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Drepanothrix asiatica Dadykin & Pereboev, 2026, sp. nov.

Identification

Clé publique

radar:r-17577fb663ccc2a30c7d7bc7065d5840

Auteurs

Dadykin, Ivan A. · Pereboev, Dmitry D.

Année déclarée

2026

Langue déclarée

und

Type source

Text

Première détection

2026-11-13T08:38:51.753224+00:00

Dernière observation des métadonnées

2026-11-13T08:38:51.753224+00:00

Dernière vérification HTTP

Non effectuée

Institutions déclarées par la source

A. N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, Leninsky Prospect 33, Moscow 119071, Russia.

Résumé documentaire — langue originale

Drepanothrix asiatica sp. nov. urn:lsid:zoobank.org:act: 5C94EEB5-2164-4162-B604-DC7AC93BE9CC Figs 6–13 Drepanothrix dentata – Smirnov 1976: 164, fig. 149b; 1992: 119–121, figs 504 – 509. — Yermolayeva & Fetter 2020: fig. 2a–c. Drepanothrix cf. dentata – Dadykin et al. 2025: fig. s1. Diagnosis In the parthenogenetic female and male, dorsal valve margin has a strongly reduced dorsal tooth, or the latter is completely absent. Male postabdomen is strongly modified as compared to that of the female. Preanal angle of the postabdomen is oblique, shifted towards the postabdomen base. Male postabdominal claw is long and slender. Male postabdominal claw bears a basal pecten and a distal cluster of spinulae. Etymology The species name ‘ asiatica ’ refers to its distribution in Asia. Type material Holotype RUSSIA • ♂; Kamchatskii Krai, Kronotsky Nature Reserve, a small drying thermokarst lake; 54°13.921′ N, 160°9.696′ E; 21 Aug. 2014; E.I. Bekker and F.V. Kazansky leg.; MSU, MGU MI–287. Allotype RUSSIA • 1 ♀; same data as for holotype; MSU, MGU MI–288. Paratypes RUSSIA • 17 parthenogenetic ♀♀; same data as for holotype; MSU, MGU MI–289 • 5 parthenogenetic ♀♀, 6 ♂♂; same data as for holotype; ZIN, ZIN 55222 • 3 parthenogenetic ♀♀, 2 ephippial ♀♀, 5 ♂♂; same data as for holotype; IEE, IEE AAK 2026–012 • 6 parthenogenetic ♀♀; Sakhalin Area, Kuril Archipelago, a small sphagnal bog in Simushir Island; 47°7.088′ N, 152°16.452′ E; 22 Jul. 2019; M.O. Ivanova leg.; ZIN, ZIN 55223 • 7 parthenogenetic ♀♀; same data as for preceding; IEE, IEE AAK 2026–011. Other material examined RUSSIA • 6 parthenogenetic ♀♀; Khabarovskii Krai, a small lake at eastern shore of the Nikolay Bay; 53°54.000′ N, 138°41.770′ E; 27 Aug. 2021; O. Shpak leg.; IEE, IEE AAK M–7069 • 4 parthenogenetic ♀♀; same data as for preceding; ZIN, ZIN 55224 • 3 parthenogenetic ♀♀; Sakhalin Area, Sakhalin Island, a sphagnal lake near Pokrovka Village; 47°19.234′ N, 142°42.432′ E; 15 Sep. 2008; A.A. Kotov and N.M. Korovchinsky leg.; IEE, IEE AAK M–0864 • 3 parthenogenetic ♀♀; Sakhalin Area, Kuril Archipelago, a small sphagnal bog in Simushir Island; 47°6.040′ N, 152°14.262′ E; 22 Jul. 2019; M.O. Ivanova leg.; IEE, IEE AAK M–6526 • 11 parthenogenetic ♀♀, 1 ♂; same data as for preceding; 47°7.088′ N, 152°16.452′ E; same data as for preceding; IEE, IEE AAK M–6527 • 5 parthenogenetic ♀♀; Kamchatskii Krai, Kronotsky Nature Reserve, a small thermokarst lake; 54°14.162′ N, 160°9.756′ E; 21 Aug. 2014; E.I. Bekker and F.V. Kazansky leg.; IEE, IEE AAK M–3029 • 1 parthenogenetic ♀; same data as for preceding; IEE AAK M–3028 • 3 parthenogenetic ♀♀; Kamchatskii Krai, Karaginsky Island, a small slightly brackish lake; 58°33.621′ N, 163°29.034′ E; 16 Jul. 2022; I.A. Dadykin leg.; IEE, IEE AAK M–7655 • 2 parthenogenetic ♀♀; Kamchatskii Krai, Karaginsky Island, a small lake with muddy sediment; 58°58.135′ N, 163°53.052′ E; 5 Aug. 2022; I.A. Dadykin leg.; IEE, IEE AAK M–7720 • 3 parthenogenetic ♀♀; Kamchatskii Krai, Bering Island, a small tundra lake near Nikolskoe Village; 55°13.291′ N, 166°0.654′ E; 28 Sep. 2020; O. Krylovich, E. Kuzmicheva and O. Smyshlyaeva leg.; IEE, IEE AAK M–6493 • 1 parthenogenetic ♀; Chukotskii Autonomous Region, a small pool in the vicinity of Anadyr River; 65° N, 171° E; 7 Aug. 1972; N.N. Smirnov leg.; MSU, MGU MIs 1178. Description Parthenogenetic female BODY. Length 0.35–0.8 mm. Body is ovoid in lateral view (length: height= 0.66–0.75), flattened laterally (width:length= 0.35–0.42) (Figs 6A–B, 7A–C, 8A–B, F–H). Dorsal keel is well pronounced in both head anterior portion and valves, but is absent in posterior head portion (Fig. 7B). A deep cervical groove is located on each lateral side, preceded by a transverse cuticular ridge (Figs 6B, 7B). The cervical grooves do not intercept dorsally. Dorsal tooth is usually absent; very rarely a minute tooth is present (Figs 6A, C–G, 7A, 8A–B, F–I). Posterodorsal body angle is widely rounded; ventral body margin is evenly convex (Figs 6A, 7A). Carapace is ornamented with irregular polygons becoming more elongate towards the ventral and posterior valve margins (Figs 6A, 7A, D). Ventral valve margin bears a row of 35–40 flattened cuticular flanges subequal in size, which do not reach the posterodorsal valve angle (Fig. 7A, E). A long feather-like seta is attached posteriorly to each flange at the inner side of the valve margin (Fig. 7E). A cluster of setulae runs along the inner side of the valve margin, along the flange (Fig. 7E). HEAD. Large (HL/BL = 0.49–0.50), strongly flattened laterally (length: width 1.3–1.5). Head shape, compound eye and ocellus conform to the generic diagnosis (Figs 6A–B, H–I, 7A–C). Dorsal organ is as typical for the genus (Figs 6H–I, 7B, H–I). Lateral head pores are absent. Frontal pore is small, horseshoe-shaped, located near the anterodorsal head angle (Fig. 7J). Thorax, gut and abdomen conform to the generic diagnosis. POSTABDOMEN. Shape and armature conform to the generic diagnosis (postabdomen is 0.2× as long as the body, 1.3–1.4× as long as high; preanal margin is 3.5–4 × as long as the anal margin) (Figs 6J, 7F). Postabdominal claw is short and stout, 0.3–0.35 × as long as the postabdomen, 3.6–4.0 × as long as high, slightly incurved. Basal spine of the claw is rather short, 1.0–1.1 × the claw width (Figs 6J–K, 7G). Both the lateral and the medial claw sides bear two clusters of spinulae which do not form distinct pectens (Figs 6K, 7G). Postabdominal setae are as typical for the genus. LABRUM. Large and wide, approximately triangular in lateral view (Figs 9A, 10A). Labrum armature and shape are as typical for the genus. ANTENNA I. Conforms to the generic diagnosis (Figs 7A, C, 9A–C, 10B–C). Basal seta of the antenna I is 0.15–0.20× length of the antenna I. Antenna I apex bears nine terminal aesthetascs of subequal size, 0.31–0.35× as long as antenna I. ANTENNA II. 0.95–1.1 × as long as the body (Figs 6A, 7A). Morphology of antenna II conforms to the generic diagnosis (Figs 9D–I, 10D–H); endopodite is 0.78–0.85× as long as the exopodite (Figs 9D, 10D). Swimming seta of the endopodal segment 1 is 2.1–2.2× length of endopodite segments; swimming seta of the endopodal segment 2 is 2.1–2.25 × length of the endopodite segments. Setal armature conforms to the generic diagnosis (Figs 9F–I, 10E–H). Spine lengths relative to their segments: exopodal segment 2, 0.6–0.65 ×; exopodal segment 4, 0.4–0.5×; endopodal segment 3, 0.3–0.4× (Figs 9D, 10D). MANDIBLE. Large, 2.8–3.1 × eye diameter (Fig. 10J). Mandible armature is as typical for the genus (Fig. 9K–M). MAXILLA I. Small, spatulate, armed with three thick feather-like setae subequal in size (Fig. 9N). Maxilla II is absent. THORACIC APPENDAGES. I–V conform to the generic diagnosis (Figs 10I–J, 11). THORACIC LIMB I. As typical for the genus (Figs 10I–J, 11A). The outer distal lobe (ODL) is cylindrical, directed posteriorly, bears two setae (a, b). Seta a is attached subterminally, thin, bisegmented, bilaterally armed with short setulae. Seta b is attached terminally, long, thick, with apical segment armed with a row of spinulae (Fig. 11A–B). The inner distal lobe (IDL) bears three bisegmented setae (1–3). Seta 1 is the longest, seta 2 is 0.7–0.8 × the length of seta 1; both setae 1 and 2 are armed with a row of setulae. Seta 3 is naked and 0.40–0.45 × the length of seta 1 (Figs 10I–J, 11A–B). Seta 4 slightly exceeds setae 5 and 6 in length; the proximal portion of seta 4 is almost naked, with few apical spines; the distal portion is unilaterally setulated. Setae 5 and 6 are similar in length and structure; both are thick, bilaterally armed with short spinulae not reaching the setal tip (Fig. 11C). Seta 7 is slightly shorter than seta 8; both the proximal and distal portions of seta 7 bear a row of spinulae extending only halfway to the tip (Fig. 11C). Setae 8 and 9 are similar in structure, with proximal portion armed with a row of spinulae, and distal portion bilaterally armed with long setulae (Fig. 11C). Seta 3’ is similar in structure to seta 2’ but 1.3× longer (Fig. 11C, E). Setae 10–12 are similar in structure to the setae 8 and 9; setae 9–11 are subequal in size, seta 12 is slightly shorter (Fig. 11C). Seta 13 is short and thin, 0.4–0.5× as long as seta 12, bisegmented, with a distal armature of long setulae (Fig. 11C). Seta α is 2.0 × as long as seta β (Fig. 11C). Ejector hooks and epipodite are as typical for the genus (Fig. 11A). THORACIC LIMB II. Structure typical for the genus (Fig. 11F–H). Exopodite seta a is the longest and the thickest, 1.4–1.5× as long as seta b, armed with long setulae; setae b and c are short and thin, closely spaced, covered by short setulae; seta b is 1.5× as long as seta c (Fig. 11F). Scraping setae 1’ and 2’ are similar in structure, thin, moderately incurved, unilaterally armed with thin spinulae; seta 1’ is 1.3–1.4 × the length of seta 2’. Scraper 3’ is 0.8 × as long as the scraper 2’; scraper 3’ is only slightly incurved and armed with ~15 relatively thick spinulae (Fig. 11F). Scrapers 4’ and 5’ are short and stout, scraper 3’ 1.3–1.4 × as long as the scraper 4’ and 1.5–1.6 × as long as the scraper 5’. The scrapers 4’ and 5’ are almost straight, armed with few (up to 12) thick spines; the distalmost spine of each scraper is the longest and the thickest (Fig. 11F). Scrapers 6’–8’ are subequal in size, 0.7× as long as the scraper 5’, almost straight, armed with relatively numerous (more than 15) thin spinulae; inner scrapers have a finer armature (Fig. 11F). Posterior limb elements and gnathobase are as typical for the genus (Fig. 11G–H). Filtering comb consists of six bisegmented feather-like setae similar in length and structure (Fig. 11F, H). THORACIC LIMB III. Conforms to the generic diagnosis (Fig. 11I). Seta b is 1.1–1.6 × the length of seta a, the setae are closely spaced, located on the outer side of theexopodite, bisegmented, setulose. Setae c–e are closely spaced, located at the distal exopodite portion. Seta c is slightly longer than seta a (Sc/Sa = 1.4), thin, unisegmented, armed with sparse long setulae along their entire length. Seta d is the longest, 2.8× as long as seta a, 1.7–1.8× as long as seta b, 1.9× as long as seta c, 2.9× as long as seta e. Seta d is thick, bisegmented, bilaterally armed with short setulae along its entire length. Seta e is relatively short and thick, unisegmented, slightly incurved, bilaterally armed with sparse spinulae. Inner limb portion is as typical for the genus. Setae 1’ and 1 are subequal in size, short and thick, bisegmented; seta 1’ is naked, seta 1 is geniculate, unilaterally armed with long setulae. Setae 2–4 are similar in structure, 0.8× as long as seta 1’, stout, bilaterally armed with long setulae along their entire length (Fig. 11I). Seta 2’ is 0.4–0.5× as long as seta 1’, bisegmented, bearing short setulae (Fig. 11J). Inner part of the inner portion bears five anterior setae (3’–7’) and four posterior setae (5–8). Anterior setae are bisegmented, naked, seta 3’ is the shortest, 0.75× as long as seta 4’; setae 4’–7’ are subequal in size (Fig. 11J). Posterior setae 5–8 are similar in structure, bisegmented; the distal portion of each anterior seta is bilaterally armed with short setulae (Fig. 11I). Gnathobase is as typical for the genus (Fig. 11I). THORACIC LIMB IV. Structure typical for the genus (Fig. 11K). Exopodite seta a is the shortest, unisegmented, armed with long setulae along its entire length; setae b and c are closely spaced, seta b is the longest, 2.7–2.8× as long as seta a, 1.5× as long as seta c. Seta b is unisegmented, with a bilateral armature of short setulae in its distal portion. Seta c is bisegmented, with an inflated proximal portion; seta c is armed with long sparse setulae along its entire length (Fig. 11K). Inner portion seta 1’ is 1.9–2.0 × as long as setae 2’–4’; seta 1’ is bisegmented, with the distal portion bearing a bilateral armature of long spinulae. Setae 2’–4’ are similar in structure, short, bisegmented, with an inflated basal portion and a narrow flattened distal portion that is asymmetrically armed with long spinulae (Fig. 11K). Posterior setae 1–4 are similar in structure, short, bisegmented, with the distal segment armed with short setulae (Fig. 11K). Location of sensory elements and gnathobase structure conform to the generic diagnosis (Fig. 11K). The filtering comb comprises four setae. THORACIC LIMB V. Smallest limb (Fig. 11L). Seta a is the longest, 3.9–4.0 × as long as seta 1, 2× as long as seta 2, 3 × as long as seta 3. Seta a is bisegmented, inflated at its base, bilaterally armed with sparse setulae along its entire length (Fig. 11L). Setae of inner lobe are short, unisegmented, armed with short setulae along its entire length (Fig. 11L). Ephippial female BODY. Length is 0.55–0.65 mm (Figs 8C–D, 12A). The body is ovoid in lateral view, flattened laterally (height: length = 0.7–0.8; width:length = 0.3–0.4). General morphology and structure of appendages are similar to those of the adult parthenogenetic female. The dorsal keel of the carapace is reduced. Dorsal valve margin is angulate in lateral view, lacking a dorsal tooth (Figs 8C–D, 12A). Valve ornamentation is similar to that of the parthenogenetic female. Ephippium is thin, transparent, lacks a well-defined ventral margin and specific sculpture, and contains two eggs (Figs 8C–D, 12A). Male BODY. Length is 0.45–0.55 mm. The body is ovoid in lateral view, flattened laterally (height: length = 0.65–0.7; width:length=0.3). General morphology closely resembles that of the juvenile parthenogenetic female (Figs 8E, 12B, 13A–B). The dorsal keel is well developed on both the head and carapace. The dorsal tooth is either completely absent or reduced to a low bump (Figs 8E, 12B, 13A–B). Posterodorsal angle is weakly developed or absent (Figs 12B, 13A–B). Ventral valve margin forms a wide rounded projection at the level of thoracic limb I (Figs 12C–D, 13A); the projection bears enlarged marginal teeth (Figs 12C–D), while its marginal setae are similar in length and thickness to the others (Figs 8E, 12C, 13A). GENERAL HEAD MORPHOLOGY. Similar to that of parthenogenetic female. THORAX AND ABDOMEN. As in parthenogenetic female. POSTABDOMEN. Relatively small (0.3 × body length), flattened laterally (Figs 8E, 12E, 13C). Postabdomen is subtriangular in lateral view, narrowing distally (Figs 12E, 13C). The preanal angle is oblique (~150°), located at the middle of the preanal margin. The preanal margin of postabdomen is armed with 9–10 transverse rows of setulae in its proximal portion and 5–6 rows of setulae in its distal portion (Figs 12E, 13C). The lateral surface of the preanal portion bears transverse clusters of setulae, forming three longitudinal rows: ventral setulae, long anterior to the preanal angle and short posterior to the angle; medial setulae, relatively short, increasing in length towards the postabdomen base; marginal setulae, long anterior to the preanal angle and short posterior to the angle (Figs 12E, 13C). Postabdomen anal portion is relatively short, 0.25–0.3× the length of the preanal portion. A distinct depression is present between preanal and anal margins. Anal portion bears 2–3 clusters of spines and several longitudinal groups of short setulae (Figs 12E, 13C). Postabdominal claw is relatively long and thin, 0.4× as long as the postabdomen, 4.3–4.4 × as long as wide, slightly incurved (Figs 12E–G, 13D). Lateral claw surface bears a proximal pecten and a distal cluster of short spinulae (Fig. 12F–G); medial claw surface is armed with a cluster of short spinulae stretched along the basal and middle claw portions (Fig. 13D). Basal spine is relatively short, 0.5–0.6 × width of the claw; an additional short spine is usually located at the base of the basal spine (Figs 12F–G). Vas deferens runs along the ventral postabdomen margin, gonopore is located subterminally at the low projection (Fig. 12E). ANTENNA I. Similar to that of the female in relative size and shape. An accessory seta (ms) is located at the anterior edge of the appendage. Male accessory seta is 0.8–1.0 × as long as basal sensory seta of the antenna I, slightly flattened, wide at base and narrowing distally, lacking armature (Figs 12H–I, 13E). ANTENNA II. Similar to that of the female in relative size and shape but bears two additional sensory setae at the distal end of basipodite (Figs 12J, 13F–G). Distal basipodite setae are subequal in size, 1.3–1.4 × the length of the distal burrowing spine, slightly incurved, reaching distal margin of the antenna II exopodal segment 2. Both setae have a distal bilateral armature of short, thin setulae (Fig. 13G). LABRUM AND MOUTH PARTS. As in parthenogenetic female. THORACIC LIMBS. Largely similar to those of the female, except for limb I. THORACIC LIMB I. Largest, folded medially (Fig. 12K–L). A small rounded subdistal lobe (SDL) is located at the anteromedial limb surface, proximally to the inner distal lobe (IDL) (Figs 12K–L, 13H). The subdistal lobe is slightly flattened dorsoventrally, approximately reaching the tip of the IDL hook. The anterior surface of the SDL bears three rows of flattened spinulae and two bisegmented setae (X and Y) (Figs 12L, 13J–K). Seta X is 1.4× as long as seta Y, naked. Seta Y has a distal unilateral armature of short setulae (Figs 12K, 13J). The outer distal lobe (ODL) bears a long thick apical seta b and a short feather-like seta a at its base, 0.15 × as long as seta b (Fig. 12L). Inner distal lobe (IDL) has a large incurved hook subdistally; the hook is cylindrical in cross-section, smooth, at most bearing few small solitary spinulae in distal portion (Fig. 13H). The hook tip is armed with three transverse rows of closely spaced, flattened spinulae (Figs 12M, 13I). Distal IDL portion bears four setae (1–3, Z). Seta 1 is the longest, 1.4 × as long as seta 2, 1.5 × as long as seta 3. Seta 1 is bisegmented, with a naked, slightly incurved basal portion 4.7 × as long as the distal portion; the distal portion is short, slightly incurved, armed with thin spinulae (Figs 12K–L, 13I). Seta 2 is long, with a distal portion exceeding in length the basal portion; seta 2 distal portion is unilaterally armed with long setulae; seta 3 is similar to seta 2 but shorter, it is located between setae 1 and 2 (Figs 12K–L, 13I). Male accessory seta (Z) is located on the anterior side of the IDL, 0.3× as long as seta 3, naked (Figs 12K–L, 13I). Limb I inner portion has a similar structure to that of the female, but lacks seta 1’ (Fig. 12K). Differential diagnosis Parthenogenetic females and males of Drepanothrix asiatica sp. nov. differ from those of D. dentata in the size of the dorsal tooth, well developed in D. dentata (Figs 1A, D, H, 2A, H) but strongly reduced to absent in D. asiatica (Figs 6A, C–G, 7A, 12B, 13H–L). However, gamogenetic females of both species have a reduced or absent dorsal tooth and cannot be reliably distinguished based on morphology (Figs 1E, 2F–G, 12A). Males of D. asiatica sp. nov. also differ from those of D. dentata in postabdomen shape and armature, see below. In D. dentata, the postabdomen is subquadrangular in lateral view, with preanal angle approximately right, shifted towards the anal opening; the anterior part of the preanal portion is much longer than the posterior one (Figs 1I, 2J). In contrast, males of D. asiatica have a subtriangular postabdomen with oblique preanal angle located in the middle of the postabdomen preanal portion (Figs 12E, 13C). The shape of the postabdominal claw also differs between the two species. In D. dentata, the postabdominal claws are short and stout (0.3× postabdomen length, 2.7–3.2× as long as wide), bearing two clusters of spinulae that do not form a pecten (Figs 1J–K, 2K–L). In D. asiatica, the claws are relatively long and slender (0.4× postabdomen length, 4.3–4.4 × as long as wide), with the lateral surface of the claw bearing a proximal pecten of spinulae and a distal cluster not forming a pecten (Fig. 12F–G). The observed differences between D. asiatica sp. nov. and D. dentata are summarized in Table 2. Remarks The known range of Drepanothrix asiatica sp. nov. includes eastern and northern Kamchatka (Dadykin et al. 2025), Bering Island (Novichkova & Chertoprud 2015), Chukotka Peninsula (Smirnov 1976), Khabarovsk Territory, Magadan Area (Streletskaya 2010), Sakhalin Island, the Kuril Islands (Uéno 1932), and northern Japan (Inoue 1968). No populations of Drepanothrix were found in the Russian portion of the Amur basin (Kotov et al. 2011; Garibian et al. 2021b) or northern China (Ji et al. 2015). Also, a record of parthenogenetic Drepanothrix with a reduced dorsal tooth from Irkutsk Area (Yermolayeva & Fetter 2020: fig. 2a, c) likely refers to D. asiatica. This indicates that the species may be widely distributed in East Asia. Drepanothrix asiatica sp. nov. occurs in a variety of water bodies, including Sphagnum bogs and lakes, and slightly brackish seashore pools. The species is relatively rare and occurs on muddy sediment or plant litter in the littoral zone. The lifestyle of D. asiatica has not been studied so far. However, it is likely similar to its sibling species D. dentata, which is adapted for burrowing and detritus feeding (Fryer 1974; Kotov 2006) but also inhabits submerged macrophytes (Błedzki & Rybak 2016; Korovchinsky & Kotov 2021). Genetic variability We obtained 15 COI, 23 16S rDNA, and 7 ITS1 sequences (Supp. file 2: Table S1). We combined these data with seven sequences of the Folmer’s COI and two of the 16S rDNA from the NCBI GenBank. Final alignment lengths were: COI, 629 bp; 16S rRNA, 403 bp; ITS1, 492 bp. The best-fitting model for the multigene phylogram was TPM3u+F+I. Three major phylogroups were recognized within Drepanothrix: European D. dentata s. str., East Eurasian D. asiatica sp. nov., and Canadian D. cf. dentata (Figs 14, 15A). Notably, macrothricid sequences available in the GenBank formed very long branches when placed as the outgroup for Drepanothrix (Fig. 15A). Therefore, we reconstructed the midpoint-root multigene ML phylogram (Fig. 15B) to reveal the relative position of the major clades. In this case, European and Canadian phylogroups appeared to be closer to each other than to the East Eurasian clade (Fig. 15B). Analyses of individual gene fragments also recovered the three clades (Supp. file 1: Fig. S1), though branch support was low for the 16S rDNA tree (Supp. file 1: Fig. S1B). Distances between phylogroups revealed by COI barcoding were significantly higher than the intragroup variability (Fig. 16). The 16S rRNA nucleotide variability did not allow us to distinguish the phylogroups with confidence (Fig. 16; Supp. file 1: S1B), as the sequences had only 1–2% of differing sites. The ITS1 variability was also significant (Supp. file 1: Fig. S1C), but ITS1 data was available for only a few specimens, none from the Canadian clade. Mitochondrial genomes For both Drepanothrix dentata and Macrothrix triserialis, all the expected mitochondrial genes (13 PCGs, 2 rRNA, 22 tRNA) have been recovered. In both cases, mitogenome length is about 15 kbp, and GC content is ca 31%. Unexpectedly, the mitochondrial genomes of D. dentata and M. triserialis differ by gene order. In D. dentata, a non-coding region bordered by tRNA genes (a putative control region) is situated between the srRNA and lrRNA genes (Fig. 17A). In contrast, in M. triserialis the rRNA genes are separated only by a single tRNA (as typical for animal mitochondria), and putative control region is located after the srRNA gene (Fig. 17B). The mitogenome structure of D. dentata was verified by PCR with subsequent direct sequencing of the region in another sample of D. dentata. The sequenced region is very similar to the assembled one and minor differences between them are expected since they are obtained from different organisms (Supp. file 3). In this respect, the unusual genome structure of Drepanothrix is unlikely to be a result of incorrect assembling or annotation. The phylogenetic position of Drepanothrix is also surprising. Our phylogenetic analysis retained highly supported clades of Daphniidae Straus, 1820, Moinidae Goulden, 1968, Bosminidae Baird, 1845, and Chydoridae Dybowski & Grochowski, 1894 + Eurycercidae Kurz, 1875 (Fig. 18). The relative position of these clades is unresolved. Macrothrix triserialis is considered a sister taxon to Moinidae and forms a well-supported clade with the latter. At the same time, D. dentata is placed in a basal position to all other anomopods, although the support for this node is weak (Fig. 18). Therefore, Macrothricidae appears to be a non-monophyletic group according to our data.

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10.5281/zenodo.22907971

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