head, antennules (54.7 – 66.0% of body length) with enlarged basal part; conspicuous bulge near base of each antennule. Distal outer end of antennal basipodite with large spine (Fig. 24). Copulatory appendages, enlarging distally (Fig.

26), first thoracic limbs with massive apical endital clasping hooks (Fig. 25) bearing few spinules along inner margin, and specific naked seta with strongly enlarged base. Body length 0.71 – 0.98 mm (0.5 – 0.7 mm according to Korinek, 1987). Juveniles similar to adults but with relatively smaller head, longer swimming antennae having fewer setae (3+7) on the upper antennal branch and fewer denticles on valve margin. Intra- and interpopulation variability Populations of D. dubium differ in body size including specimens from neighbouring localities (e.g. NN 4, 5 in Table 1). In general, representatives were larger in northern areas and smaller in the tropics (Thailand, Malaysia, Sri Lanka: av. body length 0.83–0.94 mm) (Table 1). However, mature females of small size (0.56–0.70 mm) were found in Jilinshi (Jiling Prov., North of China). Unfortunately most of the latter were deformed, with broken swimming antennae and crumpled valves. The shape and relative size of the head was quite variable (Figs 1, 18, 19, 27, 28, 37 and 38). The largest size was observed in representatives from Hoan Kiom (Hanoi, Vietnam), and the smallest in Thai specimens.The individuals from Lake Khanka (Russian Far East) had the lowest head (26.5%). Head size depended on the development of antennal muscles, and was usually positively connected with antennal length. Only in Qianqishuiku Reservoir (Inner Mongolia, China), the latter were rather short, (65.0%) in specimens with massive head. The antennal basipodite was mostly long but in individuals from Thailand, and especially from Lake Khanka, it was relatively short compared with the branch length (Table 1). The proximal segment of the upper 2-segmented antennal branch was usually wide (Fig. 20). However, in Thai specimens, it varied from narrow to rather wide. The spine on the end of this segment also varied in size and position, as well as the shape of the outgrowth below it. The apical spine of distal segment of upper antennal branch is of special interest being extremely variable. It may be straight (Figs 4, 7 and 32), slightly curved (Figs 5, 6 and 22) or strongly curved (Figs 21, 23, 31, 40 and 41). Table 2 shows this variable spine in specimens from different regions. The straight spine was mostly characteristic of northern populations, and strongly curved ones occured in southern populations (the ratio of populations with straight or

81

Figures 27–36. Diaphanosoma dubium, female (North Vietnam: 27, 30, 34, 36 – fish pond E5; 28, 31, 35 – Hoan Kiom, Hanoi; 29 – Kaiyan, Laoning Prov., China; 32 – Harchaki, Beltali, Mymensingh, Bangladesh; 33 – lake Buir-nor, Mongolia). 27, 28. general lateral view; 29. antennula; 30–32. distal end of second segment of upper antennal branch; 33–35. armament of postero-ventral valve margin; 36. denticles of postero-ventral valve margin.

82

Figures 37–49. Diaphanosoma dubium, female (Sri Lanka: 37, 40, 45, 47 – Parakrama Samudra reservoir; 43 – Yodawewa; 38, 39, 42, 44, 49 – Thung Sang swamp, Khon-Kaen Prov., Thailand; 41, 48 – Kuala Kangsar, Malaysia; 46 – Mymensingh, Bangladesh). 37, 38. lateral view; 39. first segment of upper antennal branch; 40, 42. distal end of second segment of upper antennal branch; 42. apical spine of second segment of upper antennal branch; 43. ventral and posterior valve margin, inside; 44–48. armaure of postero-ventral valve margin; 49. postabdomen, lateral view.

83 Table 2. The presence of apical antennal spine of various shape in specimens of Diaphanosoma dubium from different regions Region Straight or slightly curved

Russian Far East Mongolia Central Asia North China Central-East China South China North Vietnam Bangladesh Thailand Sri Lanka Malaysia

Spine shape (number of populations) Strongly curved Straight, slightly or strongly curved

11 1 2 17 1 3 1 4 1 2 –

slightly curved spines decreased from north to south). At the same time, individuals of some populations possessed spines of different shape (Figs 40 and 42); sometimes even the spines on the antennae of one specimen were different. The eye was relatively larger (up to 10.1%) in populations of smaller individuals (Hoan Kiom, Vietnam; Thailand) (Table 1). The specimens from lake Khanka had especially long setae natatoriae, while in fish pond E5 (Vietnam) they were quite short (Table 1). The valve shape, especially of the posterior valve margin, varied sometimes within one population from quite oblique (Figs 18 and 37) to straight (Figs 19, 27 and 38). In general, the number of denticles along the postero-ventral valve margin correlated with body size, and were more numerous in large specimens from lake Boir-nor (Mongolia), Quanqishuiku Reservoir (Inner Mongolia, China) and fish pond E5 (Vietnam). At the same time, representatives of similar size from some populations (e.g. Hoan Kiom, Vietnam and Thung Sang swamp, Thailand) had a different number of denticles. Remarks Manuilova’s (1964) description of the species erroneously mentioned short setae natatoriae and omitted such as diagnostic features the ventral inflexion and armament of the postero-ventral valve margin. The large relative length of the swimming antennae was

– – 1 7 4 4 2 1 1 3 3

– – – 4 1 – – – – – –

Straight/strongly curved spine ratio

3.9:1

0.82:1

0.43:1

indicated but not illustrated. I suggest this mislead Chiang & Du (1979), who knew about the description of D. dubium but incorrectly identified their specimens as D. leuchtenbergianum, following a tradition which goes back to Lilljeborg (1901) and focuses on relative antenna length. The following authors presented incorrect details: eight aestetascs on antennules and 10–25 denticles along postero-ventral valve margin (Korinek, 1987), or a small spine instead of a fine seta on the outer side of basipodital distal end (Korovchinsky, 1992). D. dubium, studied over its range is rather diverse in morphology. Small individuals from Jilinshi (China) have been discussed above. Representatives from tropical regions look rather specific in general appearance (small body size, comparatively small head, large eye in specimens from Thailand and Philippines), and structures of swimming antennae (usual presence of strongly curved apical spine of the upper antennal branch). The taxonomic status of these populations should be studied further. Differential diagnosis D. dubium differs from D. modigliani in having a larger head, eye, longer swimming antennae, fewer denticles on the postero-ventral valve margin (8–40 vs 55–86), a longer ventral valve inflexion not shifted proximal, and a postabdomen with a prominent dorsal side (Table 3). D. dubium is close to D. tropicum sp.nov. (Korovchinsky, 1998), which co-occurs with it in

84 Table 3. The morphological differences between D. dubium Manuilova, D. tropicum Korovchinsky, D. modigliani Richard and D. pseudodubium sp. nov. Traits

D. dubium

D. tropicum

D. modigliani

D. pseudodubium

1. Spine on the end of upper antennal branch

Curved or straight

Strongly curved

Slightly curved or straight

Straight

2. Armature of antennal basipodite end

Seta

Seta

Seta

Spince

3. Ventral valve inflexion

Not shifted or slightly shifted Not shifted proximad proximad

4. Denticles of ventro-posterior valve margin

Comparatively small, sparse and not numerous (8–40, usually 12–29)

Comparatively large and Small and numerous (55–86) not numerous (22–58, usually 25–43)

Large, densely set and not numerous (23–37)

5. Dorsal spine near posterior valve margin

Absent

Absent

Absent

Present

6. Postabdomen dorsal side

Prominent

Prominent

Not prominent

Not prominent

7. Head length:Body length (%)

49.7

44.6

39.8

45.0

8. Head heigth:Body length (%)

28.8

25.0

21.7

25.3

9. Diameter of eye: Body length (%)

8.7

7.8

6.6

12.0

69.6

63.7

86.1

10. Length of swimming antennae: 70.0 Body length (%)

subtropical and tropical Asia. A preliminary differentiation (Korovchinsky, op.cit.), was based on material from few populations. Examination of additional abundant material revealed that D. dubium from some Thai populations had a smaller head, with a straighter posterior valve margin having more numerous denticles reminded D. tropicum. But, D. dubium differs from the latter species by an even more massive head (av. length and height 49.7 and 28.8% vs 44.6 and 25.0% of body length, respectively), and by a lower posterior part of the valves, usually with a prominent dorso-posterior angle and less numerous (8–40, mostly 12–29 vs 22–58, mostly 25–43, respectively), smaller and more sparse marginal denticles. Even in larger D. dubium these denticles were fewer than in D. tropicum (Fig. 61). Besides, the apical spines of the second segment of the upper antennal branch in D. dubium are of different shape. In D. tropicum, they are always strongly curved (Table 3). Differences with the new species, D. pseudodubium, will be indicated below.

Comparatively short and shifted Not shifted proximad proximad

Type material The type material of D. dubium from lake Bolon (coll. Boldovsky, 1934) in the Zoological Institute (StPeterburg, Russia) consists of four syntypes (4 ad). We designated the largest female (body length 1.46 mm) as lectotype (N 10159-18L), and three others as paralectotypes (NN 10160–10162). Korinek (1987) earlier designated a topotype, deposited in the British Museum of Natural History in London (N 1985.000). Diaphanosoma pseudodubium sp. nov. Diagnosis: Head large with greatly protruding dorsum. Swimming antennae extremely long, their upper branch noticeably exceeding the posterior valve margin. Apical end of antennal basipodite with large stout spine. Comparatively large spine at apical end of upper 2-segmented antennal branch. Posterior and postero-ventral valve margins with long row of 23–37, densely set, stout denticles with thin setules between them. Inner dorsal spine near posterior valve margins. Postabdomen rectangular, not prominent dorsally.

85

Figures 50–60. Diaphanosoma pseudodubium sp.nov., female, holotype (lake Dabanda, Amur river system, Russian Far East). 50. lateral view; 51. distal outer part of antennal basipodite; 52. first segment of upper antennal branch; 53. distal end of first segment of upper antennal branch; 54. distal end of second segment of upper antennal branch; 55. distal end of lower antennal branch; 56. armament of postero-ventral valve margin; 57. denticles of postero-ventral valve margin; 58. inner dorsal spine near posterior valve margin; 59. postabdomen, lateral view; 60. dorsal part of posterior valve margin.

86

Figure 61. Relationship between body length and number of denticles on postero-ventral valve margin in Diaphanosoma tropicum (1 – Old Pottery pond, Malaysia; 2 – Ipoh, Malaysia; 3 – Chandrica wewa, Sri Lanka) and D. dubium (4 – lake Buir-nor, Mongolia; 5 – Qianqishuiku reservoir, Inner Mongolia, China; 6 – fish pond E5, North Vietnam).

Parthenogenetic female. Head (Fig. 50) large (av. length 44.9–45.1% and av. height 24.4–26.2% of body length), its dorsum greatly protruding; anterior body part cone-shaped. Ventrally, anterior part of head with widely rounded bulge under the eye. Eye comparatively large (10.0–14.1%), closest to ventral side of head. Antennules with short cylinder-like basal part and long setulated sensory seta. Swimming antennae extremely long (85.0–87.2%), with long basipodite and comparatively long branches, the upper of which noticeable exceeds posterior valve margin (Fig. 50). At apical end of basipodite (Fig. 51), one small dorsal outgrowth corresponding to another one at the base of the upper antennal branch. At middle of outer side, a comparatively large and stout spine. End of proximal rather narrow segment of upper 2-segmented branch with comparatively large spine and quadrangular outgrowth below it, having a minute dorsal prominence (Figs 52 and 53). End of distal segment (Fig. 54) with large straight spine, adjacent acute inner outgrowth, and second, rounded outgrowth on the outer side. Antennal seta formula 4-8/0-1-4. Valves oblong-oval, upper posterior angle somewhat protruding upward. Posterior margin comparatively low and straight, more or less protruding dorsally, then curving down and forward, gradually passing into ventral margin (Figs 56 and 60), with large ventral infexion, not shifted proximally, and 8– 12 long, feathered setae. The distalmost setae may

sit on lower part of postero-ventral margin. The latter and half of posterior margin with long row of 23– 37 stout denticles (Figs 56 and 57), reducing in size dorsally, their number usually different on both valves: 34/30, 25/28, 31/29, 37/33, etc. The row of denticles subdivided into unsharply delineated groups by 2–5 with thin setules between them. Finely spinulated inner dorsal spine at posterior valve margin (Figs 56 and 58). Postabdomen rectangular, not prominent dorsally, laterally with rows and groups of minute spinules. Claws relatively large, not much incurved, with rather large and stout basal spines (Fig. 59). Along the dorsal edge, a row of spinules; some smaller rows of spinules also laterally. Setae natatoriae long (84.6–85.5). Body length 0.83–1.09 mm. Male unknown.

Differential diagnosis Similar to D. dubium in general appearance, especially in having a large, dorsally protruding head, but differing from it by its extremely long swimming antennae with a stout spine on the outer distal basipodital end, and the presence of a dorsal spine at the posterior valve margin. It possesses a more densely saw-like denticulation on the postero-ventral and posterior valve as well. Its postabdomen and claws are of different structure too (Table 3).

87 Geographical distribution So far it was found only in two lakes of the lower Amur River (Russian Far East). Type material Holotype: a parthenogenetic female 1.09 mm long from lake Dabanda (lower Amur river), in a tube with formalin deposited in the collection of the Zoological Museum of Moscow State University (Ml-1). Paratypes: one parthenogenetic female from lake Pir, deposited in the Natural History Museum (London) (1997. 1737). All other specimens in the author’s collection. Etymology The species was named D. pseudodubium after its superficial similarity with D. dubium.

Discussion Morphology and taxonomy D. dubium, D. tropicum, D. modigliani and D. pseudodubium undoubtedly represent a group of closely related species, widely distributed in Eastern and Southern Asia. The first three share a number of morphological traits such as large, dorsally protruding head with eye in ventral position, a fine seta (not spine) on the outer side of the tip of the antennal basipodite, denticulated antennal segments (especially an apical spine on the second segment of the upper branch), pattern of denticulation of the postero-ventral valve margin and absence of an inner dorsal spine at the posterior valve margin. D. pseudodubium stands apart by such different structures as a stout spine (not seta) on the end of the antennal basipodite, and an inner dorsal spine at the posterior valve margin. On the other hand, its head, antennal denticulation and valve margin armament are characteristic of the species group. Members of the group seem morphologically advanced, having an extremely well-developed locomotory apparatus. Only the antennules with setules look primitive, reminding us of D. senegal (Korovchinsky, 1991b). D. dubium possesses a number of peculiar morphological features, and it seems strange that this species

was not described decades ago, when the investigation of East Asian zooplankton started. At that time, D. mongolianum and D. chankensis, which differ less from D. brachyurum, were described (Ueno, 1938, 1939), but D. dubium continued to be regarded as a variety of the latter. But taxonomy of Diaphanosoma was based on few traditional traits, such as the relative length of swimming antennae and the structure of the ventral valve inflexion (Lilljeborg, 1901; Brehm; 1933; Korovchinsky, 1987). According to this system, species were subdivided in two groups – with and without ventral inflexion (in the modern sense, with a wide and narrow inflexion, respectively). Ueno (1938) described the developed ventral inflexion in D. mongolianum, which is present in all diaphanosoms, but incorrectly interpreted it to be similar with D. excisum and D. sarsi, which have a wide valve inflexion. It then appeared that the former species differs from the latter two in having a dorsally protruding head and another type of valve denticulation, which are currently regarded as diagnostic features. Thus, an initial mistake led to the correct description of D. mongolianum. The poorly described D. brachyurum was interpreted as a variable taxon, that ‘lacked’ a ventral inflexion, had a variable head shape, and swimming antennae (Ueno, 1937a). For this reason, D. dubium, with its inconspicuous ventral inflexion, was accepted as a variety. When Ueno (1939) paid more attention to the head shape and valve denticulation as taxonomic traits, his studies in continental East Asia were interrupted. After its description by Manuilova (1964), D. dubium continued to be poorly known. About 20 years later, it was shortly described from India (Kanduru, 1981) (this author distinguished D. dubium and ‘D. modigliani’) and Bangladesh (Hossain, 1982) but these data were unpublished and not included in the species lists by Sharma & Michael (1987) and Michael & Sharma (1988). In other regions of tropical Asia (Malaysia, Sri Lanka, Thailand, Philippines) only D. ‘modigliani’ was recorded (Mamaril & Fernando, 1978; Idris & Fernando, 1981; Rajapaksa, 1981; Rajapaksa & Fernando, 1982; Idris, 1983; Fernando & Rajapaksa, 1983; Boonsom, 1984; Mamaril, 1986; Piyasiri & Jayakody, 1991). At least two valid species (D. dubium, D. tropicum) have been confused under the name (Korovchinsky, 1998), due to incorrect interpretation of valve denticulation. D. dubium is considered as having of less than 20 denticles along the posteroventral margin, whereas in ‘D. modigliani’ these are

88 more numerous (Rajapaksa & Fernando, 1982). It became evident that D. dubium usually has more denticles on the valve margins (see Table 1), thus it was considered as ‘D. modigliani’ as well (e.g. in Parakrama Samudra Reservoir, Sri Lanka) (Fernando & Rajapaksa, 1983). The above mentioned conspicuous morphological differences between populations of D. dubium, especially from temperate and tropical regions, raises questions about their conspecificity. At the same time, interpopulation variability within one region may be rather pronounced (e.g. the populations from the Russian Far East and Mongolia (Figs 18 and 19), Vietnam (Figs 27 and 28), Sri Lanka and Thailand (Figs 37 and 38)). Does the variability in shape of the apical antennal spine (Table 2) reflect a genetic difference or just clonal diversity? Only genetic investigations may solve this problem. There are other examples of interpopulation differentiation in species with wide latitudinal distribution. Thus, populations of North American Pleuroxus denticulatus, and Eurycercus from northern and southern regions differ at the species level but are practically identical morphologically (Hann, 1982; Shan & Frey, 1983; Frey, 1986). On the other hand, some well studied Chydoridae (Oxyurella and Disparalona) do not demonstrate such a pattern (Michael & Frey, 1983, 1984). The data on other Cladocera are contradictory in respect of latitudinal, ecological, genetic and taxonomic differentiation (Hebert et al., 1989; Ward et al., 1994; Hann, 1995; Hebert & Finston, 1996). In particular, a relationschip between genetic divergence and geographic distance has not been confirmed. Some notes on biology In spite of wide geographical distribution and abundance, the biology of D. dubium is poorly known. Here, I summarize some scattered facts on the subject. D. dubium inhabits the pelagic and littoral of large and small lakes, reservoirs, ponds (e.g. Lotus ponds), swamps and rice-fields. Limited data on physical- and chemical conditions indicate its occurrence in fresh waters with pH 7.2–8.5. Korinek (1987) incorrectly recorded D. dubium in brackish-water Dalai-nor, where Ueno (1938) only found D. mongolianum, while a D. brachyurum with large elongated head (possibly D. dubium) was obtained from neighbouring lake Hailar. D. dubium obviously tolerates high temperature (28 ◦ C in Jiling

Figure 62. Size-frequency distribution of D. dubium specimens from two populations (A – Kuala Kangsar, Malaysia, 11.10.1974; B – Mymensingh, Bangladesh, 27.11.1979). Black parts – ovigerous females, arrows indicate the minimal size of ovigerous female.

Province, China), and is abundant in summer in subtropical eastern China (Hodgkiss & Chan, 1976). In subtropical lake Tai-hu and Plover Core reservoir (East China) (‘D. dubium leuchtenbergianum’) it was common from May to November, but rare in winter (Du et al., 1964; Hodgkiss & Chan, 1976). In Bangladesh, it was found in December, and in Sri Lanka in January and April (Piyasiri & Jayakody, 1991). It dominates zooplankton communities (up to 90 ind l−1 of total planktonic crustaceans) and performs daily vertical migrations (Hodgkiss & Chan, 1976). The size-frequency distribution of two populations from Malaysia and Bangladesh is shown in Figure 62. Juveniles predominated in the former, adult parthenogenetic females in the latter. The juveniles had a minimum body length 0.28 mm and ovigerous females were 0.63–0.64 mm (0.56 mm in population from Jilinshi, China) whereas maximum body length reached 1.12–1.23 mm (up to 1.54 mm in general). Most females carried 1–8, usually 1–4 eggs or embryos in their brood pouches. The fertility was high

89 Table 4. Co-occurrence of Diaphanosoma dubium with Limnosida frontosa and other Diaphanosoma species Region

Lakes of Amur river Primorsky Territory Central Asia Central China Central-East Chine South China North Vietnam Thailand Philippines Malaysia Bangladesh Sri Lanka

Limnosida Diaphanosma D. mongolianum D. chankensis D. macrophthalma D. dumonti D. sarsi D. excisum frontosa orghidani +

+ + + +

+ + +

+ + + +

+ +

+

+ + +

(3.2 and 2.0 eggs per female, in the latter many eggs looked resorbed). Males occurred in July–October in the northern part of the range while in the south they were absent. Table 4 summarizes the co-occurrence of D. dubium with other Sididae: Limnosida frontosa and seven other Diaphanosoma species. Limnosida and D. orghidani transamurensis, supplemented by D. mongolianum and D. macrophthalma were most usual in the north, whereas in the south they were substituted by D. sarsi and D. excisum. The highest species richness was observed in Central-East China. Mostly D. dubium co-occurred with one Diaphanosoma species (often D. excisum in North Vietnam) sometimes with two (D. mongolianum and D. macrophthalma in Inner Mongolia), D. excisum, D.o.transamurensis and D. sarsi in different combinations (in Bangladesh, Thailand and Philippines), and once with three species (D. mongolianum, D. macrophthalma, D. sarsi, in a pond of the Kashkadarja fish-farm Uzbekistan). This represents the highest registered local species diversity of the genus in the Eastern Hemisphere (Korovchinsky & Mirabdullaev, 1994). In general, D. dubium is the largest species in this size assemblage, but average size of mature females is usually reaching just 0.9-1.0 mm in populations from Malaysia and Bangladesh (Fig. 62). This fact, coupled with a strongly developed swimming apparatus may ensure the survival of the species under the high predation pressure of the tropics (Kerfoot & Lynch, 1987;

+

+ + + + + + +

Korovchinsky, 1990, 1998; Dumont, 1994; Dumont & Segers, 1996). Geographical distribution D. dubium covers an extensive range, from the lower Amur River in the north to the equatorial zone (Malaysia, Sri Lanka) and from Central Asia and Northern India in the west to Japan and the Philippines in the east (Fig. 63). In Amur region, it is known from the mouth of the Sungari river to lake Orel’ near the Amur mouth (53◦ 300 N), where it is found in all flood-plain lakes. To the south, it occurs extremely from lake Khanka and neighbouring waters in Primorsky Territory through Northern China to Inner Mongolia and lake Buir-nor in Eastern Mongolia. Common all over eastern China, this species’ western limit distribution may lie in Central Sychuan and Western Yunnan, in agreement with Chiang & Du (1979). Obviously, it does not extend through Southern Siberia, Mongolia and western China’s deserts with saline and brackish waterbodies and high altitude. Instead, it reaches to the south, through Bangladesh to Central and Northern India, and Sri Lanka. D. dubium is often local within its range. Thus, it was found in 30% of samples from China (more or less in the same proportion in Inner Mongolia, NorthEastern and Eastern regions), and in 76% of samples from North Vietnam. It was absent from 14 samples from Laos (Vientiane City) (unpublished data). In southernmost regions (Malaysia, Sri Lanka), D. dubium seems rare, but may have been confused with D.

90

Figure 63. Geographical distribution of D. dubium (1 – previously known localities, 2 – new localities) and D. pseudodubium (3). One dot may include several localities.

tropicum (‘D. modigliani’), as well as in India where it has been recorded in the centre (Kanduru, 1981) and in the vicinity of Delhi City (present paper). Until recently, D. dubium was not found in Central Asia and Kazakhstan (Korovchinsky & Mirabdullaev, 1994). A supposed occurrence in Kapchagayskoye

Reservoir (Ibrasheva & Smirnova, 1983) is incorrect (Korovchinsky, 1987). The same is true for its record from the South-Western Ukraine (Polyschuk, 1974) where it probably was confused with D. mongolianum. The Central Asian localities do not seem directly connected with the main range. A northern connection

91 through Mongolia and Western China is improbable (D. dubium has never been recorded in well studied lakes in Western Mongolia), and the Indian localities also look few and distant. It is, therefore, probable that D. dubium was introduced to Uzbekistan and Kazakhstan with Far Eastern fish. This suggestion is supported by the fact restriction of the species to fish ponds with Hypophthalmichthys molitrix. For the same reason, the occurrence of D. dubium in India and Sri Lanka may also be a recent introduction. D. pseudodubium, finally, is undoubtedly a rare species, and more samples are needed to understand its distribution.

Acknowledgements I am indebted to Prof. H. J. Dumont (Ghent University, Belgium), Prof. C. H. Fernando (Waterloo University, Canada), Dr M. V. Geptner (Zoological Museum of Moscow State University) and Dr L. A. Kutikova (Zoological Institute, St-Peterburg) for the possibility to work in their laboratories and borrow material for this study. The late Prof. D. G. Frey and others mentioned in the list of material, supplied me with valuable samples as well. Prof. H. J. Dumont kindly edited the manuscript, and Mrs C. De Clerk retyped it nicely. This work was supported by the Russian Foundation for Basic Research (grant N 99-04-48969).

Addendum After accepting of the manuscript for publication D. dubium was found recorded in West Bengal (India) under the name “D. brachyurum” (Venkataraman & Das, 1994). This species has also been found in the sample from Lake Shitaka (Ohito Prefecture, Kyushu, Japan, 21. 04. 1984; 33◦ 150 N; 131◦ 270 E) kindly sent to me by Dr. S. Tanaka (Toyama University, Japan). The suggested wide distribution of D. dubium in Kazakhstan (T.S. Stuge, E.G. Krupa, pers. comm.) needs further confirmation.

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