A Review of the Genus Thermocyclops - Zoological Studies

Chaicharoen et al. – Review of Thermocyclops in Cambodia 781framing a project with the goal of revising thefreshwater cyclopoid and calanoid fauna ofCambodia, we organized 3 collecting trips in 2007and visited 7 provinces of the country. The presentreport is based on that material.MATERIALS AND METHODSIn total, 252 samples were analyzed from7 provinces (Banteay Meanchey, Battambong,Siem Reap, Kampong Thom, Pursat, Kratie,and Stung Treng) of Cambodia. Collection dataare given at the descriptions of the particularspecies, and the localities are also shown on amap (Fig. 1). Unless otherwise stated, specimenswere collected by the senior author. Specimenswere measured in glycerol, with bright-field anddifferential interference contrast optics. Drawingswere made using a camera lucida on an OlympusBX50 compound microscope (Tokyo, Japan).Telescoping segments of the prosome andurosome were measured separately, yet bodylength (BL) was measured as the distance betweenthe anteriormost point of the cephalothorax andposteriormost point of the caudal ramus. Thelength of pediger 4 was measured as the distancebetween its anteriormost and posteriormost points.Only females were identified and are describedhere, as the identification keys (e.g.Mirabdullayev et al. 2003) do not include charactersof the male, and information on male morphologyis very fragmentary.The following abbreviations were used: enp,endopodite; exp, exopodite; P1-P4, swimminglegs 1 to 4; S1, medialmost terminal caudal seta;S2, inner median terminal caudal seta; S3, outermedian terminal caudal seta; S4, lateralmostterminal caudal seta; S5, dorsal caudal seta;SMNK, Staatliches Museum für NaturkundeKarlsruhe (Karlsruhe, Germany).NTHAILANDLAOS PDRBantean MeancheySiem ReapStung TrenghMekong RiverLake SapKampong ThomKratieBattambongPursatVIETNAMFig. 1. Collecting localities of Thermocyclops species in Cambodia.

782 Zoological Studies 50(6): 780-803 (2011)TAXONOMYThermocyclops wolterecki Kiefer 1938(Figs. 2-8)Thermocyclops wolterecki Kiefer 1938a: 54-98, figs. 24-28;Defaye et al. 1987: 3144-3153, figs. 30-34; Mirabdullayevet al. 2003: 271, fig. 128; Alekseev and Sanoamuang2006: 277-290, table 2.Material examined: Type material: Lectotype(female): T. wolterecki n. sp. Kiefer 8.5.38;Mindanao, Lanaosee Woltereck Phil. 151, 3undissected females (lectotype marked by arrowon slide) SMNK slide 4005. Paralectotypes:T. wolterecki n. sp. Kiefer 8.5.38; Mindanao,Lanaosee Woltereck Phil. 151, 2 undissectedfemales, SMNK slide 4005. T. wolterecki n. sp., 1undissected female (together with 1 undissectedfemale of T. hyalinus), Kiefer 8.5.38; Mindanao,Lanaosee Woltereck Phil. 151, SMNK slide 4007(Franke 1989).Other material: The Philippines: T. woltereckiPhilippines, Mindanao, Lanaosee, coll. Woltereck(Phil. 151), G: 1092 SMNK, glas 4905 (Franke1989), 1 . Cambodia: Kampong Cham-Kratieborder, Dambei Dist., canal, 12°07'N, 105°53'E,9 June 2007, 1 , slide CB5(1A,B); Kratie Prov.,Bos Leav Dist., Ta Aim, stream, 12°21'N, 106°03'E,10 June 2007, 1 , slide CB11(1A,B); Kratie Prov.,Kratie Dist., Kratie, stream, 12°42'N, 106°07'E, 10June 2007, 1 , CB21(1A,B); Stung Treng Prov.,Stung Treng Dist., small pond, 13°31'N, 105°59'E,11 June 2007, 1 , slide CB36(1A,B); Stung TrengProv., Stung Treng Dist., temporary pond, 13°16'N,106°06'E, 11 June 2007, 1 , slide CB46(1A,B);Siem Reap Prov., Sotnikum Dist., Lveate, canal,13°24'N 103°47'E, 26 Oct. 2007, 10 , slideCB55(1A,B-10A,B); Kampong Thom Prov., BarayDist., Sroyong, canal, 12°12'N, 105°07'E, 14 June2007, 1 female, slide CB71(1A,B); Pursat Prov.,12°41'N, 103°36'E, 26 Oct. 2007, 10 , slideCB99(1A,B-10A,B).Redescription (based on specimens fromLake Lanao): Female length 570-620 µm (lectotype~570 µm); cephalothorax width/genital doublesomitewidth: 2.68-3.18 (lectotype 2.68).Pediger 5 without ornamentation (Fig.2A, C). Genital double-somite (Fig. 2C, D) aslong as wide or slightly longer. Lateral arms ofseminal receptacle (Fig. 2C, D) slightly curvedposteriorly. Posterior margin of anal somite withfew spinules ventrally (Fig. 2B). Caudal rami (Fig.2B) 2.2-2.5-times as long as wide (in lectotype2.31), without hairs on medial margin. No spinulesat implantation of lateral seta and S4. S1/caudalrami = 2.2-2.4; S1/S4 = 2.3-2.5; S1/S5 = 1.6-1.8 (inlectotype 2.36, 2.33, and 1.45, respectively). Tipof S2 curved ventrally (Fig. 2B).Antennule 17-segmented (Figs. 3A, B, 6A,B), reaching pediger 2. Armature formula: 8, 4,2, 6, 4, 1+spine, 2, 1, 1, 0, 1, 1+aesthetasc, 0, 1,2, 2+aesthetasc, 7+aesthetasc. Last 2 segments(Figs. 3B, 6B) bearing hyaline membrane, membraneon segment 17 not extending beyondinsertion of medial seta, without notch. Aesthetascson segments 12 and 16 reaching distalmargin of segments 14 and 17, respectively.Lateral seta on segment 15 (Figs. 3B, 6B) notreaching middle of segment 16. Antennal enp2with 9 setae. Posterior ornamentation of coxobasis(Figs. 3C, 6D): robust spinules in longitudinal andoblique rows near lateral margin; group of tinyspinules between oblique and longitudinal rows;few spinules on medial margin near base. Anteriorsurface of coxobasis (Figs. 3D, 6E) armed withspinules in short longitudinal row in proximal 1/2 ofsegment near lateral margin.Mandible (Fig. 3E) with palp bearing 2 longand 1 short setae, no ornamentation near palp.Maxillule (Fig. 3F) with armature common in family,no ornamentation on maxillulary palp. Maxilla(Fig. 3G) with syncoxopodite, basipodite, and2-segmented endopodite; armature formula: 5(syncoxopodite with 3 endites, 2, 1, and 2 setae,respectively), 2, 2, and 3. No ornamentation onsyncoxopodite.Medial spine of P1 basipodite (Fig. 4 A)reaching distal margin of endopodite 2. Fewshort setules present on lateral edge of spine.Medial expansion of basipodites of P1-P3 withhairs, no ornamentation on P4 (Fig. 4D). Distalprotuberances of P1-P4 couplers (Fig. 4A-D)rounded. Spinules robust on protuberances ofP1-P3, and tiny on protuberances of P4. P1-P3 couplers anteriorly and posteriorly bare. P4coupler with 1 row of hairs near distal margin and1 row of spinule-like elements in middle (Fig. 4D)in specimens from Lake Lanao. On posteriorsurface on P4 coxopodite, many spinules alongdistal margin, group of spinules arranged in rowat laterodistal angle, and many small spinulesnear proximal margin. P4 enp3 (Fig. 4D) 3.12-3.69 (in lectotype ~3.5)-times as long as wide; ofapical spines, medial one 2.0-2.4-times as longas lateral, medial spine 0.77-0.89-times as longas endopodite 3 (in lectotype 0.83). P5 (Fig. 1A)typical for genus.

Chaicharoen et al. – Review of Thermocyclops in Cambodia 783Variability: Variation in the morphometrictraits is shown in tables 1, 2. The Philippineand Cambodian populations differ in somemorphometric and qualitative morphologicalcharacters. Twenty-three morphometric characterswere measured in the Cambodian populationand in material from the type locality, Lake Lanao(Tables 1, 2). Dice-Leraas diagrams (Fig. 5)point to the separation of the 2 populations in thelengths of the body, caudal rami, inner terminalcaudal seta (S2), and dorsal caudal seta (S5).A t-test confirmed significant differences in themeans of these traits (body length: n = 15, p < 0.01;length of caudal rami: n = 15, p < 0.01; lengthof s2: n = 15, p < 0.01; and length of s5: n = 15,p < 0.01) between Cambodian and Philippinefemales. The qualitative morphological charactersof the Cambodian specimens however almost fullymatch those of females from Lake Lanao, with onlythe ornamentation of the P4 coupler and tip of S2differing between them. In Cambodian females(Fig. 7B), the P4 coupler bears 2 rows of hairs (inthe middle and next to the distal margin), while inPhilippine specimens, 1 hair-row appears near thedistal margin and 1 row of spinule-like elementsis present in the middle (Fig. 4D). The tip of S2 is(A)(B)(C)(D)Fig. 2. Thermocyclops wolterecki, female (Lake Lanao, the Philippines). (A) Urosome, ventral view; (B) caudal rami, ventral view; (C, D)genital double-somite, ventral view. (A, B) SMNK Glas 4905; (C, D) paralectotypes SMNK 4005. Scale bars = 50 µm.

784 Zoological Studies 50(6): 780-803 (2011)(A)(B)(C)(D)(E)(F)(G)Fig. 3. Thermocyclops wolterecki, female (Lake Lanao, the Philippines). (A, B) Antennule, anterior view: (A) segments 1-14; (B)segments 13-17; (C) antenna, posterior view; (D) antennal coxobasis, anterior view; (E) mandible; (F) maxillule, posterior view; (G)maxilla, anterior view. (A-G) SMNK Glas 4905. Scale bars = 50 µm.

Chaicharoen et al. – Review of Thermocyclops in Cambodia 785ventrally curved in Philippine (Fig. 2B) but straightin Cambodian specimens (Fig. 7C).Remarks: Kiefer (1938a) originally describedthe species from Lake Lanao (Mindanao, thePhilippines). He did not designate a holotype;therefore herein we designated a lectotype fromamong the syntypes (Fig. 8). Defaye et al. (1987)reported T. wolterecki from Papua New Guinea,and Alekseev and Sanoamuang (2006) foundit in Thailand. The geographic distribution of T.wolterecki seems to be restricted to Asia [ThePhilippines (Mindanao), Thailand, and Cambodia]and Papua New Guinea.Four morphometric characters (lengths of thebody, caudal rami, and S2 and S5 caudal setae),and 2 qualitative characters (ornamentation of theP4 coupler and tip of S2 caudal setae) significantlydiffered between the Cambodian and Lake Lanaopopulations.Lake Lanao was supposedly formed inthe late Tertiary. It is the deepest lake in thePhilippines, with a maximum depth of 112 m, and(A)(B)(C)(D)Fig. 4. Thermocyclops wolterecki, female (Lake Lanao, the Philippines). (A) P1, posterior view; (B) P2, posterior view; (C) P3,posterior view; (D) P4, posterior view. (A-D) SMNK Glas 4905. Scale bar = 50 µm.

786 Zoological Studies 50(6): 780-803 (2011)Body length (µm)Caudal ramus (µm)690670650630610590570550CambodiaLake Lanao(Philippines)424140393837363534CambodiaLake Lanao(Philippines)S2 (µm)S5 (µm)230220Lake Lanao(Philippines)7065Lake Lanao(Philippines)2106020055190180Cambodia5045Cambodia170401603515030Fig. 5. Comparison of morphometric traits of Lake Lanao and Cambodian populations of Thermocyclops wolterecki. Diagrams showthe mean, range, and confidence intervals (± 2 standard errors).Table 1. Morphometric data on Thermocyclops wolterecki in Lake Lanao (Mindanao, the Philippines,SMNK) and Cambodia (CB 55). BL, body length; C, Cambodia; Cep, cephalothorax; CR, caudal ramus; GS,genital double-somite; l, length; nd, no data; P, Philippines; Pro, prosome; Uro, urosome; w, width. M, mean;SD, standard deviation; SE, standard errorNo BL (µm) Cep l/w Pro l (µm) GS (l/w) GS w/Cep w Uro l (µm) Pro l/Uro l CR l (µm) CR l/wC P C P C P C P C P C P C P C P C P1 610 570 1.15 1.01 415 357.5 1.35 1.11 0.36 0.36 285 232 1.46 1.81 40 39 2.00 2.432 660 590 1.16 1.01 452.5 362.5 1.42 1.11 0.40 0.36 287.5 235 1.57 1.47 40 38 2.16 2.373 660 570 1.15 1.02 422.5 362.5 1.26 1.10 0.35 0.35 297.5 240 1.42 1.51 42 37 2.26 2.314 640 620 1.15 1.06 417.5 362.5 1.52 1.11 0.36 0.35 290 232 1.43 1.56 40 35 2.00 2.505 660 nd 1.21 nd 355 nd 1.35 1.00 0.42 nd 297.5 228 1.05 nd 42 38 2.10 2.316 610 - 1.17 - 417.5 - 1.46 - 0.35 - 302.5 - 1.38 - 44 - 2.22 -7 610 - 1.15 - 407.5 - 1.28 - 0.34 - 300 - 1.35 - 40 - 2.10 -8 620 - 1.15 - 412.5 - 1.25 - 0.33 - 282.5 - 1.46 - 40 - 2.10 -9 600 - 1.22 - 352.5 - 1.17 - 0.39 - 297.5 - 1.18 - 40 - 2.10 -10 630 - 1.16 - 387.5 - 1.25 - 0.35 - 287.5 - 1.34 - 42 - 2.10 -SE 7.45 11.8 0.01 0.02 9.77 1.25 0.03 0.02 0/01 0.002 2.22 1.98 0.05 0.08 0.45 0.68 0.03 0.04SD 23.57 23.6 0.03 0.04 30.89 2.5 0.11 0.05 0.03 0.01 7.02 4.41 0.15 0.15 1.41 1.52 0.08 0.08M 630 587.5 1.17 1.05 404 361.2 1.33 1.09 0.37 0.35 293 233.5 1.37 1.58 41 37.4 2.11 2.38

Chaicharoen et al. – Review of Thermocyclops in Cambodia 787is home to many endemic invertebrate and fishspecies, e.g., 18 endemic cyprinid species (Myers1960, Frey 1969). In contrast, in Cambodia, T.wolterecki was collected from small, shallow waterbodies such as ponds, rice paddies, and canalswith some vegetation along the edges. Literaturedata suggest that some morphometric characterscan be environment-dependent. Large-scalecomparisons made in Cyclops scutifer G. O. Sarsfrom Eurasia and North America (Elgmork andHalvorsen 1988) showed that morphometric traitswere correlated with environmental factors suchas depth, temperature, and trophic condition.Relationships between the habitat and differentmorphological characters were also found inother cyclopid taxa. Mesocyclops leuckarti(A)(B)(C)(D)(E)Fig. 6. Thermocyclops wolterecki, female (Cambodia). (A, B) Antennule, anterior view: (A) segments 1-10; (B) segments 11-17; (C)pediger 5 and genital double-somite, ventral view; (D, E) antenna: (D) posterior view; (E) coxobasis, anterior view. (A-E) Locality CB99.Scale bars = 50 µm.

788 Zoological Studies 50(6): 780-803 (2011)bodanicola (population from Lake Constance,Germany) (Kiefer 1938b), a “subspecies” of M.leuckarti, showed a smaller body length andrelatively longer caudal rami and caudal setaeamong other traits. However, the occurrence ofintermediate forms, the geographical distribution,and successful hybridization of the “bodanicola”and typical leuckarti forms (Einsle 1968, Kiefer1978) indicated that M. leuckarti bodanicola wasa pelagic ecotype rather than a subspecies of M.leuckarti (Hołyńska et al. 2003). Hołyńska (1997)also reported intraspecific variation in M. dissimilis,where the littoral form (Lake Kitaura, Honshu,Japan) showed a larger body length, relativelylonger medial spine but shorter lateral seta onP5, as well as shorter caudal rami, P4 enp3,and dorsal caudal seta, compared to a pelagicpopulation (Lake Biwa, Honshu, Japan). Hołyńskainterpreted the differences as adaptations to thepelagic/littoral mode of life. In T. kawamurai, 1940,intraspecific variation was reported in both thebody ratios and spinule ornamentation of the P3coupler (Mirabdullayev 2006).We suppose that curved or straight tips of(A)(B)(C)Fig. 7. Thermocyclops wolterecki, female (Cambodia). (A) P3, posterior view; (B) P4, posterior view; (C) caudal rami and setae,ventral view. (A-C) Locality CB99. Scale bar = 50 µm.

Chaicharoen et al. – Review of Thermocyclops in Cambodia 789S2 caudal setae are presumably an environmentdependentcharacter, which vary from straight tipsin the littoral population (Cambodia) to stronglycurved tips in a pelagic habitat (Lake Lanao).More data are needed on the morphometrics,and S2 and P4 coupler morphology in both thelittoral and pelagic populations in Lake Lanao andCambodia to answer the following questions: Dothe littoral populations of T. wolterecki in LakeLanao have the same morphology as the smallwater-bodypopulations in Cambodia?; and Doforms with intermediate morphologies exist?Fig. 8. Position of the syntypes of Thermocyclops woltereckion slide SMNK 4105. The lectotype designated herein ismarked with an arrow.Thermocyclops maheensis (Lindberg, 1941)(Figs. 9-12)Mesocyclops (Thermocyclops) maheensis Lindberg 1941: 259-265, fig. 1, table 1; Herbst 1986: 165-180; Thermocyclopsmaheensis Mirabdullayev et al. 2003: 246, fig. 113;Alekseev and Sanoamuang 2006: 277-290, table 2.Material examined: Cambodia: Kratie Prov.,Sambo Dist., Kbal Damrey, pond, 12°50'N,106°10'E, 14 Feb. 2007, 1 , slide CB20(1A,B);Kratie Prov., pond, 12°51'N, 106°11'E, 14 Feb.2007, 1 , slide CB21(1A,B); Stung Treng Prov.,irrigation canal, 13°31'N, 105°59'E, 15 June2007, 1 , slide CB31(1A,B); Stung Treng Prov.,temporary pond, 13°19'N, 106°06'E, 12 June2007, 1 slide CB45(1A,B); Stung Treng Prov.,pond, 13°16'N, 106°06'E, 12 June 2007, 1 , slideCB46(1A,B).Diagnosis: Female (Cambodia). Pediger5 without lateral hairs or spinules (Fig. 9A).Seminal receptacle cruciform, lateral arms curvedposteriorly. Caudal rami (Fig. 9B) with pits onventral surface, no medial hairs. No spinules atimplantation of lateral seta or S4. Tip of S2 varyingfrom straight to strongly curved ventrally.Antennule (Fig. 10A-C) 17-segmented,reaching posterior margin of pediger 4. Hyalinemembrane on last segment extending beyondinsertion of medial seta of segment, withoutnotch. Antennal (Fig. 11B) enp2 with 7 setae.Table 2. Morphometric data on Thermocyclops wolterecki in Lake Lanao (Mindanao, the Philippines,SMNK) and Cambodia (CB 55). C, Cambodia; CR, length of caudal ramus; m/l, medial spine/lateral spine ofP4 endopodite 3; P, Philippines; P4 enp3, P4 endopodite 3 length/width; S1, length of medialmost terminalcaudal seta; S2, length of inner median terminal caudal seta; S3, length of outer median terminal caudalseta; S4, length of lateralmost terminal caudal seta; S5, length of dorsal caudal seta; S6: length of lateralcaudal seta; SE, standard error; M, mean; SD, standard deviationNo S1 (µm) S2 (µm) S3 (µm) S4 (µm) S5 (µm) S6 (µm) S1/CR S1/S4 S1/S5 P4 enp3 m/lC P C P C P C P C P C P C P C P C P C P C P1 105 87 162 207 150 150 45 37.5 40 63 20 24 2.6 2.2 2.33 2.33 2.63 1.39 3.12 3.58 2.00 2.052 100 87 160 200 138 140 45 37.5 44 61 20 26 2.5 2.3 2.22 2.33 2.27 1.43 3.33 2.98 1.95 1.893 110 87 175 222 150 148 45 37.5 40 60 22 25 2.6 2.4 2.44 2.33 2.75 1.46 3.2 3.50 1.90 1.944 100 87 172 220 150 143 45 37.5 40 60 20 24 2.5 2.5 2.22 2.33 2.5 1.46 3.33 3.08 2.00 2.05 103 95 170 222 150 150 48 36 40 65 22 28 2.4 2.5 2.14 2.64 2.56 1.46 3.18 3.41 1.90 2.16 105 - 172.5 - 150 - 42.5 - 39 - 20 - 2.39 - 2.47 - 2.69 - 3.42 - 1.95 -7 100 - 175 - 153 - 42.5 - 40 - 20 - 2.50 - 2.35 - 2.5 - 3.42 - 2.00 -8 100 - 162.5 - 143 - 47.5 - 40 - 20 - 2.50 - 2.11 - 2.5 - 3.5 - 1.90 -9 103 - 162.5 - 133 - 45 - 43 - 22.5 - 2.56 - 2.28 - 2.38 - 3.42 - 1.90 -10 100 - 150 - 138 - 47.5 - 40 - 20 - 2.38 - 2.11 - 2.5 - 3.2 - 2.10 -SE 1.05 1.5 2.56 4.58 2.25 2.04 0.61 0.3 0.5 0.97 0.38 0.7 0.03 0.05 0.03 0.06 0.04 0.01 0.04 0.12 0.02 0.04SD 3.33 3.3 8.1 10.2 7.12 4.54 1.92 0.7 1.5 2.17 1.21 1.6 0.08 0.12 0.13 0.14 0.14 0.03 0.13 0.27 0.07 0.09M 103 89 166.3 214.5 145 146 45.3 37 40 61.8 20.8 25.4 2.50 2.38 2.27 2.39 2.53 1.44 3.31 3.31 1.96 2.00

790 Zoological Studies 50(6): 780-803 (2011)(A)(B)Fig. 9. Thermocyclops maheensis, female (Cambodia). (A) Pediger 5 and genital double-somite, ventral view; (B) caudal rami, ventralview. (A) Locality CB21, (B) locality CB20. Scale bar = 50 µm.(A)(B)(C)Fig. 10. Thermocyclops maheensis, female (Cambodia). (A-C) Antennule, anterior view: (A) segments 1-7; (B) segments 8-15; (C)segments 15-17. (A-C) Locality CB21. Scale bar = 50 µm.

Chaicharoen et al. – Review of Thermocyclops in Cambodia 791Posterior ornamentation of antennal coxobasis(Fig. 11B): 8-14 robust spinules in longitudinalrow and 5 or 6 spinules in oblique row near lateralmargin; group of tiny spinules between obliqueand longitudinal rows absent (usually present inThermocyclops); few spinules on medial marginnear base. Antennal coxobasis (Fig. 11A)anteriorly with spinules in short longitudinal rowin proximal 1/2 of segment near lateral margin.Lateral protuberances of labrum with small teeth(Fig. 11C), distal fringe hairs in groups. Palp ofmandible (Fig. 11D) bearing 2 long and 1 shortsetae, no ornamentation near palp. Maxillule(Fig. 11E) with armature common in family,maxillulary palp (Fig. 11F) without ornamentation.Syncoxopodite of maxilla (Fig. 11G) without spinuleornamentation. Syncoxopodite of maxilliped (Fig.11H) with transverse rows of spinules in middle ofsegment.Medial spine of P1 basipodite (Fig. 12A)reaching distal margin of enp2. Medial expansionof basipodite of P1-P3 pilose (Fig. 12A-C), that ofP4 bare (Fig. 12D). Distal protuberances of P1-P4 couplers (Fig. 12A-D) rounded and withoutspinules. P1-P4 couplers anteriorly and posteriorlybare. P5 typical for genus. For morphometric datasee table 3.Remarks: Cambodian females differ fromIndian specimens (Lindberg 1941, Mirabdullayevet al. 2003) in 3 characters. Tips of the S2 caudalsetae are strongly curved in Indian specimens, yetthey vary from straight to strongly curved in theCambodian population. In Cambodian females,the medial expansion of the basipodite is piloseon P1-P3 and bare on P4, while in the Mysorepopulation, the basipodite is pilose on P1 and bareon P2-P4. The anal somite ventrally bears 9 or10 spinules on the posterior margin in Cambodian(B)(C)(D)(A)(E)(G)(H)(F)Fig. 11. Thermocyclops maheensis, female (Cambodia). (A) Antennal coxobasis, anterior view; (B) antenna, posterior view; (C)labrum; (D) mandible; (E, F) maxillule: (E) maxillule, posterior view; (F) maxillulary palp, anterior view; (G) maxilla, anterior view, setaeon the proximalmost endite of the syncoxopodite are separately figured; (H) maxilliped, anterior view. (A-H) Locality CB21. Scale bars= 50 µm.

792 Zoological Studies 50(6): 780-803 (2011)(A)(B)(C)(D)Fig. 12. Thermocyclops maheensis, female (Cambodia). (A) P1, posterior view; (B) P2, posterior view; (C) P3, posterior view; (D) P4,posterior view. (A) Locality CB21, (B-D) locality CB20. Scale bar = 50 µm.Table 3. Morphometric data on Thermocyclops (female) from Cambodia. BL, body length; GS(l/w), genitaldouble-somite length/width; Cep/GS, cephalothorax width/genital double-somite width; CR(l/w), caudalrami length/width; S1/CR, length of medialmost terminal caudal seta/ length of caudal rami; S1/S4, lengthof medialmost terminal caudal seta/length of lateralmost terminal caudal seta; S1/S5, length of medialmostterminal caudal seta/length of dorsal caudal seta; P4 enp3 l/w, P4 endopodite 3 length/width; P4 enp3spines, P4 endopodite 3 medial apical spine/lateral apical spine; P4 enp 3 spine/segment, medial apicalspine of P4 enp 3/P4 enp3 lengthSpecies BL (µm) GS(l/w) Cep/GS CR(l/w) S1/CR S1/S4 S1/S5P4 enp3l/w spines spine/ segmentT. crassus 680-780 1.17-1.23 2.57-3.12 1.88-2.25 2.90-3.33 2.55-2.89 2.37-2.75 2.87-3.30 1.80-2.83 0.85-0.95T. decipiens 760-890 1.16-1.28 2.04-3.05 2.20-2.88 2.46-3.10 2.48-3.26 2.07-2.69 3.0 -4.0 2.18-3.11 0.87-0.96T. maheensis 810-950 1.06-1.36 1.38-1.48 3.17-3.63 2.10-2.40 2.50-3.50 1.09-1.45 2.80-3.44 1.87-2.53 0.90-0.98T. rylovi 780-860 1.02-1.09 2.39-2.75 2.39-3.75 1.78-2.28 2.45-2.71 2.19-2.90 2.09-3.46 1.90-2.75 0.79-0.91T. vermifer 780-800 1.09-1.27 2.30-2.90 2.20-2.80 2.10-2.90 2.20-2.90 1.80-2.80 2.94-3.64 2.16-3.05 0.85-0.98

Chaicharoen et al. – Review of Thermocyclops in Cambodia 793females, while 0-6 spinules are present in SouthIndian specimens.Thermocyclops maheensis was describedfrom Mahé in South India (Lindberg 1941).Alekseev and Sanoamuang (2006) reported thespecies from the Nampong River in northeasternThailand. The occurrence data provided herefrom Cambodia (Kratie and Stung Treng) are theeasternmost records of this species.Thermocyclops vermifer (Lindberg 1935)(Fig. 13)Mesocyclops rylovi vermifer Lindberg 1935 (in part): 415-419,figs. 7-9; Mesocyclops vermifer Lindberg 1938: 211-236; Mesocyclops (Thermocyclops) vermifer Lindberg1942: 139-190; Thermocyclops rylovi vermifer Lindberg1959: 1-26; Thermocyclops vermifer Mirabdullayev andKuzmetov 1997: 201-212; Mirabdullayev et al. 2003: 275-277; Guo 1999: 87-95, figs. 13-22.(A) (B) (C)(D)(E)(G)(H)(F)(I)Fig. 13. Thermocyclops vermifer, female (Cambodia). (A) Pediger 5 and genital double-somite, ventral view; (B) antennular segments12-17; (C, D) antenna: (C) posterior view; (D) coxobasis, anterior view; (E, F) P1: (E) protopodite and exopodite posterior view; (F)endopodite, posterior view; (G) P4, posterior view; (H) P1 coupler, anterior view; (I) P3 coupler, anterior view. (A-I) Locality CB20.Scale bar = 50 µm.

794 Zoological Studies 50(6): 780-803 (2011)Thermocyclops crassus morpha kairakkumensis Ulomsky 1963:95-123.Material examined: Cambodia: KratieProv., Kratie Dist., Chang Krong, pond, 12°35'N,106°05'E, 10 June 2007, 1 , slide CB17(1A,B);Kratie Prov., Sambo Dist., Kbal Damrey, permanentpond, 12°50'N, 106°10'E, 14 Feb. 2007, 1 , slideCB20(1A,B); Pursat Prov., Sbr Prah Dist., DongKrasain, swamp, 12°20'N, 106°16'E, 28 Oct. 2007,1 , slide CB73(1A,B); Battambong Prov., SangkeiDist., Kampong Preang, irrigation canal, 12°54'N,103°21'E, 20 Feb. 2007, 1 , slide CB77(1A,B).Diagnosis: Female (Cambodia). Pediger5 (Fig. 13A) without hairs or spinules on lateralsurface. Genital double-somite as long as wideor slightly longer, with transverse rows of pits(not shown on drawing). Lateral arms of seminalreceptacle (Fig. 13A) slightly curved posteriorly.Caudal rami without hairs on medial margin. Nospinules at implantation of lateral seta or S4. Tipof S2 slightly curved ventrally.Antennule 17-segmented, hyaline membraneon last segment not extending beyondimplantation of medial seta, without notch (Fig.13B). Aesthetascs on segments 12 and 16reaching beyond middle of segments 14 and 17,respectively. Lateral seta on segment 15 (Fig.13B) not reaching middle of segment 16. Antennalenp2 with 9 setae. Posterior ornamentationof coxobasis (Fig. 13C): 7-9 robust spinules inlongitudinal and 7 spinules in oblique rows nearlateral margin; group of tiny spinules betweenoblique and longitudinal rows; few spinules ondistal 1/2 of segment near medial margin. Anteriorsurface of coxobasis (Fig. 13D) armed with 6-8spinules in longitudinal row on proximal 1/2 ofsegment near lateral margin.Maxillulary palp spinulose. Syncoxopoditeof maxilliped with large spinules at height ofinsertion of proximalmost seta, small spinulesdistal to former group, and tiny spinules at heightof insertion of distalmost seta.Medial spine of P1 basipodite (Fig. 13E)reaching beyond distal margin of enp2, with shortsetules. Medial expansion of basipodite of P1-P3 pilose (Fig. 13E), that of P4 (Fig. 13G) withtiny distal spinules. P1-P3 couplers (Fig. 13H, I;P2 coupler not figured) bare on posterior surface,yet group of tiny hairs present on anterior surface;hairs on anterior surface of P2 coupler difficult toobserve. P4 coupler bearing 2 rows of hairs onposterior surface, and bare on anterior surface.P5 typical for genus. For morphometric data seetable 3.Remarks: The Cambodian T. vermifer differsfrom the original description (Lindberg 1935) inthe lateral ornamentation of pediger 5, which ispilose in Indian females but bare in Cambodianpopulations. Cambodian specimens slightly differfrom the Central Asian population in the medialexpansion of the basipodite of P4, which is armedwith tiny spinules in Cambodia but bare in CentralAsia (Mirabdullayev and Kuzmetov 1997).Thermocyclops vermifer is known from India(Lindberg 1935 1938), Central Asia (Pakistan,Afghanistan, Tajikistan, Uzbekistan, southernKazakhstan, and Turkmenistan) (Mirabdullayevand Kuzmetov 1997, Mirabdullayev et al. 1998),China (Guo 1999), and Southeast Asia (Cambodia:our record).Lindberg (1935) described T. vermifer fromIndia (Deccan) under the name Mesocyclops rylovivermifer, and later Lindberg (1938) raised the taxonto species level. In the original description, there isno mention that Lindberg would designate the typeof M. rylovi vermifer. In a paper on Thermocyclopsfrom the Wallacea-Expedition, Kiefer (1938a),based on comparisons with material providedby Lindberg, stated that T. vermifer was a juniorsynonym of T. decipiens. However, Kiefer did notmention that the examined specimens obtainedfrom Lindberg would have been the type(s) of T.vermifer, nor did he provide drawings, or localityor measurement data on Lindberg’s specimens.Moreover, in a subsequent publication, Kiefer(1978) wrote that he had received no materialof T. vermifer from Lindberg. Mirabdullayev andKuzmetov (1997) and Mirabdullayev et al. (2003)did not accept the synonymy of T. vermifer with T.decipiens, and here we use the name T. vermiferin the same sense as it was applied in the abovementioned2 publications.Thermocyclops rylovi (Smirnov 1929)(Fig. 14)Mesocyclops rylovi Smirnov 1929: 38-42, figs. 1-5; Mesocyclops(Thermocyclops) rylovi Kiefer 1929a: 85; Thermocyclopsrylovi Kiefer 1978: 213-214, fig. 92A; Mirabdullayev et al.2003: 269-271, fig. 127; Hołyńska 2006: 342-344, figs.15-18; Alekseev and Sanoamuang 2006: 277-290, table 2.Thermocyclops neglectus prolatus Kiefer 1952: 71, figs. 56, 58,59, tables VI, XI.Material examined: Cambodia: Kratie Prov.,Kratie Dist., pond, 12°31'N, 106°04'E, 11 June2007, 1 , slide CB13(1A,B); Stung Treng Prov.,Stung Treng Dist., Sreipo, stream, 13°31'N,

Chaicharoen et al. – Review of Thermocyclops in Cambodia 795105°59'E, 11 June 2007, 1 , slide CB28(1A,B);Stung Treng Prov., Stung Treng Dist., Srah Russey,stream, 13°31'N, 105°59'E, 11 June 2007, 1 ,slide CB30(1A,B); Stung Treng Prov., Stung TrengDist., pond, 13°31'N, 105°59'E, 12 June 2007, 1 ,slide CB36(1A,B); Kampong Thom Prov., BarayDist., Sroyong, canal, 12°12'N, 105°07'E, 14 June2007, 1 , slide CB72(1A,B).Diagnosis: Female (Cambodia). Pediger5 with lateral hairs. Genital double-somite (Fig.14A) as long as wide, with transverse rows of pits.Lateral arms of seminal receptacles slightly curvedposteriorly. Caudal rami without medial hairs. Nospinules at implantation of lateral seta or S4. Tipof S2 straight.Hyaline membrane on last antennularysegment proximally extending to insertion of medialseta, without notch. Antennal enp2 with 9 setae.Posterior ornamentation of antennal coxobasis(Fig. 14B): 5 or 6 robust spinules in oblique row,and 7 or 8 spinules in longitudinal row near lateralmargin; group of tiny spinules present betweenoblique and longitudinal rows; oblique field of smallspinules present close to insertion of medial setae;a few tiny spinules arranged in row in middle; afew small spinules present on lateral margin near(A)(D)(B)(E)(C)Fig. 14. Thermocyclops rylovi, female (Cambodia). (A) Pediger 5 and genital double-somite, ventral view; (B, C) antenna: (B) posteriorview; (C) coxobasis, anterior view; (D, E) P4, posterior view: (D) protopodite, exp1-2, and enp1-2; (E) exp3 and enp3. (A-E) LocalityCB36. Scale bar = 50 µm.

796 Zoological Studies 50(6): 780-803 (2011)base. Anterior surface of antennal coxobasis (Fig.14C) bearing 5-8 spinules in longitudinal row onproximal 1/2 of segment near lateral margin.Medial spine of P1 basipodite reaching distalmargin of enp2 (not figured). Medial expansion ofbasipodite of P1-P3 pilose, that of P4 with distalspinules on posterior surface (Fig. 14D). Couplersof P1-P3 bare, while coupler of P4 posteriorlypilose. P5 typical for genus. For morphometricdata see table 3.Remarks: The Cambodian population differsfrom the Uzbekistan (Mirabdullayev and Kuzmetov1997) and Australian populations (Hołyńska 2006)in 3 characters. Tiny distal spinules are presenton the posterior surface of medial expansionsof the P4 basipodite in both the Cambodian andAustralian populations, but were not reportedin Central Asian specimens. On the antennalcoxobasis, tiny spinules between the longitudinaland oblique rows are present in specimens fromCambodia and Uzbekistan (Mirabdullayev et al.2003), but absent from the Australian population.On the other hand, a group of small spinules nearthe insertion of the medial setae of the antennalcoxobasis is present in the Australian population,but absent from specimens of Uzbekistan andCambodia.Thermocyclops rylovi was first describedfrom the Caucasus (Smirnov 1929), and it wasalso reported from Central Asia (Uzbekistan)(Mirabdullayev and Kuzmetov 1997), Iran (Lindberg1936 1942), Afghanistan (Lindberg 1959), Pakistan(Defaye et al. 1987), India (Lindberg 1935, Defayeet al. 1987), and Australia (Hołyńska 2006). InSoutheast Asia this species is known only fromThailand (Mirabdullayev et al. 2003, Alekseev andSanoamuang 2006) and Cambodia. To the west,the range of the species extends as far as Ethiopiaand Uganda (referred to as T. neglectus prolatusby Kiefer (1952), but considered by Mirabdullayevet al. 2003 as a junior synonym of T. rylovi).M a n y o b s e r v a t i o n s i n C e n t r a l A s i a(Mirabdullayev et al. 2003), Iran (Lindberg 1942),and Australia (Hołyńska 2006) indicate the droughtand salinity tolerance of the species.Thermocyclops decipiens (Kiefer 1929)(Figs. 15, 16)Mesocyclops (Thermocyclops) decipiens Kiefer 1929b: 136, fig.12; Thermocyclops decipiens Mirabdullayev et al. 2003:257, 260, fig. 121; Hołyńska 2006: 345-346, figs. 21, 22;Alekseev and Sanoamuang 2006: 277-290, table 2.Material examined: Cambodia: BanteayMeanchey Prov., Srey Sophorn Dist., Sei Sen,pond 13°33'N, 102°59'E, 12 Feb. 2007, 1 , slideCB1(1A,B); Kratie Prov., Kratie Dist., Bossliv,stream, 12°21'N, 106°03'E, 13 Feb. 2007, 1 ,slide CB15(1A,B); Kratie Prov., pond, 12°53'N,106°11'E, 14 Feb. 2007, 1 , slide CB22(1A,B);Stung Treng Prov., Stung Treng Dist., Sreipo,pond, 13°30'N, 105°59'E, 11 June 2007, 1 , slideCB27(1A,B); Stung Treng Prov., Srah RusseyDist., Sreipo, pond, 13°31'N, 105°59'E, 11 June2007, 1 , slide CB29(1A,B); Stung Trengh Prov.,Reachea Dist., Oklong, pond, 13°31'N 106°01'E,15 Feb. 2007, 1 , slide CB34(1,A,B); KratieProv., Kratie Dist., pond, 12°21'N 106°15'E, 16Feb. 2007, 1 , slide CB49(1A,B); KampongThom Prov., Baray Dist., Tropeang Chhouk,canal, 12°22'N, 105°05'E, 14 June 2007, slideCB73(1A,B).Diagnosis: Female (Cambodia). Pediger 5(Fig. 15A) with lateral spinules. Lateral arms ofseminal receptacle perpendicular to body axis andslightly curved at their extremity. Caudal rami withsmooth surface. No spinules at implantation oflateral seta or S4. Tip of S2 straight.Hyaline membrane on segment 17 notextending beyond insertion of medial seta,without notch (Fig. 15C). Aesthetasc onsegment 12 reaching middle of segment 14 (Fig.15B). Antennal enp2 with 9 setae. Posteriorornamentation of antennal coxobasis (Fig. 15E):6-8 robust spinules in longitudinal row and 4 or 5spinules in oblique row near lateral margin; groupof tiny spinules present between oblique andlongitudinal rows; a few spinules present closeto insertion of medial setae. Anterior surface ofantennal coxobasis (Fig. 15D) bearing 5 or 6 largespinules in longitudinal row on proximal 1/2 ofsegment near lateral margin.Syncoxopodite of maxilliped with largespinules at height of insertion of proximalmost seta,and a group of small spinules distally to group oflarge spinules. Medial spine of P1 basipodite (Fig.16A) reaching 2/3 of enp2, with setules along bothsides of spine. Medial expansion of basipodite ofP1-P3 pilose, that of P4 (Fig. 16D) with small distalspinules on posterior surface. P1 coupler bare onposterior surface, yet group of spinules presenton anterior surface. P2 and P3 couplers bearing2 rows of small spinules on posterior surface(Fig. 16B, C), and bare on anterior surface. P4coupler with 2 rows of long hairs on posteriorsurface (Fig. 16D), and with group of spinules onanterior surface (Fig. 16F); distal protuberances

Chaicharoen et al. – Review of Thermocyclops in Cambodia 797(A)(B)(C)(D)(E)Fig. 15. Thermocyclops decipiens, female (Cambodia). (A) Pediger 5 and genital double-somite, ventral view; (B, C) antennule: (B)segments 12-15, posterior view; (C) segments 16 and 17, anterior view; (D, E) antennal coxobasis: (D) anterior view; (E) posterior view.(A, D, E) Locality CB34, (B, C) locality CB49. Scale bars = 50 µm.(A)(B)(C)(D) (E) (F)Fig. 16. Thermocyclops decipiens, female (Cambodia). (A) P1, posterior view; (B) P2 protopodite, posterior view; (C) P3 protopodite,posterior view; (D, E) P4, posterior view: (D) protopodite, exp1-2, and enp1-2; (E) exp3 and enp3; (F) P4 coupler, anterior view. (A)Locality CB1, (B-F) locality CB34. Scale bar = 50 µm.

798 Zoological Studies 50(6): 780-803 (2011)conspicuously high. P5 typical for genus. Formorphometric data see table 3.Remarks: The Cambodian T. decipiens differsfrom the type (Kinshasa, Congo; Mirabdullayev etal. 2003) in a single character. On the posteriorsurface of the antennal coxobasis, a group ofspinules below the medial setae is present in boththe Australian (Hołyńska 2006) and Cambodianfemales (Fig. 15E), yet absent from the typematerial (Mirabdullayev et al. 2003). Thesespinules are extremely tiny in specimens from thePhilippines and Indonesia for instance; thereforeit is possible that the size reduction of spinulesmight result in the full disappearance of thisgroup in other populations (Hołyńska 2006). Theaesthetasc on antennulary segment 16 is setalikein Cambodia, while it abruptly narrows in 1Australian specimen (Hołyńska 2006). Anotherdifference is in the ornamentation of the anteriorsurface of the P2 and P3 couplers, which are barein Cambodian populations and pilose (with a fewhairs) in the Australian female.This pantropical species is known fromCentral and South America, Africa, India, SriLanka, Indonesia, and Australia (Mirabdullayevet al. 2003); in Southeast Asia it was reportedfrom Thailand (Alekseev and Sanoamuang2006), Vietnam (Mirabdullayev et al. 2003),and Cambodia (our record). It even occurs ingroundwater in West Indian islands (Pesce 1985),where it has somewhat different ornamentation ofthe P4 coupler and more-elongated caudal rami.Thermocyclops crassus (Fischer, 1853)(Figs. 17, 18)Cyclops crassus Fischer 1853: 92-93, pl. III, fig. 29;Mesocyclops crassus Sars 1914 (1913-1918): 61-62, pl.37; Mesocyclops (Thermocyclops) crassus Rylov 1948:305-306, fig. 77; Thermocyclops crassus Dussart 1969:210-213, fig. 108; Mirabdullayev et al. 2003: 265-267, fig.125; Hołyńska 2006: 344-345, figs. 19, 20.Material examined: Cambodia: BanteayMeanchey Prov., Srisophol Dist., Sei Sen, pond,13°33'N, 102°59'E, 12 Feb. 2007, 1 , slideCB1(1A,B); Prek Toam, Kratie Prov., Kratie Dist.,Bossliv, Khong River, 12°21'N, 106°03'E, 13Feb. 2007, 1 , slide CB15(1A,B); Stung Treng(A)(B)(C)(D)Fig. 17. Thermocyclops crassus, female (Cambodia). (A) Genital double-somite, ventral view; (B) antennule, segments 12-17,posterior view; (C, D) antennal coxobasis: (C) anterior view; (D) posterior view. (A) Locality CB72, (B-D) locality CB88. Scale bar =50 µm.

Chaicharoen et al. – Review of Thermocyclops in Cambodia 799Prov., Stung Treng Dist., Sreipo, pond, 13°31'N,105°59'E, 15 Feb. 2007, 1 , slide CB32(1A,B);Siem Reap Prov., Chikreng Dist., Kok Thlok Krom,pond, 13°08'N, 104°18'E, 18 Feb. 2007, 1 , slideCB65(1A,B); Siem Reap Prov., pond, 13°35'N,103°23'E, 19 Feb. 2007, 1 , slide CB72(1A,B);Battambong Prov., Mong Rusey Dist., Prey Toch,irrigation canal, 12°54'N, 103°22'E, 20 Feb. 2007,1 , slide CB87(1A,B); Siem Reap Prov., PourDist., Thnal, pond, 13°22'N 103°48'E, 15 June2007, 1 , slide CB88(1A,B).Diagnosis: Female (Cambodia). Pediger5 with lateral spinules. Lateral arms ofseminal receptacle (Fig. 17A) short, wide, andperpendicular to body axis. Caudal rami short,without hairs on medial margin. No spinulesat implantation of lateral seta or S4. Tip of S2strongly curved ventrally.Hyaline membrane of last antennularysegment proximally not extending beyond insertionof medial seta, without notch (Fig. 17B). Antennalenp2 with 9 setae. Posterior ornamentation ofcoxobasis (Fig. 17D) composed of small spinulesin longitudinal and oblique rows near lateralmargin, and a few tiny spinules on distal 1/2 nearmedial margin. Tiny spinules absent betweenoblique and longitudinal rows. Frontal surfaceof coxobasis (Fig. 17C) armed with spinules incurved row on proximal 1/2 of segment near lateralmargin. Maxillulary palp spinulose. Syncoxopodite(A)(D)(B)(C)Fig. 18. Thermocyclops crassus, female (Cambodia). (A) P1, anterior view; (B) P2, protopodite, posterior view; (C) P3, protopodite,posterior view; (D) P4, posterior view. (A-D) Locality CB88. Scale bar = 50 µm.

800 Zoological Studies 50(6): 780-803 (2011)of maxilliped with large spinules at height ofinsertion of proximalmost seta, small spinulesdistal to former group, and tiny spinules at heightof insertion of distalmost seta.Medial spine of P1 basipodite (Fig. 18A)reaching beyond distal margin of enp2. Medialexpansion of basipodites of P1-P4 (Fig. 18A-D) pilose. P1-P3 couplers bare on posterior andanterior surfaces. P4 coupler (Fig. 18D) bearing2 rows of hairs on posterior surface and bare onanterior surface; distal protuberances high. P5typical for genus. For morphometric data see table3.Remarks: Cambodian specimens differ fromEuropean and Australian females (Mirabdullayevet al. 2003, Hołyńska 2006) in 2 characters. Theposterior surface of the antennal coxobasis has asimpler spinule pattern in Cambodian females: thegroup between the longitudinal and oblique rows,and spinules near the insertion of the medial setae,which are present in European and Australianfemales, are both missing from Cambodianfemales. On the posterior surface of the P4coxopodite, lateral rows of small spinules that arepresent in European and Australian specimensare absent from Cambodian ones. The medialmargin of the basipodites of P1-P4 bears spinulesin specimens from Germany (Mirabdullayev et al.2003), yet it is pilose in Cambodian ones.Thermocyclops crassus lives in Eurasia andalso occurs in (Papua) New Guinea, and Vanuatu.It is widespread in temperate Australia, and knownfrom a few localities in North Australia and Africa(Kizito et al. 1993, Dussart and Defaye 2006).Thermocyclops crassus has a restricted distributionin southeastern Mexico and the northeastern US,which suggests that the species was introduced toAmerica (Reid 1989, Duchovnay et al. 1992, Reidand Pinto-Coelho 1994, Gutiérrez-Aguirre andSuárez-Morales 2000, Silva 2008).Lindberg (1952) reported the occurrenceof T. crassus in Cambodia from Phnom Pheng,Kandal, Pursat, and Kampong Cham, and foundthe species to be the most common representativeof the genus in the country. Our data confirmthis; T. crassus was the most often encounteredspecies and is widely distributed in the 7 provincesof Cambodia we studied.DISCUSSIONTwelve taxa, nearly 1/4 of the world fauna ofThermocyclops (55 (sub)species) (Dussart andDefaye 2006), occur in Southeast Asia: T. crassus,T. decipiens, T. maheensis, T. operculifer Kiefer,T. operculifer aberrans, T. orientalis Dussart andFernando, T. philippinensis (Marsh), T. rylovi, T.taihokuensis Harada, T. trichophorus Kiefer, T.vermifer, and T. wolterecki (Lindberg 1952, Nam etal. 1998, Mirabdullayev et al. 2003, Alekseev andSanoamuang 2006, our report). Only 3 species (T.operculifer, T. philippinensis, and T. trichophorus)seem to be endemic to the region, while therest of the Southeast Asian fauna is shared withneighboring regions of Asia and also Australia.The ranges of a few Southeast Asian taxa extendas far as Papua New Guinea (T. wolterecki) orAustralia (T. crassus, T. decipiens, T. operculiferaberrans, and T. rylovi), and dispersal from theAsian continent to Australia was suggested byHołyńska (2006). Boxshall and Defaye (2008)analyzed the occurrence of freshwater cyclopoidspecies that inhabit more than 1 zoogeographicregion, and also found that the Oriental region(Southeast Asia + India) showed the greatestsimilarity with Australia (including New Guinea).From Cambodia, 7 species are known: T.crassus, T. decipiens, T. maheensis, T. operculiferaberrans, T. rylovi, T. vermifer, and T. wolterecki(Fig. 19). With the exception of T. crassus, allThermocyclops taxa described here are newrecords for the country. For comparison, 6 specieswere reported from Thailand with an almost 3-foldlarger area.There is a single problematic Cambodianform, T. operculifer aberrans, which unfortunatelywe could not find in our samples, although aredescription (preferably from the type locality,Lake Sap) is badly needed for this poorly knowntaxon. Karanovic (2006) found this taxon insubterranean waters in Western Australia (Pilbara).He ascribed T. operculifer aberrans species rank,and considered a Malaysian taxon referred byFernando and Ponyi (1981) as Thermocyclops cf.schmeili, and a Javanese form assigned by Defayeet al. (1987) as T. operculifer to be conspecific withT. aberrans. Almost at the same time in a paperon Thermocyclops of North Queensland, Hołyńska(2006) redescribed T. operculifer, and describeda new species, T. pseudoperculifer, which is veryclosely related (even perhaps synonymous) to T.aberrans. Thermocyclops pseudoperculifer seemsto differ from T. aberrans sensu Karanovic (2006)in the ornamentation of the posterior surface of theP1 coupler (spinulose in T. aberrans from WesternAustralia and bare in T. pseudoperculifer), andsetulation of the medial spine of P1 basipodite (long

Chaicharoen et al. – Review of Thermocyclops in Cambodia 801setules present on the proximal 1/2 of the spine inT. pseudoperculifer and long setules absent fromT. aberrans of Western Australia). To resolve therelationships between the Asian and Australiantaxa, in the future we need to compare theseforms with the topotype material of T. operculiferaberrans.Identification key to Cambodian species ofThermocyclops (females)1. Hyaline membrane on last segment of antennule proximallyextending beyond insertion of medial seta (Fig. 10C); noornamentation present on posterior surface of P4 coupler...................................................T. maheensis Lindberg, 1941- Hyaline membrane on last segment of antennule notextending beyond insertion of medial seta (Fig. 17B); hairsor spinules present on posterior surface of P4 coupler.....(2)2. Lateral arms of seminal receptacle short and wide,perpendicular to body axis (Fig. 17A)........................................................................................T. crassus (Fischer, 1853)- Lateral arms of seminal receptacle elongate, slightly orstrongly curved to rear......................................................(3)3. Distal protuberances of P4 coupler armed with largespinules (Fig. 16D); P3 coupler bearing hairs or spinules onposterior or anterior surface..............................................(4)- Distal protuberances of P4 coupler armed with tiny spinules(Fig. 4D); P3 coupler posteriorly and anteriorly bare .................................................................T. wolterecki Kiefer, 19384. P4 coupler posteriorly spinulose; s1/s4 about 1.0; of apicalspines of P4 enp3, medial spine -1.6-times as long aslateral spine.............. T. operculifer aberrans Lindberg, 1952- P4 coupler posteriorly pilose; s1/s4 > 2.0; of apical spinesof P4 enp3, medial spine at least 1.8-times as long aslateral spine.......................................................................(5)5. Pediger 5 laterally bare............... T. vermifer Lindberg, 1935- Pediger 5 with lateral hairs or spinules...............................66. Transverse rows of pits present on genital double-somite(Fig. 14A); P2 and P3 couplers posteriorly bare; pediger 5with lateral hairs (Fig. 14A)............. T. rylovi (Smirnov 1929)- Transverse rows of pits absent from genital double-somite(Fig. 15A); P2 and P3 couplers posteriorly spinulose (Fig.16B, C); pediger 5 with lateral spinules (Fig. 15A).......................................................................T. decipiens Kiefer, 1929NTHAILANDLAOS PDRTWTVBantean MeancheySiem ReapTCTC TWBattambongTV TDTWTV TCTCTVTC TWPursatTDTOKampong ThomTWTDTRTCStung TrenghTMTRTCTDKratieTMTCTRTDTVTWKampong ChamTC Phom PhengTOKandalTOTOTCTakeoVIETNAMTCFig. 19. Geographic distribution of Thermocyclops in Cambodia. TC, Thermocyclops crassus; TD, T. decipiens; TM, T. maheensis; TR,T. rylovi; TV, T. vermifer; TO, T. operculifer aberrans; TW, T. wolterecki.

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