Biapertura elliptica ( Sinev, 1997 ) Sinev, 2020

Sinev, Artem Y., 2020, Re-evaluation of the genus Biapertura Smirnov, 1971 (Cladocera: Anomopoda Chydoridae), Zootaxa 4885 (3), pp. 301-335 : 318-322

Biapertura elliptica ( Sinev, 1997) comb. nov.

Sinev 1997: 55–57, Fig. 5–6 ( Alona ).

Type locality. Australia, New South Wales, Kosciuszko National Park, pool near Lake Albina ; elevation about 1920 m.a.s.l., coll. N.N. Smirnov.

Type material. Holotype at Australian Museum, access number P42716 . Paratypes (16 parthenogenetic females) at Zoological Museum of M. V. Lomonosov Moscow State University , access number Ml-15 .

Material studied here. Over 30 females from type locality, not officially designated as type material.

Material studied earlier. see Sinev (1997) for the material from the type locality. Initial description of the species was rather short by modern standards, so full description is provided.

Description. Parthenogenetic female. In lateral view, body low oval in juvenile females ( Fig.11A,B ); very regular oval, of moderate height in adults ( Fig. 11C , 12 A–D); moderately compressed laterally. Maximum height at the middle of the body. In adults height/length ratio about 0.6.

Carapace. Dorsal margin convex; postero-dorsal and postero-ventral angles broadly rounded. Posterior margin convex. Antero-ventral angle rounded. Setae of ventral margin of valves ( Fig. 11D ) and setulae of postero-ventral angle ( Fig. 11 E–F, 13A) same as in the previous species. Carapace ornamentation as dense longitudinal striae; longitudinal lines not found in studied specimens.

Head ( Fig. 11 G–H) as in the previous species. Two major head pores ( Fig. 11I , 12 E–F) of same size, with a narrow connection between them. PP about 2.5–3 IP in adults. Lateral head pores located in small depressions about 1 IP distance from midline, at the level before anterior major head pore. Striae absent around head pores. Dorsal pore ( Fig. 12G ) as elongated longitudinal depression at the dorsal midline of carapace, of about 15 µm length in adults; a small gland-like structure under it, beneath the cuticle. SEM examination reveal two very small apertures located at the middle of dorsal pore, located one before another.

Labrum ( Fig.11 J–K) of moderate size. Labral keel moderately wide, with a blunt apex. Anterior margin of keel convex or irregular; posterior margin almost straight, with two clusters of short setulae.

Thorax two times longer than abdomen. Dorsal surface of abdominal segments not saddle-shaped. Abdominal joint not developed.

Postabdomen ( Fig. 11 L–M, 12H) large, moderately high, evenly narrowing distally in postanal portion. Length about 2.5 height. Ventral margin straight. Basis of claws bordered from distal margin by clear incision. Distal margin convex, distal angle rounded, clearly protruding. Dorsal margin almost straight in postanal portion and weakly concave in anal one, with distal part about 2.5 times longer than preanal one, and with postanal portion 2.5–2.8 times longer than anal one. Preanal angle well expressed, postanal angle not defined. Preanal margin almost straight. Postanal margin ( Fig. 11N , 12I ) with about 12 well-developed, sharp composite denticles, each with 1–7 (usually 4–6) spinulae along anterior margin; size of denticles increasing distally. Length of longest denticles about 1.5 times the width of the base of postabdominal claw, and more than 3 times the width of the denticle base. Postanal portion with about 10 broad lateral fascicles, posteriormost setule of each fascicle longest, thicker than others, slightly shorter than neighboring marginal denticles. Anal portion with several smaller fascicles, spaced irregularly. Postabdominal claw ( Fig. 11O , 12I ) of moderate length, slightly longer than preanal portion of postabdomen. Basal spine long and slender, about 0.3–0.35 length of the claw. A row of 7–10 long setulae between basal spine and the base of postabdomen.

Antennule ( Fig. 14A ) of moderate size, length about 3 times width, with a cluster of several long setulae about half-length of antennule at anterior face, and 2–3 transverse rows of very short setulae below it. Antennular seta thin, more than 1/2 the length of antennule, arising subterminally. Nine terminal aesthetascs, two of them long and thick, little shorter than antennule itself, all other much shorter, about 1/2–1/3 the length of antennule.

Antenna relatively short ( Fig. 11P , 13 B–C). Antennal formula, setae 0-0-3/1-1-3, spines 1-0-1/0-0-1. Basipodite robust, with very short seta between branches, branches relatively short, all segments cylindrical, slender, middle segment in each branch shorter than others, 1.5 times shorter than basal segment. Seta arising from basal segment of endopodite thin, reaching above the end of endopodite. Seta arising from middle segment of endopodite, of similar size to apical setae. Two shortest apical setae of endopodite with a long spinule at the point of articulation. Spine on basal segment of exopodite longer than middle segment. Spines on apical segments slightly shorter than apical segments.

Limb I ( Fig. 14B ) similar to the previous species, but epipodite with projection longer than epipodite itself, IDL seta I is somewhat more slender and less curved than in two previous species.

Limb II ( Fig. 14E ) same as in the previous species.

Limb III ( Fig. 14 F–G) similar to the previous species, but distal endite with setae evenly decreasing in size basally, seta 3 much shorter than seta 2.

Limb IV ( Fig. 14 H–I). similar to the previous species, but epipodite with projection longer than epipodite itself.

Limb V ( Fig. 14 J–K). similar to the previous species, but epipodite with projection longer than epipodite itself. Two broad-based sensilla-like structures between inner face setae and filter plate somewhat bigger than in the previous species.

Limb VI ( Fig. 14L ) as elongated lobe with setulated margin.

Ephippial female and male. Unknown.

Size. In females of first juvenile instar, length 0.6–0.62 mm, height 0.33–0.34 mm; in females of second juvenile instar, length was 0.68–0.72 mm, height 0.38–0.41 mm. In adult females length 0.73–1.05 mm, height 0.46–0.65 mm.

Differential diagnosis. B. elliptica differs from most species of the genus in female postabdomen evenly narrowing distally; this character is only shared by B. martensi . B. elliptica differs from B. martensi in longer spine on basal segment of antennal exopodite, as long or slightly longer than the middle segment.

Distribution. B. elliptica is known only from type locality, a pool near Lake Albina in Kosciuszko National Park, Australia. Located at elevation 1920 m.a.s.l., Lake Albina is one of the highest mountain lakes in Australia.

Figures

FIGURE 5. Biapertura affinis (Leydig, 1860) from Klein Vaal River, Transvaal Province, Republic of South Africa, adult male. A, lateral view. B, postabdomen. C, distal portion of postabdomen. D, antennule. E, copulatory hook of thoracic limb I. F, IDL of thoracic limb I.

FIGURE 6. Biapertura kendallensis (Henry, 1919) from Ryan’s II Billabong, Bonegilla, east of Wodonga, Victoria, Australia. A–B, juvenile females of instar I and II. C–K, adult parthenogenetic female. C, lateral view. D, ventral margin of valves. E, setae of anterior group. F, setae of posterior group. G, posterior margin of valves. H, posteroventral angle of valves. I–J, head shields. K, head pores. L, ephippial female. M–N, juvenile males of instar I and II. O, adult male.

FIGURE 11. Biapertura elliptica (Sinev, 1997) from pool near Lake Albina, Kosciuszko National Park, New South Wales, Australia (type locality). A–B, juvenile females of instar I and II. C–P, adult parthenogenetic female. C, lateral view. D, ventral margin of valves. E–F, posteroventral angle of valves. G–H, head shield. I, head pores. J–K, labral keel. L–M, postabdomen. N, postanal margin of postabdomen. O, postabdominal claw. P, antenna.

FIGURE 12. Biapertura elliptica (Sinev, 1997) from pool near Lake Albina, Kosciuszko National Park, New South Wales, Australia (type locality). A–I, adult parthenogenetic female. A–B, lateral view. C, ventrolateral view. D, dorsal view. E–F, head pores. G, dorsal pores. H, postabdomen. I, postabdominal claw and distal portion of postabdomen.

FIGURE 13. Biapertura elliptica (Sinev, 1997) from pool near Lake Albina, Kosciuszko National Park, New South Wales, Australia (type locality). A–D, adult parthenogenetic female. A, posteroventral angle of valves. B–C, antenna. D, thoracic limbs.

FIGURE 14. Biapertura elliptica (Sinev, 1997) from pool near Lake Albina, Kosciuszko National Park, New South Wales, Australia (type locality). A–L, adult parthenogenetic female. A, antennule. B–L, thoracic limbs. B, limb I. С, IDL and ODL of limb I. В. inner setae of endites 1–2 of limb I. E, limb II. F, exopodite of limb III. G, distal endite of inner portion of limb III. H, exopodite of limb IV. I, inner portion of limb IV. J–K, limb V and its gnathobase filter plate. L, limb VI.