Acroperus harpae ( Baird, 1834 )

Sinev, Artem Y., 2009, Discrimination between two sibling species of Acroperus (Baird, 1843) from the Palearctic (Cladocera: Anomopoda: Chydoridae), Zootaxa 2176, pp. 1-21 : 2-10

Acroperus harpae ( Baird, 1834)

Baird, 1834: 100, Pl. II, fig. 17 ( Lynceus ); 1943: 91–92, Pl. III, fig. 7; 1850: 129, Tab. XVI, fig. 5; Koch, 1841: Heft. 36, 10 (leucoceophaloides); Leydig, 1860: 216–217, Taf. VIII, Fig. 58, 218–219 ( Lynceus striatus ), Taf. IX, Fig. 64–65 ( Lynceus leucocephalus ); Schödler, 1862: 24, Taf. I, fig. 11–16 ( leucocephalus ), 1863, Taf. I, Fig. II ( leucocephalus ); P.E. Müller, 1867: 167–168, Tab. III, fig. 15–17, Tab IV, fig. 26 ( leucocephalus ), 169–170, Tab. III, fig. 19 (cavirostris); Daday, 1888: 102, fig. 35–36 (transilvanicus); Stingelin, 1985: 239–240, pl. IV, Fig.28 ( leucocephalus ); Lilljeborg, 1900: 418–425, Tab. LXIII, fig. 14–24, Tab. LXIV, fig. 1–10; Stingelin, 1906: 326–327, Tab. 13, Fig. 1 , 2 , 6 , 11; Behning, 1941: 254 ( harpae harpae ); Smirnov, 1971: 403–406, fig. 483–489; Flössner, 1972: 284–287, Abb. 134, A–E ( harpae var. harpae ); Chiang & Du, 1979: 202–203, Fig. 134; Negrea, 1983: 300–301; Margaritora, 1985: 274–276, Fig. 109; Sars, 1993: 144–145, Pl. 102: 1–3, Pl. 103: 1–6; Alonso, 1996: 354–356, Fig. 159; Flössner, 2000: 341–343, Abb. 127 ( harpae var. harpae ), 128 ( harpae var. alonoides );

Type locality. Berwickshire, Great Britain, United Kingdom ( Baird 1834).

Type material: non-existent.

Material studied (* - samples, where A. harpae coexisted with A. angustatus ): over 100 parthenogenetic females, numerous ephippial females and males from Lithuania, Vilnius Region, a channel in Arvydai Fishery Farm, 16.10.1999, coll. K. Abračiauskas, AAK-1999-126; * 11 parthenogenetic females from Belarus, Vitebsk Area, Miorskii district, Lake Obsterno, 10.07.2005, coll. A.A. Palash; over 100 parthenogenetic females, numerous ephippial females and males from Russia, Murmansk Area, Khibiny Mountains, Lake Malyi Vud'yavr, 11.08.2000, coll. A.Yu. Sinev; * over 200 parthenogenetic females, numerous ephippial females and males from Russia, Moscow Area, Ruza District, Glubokoe Lake, N 55°45.217’ E 36°30.250’, 06-09.2007 and 0 8.2008, coll. A.Yu. Sinev; * four parthenogenetic females from Russia, Karelia Republic, a rock pool near Lake Ukmozero, 26.08.1986, coll. N.N. Smirnov, AAK-1999-039; * parthenogenetic female, ephippial female, adult male, juvenile male of instar II from Russia, Novgorod Velikii Area, Valdai District, Lake Edrovskoje near village Edrovo, 10.10.1993, coll. A.O. Bienkovski, AAK-1999-041; seven parthenogenetic females from Russia, Yaroslavl Area, Uglich Reservoir 23.07.1962, coll. N.N. Smirnov, AAK-1999-090; eight parthenogenetic females from Russia, Khanty-Mansi Autonomous Area, Lake Pionerskoe near town of Nizhnevartovsk 60º55.574' N, 76°28.749' E, 23.07.2005, coll. A.A. Kotov, AAK- 2005-324; 3 parthenogenetic females from Russia, Khanty-Mansi Autonomous Area, Stariy Vartovsk, an oxbow lake near Pavlovskie Dachi, 60º51.569' N, 76º39.944' E, 23.07.2005, coll. A.A. Kotov; * 14 parthenogenetic females from Russia, Irkutsk Area, Barguzinka river close to coast of Lake Baikal, 0 4.08.2005, coll. A. Evseev; * over 40 parthenogenetic females from Russia, Jewish Autonomous Area, an oxbow lake of Tunguska River, after the village of Partizanskaya, 10.09.2007 coll. N.M. Korovchinsky, NMK-2804; over 30 parthenogenetic females from Russia, Khabarovsk Territory, an affluent of River Sjumnjur (right bank), near railway station of Bolon', 49º 53.906' N, 136º08.552' E, 0 5.09.2007, coll. A.A. Kotov & N.M. Korovchinsky, NMK-2763; * 6 parthenogenetic females from Russia, Khabarovsk Territory, a small lake near bridge across the River Pir, 48º59,00' N, 136º24.64' E, 0 7.09.2007, coll. A.A. Kotov & N.M. Korovchinsky, NMK-2780; over 50 parthenogenetic females from Russia, Sakhalin Island, lake near Pokrovka village, 47º19.235' N, 142º42.428' E, 15.09.2008, coll. A.A. Kotov & N.M. Korovchinsky NMK- 2902.

Description. Parthenogenetic female: Body with well-expressed dorsal keel, of variable shape ( Fig 1 A–C, H–J, 2A–B), usually moderately high, oval to subrectangular (height/length ratio from 0.49 to 0.72 in adult), with maximum height before or at the midline, strongly compressed laterally. Dorsal margin from highly arched to moderately convex, without depression between valves and head shield. Postero-dorsal angle always rounded, posterior margin weakly to moderately concave. Postero-ventral angles broadly rounded, provided with 1–3 small denticles with narrow bases, with small setules between ( Fig. 2 C–D, 3,B–C). A row of 100–130 setules along posterior margin on inner side of carapace. Ventral margin from almost straight to irregularly convex. About 65–70 ventral setae, about ten anteriormost setae long, next 20 setae short, posterior setae of intermediate length. Antero-ventral angle rounded. Valves with prominent sculpture ( Fig. 2 E, 3A) as diagonal, almost never anostomosing lines, in postero-ventral portion of valves curved upward. SEM examination reveals fine connecting striae between them.

Degree of keel development varies greatly from population to population (see Fig. 1 ). Distance between eye and margin of keel varies from 0.8 to 3.6 eye diameters. In lateral view, rostrum pointed downward ( Fig. 3 B), it shape varies depending on size of keel. Eye 2–3 times larger than ocellus (see Fig.1 ). Three connected main head pores located on a widened area of head shield keel ( Fig. 2 F–G). PP = 0.4–0.8 IP. Lateral pores minute, located at the distance of 1.5–2 IP from midline, at level before anterior main pore. Labrum with narrow subtriangular keel, height about twice width ( Fig. 3 D–E). Apex of keel rounded, dorsal margin without setae.

Postabdomen ( Fig. 2 H, 3F–G) long and narrow, with parallel margins or, in larger specimens, slightly narrowing distally, length about four times height. Ventral margin almost straight. Basis of claws bordered from distal margin by clear incision. Distal margin straight, distal angle prominent, broadly rounded. Dorsal margin almost straight. Distal part of dorsal margin 3–3.5 times longer than preanal one, with preanal portion about 1.5 times longer than anal. Preanal angle weakly defined, postanal angle not defined. Postanal and anal margins of postabdomen provided with groups of minute denticles, similar to these in male postabdomen of most Aloninae . 14–20 lateral fascicles of long setules, in distalmost fascicles length of setules exceed the width of base of postabdominal claw. A cluster of long setules located near the base of postabdominal claws.

Postabdominal claw long, almost straight, as long as anal portion of postabdomen. Basal spine long, straight and thin, about 0.4 length of claw itself, bearing 7–12 setules. A prominent spine located at the middle of the claw.

Antennule long and narrow ( Fig. 4 A), with length about 4–5 widths, with 3 transverse rows of short setules at anterior face. Eight terminal aesthetascs, one of them two times longer and thicker than others, almost as long as antennula itself. Single lasteral aesthetasc arise near the base of antenular seta, subequal to the largest terminal aesthetasc. Antennular seta thin, less than 1/3 length of antennule, arising at 2/3 distance from the base.

Antenna long, about 1/4 of body length ( Fig. 2 I–J, 4B). Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/ 0-0-1. Branches long and slender, exopodite shorter than endopodite, reaching only to the middle of endopodite apical segment. Seta arising from basal segment of endopodite short, less than 2/3 length of a middle segment. Seta arising from middle segment of endopodite 1.5 times longer than apical segment. Apical setae of exopodite differentiated in size, one of them two times thicker and much longer than other apical setae. Spine on basal segment of exopodite about 1\3 length of middle segment. Apical spines about 1/3 length of apical segments.

Thoracic limbs: six pairs.

Llimb I of moderate size ( Fig. 4 C). Epipodite rounded, with curved finger-like projection longer that epipodite itself. Accessory seta short. ODL ( Fig. 4 D) with one long seta, with minute setules in distal part. IDL with three setae and several clusters of hard setules. 1st IDL large and broad, claw-like, strongly curved, both 2nd and 3rd IDL setae 2-segmented, with setules in distal part, 3rd seta slightly shorte than ODL seta, 2nd seta about 2/3 length of 3rd seta.

Endite 3 with four setae subequal in length ( Fig 4 E). Endite 2 with two long distally setulated setae, both of them shorter than ODL seta, a shorter seta near their base, and a naked seta and a small sensillum near on anterior face of limb. Endite 1 with two 2-segmented setae, short seta shifted to the limb base, and a long naked seta on anterior face of limb, two time longer than naked seta of endite 2. Five-six rows of setules on ventral face of limb. Two ejector hooks of similar size. Maxillar process ending in single short setae.

Limb II subtriangular ( Fig. 5 A). Exopodite narrow, elongated, with very short. Inner portion of limb (“endopodite”) with eight scraping spines; small seta located between bases of exopodite and distalmost scraper. Spines 1–5 long, increasing progressively in length distally. Spines 6–8 short, subequal in length, onlu slightly thicker than spine 5. Distal armature of gnathobase with four elements. Filter plate with seven setae, the posteriormost member considerably shorter, a cluster of long setules located near its base.

Limb III: epipodite oval, without any projection. Exopodite ( Fig. 5 B) subtriangular, with seven setae, seta 3 being longest, seta 6 and 7 of about 2/3 and 1/3 length of seta 3, respectively, other seta very short. Seta 3 armed with very long, hard setules in distal part and shorter setules in basal part, other setae with short setules. Distal endite with three setae decreasing in length basally ( Fig. 5 C). Two distalmost setae very slender, sharp, with about 5 long denticles, a small sensillum between their bases; basalmost setae flat, setulated in distal part. Basal endite with four stiff, setulated distally setae, subequal in length. Gnathobase not clearly separated from basal endite. Four soft setae increasing in size basally ( Fig. 5 D), small sensillum near the base of distalmost seta. Distal armature of gnathobase with three elements. First one an elongated, cylindrical sensillum, the second geniculated seta, the third - spines with forked tip. Filter plate III with seven setae.

Limb IV: epipodite oval, with finger-like projection longer that epipodite itself. Exopodite ( Fig. 5 E) of irregular shape, with six setae, divided into lateral and distal group of three setae in each. Seta 3 being longest, seta 1–2 and 5–6 about 1/3 length of seta 3, seta 4 very short. Setae 1–4 flat, plumose, on setae 1–2 setules long, on setae 3–4 much shorter, setae 5–6 slender, seta 5 with several long setules at the middle. Inner portion of limb IV with four setae and sensillum. ( Fig. 5 F). Scraping seta short, with wide base and small denticles in distal part, flaming-torch setae with elongated basal part and short, slender distal part, each armed with four to seven long setules; longest of these setules equal in length to the modified setae bearing them. Sensillum located on the inner part of endite, not on its margin, as common for Aloninae .Three soft setae, much shorter than filter plate setae, increasing in size basally Gnathobase with long two-segmented seta and a small hillock distally. Filter plate with five setae.

Limb V ( Fig. 5 G). Epipodite suboval, with finger-like projection two times longer that epipodite itself. Exopodite irregular, subdivided into two lobes, the incursion between lobes broad, trapezium-shaped. Exopodite with four plumose setae, their length gradually decreases from seta one to seta four. Seta four two times thicker than other setae. Inner limb portion as elongated narrow lobe, with short setules on the inner margin. At inner face, two setulated in distal part setae subequal in length, the distal one two times thicker than proximal. Filter plate with three short setae increasing in size distally.

Limb VI ( Fig. 5 H) very small in comparison with other limbs, a small rounded lobe, with setulated margin.

Ephippial female. Body similar in shape to that of parthenogenetic females ( Fig. 1 D), but newer low, height-length ratio in studied material from 0.61 to 0.73. Ephippium yellow-brown, transparent.

Juvenile male of instar I of same shape and size as juvenile female of same instar ( Fig. 1 E), with keel on head and valves. Postabdomen of same shape and armament as in female ( Fig. 3 I), sperm duct opening almost at the middle of ventral margin where a small notch is present. Antennule as for female. Thoracic limb I ( Fig. 4 F) with Anlage of copulatory hook as a short process, IDL same as in female.

Juvenile male of instar II of same shape and size as juvenile female of same instar ( Fig. 1 F), with keel on head and valves. Postabdomen of same armament as in female ( Fig. 3 J), sperm ducts opening close to the end of postabdomen, ventral margin with convex part before the gonopores, and a small notch after them. Antennule of same shape as in female ( Fig. 4 G), with short Anlage of male seta on inner side, aesthetascs same as in female. Thoracic limb I with curved copulatory hook, its free arm of about 2/3 length of ODL seta ( Fig. 6 ). The IDL with three setae of same morphology as in the female and an Anlage of a male seta. Ventral face of limb with anlage of copulatory brush setae and about ten long stiff setules under it.

Adult male. Similar in shape to juvenile female of instar II but slightly larger, head and valves with a ridge in place of female keel ( Fig. 1 G, 2K–L). Maximum height at the second fourth of the body, height/length ratio about 0.67. Dorsal margin of valves highly arched.

Postabdomen long and narrow, very slightly narrowing distally ( Fig. 2 M, 3G). Preanal angle well-defined, preanal angle not defined, distal portion 2.5 times loner than preanal. Postabdominal claws situated on small protrusion in the middle of distal margin of postabdomen. The spermoducts open above the protrusion, posteroventral and posterodorsal angles distinctly rounded. Marginal setules and lateral fascicles of setules same as in female. Postabdominal claw of same size as in female, significantly longer than preanal portion of postabdomen.

Antennule of same shape as in female ( Fig. 4 I), with two long lateral aesthetascs and 9 terminal aesthetascs, one of them significantly longer and thicker than others. Male seta located on dz distance from the base, not reaching the end of antennule. Limb I ( Fig. 4 J–K) with U-shaped copulatory hook, length of free arm about half that of the limb itself. The IDL has four setae; IDL seta 1 same as in femele, IDL setae two and three much thinner than in female, the male seta quite long, little shorter then IDL seta two. The copulatory brush seta small, shorter then first IDL seta. Ventral face of the limb under the copulatory brush with cluster of about five short stiff setules, followed by row of about 12 very long setules. About 15 shorter stiff setules along the border of endite three.

Size. Length of female of juvenile instar I— 0.37–0.42 mm, of juvenile instar II— 0.43–0.51 mm, of adult female— 0.50–0.82 mm. Length of male of juvenile instar I— 0.38–0.41 mm, of instar II— 0.43–0.47 mm, of adult male— 0.46–0.52 mm.

Figures

FIGURE 1. Acroperus harpae (Baird, 1834). A – H—specimens from Russia, Murmansk Area, Khibiny Mountains, Lake Malyi Vud'yavr: A – B—juvenile females of instar I – II, C—parthenogenetic female, D—ephippial female, E – F—juvenile males of instar I – II, G—adult male; H – J—parthenogenetic females: H - from Russia, Moscow Area, Ruza District, Glubokoe Lake, I-from Belarus, Vitebsk Area, Miorskii district, Lake Obsterno, J - from Russia, Irkutsk Area, Barguzinka river close to coast of Lake Baikal coast. Scale bar 0.2 mm.

FIGURE 2. Acroperus harpae (Baird, 1834) from Russia, Moscow Area, Ruza District, Glubokoe Lake, A – J—parthenogenetic female: A—specimen in lateral view, B—specimen in anterodorsal view, C – D—denticles of the valves, E—posterior portion of valves in anteroventral view, F—head pores (lateral pore indicated by arrow), G—main head pores, H—postabdomen, I—antenna, J—apical setae of antenna; K – M—adult male: K—specimen in lateral view, L—specimen in anterodorsal view, M—posterior portion of postabdomen. Scale bars: 0.1 mm for A, B, L, K, 0.05 mm for E, H, I, J, 0.01 mm for F, G, 0.005 mm for C, D.

FIGURE 3. Acroperus harpae (Baird, 1834) from Russia, Murmansk Area, Khibiny Mountains, Lake Malyi Vud'yavr. A – F—parthenogenetic female: A—valve, B – C—denticles of left and right valves of same specimens, D—head (note the one of antennules appears reaching the rostrum), E—outlines of labral keel, F – G—postabdomens; H – I—postabdomens of juvenile males of instar I – II; J—postabdomen of adult male. Scale bars: 0.1 mm for A, 0.05 mm for B – C, D – E and F – G.

FIGURE 4. Acroperus harpae (Baird, 1834) from Russia, Murmansk Area, Khibiny Mountains, Lake Malyi Vud'yavr. A – E—parthenogenetic female: A—antennule, B—antenna, C – D—outer and inner part of thoracic limb I, E—endites of limb II; F—juvenile male of instar I, inner part of thoracic limb I; G – H - juvenile male of instar II, G—antennule, H—inner part of thorachic limb I; I – K—adult male, I—antenna, J – K—outer and inner part of thoracic limb I. Scale bars: 0.05 mm.

FIGURE 5. Acroperus harpae (Baird, 1834) from Russia, Murmansk Area, Khibiny Mountains, Lake Malyi Vud'yavr, parthenogenetic female, thoracic limbs: A—limb II, B—expodite of limb III, C – D—inner part of limb III, E—exopodite of limb IV, F—inner part of limb IV; G—limb V, H – limb VI. Scale bars: 0.05 mm.

FIGURE 6. Acroperus angustatus Sars, 1863. A – H—specimens from Germany, Berlin Area, Petersdorfersee Lake: A – B—juvenile females of instar I – II, C—parthenogenetic female, D – E—ephippial female, F – G—juvenile males of instar I – II, H—adult male; I – K—parthenogenetic females: I—from Norway, Oslo, Lake Ostensjovand (specimen from G. O. Sars collection, slide F 9012), J—from Belarus, Vitebsk Area, Miorskii district, Lake Obsterno, K - from Russia, Chita Area, Chita town, Lake Kenon. Scale bar 0.2 mm.