Rhynchotalona weiri, Sinev, Artem Y. & Kotov, Alexey A., 2014

Sinev, Artem Y. & Kotov, Alexey A., 2014, Revision of the Holarctic genus Rhynchotalona Norman, 1903 (Anomopoda: Chydoridae), Zootaxa 3841 (2), pp. 188-210 : 196-201

Rhynchotalona weiri sp. nov.

Herrick, 1884: Pl. I, figs 12–13 ( Alona dentata ).

Etymology. The species name honors Dr. Alexander Weir, director of Cranberry Lake Biological Station (SUNY ISF, USA).

Type locality. Long Pond, Plymouth County, Mass., USA, coll. 28.08.1961 by Eleanor Brown, number of sample in Frey's collection DGF 0 602.

Type material. Holotype: parthenogenetic female from the type locality, USNM 1207841.

Allotype: male from the type locality, USNM 1207842.

Paratypes. over 40 parthenogenetic females from type locality, USNM 1207834; 14 parthenogenetic females, 2 males, paratypes, Lake of Two Rivers, Algonquin Park, Ontario, Canada, coll. 0 9.10.1982 by D.G. Frey, (separated from sample DGF 6450), USNM 1207833; over 40 parthenogenetic females from Cranberry Lake, St. Laurence County, N.Y., USA, coll. 0 8.2006, by A.Y. Sinev; several parthenogenetic females from Walden Pond, Essex County, Mass., USA, coll. 22.06.2004 by W. Pill & A. A. Kotov, AAK 2005-248.

Diagnosis. Female. Rhynchotalona species of small size, length up to 0.43 mm. Valves from previous molts frequently retained. Ventral margin of valves with posterior group of setae of moderate length. Rostrum short for the genus, only 1.5 times or less longer than antennule, evenly curved. Major head pore as broad, rounded rimmed field, slightly narrowing posteriorly, length about 2 width. Postabdomen narrowing distally in anal portion, in postanal portion with parallel margins, length about 3 heights. Postanal margin with 2, rarely 3 large, sharp, single marginal denticles, more robust than in the previous species, followed by 2–3 groups of 1–3 much smaller thin denticles. Lateral fascicles of setules in postanal portion consisting of 3–4, rarely 5 long setules, distal setules in fascicles only 1.5 times shorter than distal marginal denticle. Postabdominal claw as for genus. Antennule with antennal sensory seta arising at 1/3 distance from base. Antenna with spine on proximal segment of exopodite about 1/2 length of middle segment, apical spines shorter than apical segments.Limb I with IDL setae 2–3 longer and more slender than in R. falcata . Limb II with scraper 3 longer than scrapers 2 and 4. Exopodites III and IV of similar size with exopodite V. Limb VI large, of same size as exopodite V, with long, thick setules.

Male. Postabdomen with almost parallel margins in proximal half of preanal portion and strongly narrowing in distal half of postanal portion. Antennule with male seta located in its middle. Limb I with about 10 long, thin setules on ventral face of limb below copulatory brush.

Description. Parthenogenetic female. General. Body shape ( Fig. 5 A–C, 6A–D) and morphology of valves ( Fig. 5 D–E, 6E) as for genus. Ventral margin of valves with posterior group of setae of moderate length. Valves from previous molts frequently retained.

Head as for genus. Rostrum short for the genus, only 1.5 times or less longer than antennule, evenly curved ( Fig. 7 F). Head shield ( Fig. 5 F) as for genus. Major head pore as broad, rounded rimmed field, slightly narrowing posteriorly; length about 2 widths( Fig. 5 G–H, 6G). Lateral head pores as for genus. Labrum as for genus, examination under high magnification did not reveal any lateral groups of setules( Fig. 7 A).

Postabdomen ( Fig. 6 H–I, 7B–C) narrowing distally in anal portion, in postanal portion with parallel margins, length about 2.8 heights. Postanal margin with 2, rarely 3 large, sharp, single marginal denticles, more robust than in the previous species, followed by 2–3 groups of 1–3 much smaller thin denticles. Lateral fascicles of setules in postanal portion consisting of 3–4, rarely 5 long setules, distal setules in fascicles only 1.5 times shorter than distal marginal denticle. Postabdominal claw as for genus.

Antennule as for genus ( Fig. 6 J, 7D), antennal seta arising at 1/3 distance from the base.

Antenna ( Fig. 6 K, 7E) as for genus. Spine on proximal segment of exopodite about 1/2 length of middle segment. Apical spines shorter than apical segments.

Limb I ( Fig. 8 A–B) as for genus, IDL setae 2–3 longer and more slender than in R. falcata .

Limb II ( Fig. 8 C) as for genus, scraper 3 longer and only slightly thicker than scrapers 2 and 4.

Limb III ( Fig. 8 D) as for genus, exopodite more large than in R. falcata , only 1.5 times smaller than exopodite V, length of seta 3 about four heights of exopodite.

Limb IV ( Fig. 8 D–F) as for genus, epipodite with long process, more two times longer than epipodite itself, exopodite larger than in R. falcata , only 1.5 times smaller than exopodite V, length of seta 3 about two heights of exopodite. Inner portion of limb with scraping seta (1) as long as largest flaming-torch seta (2).

Limb V ( Fig. 8 G) as for genus.

Limb VI ( Fig. 6 H) large, of same size as exopodite V, with long, thick setules.

Ephippial female: Body of similar outline with parthenogenetic female. Ephippium is yellow-brown, without longitudinal lines. No specimens retaining valves from the previous molts were found in the studied material.

Male. General. Body shape ( Fig. 5 J–L) low oval, height-length ratio 0.45–0.46. Males frequently retain valves from the previous molts.

Head. Rostrum as for genus, ocellus of similar size with eye.

Postabdomen ( Fig. 7 F) as for genus, smaller than in the previous species, with almost parallel margins in proximal half of preanal portion and strongly narrowing in distal half of postanal portion.

Antennule ( Fig. 7 G) as for genus, male seta located at the middle of antennule.

Limb I ( Fig. 8 I–J) as for genus, ventral face of limb below copulatory brush with about 10 long, thick setules.

Size: in juvenile females of instar II, length 0.35–0.36 mm, height 0.17–0.18 mm, in adult females, length 0.39–0.43 mm, height 0.20–0.24 mm. In two studied adult males, length was 0.30 and 0.31 mm, respectively; height of both specimens was 0.14 mm.

Differential diagnosis. R. weiri sp. nov. differs from from all other species of the genus by its short rostrum, shape of female postabdomen and short and wide major head pore. For other differences see Table 1 .

Distribution and ecology. Range probably including South-East regions of Canada and North-East regions of USA, but exact borders currently unclear. In mesotrophic Cranberry lake, Adirondacks mountains, R. weiry sp. nov. was found in open littoral, on sandy bottom, such habitat is also typical for R. falcata in Eurasia ( Smirnov, 1971).

Species R. falcata R. weiri R. longiseta R. kistarae

Female

Figures

FIGURE 5. Rhynchotalona weiri sp. nov. from Cranberry lake, Adirondack mountains, New York State, USA. A, juvenile female of instar II. B, adult parthenogenetic female. B – C, lateral view. D, posterior part of ventral margin of valve. E, posteroventral angle of valves. F, head shield. G – H, head pores. I, ephippial female. J – L, adult male. J – K, lateral view. L, ventral view. Scale bars: 0.1 mm for A – D, F, I – L; 0.05 mm for E, G – H.

FIGURE 6. Rhynchotalona weiri sp. nov. from Cranberry lake, Adirondack mountains, New York State, USA, parthenogenetic females. A, lateral view. B – C, antero-lateral view. D, dorso-lateral view. E, antero-ventral corners of valves. F, rostrum. G, major head pore (partially covered by old valves). H, postabdomen and abdomen. I, postabdomen. J, antennule. K, antenna. Scale bars: 0.1 mm for A – D, 0.05 mm for H – I; 0.01 mm for E – G, J – K.

FIGURE 7. Rhynchotalona weiri sp. nov. from Cranberry lake, Adirondack mountains, New York State, USA. A – E, parthenogenetic female. A, labrum. B – C, postabdomen. D, antennule. E, antenna. F – G, male. F, postbadomen. G, antennule. Scale bar 0.05 mm.

FIGURE 8. Rhynchotalona weiri sp. nov. from Cranberry lake, Adirondack mountains, New York State, USA. A – H, parthenogenetic female, thoracic limbs. A, limb I. B, ODL and IDL of limb I. C, limb II. D, exopodite and distal endite of limb III. E, exopodite of limb IV. F, inner portion of limb IV. G, limb V (praepipodite not shown). H, limb VI. I – K, adult male, thoracic limb I: I, general view; J, ODL and copulatory hook; I, IDL. Scale bar 0.05 mm.