Rhantus procul sp. nov.

Fig. 1 A – F

Type locality.

Tojo-Una-Una [1°35'4.41"S, 120°55'28.10"E], Sulteng, Mt. Pompangeo, Central Sulawesi, Indonesia.

Type material.

Holotype • Male: “ Indonesia, Sulawesi, Sulteng, Tojo Una-Una, Mt. Pompangeo, from 1°35'4.41"S, 120°55'28.10"E to 1°35'9.22"S, 120°55'30.44"E, 1900 m, 28. II. 2020 - Track 2 (WP 42-49) leg. Narakusumo ”; “ HOLOTYPE Rhantus procul sp. nov. Narakusumo, Fahri, Hendrich, Balke des. 2025 ” [red printed label] (MZB).

Paratypes • 2 males and 1 female, same data as holotype (MZB, ZSM) • 1 female, “ Indonesia, Sulawesi, Sulteng, Tojo Una-Una, Mt. Pompangeo, from 1°35'11.81"S, 120°55'39.50"E to 1°35'7.59"S, 120°55'37.34"E, 2000 m, 1. III. 2020 - Track 3 (WP 71-81) leg. Narakusumo ” (MZB). All specimens bear our red printed paratype labels.

Description.

Holotype. A medium-sized Rhantus species, total length of holotype 10.3 mm, length without head 9.5 mm, greatest width 5.2 mm.

Colour: Head black, with contrasting orange marks as in Fig. 1 A. Pronotum yellow-orange, with a basal and discal patch black. Elytron orange, with black irrorations. Body appendages, epipleuron and hind margins of abdominal sternites dark ferruginous, rest of venter black.

Surface sculpture: Head with irregular meshes and dense, fine punctation, no microreticulation visible (Fig. 1 B); clypeus with double punctation only. Pronotum with irregular meshes and dense, distinct double punctation, disc with double punctation only; no microreticulation visible on pronotum (Fig. 1 B). Elytron with three longitudinal rows of deeper punctures, distinct, irregular polygonal meshes and fine punctation; with distinct though sometimes faint microreticulation within the meshes.

Structures: Pronotum with broad and conspicuous lateral bead, not reaching anterior angle (Fig. 1 A, B). Lateral wings of metaventrite triangular; hind wings fully developed. Last ventrite rounded apically.

Tarsal characters: Protarsal claws (Fig. 1 C) of almost equal length, both claws slightly shorter than tarsomere V. Claws slender and evenly curved and with no particular modification (e. g. not dentate or with irregular curvature).

Mesotarsal claws of equal length, evenly curved, shorter than fifth protarsomere. Pro- and mesotarsomeres 1–3 not dilated laterally, with four transverse rows of stalked suction discs ventrally. Number of discs per row (tarsomere on which row occurs given in parentheses): pro: 7 (I) / 6 (I) / 6 (II) / 5 (III); meso: 7 (I) / 7 (I) / 7 (II) / 5 (III).

Genital structure: Median lobe of aedeagus (Fig. 1 E, D), longish curvature in lateral view; parameres with fringe of yellow hairs, apically acute, not trumpet shaped (Fig. 1 F).

Variation. Body length varies from 10.2–10.8 mm. The discal dark spot on pronotum can be slightly more extended than in the holotype (Fig. 1 A), the same is true for the basal dark spot. Both can be approaching but do not connect. Females, color as in male, dorsal surface matt; elytral sculpture with stronger microreticulation than in male. Tarsomere without ventral stalked suction discs.

Etymology.

The specific epithet “ procul ” is a Latin adverb meaning “ far away ” or “ from afar ”. The name is treated here as a noun in apposition and, in accordance with article 34.2. 1 of the ICZN code, is thus considered indeclinable. The name refers to the large geographical distance between the type locality of the new species and Rhantus interclusus (Walker, 1858) from Sri Lanka, which is closest in terms of genital morphology.

Diagnosis.

A species well delineated from all other Indonesian Rhantus by the form of the median lobe in lateral view (Fig. 1 E, D). Its flattened basic shape is essentially the same as in R. interclusus (Fig. 1 H), described from the Central Mountain Ranges of Sri Lanka and endemic to that island. Both species can be easily separated by the coloration of their pronotums (Fig. 1 A, G). Furthermore, R. interclusus is slightly larger and broader than R. procul sp. nov., and has the slightly different curvature of the median lobe.

Females of R. procul sp. nov. and R. interclusus can also be differentiated from one another based on body size and dorsal coloration.

The only other known species of Rhantus occurring in Sulawesi is R. suturalis (Fig. 2 A), whose median lobe is tubular, not flattened (Fig. 2 B). The male pro- and mesotarsomeres 1–3 in R. suturalis are weakly dilated, laterally compressed; protarsal claws short, anterior claw arcuate subbasally, about 1 ½ times as long as posterior claw which is very narrow and strongly arcuate in distal half (Fig. 2 C).

The shape of the parameres of R. suturalis is essentially a generic “ Rhantus - shape ”. The lack of slightly trumpet-shaped, presumably suction setae is supposedly the ancestral state.

Distribution.

Only known from the type locality in Central Sulawesi, Indonesia (Fig. 3).

Habitat.

(Fig. 4). Rhantus procul sp. nov. was collected from small, shallow forest streams at ca. 1,900 –2,000 m a. s. l. elevation on Mt. Pompangeo. The streams had sandy and gravelly substrates, clear water, and were shaded by dense montane rainforest with abundant trees with ferns, mosses and epiphytic plants. The surrounding vegetation created a cool and humid microclimate typical of high-elevation tropical forest.