Arcobaetis sumatrensis, 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 sumatrensis sp. nov.

Figs 6 , 7 , 8 , 9 , 19

Type material.

Holotype. Indonesia • female larva (premature); Sumatra Barat, Harau Canyon, stream near Ikbal’s cottage, UN11; 00°06'26"S, 100°40'22"E; 520 m; 23.vi.2012; leg. M. Balke; on slide; GBIFCH00592617; MZB. Paratypes. 1 larva; same data as holotype; on slide; GBIFCH00975679; MZL • 1 larva; Sumatra Barat, Bukit Barisan, above Padang, creek, UN3; 00°56'44"S, 100°32'44"E; 1047 m; 8.xi.2011; leg. M. Balke; on slide; GBIFCH00975704; MZL.

Diagnosis.

Larva (Table 1 ). The following combination of characters distinguish A. sumatrensis sp. nov. from other species of Arcobaetis gen. nov.: A) distal margins of segments in middle part of flagellum without enlarged spines; B) labial palp segment III sub-rectangular, at base smaller than distal margin of segment II (Fig. 7h ); C) hind protoptera absent; D) claw with single row of denticles, ca. six distalmost denticles larger, other denticles minute (Fig. 8b ); E) tergalii present on abdominal segments II-VII (Fig. 8c-h; F ) posterior margin of tergum IV with triangular spines, wider than long (Fig. 7i ).

Description.

Larva (Figs 6 - 9 ). Body length ca. 4.6 mm.

Cuticular colouration (Fig. 6a-c ). Head, thorax, and abdomen dorsally brown, ventrally ochre. Legs ochre, joining of femur and tibia dark brown; middle part of tibia pale brown. Caudalii pale brown.

Hypodermal colouration. Abdomen dorsally with narrow reddish transverse stripes on intersegmental membranes (Fig. 6a ).

Antenna. Flagellum in middle part without enlarged spines at distal margin of segments.

Labrum (Fig. 7a ). Length 0.7 × maximum width. Dorsally with sub-median seta and sub-marginal arc of two simple setae.

Right mandible (Fig. 7b, c ). Incisor with five denticles; kinetodontium with three denticles.

Left mandible (Fig. 7d, e ). Incisor with four denticles; kinetodontium with three denticles.

Hypopharynx and superlinguae (Fig. 7f ). Lingua as long as superlinguae, longer than broad. Superlinguae distally straight; lateral margins rounded; fine, long, simple setae along distal margin.

Maxilla (Fig. 7g ). Galea-lacinia ventrally with two simple setae just proximad of canines. Medially with one pectinate, spine-like seta and ca. five short to long, simple setae. Maxillary palp approx. 1.5 × 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. 7h-j ). Inner margin of glossa with ca. ten spine-like setae; apex with three long and one medium robust setae; outer margin with ca. nine spine-like setae; paraglossa ventrally with ca. two medium, simple setae in anteromedial area; dorsally with arc of ca. ten 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-rectangular; 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 8a, b , 9a-c ). Long and slender, middle, and hind legs slenderer than fore leg. Ratio of leg segments: fore leg 1.4:1.0:0.8:0.2, middle legs 1.3:1.0:0.6:0.2 and hind legs 1.2:1.0:0.6:0.1. Femur. Length of fore femur ca. 4.4 × maximum width, outer and inner margins almost parallel; length of middle and hind femora> 5 × maximum width, outer margins slightly concave. Outer margin with row of ca. seven short, curved, spine-like setae, on fore leg larger than on middle and hind legs. On ventral side of fore leg with short, spine-like, pectinate, pointed setae; nearly absent on middle and hind legs. Tibia. Short, stout, pointed, pectinate setae irregularly 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 middle and hind legs with few medium, spine-like setae. Patella-tibial suture on proximal ¹/4 of tibia on all legs. Tarsus. Inner margin with row of short, curved, pectinate, spine-like setae; outer margin without spine-like setae. Claw with single row of denticles, ca. six distalmost denticles larger and directed distad, other denticles minute.

Abdominal terga (Fig. 8i, j ). Posterior margin of terga: I smooth, without spines; II-IV with short triangular spines, wider than long; V with triangular spines approx. as wide as long; VI-IX with triangular spines longer than wide, sharply pointed; row of spines on tergum IX interrupted by smaller spines in middle part behind bases of submedian setae (similar to Fig. 15j ).

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

Tergalii (Figs 8c-h , 9d ). Present on abdominal segments II-VII. Tracheation partially extending toward inner and outer margins. Margins with minute denticles intercalating short, simple setae.

Paraproct (Fig. 8k ). Posterior margin with ca. 13 stout spines. Surface scattered with scale bases and micropores.

Caudalii (Fig. 9f ). Cerci and paracercus with small, rather wide, triangular, pointed spines on posterior margin of each segment; on outer side of cerci two somewhat longer spines on each 2nd segment, no such longer spines on paracercus.

Etymology.

The specific epithet refers to the type locality in Sumatra (Indonesia).

Distribution.

Indonesia: Sumatra (Fig. 12b ).

Biological aspects.

The species was found at altitudes of 520 m and 1050 m.

Figures

Figure 6. Arcobaetis sumatrensis sp. nov., larva, habitus (holotype) a dorsal view b lateral view c ventral view. Scale bar: 1 mm

Figure 7. Arcobaetis sumatrensis 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 labium (left: ventral view; right: dorsal view) i apex of paraglossa (ventral view) j apex of paraglossa (dorsal view).

Figure 8. Arcobaetis sumatrensis sp. nov., larva a foreleg b fore claw c tergalius II d tergalius III e tergalius IV f tergalius V g tergalius VI h tergalius VII i tergum IV j scale on tergum IV k paraproct.

Figure 9. Arcobaetis sumatrensis sp. nov., larva a foreleg b middle leg c hind leg d tergalius IV e head f fragment of cercus (lateral view). Scale bars: 0.1 mm.

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.