Baetis pentaphyllus Tiunova & Semenchenko 2019, sp. nov.

Baetis pentaphyllus sp. nov.

urn:lsid:zoobank.org:pub: 32A67029-582F-40C3-9B40-66FEA0881566

(Figs 1–26)

Material. Holotype larva. RUSSIAN FEDERATION: AMURSKAYA OBLAST’: Zeyskii Reserve, Zeya Reservoir Basin, Bolshoi Garmakan River, about 300 m above mouth, N 53°53.148 E 127°11.626, 02.VII.2015, T. Tiunova. Paratypes: collected the same data and place as holotype: 5 larvae, 1 larva (BAE-BGAR1_110); same locality, 08.VII.2015, 4 larvae, T. Tiunova; Zeya Reservoir Basin: Malyi Garmakan River, about 500 m above mouth, N 53°52.295 E 127°10.459, 06.VII.2015, 3 larvae, T. Tiunova; Shirokovka River, about 700 m above mouth, 07.VII.2014, 5 larvae, T. Tiunova. CHUKOTKA AUTONOMOUS DISTRICT, Kolyma River Basin, Malyi Keperweim River, 2 mature larvae, N 68°23.151; E 166°80.348, 03.VIII.2016, A. Semenchenko.

Description. Larvae (in alcohol). Length (mm): body 4.6–5.7; cerci 2.5–3.1. General body colour brown (Figs 1–4). Head: brown. Antennae brownish, slightly longer than ½ of body length. Scape and pedicel with hair-like setae only. Labrum distinctly wider than long (the width/length ratio 1.69–1.70); dorsal surface with 1 + 6–7 long submarginal setae, arranged in uneven row and row long pointed setae laterally on both margins (Fig. 5). Canines of left mandible with eight teeth divided into two groups (Figs 6, 12). Incisor (outer group) with four teeth; outermost tooth broadened and rounded apically; kinetodontium (inner group) with four small teeth. Both groups separated by a shallow incision. Left prostheca toothbrush-like (Figs 6, 12). The right mandible canines are also separated into two groups of teeth (Figs 7, 11). Incisor with three teeth, first tooth widened and rounded apically; kinetodontium with four teeth, from which second largest. Between the kinetodontium and incisor there is a groove. Right prostheca with four non-pointed teeth (Figs 7, 11). Maxillary palp two-segmented, individual segments approximately equal in length; surface of both segments covered with hair-like seta, which occur more densely on distal part of second segment (Fig. 13). Second segment of labial palpus with rounded apicomedial projection, its width 1.1 times wider than the base of third segment; third segment almost symmetrical rounded, relatively wide (Fig. 9); dorsal surface with a row of 4–5 long pointed setae on second segment and long pointed stout setae in apical margin of third segment; ventral surface of third segment covered numerous stout setae accompanied by hair-like seta (Fig. 9). Labium with paraglossae concave in middle, nearly two times wider than glossae; with 7–8 pairs of long stout bristles form three irregular rows on tip and long stout setae near apex; 5–6 long bristles located along outer margin and two stout setae near apex of inner margin (Figs 10, 14). Glossae relatively slender, with row 6–7 of long setae on inner margin and 5–6 bristles on outer margin and by one long stout seta located near apex (Figs 10, 14). Thorax: brown with whitish diffuse spots. Anterior margins of pro- and mesonotum darker (Figs 1–2). Legs whitish, joints of leg segments brown (Fig. 15). Femora pale, at edges darker; outer margin with row of long and pointed bristles and short setae located irregular; inner margin with villopore and small pointed setae located irregularly (Fig. 15). Tibia and tarsus brown in apical part. Stout setae arranged in regular row along inner margin of tibia and tarsi and setae of different sizes located along outer margin. Claws brown, with row of 10–11 teeth and a pair of subapical setae (Fig. 16). Abdomen: terga I–VIII brown, lateral area lighter; a pair of dark brown spots located near anterior margin; lateral and posterior margins dark brown (Fig. 1); terga I–VI with median light longitudinal stripe; terga IX–X brown, lighter than other terga; posterior margin of terga with broad, rounded apically teeth (Figs 17, 24). Sterna generally light brown with brown diffused spots near anterior margins (Fig. 3.) Paraproct serrated on posterior part of inner margin (10–13 large pointed teeth of different size) and outer part of posterior part (approximately 19–22 teeth diminishing proximally) (Fig. 18). Five pairs of elongated, oval-shaped tergalii located on III–VII tergites (Fig. 4), approximately 2.5 times longer than broad, rounded (Figs. 19–23), and 1.8–2.0 times longer than corresponding segment (Fig. 4); all tergalii white, tracheation poorly visible; margins hairy; hairs inserted in small teeth bases. Tergalii I and III almost equal length (Figs. 4, 19, 20), tergalii IV slightly shorter than III (Figs. 4, 22, 23). Tergalius II is the largest, 1.2 times longer than the first and 1.6 times longer than V (Figs. 4, 26). Caudal filaments brownish (Figs. 1, 3). Cerci three times longer than paracercus (Fig. 2).

Diagnosis. By the morphological characteristics, the larvae of Baetis pentaphyllus sp. nov. can be distinguishable from those of other Baetis species by the presence of only five pairs of tergalii on segments III–VII. Larvae of B. pentaphyllus sp. nov. can be distinguished from all Palaearctic representatives of the Baetis species-groups as defined by Müller-Liebenau (1969) and Jacob (2003) by the following combination of morphological characters: from the propingulus - and atrebatinus -groups by absence lateroapical protuberance on scape and incurvation on distal segment of maxillary palp, subapical bristles of claw, medioapical projection paraproct; from rhodani -group absence of robust setae on the antennal scape and pedicel and medioapical projection paraproct, subapical bristles of claw; from vernus - and lutheri - groups by the extent of medioapical protuberance on segment 2 of labial palp, form of femoral setae, which apically rounded, absent subapical bristles of claw, medioapical projection paraproct and thick, spine-like setae on gill margins; from buceratus -, fuscatus - and rhodani -groups absence of dark band on caudal filaments and medioapical projection on paraproct (Ikonomov 1962; Müller-Liebenau 1967, 1969; Morihara & McCafferty 1979; Jacob 2003; Godunko et al. 2004; Bauernfeind & Soldán 2012; Sroka, 2012; Soldan & Godunko 2012).

Distribution. Known from two habitats in the Far East of Russia: Amurskaya oblast’ (Figs 27–28) and Chukotka Autonomous District. The larvae of the new species were found in swift riffles with cobble and gravel substrate. Water temperature was 6–9 °C, depth 10–20 сm. Etymology. The species name is derived from the Latin word pentaphyllus, which means five-petalled.