Isognathotermes planifrons (Sjöstedt, 1924)

Josens, Guy, Deligne, Jean, Harry, Myriam, Roy, Virginie, Akama, Pierre D., Coulibaly, Tenon, Dosso, Kanvaly, Goergen, Georg, Hasson, Michel, Kasangij, Patrick Kasangij A, Kifukieto, Carmel, Ru, Bruno Le, Loko, Laura Estelle Yêyinou, Ndiaye, Abdoulaye Baila, Roisin, Yves, Sion, Noémie, Šobotnik, Jan, Stiblik, Petr, Kuenda, Soki Kue Di, Traoré, Saran, Viage, Manuela, Wango, Solange Patricia, Kaymak, Esra, Bourguignon, Thomas & Hellemans, Simon, 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, pp. 1-197 : 112-122

Isognathotermes planifrons (Sjöstedt, 1924)

Figs 26–31, 33, 57–59, distribution map: Fig. 47; Table 12

Cubitermes planifrons Sjöstedt, 1924b: 255–256 .

Cubitermes fungifaber var. elongata Sjöstedt, 1924b: 256 . S yn. nov.

Cubitermes loubetsiensis Sjöstedt, 1924c: 493 . S yn. nov.

Mirotermes ( Cubitermes) gaigei Emerson, 1928: 516–517 , fig. 59. S yn. nov.

Mirotermes ( Cubitermes) loubetsiensis – Emerson 1928: 515–516, text-fig. 58, pl XXX.

Cubitermes planifrons – Sjöstedt 1926: 243–244. — Snyder 1949: 162. — Ruelle 1992: 500. — Krishna et al. 2013: 1931. — Josens & Deligne 2019: 60–61 .

Cubitermes sp. affinis subarquatus “spB” – Roy et al. 2006: 4–5.

Isognathotermes planifrons – Hellemans et al. 2021: 233.

Diagnosis

This species is difficult to identify from its morphology since it is located near I. finitimus and I. phalloides sp. nov. It is obviously easier to identify from its COII sequence: I. planifrons makes a clade well apart from the finitimus clade ( Hellemans et al. 2021: 231).

Best recognition, if molecular data are not available, by a combination of worker’s EVA, soldier’s mandibles curvature, and geographic origin.

The worker has a finitimus EVA ( Fig. 5) and is among the medium-sized workers of the genus Isognathotermes ( Fig. 30) but with a rather small-sized enteric valve ( Fig. 31).

The soldier has, on average and along with that of I. fungifaber , the highest left mandible apical curvature index; it is among the medium-sized soldiers of Isognathotermes ( Fig. 28); on the odd PCs of its enteric valve, the pilosity becomes very dense showing the place where a bulge exists in the worker’s valve, its finitimus pattern is therefore recognizable.

The imago is, on average, medium sized in the genus Isognathotermes ( Fig. 26) with, on average, larger eyes and ocelli than I. finitimus .

This species is also defined by its ecology and chorology: it has always been found in evergreen forests from Gabon to CAR, up to 1000 km from the Atlantic coast ( Fig. 47).

Some samples of I. planifrons are like I. fungifaber , but they have different EVAs.

Some samples of I. planifrons are like I. phalloides sp. nov.; ( Fig. 22) they have similar EVAs, but they have different caeca and geographical distributions.

Many samples of I. planifrons are like I. finitimus , ( Fig. 22) they have similar EVAs and caeca; but their geographical distributions are different, but in CAR ( Figs 38, 47).

Etymology

The epithet planifrons from the Latin planus (flat) and frons (forehead) refers to the soldier’s head morphology (not protruding frons).

Material examined

Seventy-seven samples from 29 locations. Of the 41 old museum samples examined, only one, the type, was identified as C. planifrons (and subsequently renamed “ C. fungifaber ”); six samples were labelled as C. banksi , two as C. bulbifrons , one as C. finitimus , three as C. fungifaber , one as C. fungifaber var. elongata , six as C. gaigei , one as C. loubetsiensis , one as C. subarquatus , six as Cubitermes sp. and 13 not identified.

This species also includes C. aff. subarquatus “spB” (in Roy et al. 2006).

Syntypes of Cubitermes planifrons Sjöstedt, 1924

DEMOCRATIC REPUBLIC OF THE CONGO • soldier, worker; Mukimbungu; 5°8.5′ S, 14°2.3′ E; 25 Oct. 1904; K.E. Laman leg.; study code: DJ 0296; initially C. planifrons → C. fungifaber ; AMNH.

Krishna et al. (2013: 1931) report imagines in the AMNH syntype but the sample that was examined did not contain any. They also mention that another syntype subsample is deposited in NHRM, not examined.

Paratypes from type colony of Cubitermes fungifaber var. elongata Sjöstedt, 1924 DEMOCRATIC REPUBLIC OF THE CONGO • soldier, worker; Mukimbungu; 5°8.5′ S, 14°2.3′ E; ca 1904; K.E. Laman leg.; study code: DJ 0270; initially C. fungifaber var. elongata ; AMNH

Krishna et al. (2013: 1931) mention that another syntype subsample is deposited in NHRM (not examined).

Paratypes of Mirotermes ( Cubitermes) gaigei Emerson, 1928

CAMEROON • soldier, worker; Bipindi; 3°5′ N, 10°24.5′ E; 1920; G. Zenker leg.; study code: DJ 0274; initially C. gaigei → C. fungifaber ; AMNH • soldier, worker; Bipindi; 3°5′ N, 10°24.5′ E; 1920; G. Zenker leg.; study code: DJ 0288; initially C. gaigei → C. fungifaber ; AMNH.

Paratypes of Cubitermes loubetsiensis Sjöstedt, 1924

CONGO REPUBLIC • soldier; Loubetsi; 3°12′ S, 12°10′ E; 1924; Nilsson leg.; study code: DJ 0611; initially C. loubetsiensis → C finitimus ; AMNH • soldier; Loubetsi; 3°12′ S, 12°10′ E; [no date]; Kranz leg.; study code: DJ 0281; initially C. loubetsiensis ; NHMM.

Other material examined

ANGOLA • soldier, worker, ♀ (alate); Quimucanda ; 8°5.14′ S, 15°7.43′ E; 28 Nov. 2024; J. Šobotnik leg.; study code: DJ 0973; BE_ RMCA _INS. Iso. 059898 .

CAMEROON • soldier, worker; Bipindi ; 3°5′ N, 10°24.5′ E; 1903; G. Zenker leg.; study code: DJ 0961; initially Eutermes zenkeri ; RBINS • soldier, worker, ♀ (queen); Bipindi ; 3°5′ N, 10°24.5′ E; 1920; G. Zenker leg.; study code: DJ 0276; initially C. fungifaber ; AMNH • soldier; 45 km from Abong-Mbang ; 5°16′ N, 17°38′ E; 1 Jul. 1948; P.-P. Grassé and C. Noirot leg.; study code: DJ P195; MNHN EP9900 • soldier, worker, ♂ (alate); Réserve forestière de Nyong; 3°33′ N, 11°37′ E; 5 Dec. 1949; J. Birkett-Smith and J. Dahl leg.; study code: DJ 0678; initially C. subarquatus ; NHMUK 13671991 • soldier; Eboufek ; 3°30′ N, 11°53′ E; 1 Dec. 1962; G. Becker leg.; study code: DJ U066; initially C. banksi ; NHMUK 13671829 • soldier; Akok ; 3°53′ N, 11°57′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U096; initially C. bulbifrons ; NHMUK 13671844 • soldier; Akok ; 3°53′ N, 11°57′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U097; initially C. bulbifrons ; NHMUK 13671841 • soldier; Bilik ; 3°31′ N, 11°17′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U067; initially C. banksi ; NHMUK 13671832 • soldier, ♂ (king); Bilik ; 3°31′ N, 11°17′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U091; initially C. banksi ; NHMUK 13671827 • soldier, worker; Bilik ; 3°31′ N, 11°17′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0705; initially C. banksi ; NHMUK 13671830 • soldier; Ebogo ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U093; initially C. banksi ; NHMUK 13671833 • soldier; Ebogo ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U119; initially C. gaigei ; NHMUK 13671904 • soldier, worker; Ebogo ; 3°23′ N, 11°28′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0703; initially C. banksi ; NHMUK 13671834 • soldier; Mbalmayo ; 3°28′ N, 11°31′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ U118; initially C. gaigei ; NHMUK 13671903 • ♀ (queen); Mbalmayo ; 3°31′ N, 11°30′ E; ca 1995; P. Eggleton et al. leg.; study code: DJ 0724; initially C. gaigei ; NHMUK • soldier, worker; Nsimi ; 3°10′ N, 11°58′ E; Nov. 1996; M. Harry leg.; study code: DJ 0754; GenBank no PQ679239 (mitogenome); MNHN EP9901 • soldier, worker; Nsimi ; 3°10′ N, 11°58′ E; Nov. 1996; M. Harry leg.; study code: DJ 0755; GenBank no PQ679178 (mitogenome); MNHN EP9902 • soldier; Dja forest ; 3°20.63′ N, 12°43.03′ E; 30 Mar. 2015; J. Šobotnik leg.; study code: DJ B321; BE RMCA INS. Iso. 059347 • soldier; Dja Rock ; 3°20.73′ N, 12°42.84′ E; 30 Mar. 2015; J. Šobotnik leg.; study code: DJ B319; BE RMCA INS. Iso. 059348 • soldier, worker; near Somalomo ; 3°20.7′ N, 12°42.8′ E; 30 Mar. 2015; J. Šobotnik leg.; study code: DJ 0259; BE RMCA INS. Iso. 059356 • soldier, worker; Ebogo ; 3°22.95′ N, 11°27.718′ E; 22 May 2017; Y. Roisin leg.; study code: DJ 0509; BE RMCA INS. Iso. 059361 • soldier, worker; Ebogo ; 3°22.772′ N, 11°27.899′ E; 24 May 2017; Y. Roisin leg.; study code: DJ 0518; BE RMCA INS. Iso. 059362 • soldier, worker, ♂ (king); Ebogo ; 3°22.914′ N, 11°27.8′ E; 26 May 2017; Y. Roisin leg.; study code: DJ 0519; GenBank no PQ679176 (mitogenome); BE RMCA INS. Iso. 059363 • soldier, worker; Yolo-Chimpa ; 5°35.136′ N, 10°53.301′ E; 30 May 2017; Y. Roisin leg.; study code: DJ 0508; GenBank nos MN646726 ( COI), MN685929 ( COII), MN685990 ( 28S); BE RMCA INS. Iso. 059364 • soldier, worker; Akometa ; 3°28.194′ N, 11°32.814′ E; 6 Jun. 2017; Y. Roisin leg.; study code: DJ 0507; GenBank nos MN646725 ( COI), MN685928 ( COII), MN685989 ( 28S), PQ679210 (mitogenome); BE RMCA INS. Iso. 059365 • soldier, worker, ♂ (king), ♀ (queen); Ebogo ; 3°22.935′ N, 11°27.793′ E; 7 Jun. 2017; Y. Roisin leg.; study code: DJ 0511; BE RMCA INS. Iso. 059366 • soldier, worker; Nguinda ; 4°15′ N, 12°11′ E; 23 Nov. 2023; J. Šobotnik leg.; study code: DJ 0954; GenBank no PV564654 (mitogenome); BE RMCA INS. Iso. 059489 • soldier, worker; Nguinda ; 4°15′ N, 12°11′ E; 25 Nov. 2023; J. Šobotnik leg.; study code: DJ 0951; GenBank no PV564644 (mitogenome); BE RMCA INS. Iso. 059372 • soldier, worker; Nguinda ; 4°15′ N, 12°11′ E; 25 Nov. 2023; J. Šobotnik leg.; study code: DJ 0953; GenBank no PV564645 (mitogenome); BE RMCA INS. Iso. 059488 • soldier, worker; Nguinda ; 4°15′ N, 12°11′ E; 3 Dec. 2023; J. Šobotnik leg.; study code: DJ 0950; GenBank no PV564653 (mitogenome); BE RMCA INS. Iso. 059373 • soldier; Nguinda ; 4°15′ N, 12°11′ E; 3 Dec. 2023; J. Šobotnik leg.; study code: DJ 0957; GenBank no PV564659 (mitogenome); BE RMCA INS. Iso. 059155 .

CENTRAL AFRICAN REPUBLIC • soldier; Boukoko ; 3°54′ N, 17°55′ E; 21 Jun. 1948; P.-P. Grassé and C. Noirot leg.; study code: DJ P185; MNHN EP9898 • soldier; Boukoko ; 3°54′ N, 17°55′ E; 21 Jun. 1948; P.-P. Grassé and C. Noirot leg.; study code: DJ P186; MNHN EP9899 • soldier, worker, ♀ (alate); Bounguélé ; 3°57′ N, 16°45′ E; 12 May 2007; N. Sion leg.; study code: DJ 0931; BE RMCA INS. Iso. 059355 .

CONGO REPUBLIC • soldier; Ouesso ; 1°37′ N, 16°1′ E; 27 Dec. 1956; P.-P. Grassé and C. Noirot leg.; study code: DJ P168; MNHN EP9896 • soldier, worker; Dimonika ; 4°12′ S, 12°20′ E; 21 Apr. 1983; C. Noirot leg.; study code: DJ 0930; MNHN EP9894 • soldier, worker, ♀ (queen); Loundoungou ; 2°22.973′ N, 17°4.298′ E; 3 Dec. 2017; Y. Roisin leg.; study code: DJ 0526; GenBank nos MN646728 ( COI), MN685931 ( COII), MN685992 ( 28S); BE RMCA INS.Iso.059357 • soldier, worker; Loundoungou ; 2°22.929′ N, 17°4.301′ E; 4 Dec. 2017; Y. Roisin leg.; study code: DJ 0524; GenBank no PQ679227 (mitogenome); BE RMCA INS.Iso.059358 • soldier, worker; Mokabi ; 3°8.795′ N, 16°57.826′ E; 6 Dec. 2017; Y. Roisin leg.; study code: DJ 0523; GenBank nos MN646727 ( COI), MN685930 ( COII), MN685991 ( 28S); BE RMCA INS.Iso.059359 • soldier, worker; Mokabi ; 3°9.022′ N, 16°58.214′ E; 8 Dec. 2017; Y. Roisin leg.; study code: DJ 0525; GenBank no PQ679194 (mitogenome); BE RMCA INS.Iso.059360 • soldier, worker; Loundoungou ; 2°22.93′ N, 17°4.301′ E; Dec. 2018; S. Lenz leg.; study code: DJ 0767; GenBank no PV564648 (mitogenome); BE RMCA INS.Iso.059371 .

DEMOCRATIC REPUBLIC OF THE CONGO • soldier; Mekambo ; 1°1′ N, 13°56′ E; 8 Jan. 1957; P.- P. Grassé and C. Noirot leg.; study code: DJ P171; MNHN EP9897 • soldier; Forêt de Djidji ; 0°13′ N, 11°48′ E; 26 Jan. 1957; P.-P. Grassé and C. Noirot leg.; study code: DJ P162; GenBank no PQ679182 (mitogenome); MNHN EP9895 • soldier; Route Makokou-Mekambo ; 0°41′ N, 13°2′ E; 6 Jun. 1962; J. Deligne leg.; study code: DJ U099; initially C. gaigei ; NHMUK 13671888 • soldier; Forêt des Abeilles ; 0°19′ S, 12°7′ E; 1995; C. Bordereau (?) leg.; study code: DJ P218; MNHN EP9891 • soldier; Forêt des Abeilles ; 0°19′ S, 12°7′ E; 1995; C. Bordereau (?) leg.; study code: DJ P219; MNHN EP9892 • soldier; Forêt des Abeilles ; 0°19′ S, 12°7′ E; 1995; C. Bordereau (?) leg.; study code: DJ P221; MNHN EP9893 • soldier, worker; Forêt des Abeilles ; 0°35′ S, 12°25′ E; 1995; C. Bordereau and A. Robert leg.; study code: DJ 0861; MNHN EP9889 • soldier, worker; Forêt des Abeilles ; 0°19′ S, 12°7′ E; 1995; C. Bordereau and A. Robert leg.; study code: DJ 0863; MNHN EP9890 • soldier; La Lopé N.P.; 0°15′ S, 11°35′ E; 6 Mar. 1998; M. Harry leg.; study code: DJ P236; MNHN EP9910 • soldier; La Lopé N.P.; 0°9′ S, 11°36′ E; 7 Mar. 1998; M. Harry leg.; study code: DJ P227; MNHN EP9904 • soldier; La Lopé N.P.; 0°15′ S, 11°35′ E; 7 Mar. 1998; M. Harry leg.; study code: DJ P247; MNHN EP9915 • worker; La Lopé N.P.; 0°12.7′ S, 11°33.5′ E; 7 Mar. 1998; M. Harry leg.; study code: DJ 0632; GenBank nos DQ246542 ( COII), DQ246524 ( ITS2), PQ679220 (mitogenome); initially C. aff. subarquatus “spB” (cf. Roy et al. 2006); MNHN EP9919 • soldier; La Lopé N.P.; 0°9′ S, 11°36′ E; 9 Mar. 1998; M. Harry leg.; study code: DJ P229; MNHN EP9905 • soldier, worker; La Lopé N.P.; 0°15′ S, 11°35′ E; 9 Mar. 1998; M. Harry leg.; study code: DJ 0624; GenBank nos DQ127312 ( COII), DQ246520 ( ITS2), PQ679183 (mitogenome); initially C. aff. subarquatus “spB” (cf. Roy et al. 2006); MNHN EP9918 • soldier, worker; Doda (north of La Lopé N.P.); 0°4.5′ S, 11°25.5′ E; 10 Mar. 1998; M. Harry leg.; study code: DJ 0923; MNHN EP9903 • soldier; La Lopé N.P.; 0°12′ S, 11°33′ E; 11 Mar. 1998; M. Harry leg.; study code: DJ P233; MNHN EP9908 • soldier; La Lopé N.P.; 0°12′ S, 11°33′ E; 11 Mar. 1998; M. Harry leg.; study code: DJ P234; MNHN EP9909 • soldier; La Lopé N.P.; 0°15′ S, 11°35′ E; 11 Mar. 1998; M. Harry leg.; study code: DJ P248; MNHN EP9916 • soldier; La Lopé N.P.; 0°9′ S, 11°41′ E; 15 Mar. 1998; M. Harry leg.; study code: DJ P230; MNJN EP9906 • soldier; La Lopé N.P.; 0°9′ S, 11°41′ E; 15 Mar. 1998; M. Harry leg.; study code: DJ P231; MNHN EP9907 • soldier, ♀ (queen); La Lopé N.P.; 0°15′ S, 11°35′ E; 15 Mar. 1998; M. Harry leg.; study code: DJ P245; MNHN EP9914 • worker, ♂ (king); La Lopé N.P.; 0°15′ S, 11°35′ E; 15 Mar. 1998; M. Harry leg.; study code: DJ P250; MNHN EP9917 • soldier, ♀ (queen); La Lopé N.P.; 0°15′ S, 11°35′ E; 16 Mar. 1998; M. Harry leg.; study code: DJ P238; MNHN EP9912 • soldier; La Lopé N.P.; 0°15′ S, 11°35′ E; 16 Mar. 1998; M. Harry leg.; study code: DJ P240; MNHN EP9913 • soldier; La Lopé N.P.; 0°15′ S, 11°35′ E; 23 Mar. 1998; M. Harry leg.; study code: DJ P237; MNHN EP9911 • soldier, worker; Nkobissimo [= Nkolmengboua?]; 2°14.3′ N, 11°29.25′ E; 15 Apr. 2017; G. Trembleau leg.; study code: DJ 0455; GenBank nos MN646724 ( COI), MN685927 ( COII), MN685988 ( 28S); BE RMCA INS. Iso. 059354 .

Historical review

Sjöstedt (1924b: 255–256) briefly described the soldier of this species under the name Cubitermes planifrons . Two years later, Sjöstedt (1926: 243–244) provided more detailed descriptions of all three castes, housing the species in the sub-family Termitinae . He included (1926: 218–226) C. planifrons in imagines’ and soldiers’ keys of Cubitermes species and inserted it in a “ fungifaber -Gruppe” of species with a not protruding soldier’s frons.

Snyder (1949: 162) catalogued this species under the name Cubitermes planifrons and housed it in the sub-family Termitinae .

This is one of the species that Ruelle (1992: 500) called “forgotten species”.

Krishna et al. (2013: 1931) housed Cubitermes planifrons in the sub-family Cubitermitinae . Following Emerson’s “card catalog”, they mentioned that this species might become a junior synonym of C. fungifaber ; however, this synonymy could not be accepted because C. planifrons and C. fungifaber belong to different valve pattern groups: Josens & Deligne (2019: 42–44) placed this species within the finitimus valve pattern group.

Hellemans et al. (2021: 233) placed this species in the restored genus Isognathotermes .

Cubitermes aff. subarquatus “spB” was mentioned by Roy et al. (2006) in La Lopé National Parc, Gabon. On a genetical base, it was considered a cryptic species. Hellemans et al. (2021: 233) placed this species in the restored genus Isognathotermes as synonym of I. planifrons .

Redescription

Imago

COLOUR. Head capsule: well sclerotised, fresh samples very dark, C7–C8 (C6–C 7 in long preserved imagines); fontanelle concolorous with or slightly paler than head capsule. Postclypeus C6–C7 slightly paler (one level) than head capsule. Antennae C5–C6 without any difference between proximal and distal articles. Thorax: pronotum C6–C7 as postclypeus, generally one level paler than head capsule; meso- and metanotum C5–C6, concolorous with or somewhat paler than pronotum. Legs C3–C5; tibia usually slightly (one level) darker than femur. Wings hyaline with brown to grey tinge (Cf3–Cf4), anterior veins darker. Abdomen: tergites C6–C7. Sternites appreciably paler in middle (C2–C5) with both sides darker (C4–C6); posterior sternites darker (C4–C6) than anterior.

SETATION. Head capsule, with some prominent setae set amongst a high density of short, fine setae forming a dense mat. Labrum and postclypeus with some prominent setae mixed with shorter ones. Antennae with some prominent setae, some more numerous smaller setae and, mainly distally on most articles, a bunch of very fine, bent setae (visible only at high magnification, 50 × or more). Thorax: pronotum with prominent setae mainly on margins and shorter ones in middle; meso- and metanotum with some fine, pale setae, arranged in a medio-longitudinal strip, generally visible at 20–40×. Legs very pilose, furnished (among numerous fine setae) with some stronger setae: 6–10 on the carina of fore coxa and 1–4 on the ventral side of fore coxa and sometimes also some on trochanter; tibia pilose fore, mid, and hind tibia furnished with 15–30 spines and bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively. Abdomen: tergites with many large and small setae. Sternites with long setae, erect or directed slightly forward, and many long and smaller setae directed backwards.

STRUCTURE (measurements in Table 12; Figs 26–27, 57). Size: the imagines of I. planifrons are, on average, among the medium-sized of the genus Isognathotermes ( Fig. 26). Head capsule: compound eyes nearly round; ocelli nearly round to oval, removed from eyes by a distance about equal to 0.7– 1.2 ocellus small diameter; fontanelle generally a tiny round marking. Antennae: 16 articles on alate individuals, always shortened by amputation in queens and kings. Labrum: cupola shaped. Left mandible with apical tooth on average rather small in comparison with other species of the genus ( Fig. 27) and always more prominent than first marginal; marginal teeth three in number but second one only suggested by an undulation of edge between first and third marginal teeth; only the apical tooth is acute in unworn specimens; premolar tooth with proximal end obscured or partly obscured by molar prominence in dorsal view; molar tooth bearing a rounded molar prominence dorsally and ending posteriorly in a tiny acute apophysis. Right mandible with apical tooth always more prominent than first marginal; marginal teeth two in number; first marginal tooth well developed with a sharp tip when fresh; second marginal tooth smaller and with a blunt tip even when fresh; molar tooth bearing a ventral rounded flange and ending posteriorly in a kind of heel. Thorax: pronotum appreciably wider than long and narrower than head width (including the eyes), straight to very weakly sellate with anterior lobe short and very slightly elevated. Fore coxa flanged ventrally resulting in a more or less sharp carina. Wings: R1 fused entirely with costal margin, sclerotised; Rs simple, sclerotised; M and Cu not or weakly sclerotised with 3–4 and 10–11 branches respectively. Gut: enteric valve not studied.

Soldier

COLOUR. Head capsule generally tending towards deep palette (Cd4–Cd5) becoming fader in long preserved samples; there is always a gradient from a darker frons to a paler back (e.g., from C5 to C4), smooth and extended in 60% of the samples examined but more abrupt in the remaining 40% giving the impression that the head capsule is bicolorous (as in Fig. 13). Antennae and labrum sometimes concolorous or one level paler than head capsule. Mandibles dark (C6–C8) generally with an abrupt clearing on their bases (two palette levels) which is generally the same colour as frons. Thorax and legs paler than head capsule (C2–C4) somewhat darker in long preserved samples. Abdomen grey to red-brown owing to digestive bolus.

SETATION. Head capsule with few scattered setae; on frons a dense bunch of setae surrounds and overhangs fontanelle. Antennae with some prominent setae, more numerous smaller setae and at distal extremity of distal articles, a bunch of very fine, bent setae (visible only at high magnification, 50 × or more). Labrum always with some large setae on lobes. Thorax: pro- and mesonotum with a small number of setae mainly located on margins. Legs: fore coxa bears at least one fine seta and not any spines in some (10%) samples examined but generally furnished with 1–4 spines on carina and no spines on ventral side; trochanter generally with some long lined-up setae, sometimes with five or six spines; fore, mid, and hind tibia bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively (the latter sometimes weakly developed) and a row of 6–15 spines along their shaft. Abdomen: tergites with some large setae, mainly or only on their posterior margins. Sternites with long setae, erect or slightly directed forward, often coloured, and smaller setae directed backwards.

STRUCTURE (measurements in Table 12; Figs 28, 58). Size: the soldiers of I. planifrons are medium sized in the genus Isognathotermes ( Fig. 28). Head capsule: always clearly sclerotised; appreciably longer than wide. Dorsal view: lateral sides subparallel with a narrowing near posterior third or fourth; from antennal sockets sides converge more or less clearly towards bases of mandibles; posterior side regularly rounded or (in 56% of the samples examined) with a short straight part in the middle. Upper profile almost always slightly concave; angle between extended mandibles and frons always a little obtuse; frons generally (88%) without any anterior hump, rarely with a slight hump. Gulamentum in ventral view always constricted in its posterior half, with sides of anterior part either roundly convex or forming an acute widening or even (in 36% of the samples studied) a kind of ear on each side. Antennae: of 15 articles. Labrum: always deeply bifurcate and wider than long, with sides varying from lyre shaped (in 92% of the samples examined) to straight; lobes angular, frequently with fine, whitish or translucent tips; anterior margin concave. Mandibles: sabre-like, strongly curved (on average, I. fungifaber , and I. planifrons , have the highest left mandible apical curvature index in the genus Isognathotermes ); inner edges generally smooth with one distinct but generally very small marginal tooth, near molar tooth on each mandible; mandibles clearly shorter than head; entire surface of both mandibles smooth and glossy. Right mandible generally slightly more curved than left. Thorax: pronotum sellate, as wide as 56–64% of head width, with generally entire anterior and posterior margins. Fore coxa flanged ventrally resulting in a more or less sharp carina. Gut: enteric valve seating on left side, best seen in ventral view, situated in second half of abdomen. Arrangement of enteric valve cushions showing trilateral symmetry, the odd cushions being about 20% longer than the even cushions, generally without any crest or with crests very weakly developed. Caecum always rather small, best seen in ventral view, near centre of abdomen, shortly lobed.

Worker

COLOUR. Head capsule pale (C1–C3) turning grey in long preserved samples. Antennae: proximal articles pale (C2–C3), distal articles always one to two levels darker (C4–C5). Thorax, nota and legs pale (C1–C3). Abdomen grey to red-brown owing to digestive bolus.

SETATION. Head capsule and postclypeus with few, erect, scattered setae. Labrum with few, robust scattered setae. Antennae with some prominent setae, some more numerous smaller setae and at distal extremity of distal articles, a bunch of fine, bent setae (visible only at high magnification, 50 × or more). Thorax: nota with some scattered setae. Legs: fore coxa carinated, bearing one fine seta and furnished with 3–5 spines on carina and generally 1, rarely 2 or 3 spines on ventral side; fore trochanter with 5–7 spines; fore, mid, and hind tibia bearing 3, 2, 2 apical spurs and 0, 2, 0 subapical spurs respectively (the latter sometimes weakly developed) and a row of spines. Abdomen: tergites with scattered setae. Sternites with long setae, erect or slightly directed forward, often coloured, and smaller setae directed backwards.

STRUCTURE (measurements in Table 12; Figs 30, 59). Size: the workers of I. planifrons are, on average, medium sized in the genus Isognathotermes with large overlapping on several other species ( Fig. 30). Head capsule: weakly sclerotised (except mandibles). Antennae of 14.5 articles. Labrum: cupola shaped. Left mandible: apical tooth well developed with a sharp tip when fresh; marginal teeth three in number, first marginal tooth well developed but with a blunt tip even when fresh, second marginal tooth faint (visible as an undulated edge and disappearing in worn mandibles), third marginal tooth with a blunt tip; premolar tooth with its proximal end generally hidden under molar prominence; molar tooth bearing a rounded molar prominence dorsally and ending posteriorly in a tiny acute apophysis. Right mandible: apical tooth well developed with a sharp tip when fresh; marginal teeth two in number; first marginal tooth well developed with a sharp tip when fresh; second marginal tooth smaller and with a blunt tip even when fresh; molar tooth bearing a ventral rounded flange and ending posteriorly in a kind of heel. Thorax: pronotum sellate, as wide as 63–76% of head width. Fore coxa flanged ventrally resulting in a sharp carina. Gut: enteric valve seating on left side, best seen in ventral view, situated in second half of abdomen. Arrangement of enteric valve cushions of the finitimus pattern with triradial symmetry: the odd PCs, in their downstream part, are wide and bear at that place a high density of rather short bristles on a globular bulge; supporting bristles are generally numerous: 17–31 on each side of the odd PCs; secondary cushions are wide at the upstream end, narrowing noticeably downstream with a homogeneous spine scattering. Caecum always rather small, visible in ventral view, near centre of abdomen, shortly lobed (generally three small lobes).

Chorology-ecology

The geographic distribution of I. planifrons is linked with humid, evergreen forest environments up to 800 km from the Atlantic coast: it includes the Atlantic equatorial coastal forests and the northwestern Congolian lowland forests ecoregions ( Fig. 47). This distribution is partly similar to that of I. fungifaber (but with another EVA).

Molecular data

Sixteen mitogenomes of the morphological species I. planifrons are published alongside this work (GenBank accessions: see Supp. file 3 and ‘Material examined’). The morphological species I. planifrons appears to be genetically heterogeneous, with sample DJ P141 differing from the others by a dissimilarity of over 2%, which probably makes it a cryptic species, but as it is currently unique, it has not yet been described and was moved as I. aff. planifrons in the Incertae sedis chapter. Surprisingly, two samples of I. planifrons (DJ 0754 and DJ 0755) as well as I. aff. planifrons (DJ P141) were collected almost in the same place (between Nsimi and Zoétélé, Cameroon).

After having discarded DJ P141 (which is slightly more similar to I. phallicaecalis sp. nov. and I. phalloides sp. nov.), the fifteen remaining mitogenomes exhibited a dissimilarity of up to 2.1% with each other (Supp. file 4). Our present sampling includes full mitogenomes from Gabonese samples previously published under the appellation Cubitermes aff. subarquatus “spB” by Roy et al. (2006). This species “spB” was already reassigned to I. planifrons by Hellemans et al. (2021) based on COII phylogeny (accession DQ127312 ).