Branchiobaetis borealis, Tong & Zhou & Wu, 2024

Tong, Xiaoli, Zhou, Zhiheng & Wu, Bangyi, 2024, First contribution to the genera Branchiobaetis and Megabranchiella (Ephemeroptera, Baetidae) in China, with descriptions of two new species, ZooKeys 1216, pp. 115-148 : 115-148

publication ID	https://doi.org/ 10.3897/zookeys.1216.129803
publication LSID	lsid:zoobank.org:pub:2312FE20-8C12-48B2-8D97-CFC920CCF5C2
DOI	https://doi.org/10.5281/zenodo.13983382
persistent identifier	https://treatment.plazi.org/id/B2506040-5F50-538B-811A-36BB58CAF7A4
treatment provided by	ZooKeys by Pensoft
scientific name	Branchiobaetis borealis
status	sp. nov.

Treatment

Branchiobaetis borealis sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Type material.

Holotype. China • male larva in alcohol (mature); Yunnan, Lushui City, Chengan Town, a tributary of the Nujiang River (26.2605 ° N, 98.8792 ° E, altitude 1036 m); 21. iii. 2019; leg. Xiaoli Tong GoogleMaps . Paratypes (in alcohol): • 41 mature larvae (2 on slide), locality and date as holotype, leg. Xiaoli Tong, Lin Hong, Jian Jiang GoogleMaps • 10 larvae (1 on slide); Yunnan, Weixi County, Tacheng Town, Lapu River (a tributary of the Jinsha River, 99.3507 ° E, 27.5728 ° N, altitude 2523 m); 8. xi. 2018; leg. Xiaoli Tong, Lin Hong, Haoyang Chen GoogleMaps • 13 larvae (1 on slide), Yunlong County, Caojian Town, a tributary of the Lancang River (25.6339 ° N, 99.1123 ° E, altitude 1824 m); 23. iii. 2019; leg. Xiaoli Tong, Lin Hong, Jian Jiang GoogleMaps .

Description.

Mature larva (Fig. 1 a – e View Figure 1 ). Body length (mm): female 7.2–8.5, male larvae slightly shorter than female, 6.0–7.5; antenna 2.0–3.0; cerci 3.0–4.0, paracercus ~ 3 / 4 length of cerci.

Cuticular colouration. Body mainly creamy yellow with brown maculae dorsally. Vertex and pronotum creamy yellow with irregular brown marks, meso- and metanotum creamy yellow with longitudinal brown streaks. Antennal scape and pedicel mainly off-white, flagellum pale brown. Femur of foreleg mainly off-white with dark brown apex and brown streaks along dorsal and ventral margins; tibia off-white; tarsus off-white with apical 1 / 2 dark brown; midlegs and hindlegs similar to forelegs in colour pattern. Abdominal tergites cream yellow with contrasting brown maculae as in Fig. 1 a – e View Figure 1 , tergite hypodermal colour uniformly without maculae or pigmentation (Fig. 7 d View Figure 7 ); sternites with cream shading to pale brown backwardly. Gills white with transparent main trunk and branches of tracheae. Caudalii cream to yellow-brown with brown primary swimming bristles.

Precursors of turbinate eyes in last instar male larvae normal, without elevated area with well-expressed facets.

Antenna (Fig. 1 b – e View Figure 1 ). Antenna ~ 3–4 × head width; scape smooth with fine setae sparsely; pedicel surface with fine setae and one row of tiny, rounded setae along distal margin, inner margin with tiny, triangular denticles distolaterally (Fig. 2 a View Figure 2 ).

Labrum (Fig. 2 b View Figure 2 ) nearly rectangular, width / length ratio ~ 1.6; anterior margin bordered with long and feathered setae and a deep notch; dorsally with submedial pair of long, robust bristles and submarginal arc of ~ 5 long, robust bristles on each side of midline, several fine setae scattered proximally; ventral surface with dense, fine setae medially and 6–8 short, pointed setae laterally and disto-laterally.

Left mandible (Fig. 2 c View Figure 2 ). Incisor and kinetodontium fused; incisor with three denticles, kinetodontium with three main denticles decreasing in length and one additional minute denticle between incisor and kinetodontium; prostheca robust, apex with five or six blunt denticles and two or three slender, pointed denticles; margin between prostheca and mola straight; apex of mola without tuft of setae.

Right mandible (Fig. 2 d View Figure 2 ). Incisor and kinetodontium fused; incisor with three denticles; kinetodontium with four denticles, inner margin of innermost denticle with three or four small denticles; prostheca slender with slightly wider base, apex toothbrush-like, with many sharp denticles on inner margin; margin between prostheca and mola slightly concave; apex of mola with a tuft of straight setae.

Hypopharynx and superlinguae (Fig. 4 d View Figure 4 ). Lingua subequal to superlinguae in length, with numerous fine setae apically. Superlinguae distally rounded with numerous fine setae along apical margin.

Maxilla (Fig. 3 a View Figure 3 ). Galea-lacinia with three robust canines; crown of galea-lacinia with one regular row of 10–13 medium-size arcuate, simple setae (Fig. 3 d View Figure 3 ), second row composed of three dentisetae and a row of 7–9 elongated pectinate setae (Fig. 3 e View Figure 3 ), 1 st dentiseta robust, canine-like with wide base, other dentisetae slender, bifid, and pectinate; ventrally with two simple, apical setae under canines (Fig. 3 c View Figure 3 ). Medially with one row of five or six long, simple setae and one spine-like seta perpendicular to lacinia margin. Maxillary palp 2 - segmented, longer than galea-lacinia, segment I shorter than segment II, apex of segment II with single tiny scale on small cone-shaped projection (Fig. 3 a View Figure 3 ). Small tongue-like accessory gill located on outer side of the articulation between stipes and cardo (Fig. 3 a, b View Figure 3 ).

Labium (Fig. 4 a View Figure 4 ). Glossae shorter and narrower than paraglossae, triangular with wide base, narrowing toward apex, inner margin of glossae with 10–12 spine-like, simple setae and outer margin with six or seven long, simple setae, apex with three robust setae; paraglossae with three rows of long, robust, distally pectinate and curved setae distoventrally and one short, simple seta in proximolateral area (Fig. 4 c View Figure 4 ); dorsal surface on distal 1 / 2 with one longitudinal row of five or six long, robust, spine-like setae near inner margin (Fig. 4 b View Figure 4 ); labial palp 3 - segmented; segment I slightly shorter than segments II and III combined, with many micropores dorsally; segment II triangular with distinct protuberance apico-laterally, ~ 1.3 × wider than base of segment III, dorsal surface with one longitudinal row of three or four medium spine-like simple setae and many micropores (Fig. 4 e View Figure 4 ); segment III similar to asymmetrical onion-shaped dome, dorsally with pointed simple setae near apex, ventral surface covered with many blunt pointed spatulate setae accompanied by fine setae (Fig. 4 f View Figure 4 ).

Hind wing pads well developed.

Forelegs (Fig. 5 b View Figure 5 ). Ratio of foreleg segments (femur to claw) 6.8: 5.4: 3.0: 1.0. Femur. Length ~ 3.4 × maximum width. Dorsal surface covered with many small oval spatulate setae accompanied by fine setae; ventral face with sparse, small, spatulate setae and fine setae. Outer margin with two rows of different type setae: one row of 13–17 medium-sized, robust, clavate setae and proximal row of 17–22 long, slender setae; additional row of small, teardrop-shaped, distally curved, hook-like setae along dorsal margin (Fig. 5 f View Figure 5 ); ventral margin with small, apically pointed or rounded, spatulate setae basally. Apex rounded with short, stout setae anteriorly, dorsoapical setal patch formed by two stout clavate setae. Villopore present and well developed (Fig. 5 c View Figure 5 ). A transparent finger-like accessory gill on inner side of coxal articulation (between coxa and prosternum) (Fig. 5 d, e View Figure 5 ); hyaline bubble-like membranous swelling between coxa and trochanter (Fig. 5 d View Figure 5 ). Tibia. Outer margin with one row of fine setae and several small, curved hook-like setae; ventral margin with row of short, stout spine-like setae. Tibio-patellar suture present. Both surfaces covered with small, apically pointed or rounded, spatulate setae alternating with hair-like setae. Tarsus. Outer margin with fine setae and one row of small, distally curved hook-like setae; ventral margin with one row of ~ 10 stout spine-like pointed setae increasing in length towards apex; both surfaces covered with small, spatulate setae alternating with hair-like setae. Claws hooked (Fig. 5 a View Figure 5 ), with one row of ~ 10 acute teeth, subapical setae absent.

Middle and hind legs similar to foreleg in structure except for lacking the finger-like accessory gills on base of coxa and the villopore larger and more obvious than that of forelegs.

Abdominal tergites and sternites both densely covered with crescent-shaped scale bases, several triangular spatulate setae, and hair-like setae. Posterior margins of tergites I – X with triangular spines increasing in length from I to X (Fig. 6 b – d View Figure 6 ). Posterior margins of sternites I – IX smooth medially, but with row of dentate protuberances laterally (as Fig. 14 b View Figure 14 ).

Gills (Fig. 6 a View Figure 6 ) present on segments I – VII and well tracheated with a transparent main trunk and branches of tracheae, ratio of gill length from I – VII = 1.1: 1.7: 1.9: 1.8: 1.7: 1.3: 1.0. External margins of all gills with small denticles intercalating fine hair-like setae, without any marginal spines or spatulate setae.

Paraproct (Fig. 7 b View Figure 7 ). Surface scattered with many micropores and hair-like setae, two or three small oval spatulate setae present near posterior margin; posterior margin with nine or ten triangular spines; surface of cercotractor smooth, with 19–22 spines marginally.

Caudalii (Fig. 7 c View Figure 7 ). Cerci with a row of swimming bristles on inner side of intersegment, each segment with row of pointed spines distally; paracercus with swimming bristles on both sides of intersegment.

Gonostyli bud. Subimaginal gonostyli folded under cuticle of last instar larvae, segments II and III sharply bent towards middle (Fig. 7 a View Figure 7 ).

Etymology.

The specific epithet borealis is the Latin masculine adjective, meaning “ northern ”, referring to the fact that this new species may represent the northernmost distribution of the genus in the Oriental Region.

Distribution

(Fig. 23 View Figure 23 ). China: Yunnan (Lushi, Weixi, and Yunlong).

Larval habitat

(Fig. 22 b View Figure 22 ). Branchiobaetis borealis sp. nov. was found in moderately rapid to swift unshaded streams with gravel substrates at altitudes from 1036 m to 2523 m in Yunnan, China. The three collection sites of the new species are respectively located in catchments of the Jinsha River (the upper reaches of the Yangtze River), Nujinag River (the upper reaches of Salween River), and Lancang River (the upper reaches of Mekong River), suggesting that B. borealis sp. nov. may be common in the Three Parallel Rivers of Yunnan Protected Areas.