Genus Isognathotermes · 等颚白蚁属

Morphology

The descriptions below are an adaptation of the original genus-level accounts; terms follow the meaning of the source, and the original is not transcribed verbatim.

Diagnostic characters

Belonging to Cubitermitinae; workers, soldiers and alates all possess a mixed segment between the midgut and the hindgut, 4 Malpighian tubules fused at their bases, and a caecum at the second hindgut pouch (P3). The worker enteric valve (EVA) is the most reliable diagnostic character of the genus, comprising the fungifaber type, the finitimus type and an intermediate type between them: in the former the odd-numbered enteric valve pads narrow at the downstream end and bear ridges, the ridges carrying long curved/hooked setae; in the latter the odd-numbered pads are more robust, swollen into a bulb at the downstream end and densely covered with short, stiff, straight setae, the transition between the two being abrupt. Ventral surface of the worker fore coxa ridged, the ridge with 2–7 spines, fore trochanter with 3–8 spines. Soldier head distinctly longer than wide (head length 2.18–3.77 mm, length/width ratio 1.22–1.67), mandibles sickle-shaped and shorter than the head length (0.66–0.92), antennae 14–15-segmented. Alate darkly coloured (C6–C8), antennae 16-segmented, fontanelle small, tibial spur formula 3:2:2 with 2 additional proximal spines on the mid tibia.

Alate

Head capsule strongly sclerotised, dark (C6–C8, fading to C4 in old specimens); fontanelle concolorous or nearly concolorous with the head capsule; postclypeus C5–C7, concolorous with the head capsule or 1–2 grades paler; antennae C4–C6, proximal and distal segments not markedly different. Head large; fontanelle generally a small round or elongate spot. Compound eyes round to short oval (major/minor diameter 1.00–1.25); ocelli round to oval (1.00–1.80). Antennae 16-segmented (only 1 of 278 alates with 17 segments); queens and kings often missing 1–4 segments through wear. Labrum bell-shaped, generally wider than long. Apical tooth of the left mandible longer than the first marginal tooth, marginal teeth 3, the second expressed only as an undulation of the cutting margin between the first and third (lost after wear); dorsal surface of the molar prominence rounded, ending posteriorly in a small pointed projection. Marginal teeth of the right mandible 2, the first sharp when fresh, the second smaller with a blunt apex; molar tooth with a rounded, lip-like ventral projection, heel-shaped posteriorly. Pronotum distinctly wider than long, narrower than the head width (including compound eyes), flat to slightly saddle-shaped, anterior lobe short and slightly raised. Ventral surface of the fore coxa ridged. Wings: R1 completely fused with the costal margin and sclerotised; Rs simple and sclerotised; M and Cu unsclerotised or weakly sclerotised, branching into 2–6 and 7–15 branches respectively. Dorsal surface of the abdomen with 10 complete, undivided tergites visible; males with 8 complete sternites visible, females with 6, followed by the subgenital plate and differentiated lateral plates. Hindgut with a mixed segment and a caecum, but the caecum relatively small.

Soldier

Head capsule generally Cd4–Cd6, becoming paler or darker in old specimens (Cf5–Cf7); frontal region often 1–2 grades darker than the posterior part, sometimes giving a distinctly bicoloured head; postmentum concolorous with the head or slightly darker; antennae and labrum 1 grade paler than the head capsule; mandibles dark (C7–C8), with an abruptly paler ring at the base, mostly of the same colour as the frontal region; thorax and legs paler than the head capsule (C3–C5). Head capsule distinctly sclerotised, distinctly longer than wide; in dorsal view the sides mostly subparallel, narrowing to varying degrees at the posterior 1/3–1/4, the sides slightly convex without obvious narrowing in incipient-colony individuals; posterior margin variable, regularly rounded, or with a short straight/concave section in the middle, or composed of three short straight/concave sections. Upper margin always more or less concave in profile; frons with or without a small frontal projection covering the fontanelle. Posterior half of the postmentum always narrowing to varying degrees in ventral view, the sides of the anterior half ranging from smoothly rounded to angular ear-like lobes. Antennae generally 15-segmented (14.5 segments in about 9%, 14 in about 6%, occasionally 13 in incipient-colony individuals). Labrum always deeply cleft, generally wider than long, the sides harp-shaped in 82% of individuals (convex in 11%, straight in 7%), the lobes subtruncate, finely white or translucent at the apex; anterior margin concave. Mandibles sickle-shaped to subapically hooked, inner margin smooth, each side with 1 distinct but usually very small marginal tooth near the molar tooth; mandibles distinctly shorter than the head, surface smooth and shining; right mandible generally slightly more curved than the left. Pronotum saddle-shaped, narrower than the head width, anterior and posterior margins generally entire. Ventral surface of the fore coxa ridged. Enteric valve situated in the left posterior part of the abdomen, mostly with triradiate symmetry; odd-numbered enteric valve pads on average 16% longer than the even-numbered ones, generally without ridges or with weak ridges; the pilosity at this site abruptly denser in finitimus-type individuals; secondary enteric valve pads broad at the upstream end and distinctly narrowing downstream.

Worker

Head capsule pale (C1–C3), turning grey in old specimens; basal antennal segments pale (C2–C3), distal segments always 1–2 grades darker (C4–C5); thorax and legs pale (C1–C3); abdomen grey to reddish brown owing to gut contents. Head capsule weakly sclerotised (except the mandibles); antennae 15-segmented, rarely 14.5 or 14, occasionally 13 in incipient-colony individuals; labrum bell-shaped, generally wider than long. Apical tooth of the left mandible well developed, sharp when fresh; marginal teeth 3, the first well developed, the second weak (visible only as an undulating cutting margin, lost after wear), the third with a blunt apex; dorsal surface of the molar prominence rounded, with a small pointed projection posteriorly. Marginal teeth of the right mandible 2, the first well developed and sharp when fresh, the second smaller with a blunt apex; molar tooth with a rounded, lip-like ventral projection, heel-shaped posteriorly. Pronotum saddle-shaped. Ventral surface of the fore coxa with a sharp ridge, the ridge with 3–7 spines (only 2 spines in 2 of 400 samples), ventral surface with 0–4 spines; fore trochanter with 5–7 spines; apical tibial spurs of the fore, mid and hind legs 3:2:2, proximal spurs 0:2:0. Enteric valve situated in the left posterior part of the abdomen, always with triradiate symmetry; of the fungifaber type, finitimus type or intermediate type depending on the species (muneris type in I. acristatus); odd-numbered enteric valve pads with generally 13–38 supporting setae on each side; secondary enteric valve pads broad at the upstream end and distinctly narrowing downstream, the spines evenly distributed. Caecum relatively small, situated near the middle of the abdomen, often with 2–3 lobules, or finger-shaped with the apex sometimes thickened.

Sources: Josens G. et al. 2025. An integrative revision of the genus Isognathotermes (Termitidae: Cubitermitinae) with description of seven new species and four new subspecies. European Journal of Taxonomy 1024: 1–197., pp. 11–27 This text is an adaptation, not a verbatim transcription of the original.