Rhynchotalona longiseta, 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 : 201-206

Rhynchotalona longiseta sp. nov.

Birge 1893: Pl 13, figs 9–10 ( Alona falcata ); Birge, 1918: p. 724, fig. 1123 ( falcata ); Dodson, Frey, 1991: Fig. 20 – 20 ( falcata ).

Etymology. The species name refers to its most characteristic feature, very long posteriormost setae of ventral margin of valves.

Type locality. Smoke lake, Algonquin Park, Ontario, Canada, coll. 0 9.10. 1982 by D.G Frey, (number of sample in Frey's collection DGF 6452).

Type material. Holotype: female from type locality, USNM 1207839.

Allotype: male from type locality, USNM 1207840.

Paratypes: 10 females, from the type locality, USNM 1207831; 30 parthenogenetic females, from Lake of Two Rivers, Algonquin Park, Ontario, Canada, coll. 0 9.10. 1982 by D.G. Frey (separated from sample DGF 6450), USNM 1207832 over 100 parthenogenetic females from white Lake, Blanden County, North Carolina, USA, coll. 27.02. 1979 by D.G. Frey DGF 4998.

Diagnosis. Female. Rhynchotalona species of moderate size, length up to 0.52 mm. Valves from previous molts rarely retained. Ventral margin of valves with very long setae of posterior group, distalmost setae being longest. Rostrum long, exceeding 2 length of antennule. Major head pore as elongated rimmed field, length about 3 width. Postabdomen narrowing distally in anal portion; in postanal portion with parallel margins, length about three times height. Postanal margin with 2, rarely 3 large, sharp, single marginal denticles, followed by 2–3 groups of 1–3 much smaller thin denticles. Lateral fascicles of setules in postanal portion consisting of 4–6 long setules, distal setules in fascicles slightly shorter than distal marginal denticle. Antennule with antennal sensory seta arising at 1 / 2 distance from the base. Antenna with spine on proximal segment of exopodite about 1 / 3 length of middle segment, apical spines shorter than apical segments. Limb I with IDL setae 2–3 moderately thick and robust. Limb II with scraper 3 longer than scrapers 2 and 4. Exopodites III and IV 1.5 times smaller than exopodite V. Limb VI large, of same size as exopodite V, with thin 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 at 2 / 3 distance from the base. Limb I with about 12 long, thin setules on ventral face of limb below copulatory brush.

Description. Parthenogenetic female. General. Body shape ( Fig. 9 A–C, 10 A–C) and morphology of valves ( Fig. 9 D) as for genus. Valves from previous molts frequently retained. Ventral margin of valves ( Fig. 9 D) with very long setae in posterior group ( Fig. 9 E–F, 10 F–G), their length increasing posteriorly, posteriormost seta being longest. Postero-ventral corner of valves with or without denticle.

Head ( Fig. 10 D) as for genus. Rostrum long, more of 3 times longer than antennule, evenly curved. Head shield ( Fig. 9 G) as for genus. Major head pore as elongated rimmed field, length about 3 widths ( Fig. 9 H, 10 E). Lateral head pores as for genus. Labrum as for genus, examination under high magnification reveals single lateral group of thin setules in posterior half of the keel ( Fig. 11 A–B).

Postabdomen ( Fig. 10 F–G, 11 C–D) with parallel margins in anal portion, weakly narrowing in postanal, length about three times height. Postanal margin with 2, rarely 3 large, sharp, single marginal denticles, similar to those of R. falcata , followed by 2–3 groups of 1–3 much smaller thin denticles. Lateral fascicles of setules in postanal portion consisting of 4–6 long setules; distal setules in fascicles slightly shorter than distal marginal denticle. Postabdominal claw as for genus.

Antennule as for genus ( Fig. 10 H, 12 A), antennal seta arising at 1 / 2 distance from the base. Antenna ( Fig. 10 J, 11 E) as for genus. Spine on proximal segment of exopodite about 1 / 3 length of middle segment. Apical spines shorter than apical segments.

Limb I ( Fig. 12 B–C) as for genus, IDL setae as in the previous species.

Limb II ( Fig. 12 D) as in the previous species, scraper 3 longer and only slightly thicker than scrapers 2 and 4.

Limb III ( Fig. 12 E–G) as for genus, exopodite as in the previous species. Scraping setae of distal endite long and slender, with long denticles, one almost 1.5 times longer than other.

Limb IV ( Fig. 12 H–I) as for genus, epipodite with short process, about half length of epipodite itself. Setae of exopodite same as in R. falcata . Inner portion of limb with scraping seta (1) longer than larges flaming-torch seta (2).

Limb V ( Fig. 12 J) as for genus.

Limb VI ( Fig. 12 K) large, larger than exopodite V, armed with thin setules.

Male. General. Only adult males were studied. Body shape low oval ( Fig. 9 I), height-length ratio about 0.49. Males retaining valves from the previous molts were not observed.

Head. Rostrum as for genus ( Fig. 3 J), ocellus larger than eye.

Postabdomen ( Fig. 11 F) similar to that of the previous species, with almost parallel margins in proximal half of preanal portion and strongly narrowing in distal half of postanal portion.

Antennule ( Fig. 11 L) as for genus, male seta located close to the end of antennule. Aestetascs were preserved badly, and we were unable to study them in detail.

Limb I ( Fig. 11 M– O) as for genus, ventral face of limb below copulatory brush with about 12 long, thick setules.

Size: In juvenile females of instar II, length 0.36–0.39 mm, height 0.18–0.2 mm. In adult females, length 0.42–0.52 mm, height 0.24–0.28 mm. In adult males, length 0.35–0.37 mm, height 0.17–0.18 mm.

Differential diagnosis. R. longiseta sp. nov. differs from all other species of the genus by long posterior setae of valves. It also differs from R. weiri sp. nov. by the long rostrum, by the shape of female and male postabdomen and by the narrow major head pore; from R. falcata by morphology of IDL setae and scrapers of limb II; from R. kistarae by longer rostrum and by the armament of postabdomen. For other differences between species, see Table 1.

Distribution and ecology. The distribution area probably includes South-East regions of Canada and North- East regions of USA. Ecology unknown, Dodson & Frey (1991, p. 751) refers to R. longiseta as “a mud dweller”, but this information should be rechecked.