Branchiobaetis megasinus, 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.13983384
persistent identifier	https://treatment.plazi.org/id/59F827E6-DFA2-4020-9B44-36480650CD3F
taxon LSID	lsid:zoobank.org:act:59F827E6-DFA2-4020-9B44-36480650CD3F
treatment provided by	ZooKeys by Pensoft
scientific name	Branchiobaetis megasinus
status	sp. nov.

Treatment

Branchiobaetis megasinus sp. nov.

Figs 8 View Figure 8 , 9 View Figure 9 , 10 View Figure 10 , 11 View Figure 11 , 12 View Figure 12 , 13 View Figure 13 , 14 View Figure 14 , 15 View Figure 15 , 16 View Figure 16 , 17 View Figure 17

Type material.

Holotype. China • male larva in alcohol (mature); Guangdong, Shenzhen, Wutongshan River (22.5972 ° N, 114.2067 ° E); 30. xii. 2023 – 1. i. 2024; leg. Zhiheng Zhou GoogleMaps . Paratypes (in alcohol): • 9 mature larvae, locality and date as holotype GoogleMaps • 3 larvae, 1 male imago (reared specimen) on slide; Tai Po Kau Forest Stream , Hong Kong; 25. ii. 1999; leg. Xiaoli Tong ; 1 larva (on slide); Tai Po Kau Forest Stream , Hong Kong; 19. xi. 1996; leg. Xiaoli Tong ; 1 larva; Tai Po Kau Forest Stream , Hong Kong; 26. ii. 1997; leg. Maria Salas ; 1 larva (on slide); Shing Mum , Hong Kong; 7. i. 1997; leg. Xiaoli Tong • 2 larvae; Ma Po Mei , Hong Kong; 10. x. 1997; leg. Xiaoli Tong ; 1 larva (on slide); Ma Po Mei , Hong Kong; 7. iii. 1998; leg. Xiaoli Tong ; 1 larva (on slide); Mt. Nankunshan , Longmen County, Guangdong; 16. ix. 1994; leg. Xiaoli Tong • 3 larvae (1 on slide), Mt. Luofushan , Boluo County, Guangdong; 31. x. 2023; leg. Xiaoli Tong, Zhiheng Zhou & Bangyi Wu • 5 larvae (1 on slide); upper reaches of Liuxihe River , Conghua, Guangzhou, Guangdong; 23–24. iii. 2024; leg. Zhiheng Zhou & Bangyi Wu .

Description.

Larva (Fig. 8 a – e View Figure 8 ). Body length (mm): female 7.0–8.5, male larvae slightly shorter than female, 6.0–7.5; antenna 3.0–4.0; cerci 3.0–4.0, paracercus ~ 4 / 5 length of cerci.

Cuticular colouration. Body mainly brown or brownish green (in life) dorsally. Vertex uniformly brown. Antennal scape brown with off-white apex, pedicel off-white, flagellum pale brown. Pronotum mainly brown with irregular dark brown marks, meso- and metanotum mainly brown with irregular cream marks near base of forewing pads and a pair of small cream spots submedially. Legs contrasting bicoloured. Femur off-white with a large dark brown band medially and dark brown macula proximally and apically; tibia off-white with dark brown macula basally and distally; tarsus off-white with dark brown band apically. Abdominal tergites I – IV and VI – IX brown with a pair of cream stripes laterally; V brown with a cream, oval macula anterior medially and a pair of cream stripes laterally; X with yellow-brown shading to cream in the anterior portion and brown in posterior 1 / 2; tergites II – VIII with a pair of oblique dark brown medio-anterior sigilla and a pair of medioposterior sigilla (Figs 13 e View Figure 13 , 14 a View Figure 14 ). Abdominal sternites with cream shading to pale brown posteriorly. Cerci cream to yellow-brown with dark brown bands medially and distally (Figs 8 a – e View Figure 8 , 15 f View Figure 15 ); paracercus cream to yellow-brown with dark brown band near terminal; primary swimming bristles dark brown.

Precursors of turbinate eyes (Figs 8 d, e View Figure 8 , 15 a, b View Figure 15 ) in last instar male larvae normal, without elevated area with well-expressed facets.

Antenna (Fig. 8 a – c View Figure 8 ). Antenna ~ 3–4 × of head width; scape smooth, without noticeable setae; inner margin of pedicel with tiny triangular denticles distolaterally (Fig. 9 a, b View Figure 9 ).

Labrum (Fig. 9 c View Figure 9 ) nearly rectangular, width / length ratio ~ 1.5; anterior margin bordered with long and feathered setae and a median notch; dorsally with submedial pair of long, robust bristles and submarginal arc of six or seven long, robust bristles on each side of midline, several fine setae scattered proximally; ventral surface with densely fine setae medially and six or seven short, pointed setae laterally and disto-laterally.

Left mandible (Fig. 9 d View Figure 9 ). Incisor and kinetodontium fused; incisor with three denticles, kinetodontium with four main denticles decreasing in length and one additional minute denticle between incisor and kinetodontium; prostheca robust, apex with four bluntly denticles and two or three long, pointed denticles; margin between prostheca and mola straight with two or three fine, pointed minute spines; apex of mola without tuft of setae.

Right mandible (Fig. 9 e View Figure 9 ). Incisor and kinetodontium fused; incisor with three denticles; kinetodontium with four denticles, inner margin of innermost denticle with three small denticles (Fig. 10 a View Figure 10 ); prostheca slender and toothbrush-like, with many sharp denticles on inner margin apically; margin between prostheca and mola slightly concave, occasionally with 1–3 fine, pointed minute spines; apex of mola with a tuft of straight setae.

Hypopharynx and superlinguae (Fig. 10 b View Figure 10 ). Lingua slightly longer than superlinguae, with numerous fine setae apically. Superlinguae distally rounded with numerous fine setae along apical margin.

Maxilla (Fig. 10 e View Figure 10 ). Galea-lacinia with three robust canines; crown of galea-lacinia with one regular row of 13–15 medium-size arcuate simple setae, second row compound of three dentisetae and row of 7–9 elongated pectinate setae; ventrally with two simple, apical setae under canines. Base of lacinia with one row of five or six long simple setae and one seta perpendicular to lacinia margin. Maxillary palp 2 - segmented, longer than galea-lacinia, two segments subequal in length; apex of segment II with single tiny scale on small cone-shaped projection (Fig. 10 d View Figure 10 ). Small tongue-like accessory gill located on outer side of the articulation between stipes and cardo (Fig. 10 c, e View Figure 10 ).

Labium (Fig. 11 a View Figure 11 ). Glossae shorter and narrower than paraglossae, triangular with wide base, narrowing toward apex, inner margin of glossae with 7–10 long, simple setae and distal 1 / 3 of outer margin with ~ 5 long, simple setae, apex with three robust setae; paraglossae with two rows of long, robust, curved setae distoventrally, dorsal surface on distal 1 / 2 with one longitudinal row of two or three long, robust, spine-like setae near inner margin (Fig. 11 b View Figure 11 ); labial palp 3 - segmented, segment I longer than segments II and III combined, with many micropores dorsally; segment II triangular with distinct protuberance apico-laterally, ~ 1.1 × wider than base of segment III, dorsal surface with one longitudinal row of three medium simple setae and many micropores (Fig. 11 c View Figure 11 ); segment III similar to asymmetrical onion-shaped dome, apex usually with a small cone-shaped projection, ventral surface covered with many spine-like, simple setae accompanied by fine setae distally (Fig. 11 c View Figure 11 ).

Hind wing pads well developed.

Forelegs (Fig. 12 b – f View Figure 12 ). Ratio of foreleg segments (femur to claw) 6.9: 5.9: 3.5: 1.0. Femur. Length ~ 3.5 × maximum width. Dorsal surface covered with numerous crescent scale bases accompanied by fine setae; ventral face with sparse crescent scale bases and fine setae. Outer margin with two rows of different type setae: one row of 10–13 long, robust, blunt pointed setae and proximal row of 13–17 slender long setae (Fig. 12 d View Figure 12 ); additional row of small, decurved hook-like setae along dorsal margin; ventral margin with small, apically pointed or rounded, spatulate setae. Apex rounded with many short, stout, hook-like setae anteriorly, dorsoapical setal patch formed by two stout setae. Villopore present and well developed (Figs 10 f View Figure 10 , 12 d View Figure 12 ). A finger-like accessory gill on inner side of coxal articulation (between coxa and prosternum); hyaline bubble-like membranous swelling between coxa and trochanter (Fig. 12 a View Figure 12 ). Tibia. Outer margin with one row of small, apically decurved hook-like setae and fine setae; ventral margin with row of longer, stout spine-like setae. Tibio-patellar suture present (Fig. 12 e View Figure 12 ). Both surfaces covered with crescent-shaped scale bases, apically oval or pointed spatulate setae alternating with hair-like setae. Tarsus. Outer margin with fine setae and one row of short, curved hook-like setae; ventral margin with one row of ~ 11 stout spine-like pointed setae increasing in length toward apex (Fig. 12 f View Figure 12 ), apex with single robust, spine-like pointed seta. Both surfaces covered with crescent scale bases. Claws hooked (Fig. 12 c View Figure 12 ), with one row of 11–13 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.

Abdominal tergites and sternites. Both tergites and sternites densely covered with crescent scale bases and sparse hair-like setae, without any spatulate setae. Posterior margins of tergites I – X with triangular spines increasing in length from I to X (Figs 13 c – e View Figure 13 , 14 a View Figure 14 ). Posterior margins of sternites I – IX smooth medially, but with row of dentate protuberances laterally (Fig. 14 b View Figure 14 ).

Gills (Fig. 13 a View Figure 13 ) present on segments I – VII and well tracheated, ratio of gill length from I – VII = 1.0: 1.8: 2.0: 1.9: 1.6: 1.3: 1.0. External margins of all gills with small denticles intercalating fine hair-like setae (Fig. 13 b View Figure 13 ), without any marginal spines or spatulate setae.

Paraproct (Fig. 14 d View Figure 14 ). Surface scattered with several crescent scale bases, fine setae and many micropores; margin with ~ 12 triangular spines; surface of cercotractor smooth, with 12–15 spines marginally.

Caudalii (Fig. 15 f View Figure 15 ). 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 folded under cuticle of last instar larvae, segment II of gonostylus bud sharply bent towards middle and segment III sharply bent towards posterolaterally (Fig. 14 c View Figure 14 ); subimaginal gonostyli extracted from last instar larva as Fig. 15 e View Figure 15 .

Male imago. Body length 6.4 mm. Forewing 6.3 mm. Cerci 18.0 mm. Turbinate eyes cylindrical (Fig. 17 b, c View Figure 17 ), slightly widened apically, stalk and facetted surface orange; ocelli off-white with dark brown basal ring. Antennae longer than head capsule; flagella pale brown, pedicels and scapes cream. Pronotum pale with dark brown maculae medially; mesonotum pale to pale brown with brown markings medially and posterolaterally; metanotum yellow-brown to dark brown; thorax dark brown laterally. Forewings hyaline (Fig. 17 d View Figure 17 ), longitudinal veins and paired marginal intercalaries yellow-brown, double intercalary veins longer than distance between corresponding longitudinal veins; costa serrated with pointed spines on basal portion (Fig. 16 b View Figure 16 ), pterostigma area transparent washed pale yellow-brown, with four or five slanting cross veins (Figs 16 c View Figure 16 , 17 d View Figure 17 ); hindwings (Fig. 17 e View Figure 17 ) with acute costal process and three longitudinal veins. Fore femur pale, arched medially (Fig. 17 g View Figure 17 ), fore tibia yellow-brown, fore tarsus pale yellow-brown; ratio of foreleg femur / tibia / tarsus = 1: 1.4: 1.4; ratio of foreleg tarsal segments = 1.0: 6.6: 5.7: 3.3: 2.0; middle and hind legs similar to foreleg in colouration except with straight femora and apical spine on fused 1 st + 2 nd and 3 rd tarsal segments (Fig. 17 f View Figure 17 ); all claws with one oval lobe and one pointed curved hook. Abdominal tergites I – VIII rust-red with anterior submedial pair of pale streaks, each with single purple-brown transverse streak along posterior margin, tergites IX – X pale. Genitalia (Figs 16 a View Figure 16 , 17 a View Figure 17 ): unistyliger cylindrical, inner margin of segment I of gonostylus with distomedial swelling and outer margin with protuberance basally (Fig. 17 a View Figure 17 ), segment III of gonostylus oblong. Cerci grey-white with rust tints basally.

Female imago. Unknown.

Etymology.

The specific epithet is a combination of mega - (derived from the Greek, meaning huge, large) and sinus (from Latin masculine adjective meaning bay or gulf). Thus, the name refers to the fact that the type series of the new species was found from the Guangdong-Hong Kong-Macao Greater Bay Area (Greater Bay Area).

Distribution

(Fig. 23 View Figure 23 ). China: Guangdong (Shenzhen, Guangzhou, Boluo, Longmen) and Hong Kong (Tai Po Kau Forest Stream, Shing Mun, Chuen Lung, Ma Po Mei, Ng Tung Chai, Mui Tsz Lam, Shek Mun Kap).

Larval habitat

(Fig. 22 a View Figure 22 ). The species usually live in moderately rapid, well-aerated riffles at low-altitude (<300 m a. s. l.) forest streams with gravel and cobble substrates. The physicochemical parameters of the type locality (Wutongshan River, Shenzhen in December) are as follows: river width 5–7 m, water depth 10–20 cm, water temperature 18.3 ° C, current velocity 0.25 m / s, DO 9.4 mg / l, pH 8.0 and TDS 43.9 mg / l.