Baetis majus Tiunova, 2021

Tiunova, Tatiana M., Semenchenko, Alexander A. & Tong, Xiaoli, 2021, Baetis majus sp. nov., new species of mayfly (Ephemeroptera: Baetidae) from Far East of Russia, Zootaxa 4965 (3), pp. 541-557 : 543-552

Baetis majus Tiunova sp. nov.

urn:lsid:zoobank.org:pub:2A2F1007-BEEA-48D9-BEE3-D64D055E4BB0

( Figs 1–41 )

Material. Holotype male imago (reared from larva, with larval skin), RUSSIAN FEDERATION: PRIMORSKIY KRAY, Shkotovskiy district, Shkotovka River, bridge, Shkotovo village , 43°04´40.83´´ N 132°21´31.72´´E, 22.V.2014, T. Tiunova . Paratypes: 2 male, 1 female imagines, 2 larvae, and one larva ( BM175 ) same data as holotype; same place, 11. V.2015, 5 larvae, T. Tiunova; same place, 15. V.2018, 27 larvae, T. Tiunova .

Description. Male imago (in alcohol) ( Fig. 1 ). Length (mm): body 4.7–5.2; forewings 5.5–5.6; cerci 12.0–13.0; femora 1.1; tibia 1.7–1.8. Head: light brown or brownish. Antennae yellowish.

Turbinate eyes moderately high ( Fig. 1 ); faceted surface oval in dorsal view, 1.2 times longer than wide; facetted surface of turbinate eyes light orange; the shaft grayish with a yellowish ring.

Thorax: Medioscutum and submedioscutum light brown; posterior scutal protuberance dark brown with light lateral sides; scutellum grayish; scuto-scutellar impression white; median longitudinal suture dark brown; sublateroscutum dark brown; anterior phragma dark brown.All legs white ( Fig. 1 ). Lengths ratio of individual foreleg segments: 1.1:1.8:0.8:0.5:0.35:0.2. Forewing transparent, all veins pale; pterostigma milky on a dark background, with 5–6 cross veins. Hind wing hyaline, transparent, and approximately 2 times longer than wide, rounded apex and two simple longitudinal veins; cross veins absent; costal projection present ( Fig. 3 ).

Abdomen: Tergum I brownish; terga II–VI yellowish or whitish, translucent ( Fig. 1 ); terga VIII–X brown with darker lateral margins. Sterna I–VI white, translucent; sterna VII–IX brown, opaque. Styliger whitish ( Fig. 4 ). Unistiliger and segment I of forceps brownish; segments II and III whitish; unistiliger with parallel margins, slightly elongated, almost as long as wide, with a distinct small projection at the apex of the inner edge; segment I of forceps conical and elongate; segment II relatively narrow, slightly widening towards the apex and with beveled inner apical margin; segment III small, well defined, strongly expanded to the apex, its length only slightly exceeds its maximum width ( Fig. 4 ). Caudal filaments whitish ( Fig. 1 ).

Female imago. Length (mm): body 5.5; forewings 6.5; cerci lost; foreleg: femora 1.0; tibia 1.3. General color of body brown ( Fig. 2 ). Head grayish, posterior margin brownish; antennae whitish. Thorax light brown, with brown median longitudinal suture. Wings transparent; all veins brownish. Legs yellowish or brownish. Abdomen terga I–VIII (with eggs) light brown without maculation; terga IX–X lighter.

Mature larvae (in alcohol): Length (mm): body 4.7–5.3; cerci 2.5–3.1. General body color brown with light maculation ( Figs 5–7 ).

Head: antennae brownish; antennal pedicel and scape without spatulas, with rare fine hair-like setae only ( Fig. 8 ); head brown with light maculation on vertex; surface of the head covered numerous strong spatulas and fine hair-like setae ( Figs 9–10 ); frons, clypeus and labrum white; fronto-clypeal suture black; gena with a pair of dark brown stripes. Eyes of female black ( Fig. 7 ), larval turbinate eyes of male light orange ( Fig. 5 ). Labrum more or less rounded (width/length ratio of 1.3); dorsal surface with 1 + 2–3 long submarginal setae, arranged in one regular row, and row of long pointed setae laterally on both margins; posterior area with rare thick and short setae ( Fig. 14 ). Canines of right mandible with 7 teeth divided into two groups; incisor with three large teeth of relatively equal size; kinetodontium with four teeth; the first, second and third relatively equal size, fourth smallest ( Figs 11 , 15 ); prostheca toothbrush-like. Left mandible canines with 7 teeth; incisor with three teeth, first two the largest; kinetodontium with four teeth, first and fourth the smallest and second the largest ( Figs 11 , 16 ); prostheca brush-like, with mostly short blunt appendages and two or three pointed ones on inner side. Maxillary palp twosegmented, surface covered with hair-like setae, more densely located on distal part of second segment; second segment longer than first segment (1.7 times) ( Fig. 17 ). Labium with paraglossae concave in middle, 1.4 times wider than glossae; apical part of paraglossae with two regular rows of long setae; 6 long bristles located along outer margin in ventral surface ( Fig. 18 ); distal part of dorsal surface of paraglossa covered with small stout setae ( Figs 12–13 ). Glossae triangular with row of 9–10 stout setae on outer and 5–6 long setae on inner margins ( Fig. 18 ). General shape of the second and third segments of the labial palp rather stocky ( Figs 19–20 ); third segment wide, its apex truncated; 1.3 times wider than the second segment; ventral surface covered with long stout setae ( Fig. 19 ); second segment with rounded apicomedial projection; dorsal surface with a row of 4–5 long pointed setae ( Fig. 20 ).

Thorax: brown with contrasting whitish or brownish stripes on the mesonotum ( Figs 5, 7 ). Mesonotum with a V-shaped white spot near anterior margin. Pronotum with a pair of light spots laterally. Legs white, joints of leg segments brown ( Fig. 6 ). Femora with brown rectangular spot near inner margin ( Fig. 21 ); outer edge with row of long, apically widened setae in distal part ( Fig. 22 ) and rounded setae in basal part; inner margin with a irregular row of small pointed setae in basal part; femoral villopore present ( Fig. 23 ). Tibia and tarsi brown in apical part; stout setae arranged in an irregular rows along outer margin of tibia ( Figs 21 , 27, 29 ) and a regular row on tarsi ( Fig. 21 , 28 ); smaller setae located along inner margin of tibia and tarsi; dorsal surface of femora, tibia and tarsi covered with small bluntly rounded spatulas ( Figs 27–29 ). Patella-tibial suture present ( Figs 21 , 27 ). Tarsal claws brown, with row of 13–15 teeth increasing in length toward apex. Apex of tarsal claw without subapical setae ( Figs 24 , 30 ). Lengths (mm) of the leg segments as follows: Foreleg: femur 0.9‒0.95; tibia 0.5‒0.6; and tarsus 0.5‒0.55. Middle leg: femur 0.9‒0.95; tibia 0.5‒0.6; and tarsus 0.5. Hind leg: femur 0.9‒1.05; tibia 0.55‒0.9; and tarsus 0.45‒0.5.

Abdomen: Terga with contrasted white and black or dark brown maculations ( Figs 5, 7 ). Tergum I brownish, posterior margin darker; terga II–VIII with a pair of antero-median light stripes and spots contoured with dark brown; terga II–III and VII darker than terga IV and VI with a pair of large white spots joining along the middle part at the posterior margin; antero-lateral corners and lateral margins white; postero-lateral corners black; terga IX and X completely white ( Figs 5, 7 ); posterior margins of tergum VI with regular row of quadrangular teeth of various sizes; surface of terga densely covered with numerous semilunar impressions, rare hair-like setae and conical spatulas ( Fig. 26 ). Sterna generally dirty white; sterna VII–VIII brownish ( Fig. 6 ). Six pairs of gills, present on abdominal segments II–VII; gills elongated, oval-shaped; all gills matt, with dark band surrounding margin and apparent tracheation; margins with numerous hair-like setae inserted at the base of small teeth ( Figs 33–38 ). Gills II and VI almost equal in length and only slightly smaller than gill III; gills IV–V equal in length, 2 times longer than wide ( Figs 35–36 ); gill VII the smallest,1.3 times shorter than gill II and 1.6 times shorter than gill V ( Fig. 38 ). Paraproct with 9–10 large pointed teeth like spines of different size ( Fig. 25 ); surface of paraproct without notched scales, with fine hair-like setae located disorderly and 3–5 rounded scales, scattered in middle area ( Figs 25 , 31–32 ). Cerci brownish with dark band at the middle and dark tips ( Figs 5–7 ).

Eggs. General form oval 102–106 μm length and 62–68 μm width ( Fig. 39 ). Chorion corrugated and densely wrinkled, with numerous small granules and with small fossae ( Fig. 40 ). One or two small and round micropyles with a collar-like ring located in the equatorial area ( Fig. 41 ).

Diagnosis. Larva. Six pairs of gills, present on abdominal segments II–VII; dorsal surface of the head, femora, tibia and tarsi covered with numerous small bluntly rounded spatulas and fine hairs ( Figs 9–10 , 27–29 ); the first tree teeth of kinetodontium and incisor of right mandible of relatively equal size ( Fig. 15 ); third segment of labial palp wide, its apex truncated; 1.3 times wider than the second segment; second segment of labial palp with rounded apicomedial projection ( Figs. 25 , 31–32 ); posterior margins of tergum VI with regular row of quadrangular teeth of various sizes ( Fig. 26 ); paraproct without notched spatulas, with fine hairs located disorderly and 3–5 rounded spatulas, scattered in middle area. Imago: hind wings with two simple longitudinal veins ( Fig. 3 ); unistiliger with parallel margins, slightly elongated, with a distinct small projection at the apex of the inner edge ( Fig. 4 ); segment III of forceps small, well defined, strongly expanded to the apex, its length only slightly exceeds its maximum width.

Distribution. Russian Far East. Baetis majus Tiunova sp. nov. is known from its type locality only ( Fig. 42 ). The larvae of the new species were found in the lower part of the river on swift riffles with cobble and gravel substrate. No larvae were found at other sites upstream of the river. Water temperature was 12–15°C, depth 20–60 cm. According to our data, the adult emergence period is May.

Etymology. The species name is derived from the Latin word majus , which means May. All the examined material was collected in May.

Results of DNA barcoding. We obtained partial COI sequences (657 bp) of one specimen (BM175) of Baetis majus Tiunova sp. nov., twelve specimens (BP30, BP34, BP35, BP178, BP179, BP190, BP358, BP387, BP388, BP672, BP674 and BP794) of B. pseudothermicus ; four specimens (BU29, BU177, BU542 and BU552) of B. ursinus ; and two specimens (BU543 and BU556) of B. ussuricus . The mean nucleotide base compositions of Baetis majus Tiunova sp. nov. were A 23.6%, C 18.4%, G 21.8% and T 36.2% across all sites for all sequences.

We used nucleotide BLAST algorithm in NCBI GenBank (nucleotide collection database) and animal identification in BOLD systems to find the nearest neighbours to Baetis majus Tiunova sp. nov. A search in GenBank showed that the nearest neighbours have a similarity less than 85% and relate to unidentified Baetis species ( KP970694 , KP970695 ) and several species of genus Acentrella . Highly similar (98.75–100%) sequences of unidentified Baetis species from China (Beijing and Hebei provinces) were found in the BOLD system, but these data was unavailable and set to private status. Probably, Baetis majus Tiunova sp. nov. inhabits also China (in provinces of Beijing and Hebei).

Bayesian phylogeny revealed two well-supported sister clades, one of which includes B. bundyiae Lehmkuhl , B. hudsonicus Ide , B. macani Kimmins , B. subalpinus Bengtsson , B brunneicolor McDunnough , B. liebenauae Keffermüller , B. vernus , B. ursinus , B. maculosus , B. majus Tiunova sp. nov., and B. michaelohubbardi Selvakumar et al. ; the second clade includes the remaining species. B. majus Tiunova sp. nov. was the earliest branching lineage in the clade and includes B. maculosus and B. ursinus ; however, support for this clade was low (Bayesian posterior probability, PP = 0.52).

Morphological and molecular data were used to construct a Bayesian tree, which revealed a polytomy node including B. majus Tiunova sp. nov. as the first lineage; B. vardarensis + B. lutheri + B. pentaphyllus ( Baetis lutheri species-group) as the second lineage; and B. braaschi + B. ilex + B. cf. gadeai + B. rhodani + B. baksan ( Baetis rhodani species-group) as the third lineage. Thus, the species-group to which B. majus Tiunova sp. nov. belongs remains unidentified ( Figs 43 , 44 ).

Figures

FIGURE 42. Locality of Baetis majus Tiunova sp. nov., Shkotovka River (Primorskiy Kray).

FIGURE 43. Bayesian tree based on mitochondrion COI gene for subgenera Baetis and Tenuibaetis form Eastern and Western Palearctic, Nearctic and Oriental regions. Specimens obtained in this study are in bold. Bayesian posterior probabilities (PP) above 0.7 are given above tree nodes.

FIGURE 44. Bayesian tree of the genus Baetis inferred from the cytochrome c oxidase I (COI) nucleotide sequence data (466 bp) and 47 morphological characters. Two species of Labiobaetis were used as outgroup. All data including species-groups are taken from Sroka (2012). Specimen obtained in this study is in bold. Bayesian posterior probabilities (PP) above 0.7 are given above tree nodes.

FIGURES 1–2. Baetis majus Tiunova sp. nov., 1, male imago, holotype, lateral view; 2, female imago, dorsal view.

FIGURES 3–4. Baetis majus Tiunova sp. nov., male imagoes, holotype: 3, hind wing; 4, unistyliger and forceps.

FIGURES 5–7. Color pattern of Baetis majus Tiunova sp. nov., larvae, paratypes: 5, male, dorsal view; 6, ventral view; 7, female, dorsal view.

FIGURES 8–13. Baetis majus Tiunova sp. nov., larvae, dorsal view, paratypes: 8, scape; 9, surface of the head; 10, spatulas on head; 11, canines of left and right mandible; 12, glossae and paraglossae; 13, setae on paraglossa. Scale bar: 8, 11–12, 0.01 mm; 9, 0.02 mm; 10, 13, 0.002 mm.

FIGURES 14–20. Baetis majus Tiunova sp. nov., larvae, details of mouthparts, paratypes: 14, labrum, dorsal view; 15, canines and prostheca of right mandible, dorsal view; 16, canines and prostheca of left mandible, dorsal view; 17, maxillary palp, dorsal view; 18, glossa and paraglossa, ventral view; 19, labial palp, ventral view; 20, labial palp, dorsal view.

FIGURES 21–26. Baetis majus Tiunova sp. nov., larvae, paratypes, dorsal view: 21, foreleg, 22, shape of long bristles on distal part of femora; 23, shape of short setae on inner margin femora; 24, tarsus claw; 25, paraproct plate; 26, posterior margin of tergum VI.

FIGURES 27–32. Baetis majus Tiunova sp. nov., larvae, paratypes: 27, 29, inner margin of fore tibia; 28, inner margin of fore tarsus; 30, tarsal claw; 31, paraproct; 32, spatulas on paraproct. Scale bar: 27–31, 0.01 mm; 32, 0.001 mm.

FIGURES 33–38. Baetis majus Tiunova sp. nov., larvae, gills shape, dorsal view, roman numbers belong to the respective gill pairs.

FIGURES 39–41. Baetis majus Tiunova sp. nov., egg: 39, general view; 40, structure of chorion; 41, micropyle.