4. Branchiobaetis hamatus sp. nov.

Figs 16, 17, 24b, 26b, 28a

Type material.

Holotype. Indonesia • Sumatra, volcano Talamau; River Pularian; 00°00'60"N, 100°00'01"E; 960 m; 01.IV.2014; leg. M. Gueuning: larva on slide; GBIFCH00422261; MZL. Paratypes. Same data as holotype; 2 larvae on slides; GBIFCH00422231, GBIFCH00422242; 20 larvae in alcohol; GBIFCH00422233, GBIFCH00422252, GBIFCH00422267, GBIFCH00422276, GBIFCH00422355, GBIFCH00422359, GBIFCH00422445, GBIFCH00422748, GBIFCH00422753, GBIFCH00422798, GBIFCH00422843, GBIFCH00423022, GBIFCH00975634, GBIFCH00975635; MZL. Indonesia • Sumatra, volcano Singgalang, River Sianok; 00°19'57"S, 100°19'19"E; 1150 m; 24.III.2014; leg. M. Gueuning; 2 larvae on slides; GBIFCH00422184, GBIFCH00423074; 13 larvae in alcohol; GBIFCH00422123, GBIFCH00422167, GBIFCH00422206, GBIFCH004208, GBIFCH00422215, GBIFCH00422216, GBIFCH00422224, GBIFCH00422797, GBIFCH00422889, GBIFCH00422938, GBIFCH01115975, GBIFCH01116020; MZL.

Differential diagnosis.

Larva. Following combination of characters distinguish B. hamatus sp. nov. from other species of Branchiobaetis gen. nov.: A) labial palp segment II with medium, rounded protuberance, segment III apically slightly pointed (Fig. 16h); B) incisor of right mandible with ventral denticle (Fig. 16b); C) dorsal margin of femur with row of medium, spine-like setae, basally longer and clavate; additional row of short, hook-like setae along margin (Fig. 17a, b); D) dorsal margin of tibia and tarsus with row of short, hook-like setae (Fig. 17a, b); E) posterior margin of tergites: I smooth, without spines; II-IX triangular, narrower and longer towards last segment (Fig. 17e); posterior margin of sternites: I-VII smooth, without spines; VIII-IX with small, spaced, triangular spines; F) tergalius IV apically slightly concave (Fig. 17f); G) paraproct with short, stout, apically rounded setae along posterior margin (Fig. 17g).

Description.

Larva (Figs 16, 17, 24b, 26b). Body length 6.8-8.5 mm. Cerci: broken. Paracercus: ca. 0.4 × body length. Antenna: ca. 2.5 × as long as head length.

Colouration (Fig. 24b). Head, thorax and abdomen dorsally brown, abdominal segment X light brown; head, thorax and abdomen ventrally light brown, scape with dark brown spot at inner lateral side. Femur light brown, apically and dorsally along margin dark brown, with large, medial, dark brown spot; tibia light brown, tarsus dark brown in distal half. Caudalii light brown, cerci darker brown in area of ca. ½ of length, paracercus darker brown parallel to cerci; primary swimming setae dark brown.

Precursors of turbinate eyes (Fig. 25c) in male last instar larvae representing a pair of subtriangular maculae; in the middle of this macula, a smaller, round, elevated area with well-expressed facets, approx. ten facets in diameter; peripheral area of the macula with indistinct facets.

Antenna (Fig. 17h). Scape distally and outside distolaterally with short, stout, apically rounded setae.

Labrum (Fig. 16a). Length 0.6 × maximum width. Submarginal arc of setae composed of 7-10 long, simple setae.

Right mandible (Fig. 16b, c). Incisor blade-like with three denticles and a ventral denticle; kinetodontium with four denticles. Margin between prostheca and mola straight, with minute denticles.

Left mandible (Fig. 16d, e). Incisor blade-like with four denticles; kinetodontium with three denticles. Margin between prostheca and mola straight, with minute denticles towards subtriangular process.

Both mandibles with lateral margins slightly convex.

Hypopharynx and superlinguae (Fig. 16f). Lingua as long as superlinguae. Lingua longer than broad; medial tuft of stout setae well developed. Superlinguae distally rounded; lateral margins rounded; fine, long, simple setae along distal margin.

Maxilla (Fig. 16g). Galea-lacinia ventrally with two simple, apical setae under canines. Medially with one pectinate, spine-like seta and five or six medium, simple setae. Maxillary palp approx. as long as galea-lacinia; palp segment II approx. as long as segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II.

Labium (Fig. 16h). Inner margin of glossa with 10-12 spine-like setae, increasing in length distally; apex with two long and one medium, robust setae; outer margin with six or seven spine-like setae; Paraglossa with two short, simple setae in anteromedial area and one in posterolateral area; dorsally with three long, spine-like setae near inner margin. Labial palp with segment I approx. as long as length of segments II and III combined. Segment I ventrally with short, fine, simple setae. Segment II with medium, rounded, distomedial protuberance; distomedial protuberance 0.3 × width of base of segment III; ventral surface with short, fine, simple setae; dorsally with 4-8 spine-like setae near outer margin. Segment III apically slightly pointed; length 0.8 × maximum width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.

Foreleg (Fig. 17a-d). Ratio of foreleg segments 1.3:1.0:0.5:0.2. Femur. Length ca. 3 × maximum width. Dorsal margin with row of 7-9 medium, curved, spine-like setae and basally 10-15 longer, clavate setae. Additional row of short, stout, hook-like setae along dorsal margin. Apex rounded, with pair of spine-like setae; short, stout, hook-like setae on anterior and posterior side. Short, stout, apically rounded setae scattered along ventral margin. Tibia. Dorsal margin with two irregular rows of short, stout, hook-like setae. On surface short, stout, hook-like setae along patella-tibial suture. Ventral margin with row of short, curved, spine-like setae, on apex a tuft of fine, simple setae. Tarsus. Dorsal margin with row of short, stout, hook-like setae and row of fine, simple setae. Claw with one row of ten or eleven denticles, distal denticle much longer than other denticles.

Terga (Fig. 17e). Surface with irregular rows of U-shaped scale bases and scattered fine, simple setae. Posterior margin of tergites: I smooth, without spines; II-IX triangular, narrower and longer towards last segment. Posterior margin of sternites: I-VII smooth, without spines; VIII-IX with small, spaced, triangular spines.

Tergalii (Figs 17f, 26b). Tracheae extending from main trunk to inner and outer margins; with light brown band along main trunk of tracheae on anal side. Tergalius I 2/3 as long as segment II, tergalius IV as long as length of segments V and 1/2 VI combined, tergalius VII as long as length of segment VIII.

Paraproct (Fig. 17g). Posterior margin with 11-16 stout spines. Short, stout, apically rounded setae near posterior margin. Surface scattered with scale bases, micropores and fine, simple setae.

Etymology.

Based on the Latin word hamatus, meaning hooked, with reference to the hook-like setae on the legs.

Distribution.

Indonesia: Sumatra (Fig. 28a).

Biological aspects.

The specimens were collected in two sites at altitudes of 940 m and 1150 m, with following physical conditions: slope 5-10%, width of stream 3-8 m, depth 1-50 cm, velocity 0.5 m/s-0.7 m/s, pH 8, stream bed dominated by boulder, stones and gravel or stones and sand respectively. One of the sites was strongly influenced by human activities, with lot of waste and brown water.