Attheyella nordenskioldii ( Lilljeborg, 1902 )

Attheyella nordenskioldii ( Lilljeborg, 1902) View in CoL

( Fig. 2)

Canthocamptus nordenskiöldii Lilljeborg, 1902: 8 View in CoL , Table 1 (fig. 7), Table 2 (figs 1–7).

* For full label data, see Material.

** GenBank accession numbers are given in parentheses. *** Specimens examined under SEM.

Canthocamptus nordenskjöldi : Brehm, 1913: 586; Borutzky, 1926: 211.

Attheyella ( Bremiella) nordenskjöldi : Chappuis, 1929: 488; Borutzky, 1931: 207; Okuneva, 2009: 114.

Attheyella ( Bremiella) nordenskjöldii : Ishida, 1987: 78.

Attheyella ( Bremiella) nordenskjöldi nordenskjöldi : Borutzky, 1952: 276; Fefilova, 2007: 68.

Attheyella ( Mrazekiella) nordenskioldi : Wells, 2007: 228.

Attheyella ( Neomrazekiella) nordenskioldii nordenskioldii View in CoL : Özdikmen & Pesce, 2006: 212.

Neomrazekiella nordenskioldi nordenskioldi : Fefilova, 2015: 147.

Attheyella ( Neomrazekiella) nordenskioldi : Novikov et al., 2021: 1465.

Attheyella ( Neomrazekiella) nordenskioldii View in CoL : Novikov & Sharafutdinova, 2022: 34 View Cited Treatment .

Atteyella nordenskioldii : Reed, 1962: 41; Connolly et al., 2022: 416; Chertoprud et al., 2022: 19; Loskutova et al., 2022: 352.

Atteyella nordenskjoldii : Erdenezul & Narangarvuu, 2020: 47.

Canthocamptus gibba Okuneva, 1983: 1343 View in CoL .

Canthocamptus gibba View in CoL : Okuneva, 1989: 26; Okuneva & Evstigneeva, 2001: 472; Wells, 2007: 208; Okuneva, 2009: 115; Novikov & Sharafutdinova, 2022: 34 (synonymised with Attheyella nordenskioldii View in CoL ).

Material examined (see also Table 1). Russia: Republic of Buryatia, Lake Baikal nr. Sukhaya Vill., 52.558°N 107.097°E, 1 August 2022, 1 female, coll. I.O. Velegzhaninov & E.I. Popova; Irkutsk Prov.: Lake Baikal nr. Bolshie Koty Vill., 51.889°N 105.038°E, 25 July 2022, 3 females, 2 males, coll. I.O. Velegzhaninov & E.I. Popova; Chernaya River nr. Bolshie Koty Vill., 51.888°N 105.037°E, 25 July 2022, 4 females, coll. I.O. Velegzhaninov & E.I. Popova; Zhilishche River nr. Bolshie Koty Vill., 51.901°N 105.064°E, 27 September 2022, 3 females, coll. T.M. Alekseeva; Krasnoyarsk Terr.: Western Sayan Mts., Ergaki Mountain Range, Lake Oiskoe, 52.841°N 93.248°E, 24 July 2021, 2 females, 1 copepodite, coll. E.B. Fefilova; Putorana Plateau, Lake Keta, 68.808°N 89.656°E, 19 August 2021, 1 female, coll. E.S. Chertoprud; Komi Republic , Bolshezemelskaya tundra, small pool, 67.6°N 62.95°E, 29 July 2010, 6 females, coll. E.B. Fefilova; Chita Prov., Balei graben, stream, 51.5°N 116.783°E, 22 August 2022, 3 females, coll. E.Yu. Afonina; Republic of Sakha ( Yakutia ), delta of Lena River nr. Tiksi, 71.630°N 128.911°E, 19 July 2021, 11 August 2022, 9 females, coll. A.A. Novikov.

DNA sequences . Nucleotide sequences of 639– 670 bp COI mtDNA gene region were obtained from seven specimens of A. nordenskioldii : three from the Chernaya River mouth (at Lake Baikal), one from Lake Baikal (depth of 14 m), and three from a lake in the Western Sayan Mountains ( Table 1). In the phylogenetic tree, these seven sequences and a sequence of a specimen from Lake Ontario formed a clade ( Fig. 1). The genetic distances between sequences in this clade were 0.0016 –0.065; the distances among A. nordenskioldii from the Baikal area including Lake Baikal and from the Western Sayan Mountains were 0.0016 –0.034, while the distances between A. nordenskioldii and other Attheyella species (from Lake Baikal and other regions) were no less than 0.238. The genetic distances among the COI sequences of different Attheyella species and several Canthocamptus species varied from 0.228 to 0.297.

Morphological analysis (n = 29). The body length of the examined specimens of A. nordenskioldii was 1.0– 1.2 mm ( Fig. 2a). The structure of caudal rami was characteristic for the species ( Fig. 2b, c, f): oval and angled with respect to the longitudinal axis of the anal somite. Caudal apical setae were diverging to the outside; outer apical setae were curved relative to the middle ( Fig. 2a, b, c, f), particularly prominent in females ( Fig. 2a, b, c). Females and males had a row of spinules on the dorsal side of the caudal rami near the dorsal seta ( Fig. 2b, f). The exopod of A2 was onesegmented, with four setae and two or three thin spinules. The endopodal lobe of P 5 in females had six setae, of which the inner was the longest and the outer was the shortest ( Fig. 2d). The exopod of P 5 in females protruded beyond the posterior margin of the endopodal lobe by half of its length and had five setae. The exopod of P 5 in males was armed similarly ( Fig. 2e); the endopodal lobe of P 5 in males has three spines.

The length of the copulatory duct of A. nordenskioldii females from the Baikal area (Lake Baikal, the Chernaya River and the Zhilishche River) vari- ed from 109 to 147 µm (averaged 125.4 + 4.6 µm), the length of the first inner seta on the basendopodal lobe of P5 was 117–137 µm (averaged 127.6 + 2.7 µm), the length of the basendopodal lobe (from the attachment point of the first inner seta to its anterior side) fluctuated in the range 80–107 µm (averaged 96.6 + 3.3 µm).

The comparison of the average values of morphometric features of A. nordenskioldii from the Baikal area with those of the specimens from other regions showed their similarity, for example, for the specimens from the Chernaya River and from Bolshezemelskaya tundra, as well as those from the Zhilishche River and from the delta of the Lena River (in the copulatory duct length) ( Table 2). It is significant that the female with the longest copulatory duct and the P5 endopodal lobe from Lake Baikal had a similar COI structure to females with the shortest copulatory duct from Lake Oiskoe in the Western Sayan Mountains.

A visualisation of the integrative index of variability including all three morphometric characteristics of A. nordenskioldii is shown in Fig. 3. Females from the Baikal area did not stand out against the general pool of the species variability.