Arcobaetis bornensis, Kaltenbach & Kluge & Gattolliat, 2023

Kaltenbach, Thomas, Kluge, Nikita J. & Gattolliat, Jean-Luc, 2023, A new, widespread genus of Baetidae from South Asia (Insecta, Ephemeroptera), ZooKeys 1168, pp. 231-266 : 231

Arcobaetis bornensis sp. nov.

Figs 10 , 11 , 12 , 19

Type material.

Holotype. Brunei • female larva (premature); Temburong District, Ulu Temburong National Park, near Kuala Belalong Field Studies Centre (KBFSC); 04°32'55"N, 115°09'27"E; 103 m; May 2014; leg. Kate Baker; on slide; GBIFCH00465126; MZL. Paratypes. 11 larvae; same data as holotype; 5 on slides; GBIFCH00465127, GBIFCH00465128, GBIFCH00465129, GBIFCH00592613, GBIFCH00592645; MZL; 6 in alcohol; GBIFCH00515212, GBIFCH00975703; MZL.

Diagnosis.

Larva (Table 1 ). The following combination of characters distinguish A. bornensis sp. nov. from other species of Arcobaetis gen. nov.: A) distal margins of segments in middle part of flagellum with enlarged spines (Fig. 11f ); B) labial palp segment III sub-quadrangular, at base narrower than distal margin of segment II (Fig. 10h ); C) hind protoptera absent; D) claw with single row of denticles, distalmost denticle larger, other denticles minute (Fig. 11b ); E) tergalii present on abdominal segments I-VII; F) posterior margin of tergum IV with triangular spines, wider than long (Fig. 11c ).

Description.

Larva (Figs 10 - 12 ). Body length ca. 3.0 mm.

Colouration. Head, thorax, and abdomen dorsally brown, ventrally ochre. Legs ecru. Caudalii pale brown.

Hypodermal colouration. Unknown.

Antenna. Flagellum in middle part with enlarged spines at distal margin of segments (Fig. 11f ).

Labrum (Fig. 10a ). Length 0.7 × maximum width. Dorsally with sub-median seta, sub-marginal arc of ca. three simple setae, and several setae in between.

Right mandible (Fig. 10b, c ). Incisor with five denticles; kinetodontium with three denticles.

Left mandible (Fig. 10d, e ). Incisor with four denticles; kinetodontium with three denticles.

Hypopharynx and superlinguae (Fig. 10f ). Lingua slightly shorter than superlinguae, longer than broad. Superlinguae distally straight; lateral margins rounded; fine, long, simple setae along distal margin.

Maxilla (Fig. 10g ). Galea-lacinia ventrally with two simple setae just proximad of canines. Medially with one pectinate, spine-like seta and ca. four medium to long, simple setae. Maxillary palp approx. 1.4 × as long as galea-lacinia; palp segment II approx. 1.2 × as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II.

Labium (Fig. 10h-j ). Inner margin of glossa with ca. nine spine-like setae; apex with three long robust setae; outer margin with ca. nine spine-like setae; paraglossa ventrally with ca. four medium, simple setae in anteromedial area; dorsally with arc of ca. seven long, spine-like setae in distal area. Labial palp with segment I 0.8 × length of segments II and III combined. Segment II dorsally with row of ca. four spine-like setae. Segment III sub-quadrangular; at base narrower than distal margin of segment II; ventral surface with short, spine-like, simple setae and short, fine, simple setae.

Hind protoptera absent.

Legs (Figs 11a, b , 12a, b ). Long and slender, hind legs slenderer than fore leg, middle legs unknown. Ratio of leg segments: fore leg 1.5:1.0:0.9:0.3, hind leg 1.4:1.0:0.7:0.2. Femur. Length of fore femur ca. 3.6 × maximum width, outer and inner margins almost parallel; length of hind femur ca. 5 × maximum width, outer margin slightly concave. Outer margin with row of ca. 7 short, curved, spine-like setae, on fore leg larger than on hind leg. On ventral side of fore leg with short, spine-like, pectinate, pointed setae; nearly absent on hind leg. Tibia. Few short, stout, pointed, pectinate setae near inner margin. Inner margin with row of short, curved, spine-like, pectinate setae, on apex two longer, curved, spine-like, pectinate setae. Outer margin with one apical, spine-like seta; on fore leg without other spine-like setae, on hind leg with few medium, spine-like setae. Patella-tibial suture on foreleg on proximal ¹/2 (difficult to see), on hind leg on proximal ¹/3. Tarsus. Inner margin with row of short, curved, pectinate, spine-like setae; outer margin without spine-like setae. Claw with one row of denticles, distalmost denticle larger and directed distad, other denticles minute.

Abdominal terga (Fig. 11c ). Posterior margin of terga: I and II smooth, without spines; III-IX with triangular spines, slightly increasing in length toward IX; wider than long on tergum IV; row of spines on tergum IX interrupted by smaller spines in middle part behind bases of submedian setae (similar to Fig. 15j ). Posterior margin of tergum X with median concavity with smaller spines (similar to Fig. 15k ).

Abdominal sternites. Posterior margins of sterna: I-V smooth, without spines; VI-IX with triangular spines.

Tergalii (Fig. 11d ). Present on abdominal segments I-VII. Tracheation limited to main trunk. Margin with minute denticles intercalating short, simple setae.

Paraproct (Fig. 11e ). Posterior margin with ca. 13 stout spines. Surface scattered with scale bases and micropores.

Caudalii. Spines of cerci and paracercus unknown.

Etymology.

The specific epithet refers to the type locality in Borneo (Brunei).

Distribution.

Brunei (Fig. 19 ).

Biological aspects

(Fig. 12c ). The species was found at an altitude of 1380 m in slow current of a small and shallow stream.

Figures

Figure 10. Arcobaetis bornensis sp. nov., larva a labrum (left: ventral view; right: dorsal view) b right mandible c right prostheca d left mandible e left prostheca f hypopharynx and superlinguae g maxilla h l abium (left: ventral view; right: dorsal view) i apex of paraglossa (ventral view) j apex of paraglossa (dorsal view).

Figure 11. Arcobaetis bornensis sp. nov., larva a foreleg b fore claw c tergum IV d tergalius IV e paraproct f antenna (right: dorsal view; left: section in lateral view).

Figure 12. Arcobaetis bornensis sp. nov., larva a foreleg b hind leg c habitat (photo Kate Baker, University Exeter, UK).

Figure 15. Arcobaetis sripadai sp. nov., larval exuviae a, b fore and middle legs (triangles show points where patella-tibial suture crosses inner margin c claw d-k posterior margins of abdominal terga II-VI and VIII-X l-m posterior margin of abdominal sterna VIII and IX of male larva n paraproct. o-p fragments of cerci (lateral view).

Figure 19. Arcobaetis gen. nov., distribution.