Eurycercus macracanthus Frey, 1973

Bekker, Eugeniya I., Kotov, Alexey A. & Taylor, Derek J., 2012, A revision of the subgenus Eurycercus (Eurycercus) Baird, 1843 emend. nov. (Cladocera: Eurycercidae) in the Holarctic with the description of a new species from Alaska, Zootaxa 3206 (1), pp. 1-40 : 10-16

Eurycercus macracanthus Frey, 1973

Figs 3–4

Eurycercus macrocanthus Frey, 1973, p. 225 –248, Figs 1–2 , 5–10 , 23, 25–26, 28–30, 33–34, 37, 40–41, 44–45, 48–51, 61–62; Chen et al. 1995, p. 68–69, Figs 1–12 .

Eurycercus macracanthus Frey, 1973, p. 593 ; Kotov et al. 2011, p. 136–138, Fig. 4 .

Type locality. " Two small ponds in the flood plain of the Amur River across the river from Khabarovsk " (Frey 1973), Jewish Autonomous Region , Russia. There is no chance to locate exact ponds according to such comments among numerous floodplain water bodies in that region. Approximate geographic coordinates: 48.53, 134.98 .

Type material. Holotype. A parthenogenetic female 1.50 mm long in alcohol, NHM 1972.4 .18.5.

Paratypes (all from type locality). Two parthenogenetic females in alcohol ( NHM 1972. 4. 18. 3–4); one parthenogenetic female in glycerine jelly ( NHM 1972.4.18.1). Two exuviae in polyvinyl lactophenol ( NHM 1972.4.18.2). One parthenogenetic female and one exuvium on slides, NNS MGU 63–64 (in Frey’s paper they have accession numbers NN 54383-54384, but the numeration was subsequently changed) ; one parthenogenetic female and one exuvium, ZIN, accession numbers 16 and 64, respectively in Frey (1973). Some other specimens were kept in the DGF .

Material examined here: Russia. Amur Area. Affluents of the Zeya River, coll. in 2006 by N. G. Sheveleva , NNS 2009-030; Lake Khasan, the plain of Zeya river, coll. in 20.07.2006 by N. G. Sheveleva , NNS 2009-036 (53.4870, 126.9428); Lake Malaya Sazanka near town of Svobodny, coll. in 2006 by N. G. Sheveleva , NNS 2009- 040 (51.1602, 128.1057); Lake Mukhinka, oxbow water body of the Zeya River near Mukhinka, coll. in 01.09.2005 by N. G. Sheveleva , AAK 2006-023 (50.5605, 127.6481); Lake Teploe, coll. in 2006 by N. G. Sheveleva , NNS 2009-037 (51.4474, 128.3738); Mouth of the Birma River, coll. in 2006 by N. G. Sheveleva , NNS 2009- 043 (51.4713, 128.4374); Mouth of the Iver River, coll. in 2006 by N. G. Sheveleva , NNS 2009-044 (51.74, 128.88); Mouth of the Ulunga River, coll. in 2006 by N. G. Sheveleva , NNS 2009-042 (53.45, 126.86); Small water bodies near Zeya Water Reservoir dam, coll. in 2006 by N. G. Sheveleva , NNS 2009-033-35 (53.7308, 127.2696); Zeya Water Reservoir, coll in 2006 by N. G. Sheveleva , NNS 2009-029 (53.7527, 127.3050); Zeya Water Reservoir near dam, coll. in 18.07.2006 by N. G. Sheveleva , NNS 2009-028 (53.7768, 127.2842). Arkhangelsk Area. A small marshy lake, Pinega Forest Reserve, coll. in 22.07.2009 by E. I. Bekker, AAK M-1034 (64.5921, 42.8550). Chelyabinsk Area. Uruzan' Pond, town of Uruzan', coll. in 07.08.2006 by A. A. Kotov, AAK M-0322 (54.8583, 58.4469). Chita Area. Sandy mine lake, town of Chita, coll. in 01.09.1991, NNS 1999-035 (52.0, 113.5). Chukot Autonomous Area. A puddle in the Region of the Anadyr River, coll. by E. A. Streletskaya, AAK 1999-076 (65, 171); A water body in the Anadyr River basin, №311, б-134-72, coll by E. A. Streletskaya, NNS 1999-015; Lake Verkhnee, Kolyma Region, coll. in 1981 by E. A. Streletskaya, NNS 1999-014. Irkutsk Area. Kurma Bay, Irkutsk Water Reservoir, coll. in 2010, AAK M-1849 (52.2499, 104.3001). Jewish Autonomous Region. Small ponds in the flood plain of the Amur River across the river from Khabarovsk, coll. in 07.08.1971 by D. G. Frey, NNS MGU 0016, 0063-0064 (48.53, 134.98). Kamchatka Area. A tundra Lake near Lake Tsentral'noje, Caldera Uzon coll. in 28.08.1995 byY. R. Galimov, AAK 2007-311 (54.49, 160.0); Lake Tsentral'noje, Caldera Uzon, coll. in 29.08.1995 by Y. R. Galimov, AAK 2007-310 (54.4961, 159.9833). Khanty-Mansi Autonomous Area. A lake in Posiolok Divniy, town of Nizhnevartovsk, coll. in 23.07.2005 by A. A. Kotov, AAK 2005-321 (60.9236, 76.4935). Komi Autonomous Republic. Kurja near Scheljajur, coll. in 10.08.1982 by AAK 1999-079 (65.33, 53.4); Lake Bezymiannoje, near the Schugor River, coll. in 24.07.1970 by V. N. Shubina, NMK 1712. Krasnoyarsk Territory. A lake near Mirnoe, coll. In 17.07.2011 by E. Y. Demidova (62.34, 89,1); Penza Area. A big lake, Sosnovka locality, vicinities of Penza, coll. in 31.05.2009 by E. I. Bekker, AAK M-1064 (53.1731, 45.0755); a lake fully covered by vegetation, locality Montazhny, viciniyies of Penza, coll. in 24.10.2009 by E. I. Bekker, AAK M-1071-73 (53.218, 45.125); a roadside lake along new road, locality Sosnovka, vicinities of Penza, coll. in 05.2009 by E. I. Bekker, AAK M- 0939 (53.1727, 45.0744); a small lake covered by Stratiotes aloides , on left side of Sosnovka-Ahuny road, vicinities of Penza, coll. in 05.2009 by E. I. Bekker, AAK M-0940 and AAK M-0930 (53.1727, 45.0744); Degtyarniy Zaton, a tributary of River Sura near village Sosnovka, vicinity of Penza, coll. in 04.10.1992 by A. O. Bienkowski & M. J. Orlova-Bienkowskaja, AAK 1999-073 (53.1759, 45.0561); 1st lake near Kordon 95, road to Akhuny, locality Sosnovka, vicinities of Penza, coll. in 08.07.2009 by E. I. Bekker, AAK M-1061 (53.1727, 45.0738). Primorski Territory. A big oxbow lake, the River Razdol’naya walley near town of Ussuriysk, coll. in 17.09.2010 by N. M. Korovchinsky, AAK M-2071 (43.8374, 131.8521); a small, almost dried pond, the River Razdol’naya walley near village of Razdol’noye, coll. in 19.09.2010 by N. M. Korovchinsky, AAK M-2081 (45.54, 131.89); a chanal with fillamentous algae, area of Lake Khanka, coll. in 11.09.2009 by N. M. Korovchinsky, NMK 2970-2971 (44.9305, 131.9764); a small swamp near the Manchzhurka River, area of Lake Khanka, coll. in 10.09.2009 by N. M. Korovchinsky, NMK 2946 (44.7961, 131.9985); a swamp on another side of road from Ilyinskoe Lake, area of Lake Khanka, coll. in 10.09.2009 by N. M. Korovchinsky, NMK 2949 (44.9211, 131.9642). Sakhalin Area. An oxbow lake of the Tym' River, coll. in 31.08.1999 by D. Zavarzin, NMK 2433 (50.9, 142.7). Taimyr Autonomous Area. A lake near river Kotuikan, coll. in 4.08.2011 by V. E. Fedosov (70.6928, 105.5169). Tomsk Area. Lake Kotets (locally named Chemuldo), coll. in 13.07.2005 by A. A. Kotov, AAK M-0114 (57.7364, 83.6171); Lake Svetloe near River Chulym, coll. in 14.07.2005 by A. A. Kotov, AAK M-0122 and AAK 2005-285 (57.8178, 84.1841). Yakutia Autonomous Republic. Lake Mutnoe, upper stream of the Markha River, coll. in 21.09.2010 by A. I. Klimovskiy, AAK M-1921; A lake, remain of the Suola River, coll. in 25.08.2010 by A. A. Kotov, AAK M- 1944 (62.0986, 130.1494); A lake, remainder of the Tuima River, coll. in 29.08.2010 by A. A. Kotov, AAK 2011- 049 (62.3368, 131.2744); an oxbow lake, River Khandyga, right bank of the Aldan River, coll. in 26.08.2010 by A. A. Kotov, AAK 2011-039 (63.112, 134.0446); A puddle near the Aldan River, coll. in 27.08.2010 by A. A. Kotov, AAK 2011-042 (63.0262, 134.0453); a swamp, right side of the "Kolyma" Federal Road near crossing with the Suola River, coll. in 25.08.2010 by A. A. Kotov, AAK M-1945 (62.0993, 130.1467); Lake Atlassovka near town of Yakutsk, coll. in 24.08.2010 by A. A. Kotov, AAK M-1938 (61.9670, 129.6204); a small lake near Lake Bolshaya Chabyda, coll. in 02.09.2010 by A. A. Kotov and A. I. Klimovsky, AAK M-1980 (61.9837; 129.3848); A swamp on Shestakovka stream originated from Lake Bolshaya Chabyda, coll. in 02.09.2010 by A. A. Kotov and A. I. Klimovsky, AAK M-1988 (61.9377, 129.4120); Lake Bolshaya Chabyda, coll. in 02.09.2010 by A. A. Kotov and A. I. Klimovsky, AAK M-1984 (61.9884, 129.3794); Lake Suordakh, left bank of the Aldan River, coll. in 27.08.2010 by A. A. Kotov, AAK M-1958 (63.0737, 133.9702); Lake Tiungjulju, coll. in 25.08.2010 by A. A. Kotov, AAK M- 1946 (62.18029, 130.6640); Lake 1 on Melnikova Island, the Lena River, coll. in 22.08.2010 by A. A. Kotov, AAK M-1933 (63.8530, 127.4713); Lake 2 on Melnikova Island, the Lena River coll. in 22.08.2010 by A. A. Kotov, AAK 2011-021 (63.8512, 127.4738); River Muna, left affluent of the Lena River, coll. in 08.2003 by V. A. Sokolova, NMK 2484; an oxbow lake 2, near Nizhnekolymsky, south bank of the Kolyma River, coll. by A. I. Klimovskiy, AAK M-1912 (68.5356, 160.9348). Yamalo-Nenets Autonomour Area. A puddle near unnamed lake in Nadymsky Gorodok, 31 km from the River Nadym mouth, coll. in 17.07.2007 by A. B. Savinetsky, AAK M-0574 (66.0599, 72.0048); Lake 2 in Nadymsky Gorodok, 31 km from Obskaya Guba, coll. in 17.07.2007 by A. B. Savinetsky, AAK M-0578 (66.2208, 72.0451); un-named lake 1 in Nadymsky Gorodok, 31 km from Obskaya Guba, coll. in 17.07.2007 by A. B. Savinetsky, AAK M-0573 (66.0602, 72.0061).

China. Nen River, Loakan zi, Jilin Province, coll. in 07.06.1973 by C. Sieh-chih, DGF 6306 (45.53, 124.28) . Lake Malaga , Xiuganmeng, coll. in 20.05.1988, AAK 1999-081 and NNS 1998-226

Diagnosis. Parthenogenetic female. Dorsal head pores on a bubble-like projection located immediately on head shield. In anterior view, body wide, not compressed laterally, median dorsal keel absent. Rostrum short. Ocellus minute. Lateral pore small, rounded. Labrum with a medium-sized median keel, terminating in a broadly rounded apex not reaching distal end of antenna I. Postabdomen with sub-parallel dorsal and ventral margins, preanal teeth pointed. Spines at base of pre-claw portion predominantly doubled. Antenna I with antennular sensory seta arising in middle. Denticles in rows encircling antennular surface especially small. On antenna II, spine situated on proximal segment of exopod somewhat shorter than second segment. Limb I IDL with a remarkably strong hook-like seta, the smallest IDL seta especially fine and short. IDL with 5–7 distal spinules, 11–16 proximal spinules, 7–9 marginal spinules and 2–4 basal spinules. Eight setae in filter plate II, eight-nine setae in filter plate III; eight-nine setae in filter plate IV, 8 setae in filter plate V.

Full redescription. Parthenogenetic female. In lateral view body sub-ovoid in larger females ( Fig. 3A ), maximum height of the body in its middle portion (BH/BL= 0.52–0.57 in juveniles and 0.66 in largest adults). Dorsal margin evenly convex, interrupted only by a bubble-like projection with head pore ( Fig. 3A , arrow). Postero-dorsal angle more or less rounded in both adults and juveniles. Posterior margin slightly convex, smoothly rounded, postero-ventral angle broadly rounded. In larger adults ventral margin with a slight prominence immediately anterior to the margin middle ( Fig. 3A , arrow). In anterior view, body wide, not compressed laterally, maximum width of body at level of mandibular articulation, median dorsal keel completely absent ( Fig. 3B ). Intestine has a single loop, posterior intestinal caecum present. Few eggs in brood pouch.

Head large, with dorsal margin regularly arched from rostrum to region of dorsal head pores. Border line between head shield and valves obscure in preserved animals. Rostrum relatively short. Frontal head pore as transverse split, located somewhat anterior to the bases of antenna I on the ventral surface of the head (its position is marked by an arrow in Fig. 3C ). Compound eye rather large, located near dorsal margin of head markedly closer to the rostral extremity than to the head pores. Ocellus small, located at antenna I base. A single major “head pore” (dorsal organ) as a ringed, sub-oval field of special cuticle located on a dorsal bubble ( Fig. 3D ). Lateral pore minute, circular and located at either side of major pore, closely to it.

Labrum fleshy body, with a medium-sized median keel, terminating in a broadly rounded apex ( Fig. 3C ), keel anterior margin slightly convex, without setulation, posterior margin almost straight. Distal labral plate with short setulation. Paired lateral projections on labrum well-developed, horn-like, with apexes directed anterior ( Fig. 3C , arrow).

Valves generally ovoid (VL/BL= 0.80–0.90 in both juveniles and largest adults), with very obscure, almost invisible reticulation. Antero-ventral portion of valves slightly prominent, with a special narrow flap ( Fig. 3A , arrow). Continuous row of setae along ventral rim of valves, the anterior most members short, setae then sharply increasing in size posterior to the prominence on ventral margin, and finally gradually decreasing in size to posteroventral valve portion. Postero-ventral angle with a row of thin spinules. This row continues to ventral portion of posterior margin.

Thorax without external traces of segmentation, with six limb pairs. Abdomen thick; no abdominal projections on dorsal part of all segments.

Postabdomen as a large (PL/BL= 0.44–0.46), relatively broad ( PH /PL= about 0.43 in juveniles and 0.48–0.50 in adults), flattened plate with sub-parallel dorsal and ventral margins ( Fig. 3E ). Anus opening distally; thus whole slightly convex dorsal margin represents preanal margin of postabdomen. Dorso-distal (preanal) angle well expressed, distal anal embayment relatively deep, dorsal portion of distal (=anal) margin straight to slightly concave. Postanal angle rounded ( Fig. 3F , arrow). Pre-claw portion of postabdomen as a conical prominence. Ventral margin of postabdomen slightly convex. Armature of the preanal margin as a series of preanal teeth, slightly and fluently increasing in size in distal direction; a small gap lacking any teeth at base of postabdominal setae ( Fig. 3G ); teeth in middle of preanal margin with sharp tips (NT= 90–92); distal most tooth somewhat larger than the others, located just on dorso-distal angle of postabdomen ( Fig. 3E ). On postanal and anal margins of postabdomen there are crescentic clusters of spines (homologues of postanal teeth of chydorids), distalmost members particularly large, predominantly clustered, teeth at base of pre-claw portion (=at distal part of anal margin) short, predominantly doubled ( Fig. 3F , arrows). Sub-parallel rows of minute setules on whole lateral surface of postabdomen (not represented in Fig. 3E due to their minute size). Postabdominal setae short (less than half of preanal margin length), bisegmented, distal segment shorter than basal one and bilaterally setulated ( Fig. 3E ). Setae located on a distinct, nut-like base ( Fig. 3G ). Postabdominal claw relatively robust (CL/PL= 0.23–0.25); with massive base; weakly and evenly tapered in distal direction, and slightly curved. Two basal spines, first (distal) long (DS/CL= 0.33–0.47), second (basal) short (BS/CL=0.2–0.27; BS/DS = about 0.6), located dorsally immediately at base of claw.

Antenna I (antennule) relatively short (AL/BL= 0.08–0.10; AL/DA=2.8–4.0); with maximal width in basal half, with its distal 2/3 evenly tapering distally ( Fig. 3H ); protruding beyond tip of rostrum. Slender antennular sensory seta about half of antenna I length, arising at antenna I middle. Nine bisegmented aesthetascs with pointed teeth around them. No setules at anterior margin of antenna I. Numerous short rows of minute denticles encircling antennular surface.

Antenna II relatively short ( Fig. 3I ). Several projections on its external surface in coxal region. On one of them with two bisegmented setae, unequal in length, next projection with semi-circular row of setules; distalmost projection inflated, with numerous strong spinules. Massive basal segment with a relatively long seta distally on anterior surface and rows of short denticles. Both branches with elongated segments, basal most members particularly elongated; all segments with rows of short denticles. Setae 0-0-3/1-1-3; both apical and lateral setae long, clearly bisegmented, with long hairs on both basal and distal segments. Spines 1-0-1/0-0-1. No additional spines on distal parts of any segments of either branch. Length of apical spines and of segments from which they arise, sub-equal; length of spine situated on proximal segment of exopod somewhat shorter than length of second segment ( Fig. 3I , arrow).

Mandibles relatively elongated, articulated with integument between head shield and valves.

Maxilla I with three densely setulated setae and a fourth short seta-like structure (as it was described for E. lamellatus by Kotov (2000). Maxilla II absent in adults and in juveniles ( Fryer 1963; Kotov 1996).

Limb I large, epipodite without a finger-like projection (not represented in Fig. 4A ). Two accessory setae, unequal in size and setulated in distal parts, are the distal most structures of the distal portion of limb I (also not represented in Fig. 4A ). Outer distal lobe with 2 setae of very unequal size on its top ( Fig. 4A , ODL). Inner distal lobe ( Fig. 4A , IDL) with three bisegmented setae, named as clasping hooks in term of Fryer (1963), generally decreasing in size towards endites, among them, a remarkable especially strong hook-like seta ( Fig. 4A , arrow). It is necessary to note that the relative size of this hook varies strongly among populations, but in any case the base of this seta occupies the whole top of the IDL in contrast to all other species ( Fig. 4B–C ), although their hook sometimes is also relatively large. Also the IDL supplied with 4 groups of spinules, named here after Hann (1982): long distal spinules (5–7 in largest adults, Fig. 4C , dis), long proximal spinules (pro, 11–16 in largest adults), short marginal spinules (mar, 7–9 in largest adults) and very short basal spinules (bas, 2–4 in largest adults); a field of minute denticles on IDL basally, named as grinding tubercles by Frey (1975). Endite III with three setulated, bisegmented posterior setae of similar size (a–c), and a setulated, stiff anterior seta 1 with a small sensillum near its base. Endite II with three posterior setae (d–f) analogous to those on eIII, and a stiff, setulated anterior seta 2, a very small sensillum near its base. Endite I with 3 posterior setae (g–i), and a stiff anterior seta 3. Two ejector hooks anteriorly on outer portion of limb corm. Well-developed maxillar process, earlier shown in embryos to be a remainder of gnathobase I ( Kotov 1996), bearing three slender, fully and densely setulated setae on inner side of limb base (not represented in Fig. 4A ).

Limb II with ovoid epipodite bearing a relatively short finger-like projection; exopodite as a small lobe ( Fig. 4D , arrow). At inner side of limb, a row of eight stiff marginal scrapers ( Fig. 4D, 1–8 ); setae 1–2 with more delicate feathering, setae 3–8 with relatively robust denticle. Posteriorly on limb corm 8 soft setae: distal most one (a) short; next two ones (b–c) longest, relatively stout, armed in distal portions by short setules; basal most ones (d–h) similarly feathered by long hairs. Distal armature of gnathobase with four setae, one of them a minute sensillum ( Fig. 4E , 1 ), located far from the others, a row of denticles (about 5 in largest adults) near it. Filter plate with 8 long, densely setulated setae; distal most seta of filter plate clearly smaller than the others, second-third ones slightly shorter than others. Additional bunch of setules basal to filter plate.

Limb III with a small pre-epipodite and a relatively large epipodite lacking a finger-like projection ( Fig. 4F ). Exopodite flat, smaller than those of limbs IV–V. Distally, five setae of unequal size ( Fig. 4F, 1–5 ), lateral group consists of three setae (6–8, armature of seta 7 not represented), setae 8 especially long. Distal portion of inner limb part forms a partly isolated lobe, distal endite sensu Kotov (1999, 2000), external endite sensu Dumont & Silva- Briano (1998) with three bisegmented anterior setae (1–3). Basal endite, internal endite sensu Dumont & Silva-Briano (1998) larger than distal endite. Marginally, a row of 4 stiff setae (4–7). Seven long soft setae of subequal size (a–g) on limb corm posteriorly. Gnathobase weakly demarcated from basal endite, distal armature with 4 members, one of them ( Fig. 4G , 1 ) a large, bottle-shaped sensillum located far from the others. Nine-eight setae in filter plate.

Limb IV with pre-epipodite as a setulated hillock; epipodite large, ovoid, with a long finger-like projection ( Fig. 4H ). Exopodite oval, with two distal, relatively stout, bisegmented setae of unequal size, armed by short setules (1–2), other six setae feathered bilaterally by very long hairs (3–8). Marginally on inner limb face, a row of four stiff anterior setae (1–4). Seta 1 slightly shorter, setae 2–4 approximately of equal size, setulated distally. Posteriorly, five soft setae (a–e) with subequal length. Distal armature of gnathobase with 4 members (1–4). One of them a long, bisegmented seta, densely feathered in distal part (2), two others small (3–4), a large, bottle-shaped sensillum (1) is a fourth member of gnathobasic armature (similar to limb III). Filter plate IV with 8–9 setae, middle ones slightly longer than marginal ones.

Limb V with pre-epipodite as a setulated hillock; epipodite with a long finger-like projection ( Fig. 4J ). Exopodite very large, with four short distal (1–4) and three large lateral (5–7) setae. Inner portion of limb with a protruding flap-like distal projection, fringed by long setules. Three marginal setae on inner face of limb, distal member slightly protruding behind distal endopodite projection, a sensillum near basalmost seta. Gnathobase with two small setae ( Fig. 4K ). Filter plate with 8 setae.

Limb VI triangular-shaped, with epipodite supplied with a relatively long finger-like projection and a bunch of setules somewhat distal to it; its inner margin setulated ( Fig. 4L ).

Ephippial female, Male. Unknown

Length. 0.90–1.73 mm in our material; 0.54–2.05 mm according to Frey (1973).

Comments. Frey’s (1973) publication was a pioneering efftort in the revision of Eurycercus . After description of several closely related species it is necessary to improve the diagnosis of E. macracanthus keeping in mind newly discovered characters discriminating this taxon from its congeners.

Distribution. The taxon was regarded as an endemic of the Amur basin (Frey 1973). Now it is obvious that this species is widely distributed in the northern Palaearctic from Far East to the Volga River basin in European Russia. In the Amur and the Lena basins E. macracanthus is the most common species of Eurycercus .

Ecology. After our study, it is obvious that E. macracanthus occurs in water bodies of very different types, from small puddles and shallow swamps to large lakes and artificial reservoirs. The most common habitat in Siberia is an oxbow lake of any size. We think that it occurs in small temporary pools only if they are partly dried remains of larger water bodies formed during spring flooding. E. macracanthus is found in the macrophyte patches in the rivers themselves.

Figures

FIGURE 1. Distribution of species from the subgenus Eurycercus (Eurycercus) emend. nov. in the Holarctic according to our original samples—no literature data included. E. lamellatus—grey circles. E. macracanthus—black circles. E. pompholygodes—solid quadrates (red in electronic version). E. microdontus—black stars. E. longirostris—grey quadrates. E. nipponica—solid triangles (green in electronic version). E. beringi sp. nov.—black crosses.

FIGURE 2. Characteristic traits of different species of Eurycercus (Eurycercus) emend. nov. A–B, E. longirostris, dorsal view and dorsal head pores in lateral view. C–D, E. lamellatus, dorsal view and dorsal head pores in lateral view. E–F, E. beringi sp. nov., dorsal view and dorsal head pores in lateral view. Rather schematic, not to scale.

FIGURE 3. Eurycercus macracanthus, parthenogenetic female from a small lake covered by Stratiotes aloides, on left side of Sosnovka-Ahuny road, vicinities of Penza, Penza Area (A); small water bodies near Zeya Water Reservoir dam, Amur Area (B); Lake Bezymiannoje, near the Schugor River, Komi Autonomous Republic (C); Degtyarniy Zaton, a tributary of River Sura near village Sosnovka, vicinity of Penza, Penza Area (D, F, H, I); Lake Svetloe near River Chulym, Tomsk Area (G, E), all in Russia. A, lateral view. B, anterior view. C, head, lateral view. D, head pores. E, postabdomen. F, its distal portion. G, its basal portion. H, antenna I. I, antenna II. Scale bar denotes 1 mm (A–B); 0.1 mm (C–H).

FIGURE 4. Eurycercus macracanthus, limbs of parthenogenetic female from Lake Svetloe near River Chulym, Tomsk Area (A–B, D–K); Degtyarniy Zaton, a tributary of River Sura near village Sosnovka, vicinity of Penza, Penza Area (C); mouth of the Ulunga River, Amur Area (L), all in Russia. A, Limb I. B–C, inner distal lobe. D, limb II. E, distal armature of its gnathobase. F, limb III. G, distal armature of its gnathobase. H, limb IV. I, distal armature of its gnathobase. J, limb V. K, distal armature of its gnathobase. L, limb VI. Scale bar denotes 0.1 mm.

FIGURE 5. Eurycercus pompholygodes, parthenogenetic female from Lake №6 near River Tareya, a tributary of River Pyasina, Taimyr Autonomous Area, Russia. A, lateral view. B, ventral view. C, anterior view. D, head. E, head pores. F, postabdomen. G, its distal portion. H, antenna I. I–J, inner distal lobe of limb I. Scale bar denotes 1 mm (A–C); 0.1 mm (D–J).

FIGURE 6. Eurycercus longirostris, parthenogenetic female from CPR WDS, California, U.S.A. (A, C, D, F, G, H, K, L); Oliver Lake, Indiana, U.S.A. (B, E, I); Lake La Luna, in the crater of the volcano Nevado de Toluca, State of Mexico, Mexico (J). A, lateral view. B, head. C, head shield. D, head pores. E, labrum, ventral view. F, setae at anterior portion of valves. G, setae at postero-ventral portion of valve. H, armature of valve posterior margin. I, postabdomen. J, its distal portion. K, antenna I. L, antenna II. Scale bar denotes 1 mm (A); 0.1 mm (B-I).

FIGURE 7. Eurycercus longirostris, limbs of parthenogenetic female from CPR WDS, California, USA (A–C, E–K); Lake La Luna, in the crater of the volcano Nevado de Toluca, State of Mexico, Mexico (D, L). A, limb I. B, its distal portion. C–D, inner distal lobe. E, limb II. F, distal armature of its gnathobase. G, limb III. H, its inner-distal portion. I, limb IV. J, limb V. K, distal armature of its gnathobase. L, limb VI. Scale bar denotes 0.1 mm.

FIGURE 8. Eurycercus nipponica, female from a swampy area (with a fresh bear trail in time of sampling) near Travianoy Cape, Kurilskoe Lake, Kamchatka Area, Russia A, parthenogenetic female, lateral view. B–C, ephippial female, lateral and anterior view. D, parthenogenetic female, ventral view. E, head. F, dorsal head pores. G, postabdomen. H, its distal portion. I, its basal portion. J, antenna I. K, antenna II. Scale bar denotes 1 mm (A–D); 0.1 mm (E–K).

FIGURE 9. Eurycercus nipponica, limbs of parthenogenetic female from a swampy area (with a fresh bear trail in time of sampling) near Travianoy Cape, Kurilskoe Lake, Kamchatka Area, Russia A, limb I. B, inner distal lobe of limb I. C, limb II. D, its distal armature. E, limb III. F, distal armature of its gnathobase. G, limb IV. H, distal armature of its gnathobase. I, limb V. J, limb VI. Scale bar denotes 0.1 mm.

FIGURE 10. Eurycercus beringi sp.nov., parthenogenetic female from Council #05: a roadside pond <1.5 m deep, 10 X 25 m, Seward Peninsula, Alaska, U.S.A. A, lateral view. B, dorsal view. C, head. D–E, head pores, lateral and dorsal view. F–G, labrum, lateral and ventral view. H, valve. I, setae at antero-ventral valve portion. J, setae at postero-ventral valve portion. K, armature of valve posterior margin. L, mandible. M, postabdomen. N, its distal portion. O, its basal portion. Scale bar denotes 1 mm (A–C, H, L–M); 0.1 mm (D–G, I–K, N–O).

FIGURE 11. Eurycercus beringi sp.nov., head and thoracic appendages of parthenogenetic female from Council #05: a roadside pond <1.5 m deep, 10 X 25 m, Seward Peninsula, Alaska, U.S.A. A, antenna I. B, antenna II. C, limb I. D, inner distal lobe of limb I. E, limb II. F, distal armature of its gnathobase. G, limb III. H, limb IV. I, distal armature of its gnathobase. J, limb V. K, distal armature of its gnathobase. K, limb VI. Scale bar denotes 0.1 mm.

FIGURE 12. Phylogram based on an alignment of mitochondrial COI sequences for the genus Eurycercus. The tree is midpoint rooted and based on the best ML tree found in PhyML 3.0 (see text). Support values are from nonparametric bootstrap and from approximate likelihood ratio tests. Values less than 70 or 0.7 are not shown. The scale bar represents substitutions per site based on a GTR+I+G model. Proposed species are numbered. See Table 1 for Genbank Accession numbers.