Branchiobaetis sabahensis ( Mueller-Liebenau , 1984) Kaltenbach & Kluge & Gattolliat, 2022

Kaltenbach, Thomas, Kluge, Nikita J. & Gattolliat, Jean-Luc, 2022, A widespread new genus of Baetidae (Baetidae, Ephemeroptera) from Southeast Asia, ZooKeys 1135, pp. 1-59 : 1

2. Branchiobaetis sabahensis ( Mueller-Liebenau, 1984) comb. nov.

Figs 12 , 13

Baetis sabahensis : Müller-Liebenau 1984b: 89; figs 3, 9, 14, 14a.

Material examined.

Malaysia • Sabah, Ranau ; 14.-16.VII.1972; leg. G. F. Edmunds; ♂ larva on slide; SPbU • Sabah, Kundasang ; 04.IX.1994; leg. S. C. Kang; ♂ larva on slide; SPbU .

B. cf. sabahensis comb. nov. material examined.

Indonesia • East Kalimantan, Bas. Malinau, River Seturan, loc. Seturan (2000-block 44-45), trib. Wok (Sungai Guang); 2°59'12"N, 116°33'11"E; 16.VI.2000; leg. P. Derleth & J.-L. Gattolliat; 3 larvae on slides; GBIFCH00592470, GBIFCH00592471, GBIFCH00592495; larva in alcohol; GBIFCH00270724; MZL • East Kalimantan, Bas. Malinau, River Seturan, loc. Seturan (2001-block 57), trib. Bengahau ; 02°59'22"N, 116°30'46"E; 19.VIII.2000; leg. P. Derleth & R. Schlaepfer; larva on slide; GBIFCH00592494; larva in alcohol; GBIFCH00270710; MZL • East Kalimantan, Bas. Malinau, riv. Seturan, loc. Seturan (2001-block 57), trib. Benganau ; 02°59'22"N, 116°30'46"E; 11.IV.2001; leg. P. Derleth & B. Feldmeyer; larva in alcohol; GBIFCH00270710; MZL .

Differential diagnosis.

Larva. Following combination of characters distinguish B. sabahensis comb. nov. from other species of Branchiobaetis gen. nov.: A) labial palp segment II with short, thumb-like protuberance; segment III rather short and wide, ca. 0.5 × length of segment II, ca. 0.8 × as long as width at base, ca. 0.7 × as long as maximal width (Fig. 12d ; Müller-Liebenau 1984b: fig. 3b); B) incisor of right mandible with ventral denticle ( Müller-Liebenau 1984b: fig. 3e; C) dorsal margin of femur with row of ca. 15 long, spine-like setae; no additional row of short setae along margin; no short, stout setae on surface of femur (Fig. 13a ; Müller-Liebenau 1984b: fig. 3k); D) posterior margin of tergite I smooth, without spines; posterior margins of tergites II-III with rounded or triangular spines, posterior margins of tergites IV-X with triangular spines (Fig. 13c ; Müller-Liebenau 1984b: fig. 14); posterior margins of sternites: I-V smooth, without spines; VI smooth, without spines, or with some small, triangular spines; VII-IX with triangular or blunt spines (Fig. 13d ).

Imago. Winged stages unknown. Judging from details revealed in last instar larva, turbinate eyes not narrowed; hind wing with costal projection; sterno-styligeral muscle present and thin.

Comments.

The original description of Baetis sabahensis Müller-Liebenau, 1984 was based on larvae, and certain similarities of this species with B. javanicus were reported. The single argument to separate B. sabahensis from B. javanicus , was the statement that " Baetis sabahensis sp. nov. is the only species in the genus with coxal gills on the first pair of legs" ( Müller-Liebenau 1984b: 92). Larva of B. javanicus was described and figured by the same author earlier ( Müller-Liebenau 1981), but the coxal and maxillary gills had not been reported (see above).

Larva of Branchiobaetis sabahensis comb. nov. can be separated from B. javanicus comb. nov. by the following characters: A) dense spines on abdominal sternite VIII (Fig. 13d ); B) presence of only one or two stout setae on paraproct, or complete absence (Fig. 13b ); C) incisor of right mandible with ventral denticle; D) labial palp segment III short and wide (Fig. 12d ; see above).

Judging by precursors of turbinate eyes developed in last instar male larva, male imago of B. sabahensis comb. nov. should differ from B. javanicus comb. nov. by usual (not narrowed) turbinate eyes (Fig. 12a ).

Branchiobaetis cf. sabahensis comb. nov. Specimens from Indonesia (Kalimantan) always have a series of stout setae along posterior margin of paraproct, contrary to specimens from Malaysia (Sabah). As there are no other differentiating characters to B. sabahensis comb. nov. from Malaysia (Sabah), we treat this population as B. cf. sabahensis comb. nov., waiting for genetic investigation of fresh material in the future.

Distribution

(Fig. 27b ). Malaysia (Borneo: Sabah); B. cf. sabahensis comb. nov. Indonesia (Borneo: Kalimantan).

Figures

Figure 12. Branchiobaetis sabahensis comb. nov., larva a head of male larva b labrum c prosternum and bases of forelegs, front view d labium.

Figure 13. Branchiobaetis sabahensis comb. nov., larva a apex of hind femur b paraproct c abdominal tergum IX d abdominal sternum VIII e tergalius.

Figure 27. Distribution maps a Branchiobaetis gen. nov. in Southeast Asia b Known species of Branchiobaetis gen. nov.