Alona irinae, Sinev, Artem Y., Alonso, Miguel & Sheveleva, Natalia G., 2009

Sinev, Artem Y., Alonso, Miguel & Sheveleva, Natalia G., 2009, New species of Alona from South-East Russia and Mongolia related to Alona salina Alonso, 1996 (Cladocera: Anomopoda: Chydoridae), Zootaxa 2326, pp. 1-23 : 2-9

Alona irinae sp. nov.

( Figs. 1–4 )

Etymology. The species named after Russian cladocerologist Irina Konstantinovna Rivier.

Type locality. Lake Khasan, in the plain of Zeya River, in the Amur Area, Russia, 53º29’22.0”N, 126º56’57.1”E.

Holotype. Parthenogenetic female, 20.07.2006, coll. N. G. Sheveleva, preserved in 80% ethanol, deposited at ZMOU, Ml-77.

Paratypes. 7 parthenogenetic females, 20.07.2006, coll. N. G. Sheveleva, preserved in 80% ethanol, deposited at ZMOU, Ml-78; 3 parthenogenetic females, ephippial female, male from lake Zurbat-Nur, Tazheran steppes, Olkhon District, Irkutsk Area, Russia 52º51’97.2”N, 106º35’42.2”E, coll. N.G. Sheveleva, deposited in the first author’s personal collection in Institute for Ecology and Evolution, Moscow.

Diagnosis.

Female. Of moderate size, length up to 0.54 mm. Body regular oval, of moderate height, height /length ratio about 0.68–0.72, maximum height at the middle of the body. Ventral margin with about 40 setae. Posteroventral corner without denticles, with numerous thin setules. Whole carapace covered by dense, broad longitudinal lines. Head shield with broadly rounded posterior margin, rostrum short and rounded. Three narrowly connected major head pores, central pore located at the middle between other pores. PP about 0.8– 0.9 IP. Lateral head pores dot-like, located at 1.0–1.2 IP distance from midline. Labral keel suboval, with rounded apex, without clusters of setules on posterior margin.

Postabdomen of moderate width (length about 2.2–2.4 height), with almost parallel margins and broadly rounded dorso-distal angle. Dorsal margin with distal part about 1.6–2.0 times longer than preanal one, with postanal portion slightly longer than anal portion, postanal portion slightly convex, anal portion slightly concave. Preanal angle moderately defined, postanal angle not defined. 2 or 3 single marginal denticles on distal angle and 8–10 clusters of smaller marginal denticles along preanal and anal margin; 9 or 10 lateral fascicles of setules; 4 or 5 fascicles in postanal portion very wide, with setules longer than marginal denticles, all setules in fascicles equally thin. Postabdominal claw of moderate length, slightly shorter than preanal portion of postabdomen. Basal spine long and thin, about 1/3 of length of claw.

Antennula with 9 terminal aesthetascs, longest of them of about half length of antennula. Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/0-0-1. Seta arising from basal segment of endopodite as long as endopodite. Spine on basal segment of exopodite shorter than middle segment. Spine from apical segment of exopodite slightly shorter than this segment. Apical spine of endopodite of same length as this segment.

Limb I with very long accessory seta, IDL of limb I with three setae, IDL seta 1 very small, two others armed with short setules distally. Exopodite of limb II with very small seta, scraping spines not differentiated. Exopodite of limb III with 6 setae, seta 3 being longest, seta 4 three times shorter than seta 5. Exopodite IV with 6 setae, setae 4 and 6 about 3/4 length of seta 5. Exopodite V with 4 setae, filter plate I consist of single seta. Epipodites IV and V without projections. Limb VI absent.

Male. Body regular oval, of moderate height, height/length ratio about 0.63–0.65, maximum height at the middle of the body. Postabdomen short, with narrowing anal portion and subrectangular postanal portion. Dorsodistal angle not defined. Sperm duct openings located almost at the end of postabdomen. Clusters of short setules in place of marginal denticles, lateral fascicles of setules same as in female. Postabdominal claw 1.5 times shorter than that of female, basal spine 2 times shorter than in female.

Antennule with 10 terminal and 2 lateral aesthetascs. Male seta arising at 1/4 length from tip, about 1/3 of antennule length. Thoracic limb I with U-shaped copulatory hook, IDL seta 1 absent, setae 2 and 3 subequal in length, male seta thick, curved, as long as seta 3.

Description. Parthenogenetic female. General: In lateral view, body regular oval, moderately high in adults ( Fig. 1 C–D, 2A–B), lower in juveniles ( Fig. 1 A–B). Maximum height at middle of body in adults, in the second quarter of the body at juveniles. In adults height/length ratio about 0.68–0.72; in juveniles of instar II, about 0.64. Dorsal margin highly arched, with small depression at the border of valves and head shield. Posterodorsal and posteroventral angles broadly rounded. Posterior margin uniformly curved. Posterodorsal angle with about 70 short thin setules of equal size, passing into a row of about 100 setules along the posterior margin ( Fig. 1 F, 2C), at some distance from the margin on inner side of carapace. Ventral margin almost straight, with about 40 setae, first 8–10 setae long, next 10 setae short, other setae of moderate length. Anteroventral angle rounded. Whole carapace covered by dense, broad longitudinal lines ( Fig. 1 E, 2A–B). Head relatively small, triangle-round in lateral view, rostrum short, pointing downward ( Fig. 2 D). Eye larger than ocellus. Distance from tip of rostrum to ocellus equal or slightly greater than that between ocellus and eye.

Head shield with maximum width behind mandibular articulation, without any prominent sculpture ( Fig. 1 G). Rostrum short, broadly rounded. Posterior margin of head shield broadly rounded. Three narrowly connected major head pores ( Fig. 2 E, 3A–B), middle pore slightly smaller than others, located at the middle between others. PP about 0.8–0.9 IP. Lateral head pores located about 1.1–1.2 IP distance from midline, at the level of the middle major head pore.

Labrum of moderate size ( Fig. 3 C–E). Distal labral plate without setulation. Labral keel of moderate width (height/width ratio about 2), with a rounded or blunt apex. Anterior margin of keel convex, posterior margin without clusters of setules.

Thorax and a bdomen subequal in length, dorsal surface of abdominal segments not saddle-shaped. No abdominal projections.

Postabdomen ( Fig.1 H–I, 2F) of moderate width, with almost parallel margins and broadly rounded dorsodistal angle. Length about 2.2–2.4 height. Ventral margin almost straight. Inflated basis of claws bordered from distal margin by clear incision. Distal margin weakly convex. Dorsal margin with distal part about 1.6– 2.0 times longer than preanal one, with postanal portion slightly longer than anal portion. Postanal portion of distal weakly convex, anal portion weakly concave. Preanal angle moderately defined, postanal angle not defined. Preanal margin weakly convex.

Postabdomen with two-three single marginal denticles on distal angle and 8–10 clusters of smaller marginal denticles, decreasing in size basally, along preanal and anal margin; 9 or 10 lateral fascicles of setules; 4 or 5 fascicles in postanal portion very wide, with setules longer than marginal denticles, fascicles in anal portion much smaller. All setules in fascicles of similar width. Postabdominal claw of moderate length, slightly shorter than preanal portion of postabdomen. Basal spine long and thin, about 1/3 of length of claw, a cluster of long setules located near its base.

Antennule ( Fig. 3 F) comparatively large, almost reaching tip of rostrum, with three-four clusters of long setules at anterior face. Length/width ratio about 3. Antennular sensory seta slender, two times shorter than antennule, arising at 2/3 distance from the base. Nine aesthetascs, three of them 1/3 longer than others, of about half length of antennule, others of similar size. All aesthetascs projecting beyond anterior margin of head shield.

Antenna short ( Fig. 2 F, 3G). Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/0-0-1. Basal segment robust, branches short and stout. Basal segments of both branches almost two times longer than middle and apical segments. Seta arising from basal segment of endopodite thin, as long as endopodite itself. Seta arising from middle segment of endopodite of slightly smaller than apical setae. Spine on basal segment of exopodite shorter then middle segment. Spine from apical segment of exopodite little shorter than this segment. Apical spine of endopodite of same length as this segment.

Thoracic limbs: five pairs.

Limb I ( Fig. 3 H–I) of moderate size. Epipodite oval, without finger-like process. Accessory seta long, about 3/4 of ODL seta. ODL with a long seta with minute setulation. IDL with 3 setae, seta 1 very small. Setae 2 and 3 subequal in length, slightly shorter than ODL seta, both with thin setules in distal part. Endite 3 with 4 setae of same length. Endite 2 with 2 setae, 2 of them long, about length of IDL seta 2, armed with robust setules in distal part, third seta similar to endite 3 setae, but longer. Endite 1 with 2 distally setulated 2- segmented setae and a very long flat seta reaching to the end of maxillar process. No naked setae and sensillae found on endites 1 and 2. Six rows of thin long setules on ventral face of limb. Two ejector hooks of similar size. Maxillar process with single seta.

Limb II: exopodite elongated, with 1 minute seta; 8 scraping spines ( Fig. 3 J), increasing in length distally, armed with small setules. Distal armature of gnathobase with 4 elements. Filter plate with 7 setae, 2 posteriormost considerably shorter than others.

Limb III: epipodite oval, without process. Exopodite ( Fig. 3 K) trapezium-shaped, with 6 setae. Seta 3 being longest, setae 5 and 1 of 2/3 and 1/3 length of seta 3, respectively, other setae very short. Distal endite with 3 setae ( Fig. 3 L), 2 distalmost members slender, sharp, with distal parts unilaterally armed with sharp, strong denticles; basalmost seta two times shorter, bilaterally armed with long setules. Basal endite, with 4 stiff setae, increasing in size in basal direction. Gnathobase not clearly separated from basal endite. Four soft setae increasing in size basally, a small sensillum near the base of distalmost seta. Distal armature of gnathobase with 4 elements. The first one elongated, cylindrical sensillum, second thin, bent seta, others 2 short spines. Filter plate III with 7 setae.

Limb IV: pre-epipodite setulated; epipodite oval, without process. Exopodite irregularly rounded ( Fig. 3 M), with 6 setae. Seta 3 longest, setae 1 and 2 about 2/3 length of seta 3, seta 5 about half length of seta 3, setae 4 and 6 shorter than seta 5. Setae 5 and 6 slender, plumose like other setae. Inner lobe of limb IV with 4 setae ( Fig. 3 N). Distalmost seta slender, sharp, armed with small setules, 3 flaming-torch setae subequal in size, armed with similar setules. Sensillum elongated. Three soft setae increasing in size basally. Gnathobase with 2-segmented seta, and pair of small hillocks distally. Filter plate with 5 setae.

Limb V: pre-epipodite setulated, epipodite oval without process ( Fig. 3 O). Exopodite oval, not divided into 2 lobes, with 4 plumose seta, decreasing in size basally. Inner limb portion a rounded lobe, with setulated inner margin. At inner face, 2 setae, one 3 times longer than another. Filter plate as a single seta, a small sensillum located near it.

Ephippial female ( Fig. 4 A) similar in shape to parthenogenetic female, ephippium dark brown, with thick longitudinal lines as on the rest of carapace, no polygons present.

Male. Only a single adult male was studied. General shape of adult male ( Fig. 4 B) similar to that of instar II juvenile female, body height/body length = 0.63–0.65. Ocellus and eye of same size as female. Postabdomen ( Fig. 4 C) short, with narrowing anal portion and subrectangular postanal portion. Dorsodistal angle not defined. Preanal angle not defined, postanal angle well-defined. Distal part of postabdomen 1.5 times longer than preanal. Sperm duct openings located ventrally almost at the end of postabdomen. Clusters of short setules in place of marginal denticles, lateral fascicles of setules same as in female. Postabdominal claw 1.5 times shorter than that of female, basal spine about 2 times shorter than in female.

Antennule slightly shorter than in female ( Fig. 4 D), with 10 terminal and 2 lateral aesthetascs of same length as terminal, but stouter. Male seta arising at 1/4 length from tip, about 1/3 of antennule length. Thoracic limb I more stout than that of female ( Fig.4 E), with with U-shaped copulatory hook, copulatory brush present. Several long setules and a row of about 15 shorter setules on ventral face of limb under copulatory brush ( Fig. 4 F). IDL seta 1 absent, setae 2 and 3 setae subequal in length, much thinner than in female, male seta thick, curved, as long as seta 3.

Size. In juvenile females of instar II length 0.40–0.45 mm, height 0.24–0.26 mm., in adult females, length 0.46–0.54 mm, height 0.28–0.33 mm. The only studied adult male has length 0.34 mm, height 0.22 mm.

Remarks. Alona irinae sp. nov. shares numerous affinities with A. salina , which separate it from most other species of the genus. These features include a long seta on basal segment of endopodite of antenna, very small IDL seta 1, very long accessory seta, very small seta of exopodite II, gnathobase filter plate consisting of single seta, etc. It differs from both A. salina and A. floessneri sp. nov. in the sculpture of the carapace, composed of dense broad longitudinal lines, in the rectangular shape of the postabdomen, and in the presence of long, single distal marginal denticles. It also differs from A. salina in the morphology of the lateral fascicles of setules of postabdomen, in IDL morphology, in the shape of male postabdomen, and in its smaller size. From A. floessneri sp. nov., A. irinae sp. nov. also differs in its regular oval body, shape and armature of male and female postabdomen, and morphology of exopodite IV. Differences between these three taxa are summarized in Table 1 . In the shape of body and sculpture of valves A. irinae sp. nov. is also similar to A. elegans Kurz, 1875 and A. orellanai Alonso, 1996 . A. elegans can be separated from A. irinae sp. nov. by the shape of postabdomen (postanal portion 1.5 times shorter than anal), by exopodite III with seta 4 as long as seta 5, and the long finger-like processes of exopodites IV–V. A. orellanai clearly differs from A. irinae in the postabdomen with two rows of lateral fascicles of setules.

Distribution and ecology. Alona irinae sp. nov. is known from two locations — the lake Zurbat-Nur in the steppes along the west coast of Lake Baikal and Lake Khasan in the plain of the Zeya River. The distance between the localities is more than 800 km, so the species is distributed over a significant area. We presume it certainly can be found in other lakes in South Siberia, Mongolia, and the Amur basin.

The Khasan Lake is a small freshwater lake located in the forest, its coastline swampy, and overgrown with vegetation. No specific data about hydrochemistry is available. A rich community of cladocerans was present in the lake during the time of sampling: Sida crystallina ortiva Korovchinsky, 1979 , Limnosida frontosa Sars, 1862 , Diaphanosoma pseudodubium Korovchinsky, 2000 , Diaphanosoma sp., Ceriodaphnia pulchella Sars, 1862 , Scapholeberis mucronata (O. F. Müller, 1776) , Pleuroxus truncatus (O. F. Müller, 1785) , Graptoleberis testudinaria (Fisher, 1851) , Eurycercus lamellatus (O. F. Müller, 1776) , Alona quadrangularis (O. F. Müller, 1776) , A. affinis (Leydig 1860) , A. costata Sars, 1862 , Chydorus cf. sphaericus (O. F. Müller, 1785) , Camptocercus lilljeborgi Schoedler, 1862 , and Polyphemus pediculus (Linnaeus, 1761) .

Zurbat-Nur lake is located in the steppe area. It is a small (about 0.12 hectare) alkaline lake with salinity 3.1–3.67 g /l, pH 8.2–10 depending on season; maximum depth about 5 m. In the sample from Zurbat-Nur lake A. irinae occurred together with Daphnia magna Straus, 1820 , Eurycercus lamellatus , Oxyurella tenuicaudis (Sars, 1862) , Alona affinis , and Camptocercus rectirostris Shoedler, 1862 . Chydorus cf. sphaericus , and Moina sp. also were recorded from this lake.

Figures

FIGURE 1. Alona irinae sp. nov., Khasan lake. A – B—juvenile female of instar II. C – I—parthenogenetic female, C – D—lateral view, E—valve, F—posterioventral angle of valve, G—head shield, H – I—postabdomen. Scale bars: 0.1 mm for A – D, G and E; 0.05 mm for F, H – I.

FIGURE 2. Alona irinae sp. nov., Khasan lake, parthenogenetic female. A – lateral view. B—front-lateral view. Cposteroventral angle of valve. D—head. E—head pores. F—postabdomen. G—antenna. Scale bar: 0.1 mm for A – B; 0.05 mm for D, F; 0.02 mm for G; 0.01 mm for C, E.

FIGURE 3. Alona irinae sp. nov., Khasan lake, parthenogenetic female. A – B—head pores. C – E—labrum. Fantennula. G—antenna. H – I—limb I and its ODL and IDL. J—limb II. K – L—exopodite and inner portion of limb III. M – N—exopodite and inner portion of limb IV. O—limb V. Scale bars: 0.1 mm for C – E, G; 0.05 mm for A – B, F, H – O.

FIGURE 4. Alona irinae sp. nov., Zurbat-Nur lake, gamogenetic individuals. A—ephippial female. B – F—adult male: B—lateral view, C—postabdomen, D—antennula, E – F—inner portion and endite 3 of limb I. Scale bars: 0.1 mm for A – B; and 0.05 mm for C – F.

Tables

TABLE 1. Differences between Alona irinae sp. nov., Alona floessneri sp. n., and Alona salina Alonso, 1996.

Character	Alona irinae sp. nov.	Alona floessneri sp. nov.	Alona salina Alonso, 1996 .
Size of adult female	Up to 0.54 mm	Up to 0.56 mm	Up to 0.6 mm
Dorsal margin of valves	highly arched, with depression at posterior part of headshield	moderately arched, without depression at posterior part of headshield	moderately arched, without depression at posterior part of headshield
Posterior margin of valves	convex	almost straight	convex
Sculpture of valves	broad, densely spaced lines	narrow lines	narrow lines
Posterio-ventral angle of valves	with about 70 short, thin setules, not organised into groups	with about 100 long, thin setules, not organised into groups	with about 50 long, thick setules in several groups
Postabdomen, postanal/ preanal parts length ratio	About 1.2	About 1.5	About 1
Lateral fascicles of setules of postabdomen	all setae of same thickness	all setae of same thickness	distalmost seta much thicker than others
Marginal denticles of postabdomen	distal denticles single, as long as setules of distal fascicles	distal denticles in groups, two times shorter than setules of distal fascicles	distal denticles in groups, two times shorter than setules of distal fascicles
IDL setae 2–3	long and narrow	long and narrow	robust, broad
Setae of exopodite IV	setae 4 and 6 about 3/4 length of seta 5	setae 4 and 6 about 2/3 length of seta 5	setae 4 and 6 slightly shorter than seta 5
Male postabdomen	narrowing in anal portion, postanal portion narrow	as A. irinae , but with distinct ventro-distal bulge	with parallel margins, postanal portion wide