Tangana asymmetrica Ramme, 1929

Hemp, Claudia, Ritchie, J. Mark, Cigliano, Maria Marta, Heller, Klaus-Gerhard, Warchalowska-Śliwa, Elżbieta, Grzywacz, Beata, Linde, Jackson, Uluar, Onur, Ngoute, Charly Oumarou & Song, Hojun, 2025, Out of sight, out of mind? Ixalidiidae, a new family of African forest grasshoppers (Orthoptera, Acridoidea) revealed by molecular phylogenetics and genital morphology, Zoosystema 47 (24), pp. 489-553 : 525-531

Tangana asymmetrica Ramme, 1929

( Figs 1; 4C; 5H; 12 D-G; 16; 17; 20B; 21H-J; 22F; Table 12 )

Tangana asymmetrica Ramme, 1929: 310 .

Ixalidium asymmetricum – Ramme 1929; incorrectly synonymised by Uvarov (1941: 30); recalled from synonymy by Johnsen & Forchhammer (1975: 38).

TYPE MATERIAL EXAMINED. — Holotype. Tanzania • ♂; Tanga; A. Karasek; MfN.

Paratype. Tanzania • ♀; Tanga; [ 5°4’S, 39°6’E]; A. Karasek leg.; NHMUK • 2♂; Tanga; [ 5°4’S, 39°6’E]; A. Karasek leg.; MfN, Berlin .

OTHER MATERIAL EXAMINED. — Tanzania • 4♂; Korogwe, Handeni, Kwa Mbisi ; 5°25’27”S, 38°1’10”E; 18.IX.1952; E. Burtt leg.; NHMUK • 6♂, 3 ♀; Korogwe, Handeni, Kwa Mbisi ; 5°25’27”S, 38°1’10”E; 20.IX.1952; E. Burtt leg.; NHMUK • 1 ♀; Tanzania, Korogwe, Handeni , Kwa Mbisi ; 5°25’27”S, 38°1’10”E; 19.IX.1952; E. Burtt leg.; NHMUK • 1 ♂; Morogoro District, Kingolwera [Kingolwira] ; 6°47’S, 37°46’E; 7.XII.1953; E. Burtt leg.; NHMUK • 1 ♂; Morogoro District, same collection data as for preceding; 10.IX.1952; E. Burtt leg.; NHMUK • 1 ♀; same collection data as for preceding; 18.XII.1953; E. Burtt leg.; NHMUK • 2 ♀, 1 nymph; Muheza District, Mlingano, Ngomeni ; 5°09’00”S, 38°53’60.0”E; IV.1952; J. Phipps leg.; NHMUK • 1 ♂; same collection data as for preceding; III.1952; J. Phipps leg.; rubber bush; NHMUK • 2♀; same collection data as for preceding; 9.IV.1952; J. Phipps leg.; NHMUK • 1 ♀; same collection data as for preceding; 30.III.1952; J. Phipps leg.; NHMUK • 1 ♀; same collection data as for preceding; V.1953; J. Phipps leg.; NHMUK • 1 ♂, 1♀; Dar es Salaam; 6°48’S, 39°17’E; 24.I.1964; E. Burtt leg.; NHMUK • 1 ♂, 1♀; same collection data as for preceding; 26.I.1964; E. Burtt leg.; NHMUK • 3♂, 7 ♀; same collection data as for preceding; 27.I.1964; E. Burtt leg.; NHMUK • 1 ♂, 2 ♀; same collection data as for preceding; 28.I.1964; E. Burtt leg.; NHMUK • 1 ♂, 3 ♀; same collection data as for preceding; 29.I.1964; E. Burtt leg.; NHMUK • 1 ♂, 1 ♀; same collection data as for preceding; 30.I.1964; E. Burtt leg.; NHMUK • 2 ♂, 5 ♀; same collection data as for preceding; 31.I.1964; E. Burtt leg.; NHMUK • 4 ♀; same collection data as for preceding; 1.II.1964; E. Burtt leg.; NHMUK • 1 ♀; same collection data as for preceding; 27.II.1964; E. Burtt leg., NHMUK • 1 ♂; Dar es Salaam, University Campus ; 17.II.1998; A. Hochkirch leg.; under trees; Coll. AH • 1 ♂; Pangani District, Kigombe [Sisal] Estate; 5°19’S, 39°1’59”E; III.1952; J. Phipps leg.; NHMUK • 14 ♂, 9 ♀, 3 nymphs; Nguru Mountains, above Turiani ; 6°09’S, 37°36’E; 5-7.XI.1964; N. D. Jago leg.; montane forest; NHMUK • 12 ♂, 7 ♀, 3 nymphs; Nguru Mountains, east foot, Mtibwa Forest Reserve, near Turiani ; 6°07’S, 37°39’E; 5.XI.1964; N. D. Jago leg.; dry woodland; NHMUK • 1 ♂, 1 ♀; Kisarawe, Kazimzumbwi Forest Reserve ; I.2016; C. Hemp leg.; lowland wet forest; Coll. CH • 1 ♂; same collection data as for preceding; V.2016; C. Hemp leg.; Coll. CH • 1 ♀; same collection data as for preceding; VIII.2017; C. Hemp leg.; Coll. CH • 1 ♀; Pangani Coast, Turtle Beach ; < 100 m a.s.l.; 5°24’S, 38°59’E; I.2000; C. Hemp leg.; Küstenwaldboden [coastal forest floor]; Coll. CH • 2 ♂; Pangani Coast, Turtle Beach ; < 100 m a.s.l.; XII.2000; C. Hemp leg.; Waldrest [forest remnant]; Coll. CH • 1 ♀; Pangani Coast, zw. Kabuko-Mwera ; 300 m a.s.l.; II.2000; C. Hemp leg.; Küstenwald [coastal forest]; Coll. CH • 1♂; Pangani Coast, Caspary Grundstück [Caspary property]; IX.2011; C. Hemp leg.; Waldboden [forest floor]; Coll. CH • 3 ♂, 1 nymph; Udzungwa Mts, Sanje trail ; 7°45’54.3”S, 36°53’23.9”E; [ 886 m a.s.l.]; 5.XII.1997; A. Hochkirch leg; grasses; Coll. AH • 1♂; Nguru Mts, Site T1 ; 30.I.1998; A. Hochkirch leg.; litter under mango tree; Coll. AH • 1 ♂; same collection data as for preceding; 3.II.1998; A. Hochkirch; Coll. AH .

Kenya • 7 ♂, 6 ♀; Tana River District, Tana River Primate National Reserve, Mchelelo Forest ; 1°53’S, 40°08’E; 4-6.II.1990; J. M. Ritchie , M. N. Mungai, J. Muli leg.; NHMUK • 1♂; Kwale District, Dzombo [Jombo] Hill, upper slope, north side ; 4°26’S, 39°13’E; 1000-1300 ft a.s.l.; 30.I.1990; J. M. Ritchie , M. N. Mungai, J. Muli leg.; forest; NHMUK • 2 ♂, 5 ♀; Lamu District, Witu Forest Reserve, 5 km E of Witu ; 2°23’S, 40°29’E; 150 ft a.s.l.; 10.VI.1975; I. A. D. & A. Robertson leg.; NHMUK .

REDESCRIPTION

Small to medium size ( Table 12 ), but typically larger than Ixalidium . Males 22-26 mm; females 27.5-31.5. Integument rugose and punctate.

Head

Antennae differentiated ( Dirsh 1965), 17-segmented, about as long as head and pronotum together, basal segments (apart from scape and pedicel) dorso-ventrally compressed, ensiform, widening markedly at segment three, widest between 3 and 6, with 8-9 distinctly less compressed and 10-17 filiform.

Head width across eyes distinctly less than pronotum length and less than pronotum width at its hind margin; head obliquely slanted in lateral view, with vertex produced and frons forming shallow obtuse angle between antennae; eyes ovoid, narrower above, oblique. Fastigium of vertex from above ( Fig. 4C) projecting over lateral ocelli and antennal bases, its maximal basal width about 1.5 times its length, with narrowly rounded rectangular apex, more angular than Ixalidium and Rowellacris Ritchie & Hemp n. gen.; median carinula cut by indistinct irregular transverse sulcus at base of fastigium, continuing onto occiput; foveolar area obsolete; frontal ridge in anterior view narrowest immediately below vertex, becoming sulcate with lateral carinae, widening between antennae, then narrowing above median ocellus; carinae subparallel below ocellus, becoming divergent and obsolete towards clypeus.

Thorax

Pronotum low tectiform, median carina crossed by 2 sulci; prozona 3-4 times longer than metazona; dorsum from above widening steadily from fore margin to hind margin. Prosternal tubercle transverse, tapered, wedge-shaped, widening laterally towards apex, sparsely setose, anterior face oblique, flat to slightly concave, posterior face vertical, flat to slight convex; apical margin slightly trilobate, with rounded angles. Meso- and metanotum tectiform, slightly raised, with median carina; mesonotum short, partly covered by metazona of pronotum, with lateral tegminal rudiments often concealed by metazona; metanotum with distinct longitudinal lateral carinae forming sharp angle at upper margin of epimeron 3; episternum 3 forming robust lateral projections above hind coxae. Mesosternal interspace broader than its length, widening posteriorly; mesosternal furcal suture with medial and lateral pits narrow. Metasternal interspace slightly broader than its length, narrowing posteriorly, tending to form two separate pits with medial portion of interspace continuous anteriorly with anterior portion of metasternum.

Legs Fore and mid legs of typical acridoid appearance, unspecialized. Hind femur moderately robust, 3.2-3.7 times as long as maximum depth, male; 3.4-3.8 times, female ( Table 12 ); hind knee with upper and lower lobes bluntly rounded; hind tibia with 7-8 outer and 9-10 inner spines; external apical spine absent; arolium large, rounded, in ventral view about as long as claw; claws thickened at base, apically strongly curved.

Abdomen

Tergites tergites medially carinate, each segment in lateral view dorsally convex, tergites 1 and 2 slightly inflated, together with metathorax forming slight hump; tympanum large, sub-oval, with ventral margin flattened or slightly concave; tergites 9 and 10 fused laterally.

External terminalia ( Fig. 5H). Abdominal tergites 9 and 10 and corresponding sternites heavily sclerotised, somewhat inflated, fused with basal portion of supra-anal plate ( Fig. 5H), which is distinctly asymmetrical, displaced to right side, overlaying and largely obscuring right cercus, its dorsal surface produced into long curved tapering process or prong; junction between basal and apical portions of supra-anal plate reflexed antero-ventrally beneath basal portion; reduced apical portion of supra-anal plate projecting caudad between tips of paraprocts, or concealed to a variable degree by antero-dorsal margin of subgenital plate; subgenital plate subconical, upwardly directed, with ventral margin concave, in lateral view tapering to acute point at apex, with short dorso-medial longitudinal sulcus broadening into marginal cleft on anterior edge.

Male genitalia

Epiphallus ( Figs 16A; 17 M-S) recessed within invagination of epiphallic membrane (epiphallic infold ( Eades 2000)), folding around and partially obscuring it when genital complex initially exposed; bridge of epiphallus extending internally capitad into two dorso-ventrally flattened spathulate apodemes, one above the other, arising from antero-dorsal and antero-ventral edges of bridge; apodemes approximately triangular viewed from above, with bridge and lateral plates of epiphallus forming short base of triangle distally; epiphallic apodemes in dorsal view ( Fig. 17P, Q, R) often markedly asymmetric, more developed on left side; In lateral view dorsal and ventral epiphallic apodemes either parallel with narrow interspace between them ( Fig. 17M) or dorsal apodeme diverging from ventral apodeme by about 20° ( Fig. 17N), or both apodemes curving away from each other by up to 45° ( Fig. 17O); epiphallic infold of ectophallic membrane divided by bridge of epiphallus and its apodemes into two subtriangular horizontal pouches, one above dorsal epiphallic apodeme and one below ventral apodeme; both pouches fol - low triangular form of dorsal and ventral epiphallic apodemes ( Fig. 17 P-S), but ventral pouch larger; postero-medial surface of bridge ( Fig. 17 P-S) forms cushion-like membranous bulge with many circular pits, presumably of sensory function; lateral sclerites of epiphallus fused to outer edges of lateral plates ( Fig. 17 P-S).

Cingulum ( Figs 16 B-D; 17C) forming low, sclerotized, but partly translucent sheath covering endophallic apodemes dorsally, tapering proximally with its anterior margin medially indented with lateral margins incorporating converging cingular apodemes ( Fig. 17A, C, E); rami of cingulum with raised and sclerotised shoulders (?suprarami of Eades 2000), flanking lightly sclerotised zygoma and enfolding endophallus laterally, fusing ventro-laterally with bilaterally separated sclerites of ventral lobe, which form two upcurved elongate compressed tapering digitate sclerotized processes directed caudad and dorsad, with their raised tips slightly overlapping, right arm slightly longer than left ( Fig. 17 G-L); both rami and ventral lobe arms heavily sclerotised and sculptured on their external surfaces with rows of fine denticles, neither continuous nor bilaterally symmetrical ( Figs 16 B-D; 17G-L); left side of rami and ventral lobe sclerites with longitudinal patches lacking denticles, but right side denticulation continuous between surfaces of rami above and ventral lobe sclerites below ( Fig. 17, J, K); vestigial remains of ventral infold visible as short ventral lobe apodeme ( Fig. 16D); arch of cingulum short, wide, joining zygoma closely to fused apical sclerites of endophallus ( Fig. 17T, U).

Endophallus ( Fig. 16 B-D; 17 T) tripartite, with apodemes formed of two distinct but continuously fused sclerites, lacking visible gonopore processes or endophallic flanges, with a longitudinal medial keel marking their junction dorsally ( Fig. 17U); ejaculatory duct with sharp bend and ancillary tissue mass (vestigial ejaculatory sac) sometimes visible anterior to its junction with endophallus ( Fig. 17A, B), duct partly enclosed below proximal portion of apodemes ( Fig. 17D, F, V) and fully enclosed and widening within their distal half ( Fig. 17V). Spermatophore sac (Sps) reduced, visible medially on dorsal surface of junction between diverging posterior ends of endophallic apodemes, anterior to arch of cingulum ( Fig. 17H, T). Endophallic apodemes (Ae) with articulated break or hinge at junction with medial sclerites (Ms) ( Fig. 17G, T), permitting considerable range of relative movement; medial and apical sclerites of endophallus continuous, proximally fused into single broad dorsal and ventral plates, of complex shape, dorso-ventrally compressed, with paired lightly sclerotised rounded dorso-lateral lobes (Dll), of unknown function, just posterior to arch of cingulum ( Fig. 17T, U) and flanking inconspicuous dorsal opening of phallotreme, hidden within short medial longitudinal groove anterior to transverse cleft between dorso-lateral lobes and inflated fused apex of endophallus; distal section of fused apical sclerites of endophallus expanding into a single hollow bulbous domed bilayered sclerite, curving upwards, with arched cavity on its postero-ventral side, partly filled by folded membranes ( Fig. 17L, V).

Female genitalia

Spermatheca ( Fig. 12) with three basal diverticula ( Fig. 12C, F) arising from vestibule one above another; most ventral one sac-like, short and wide; middle one elongate sac-like, almost as long as dorsal ovipositor valves and apodemes together; dorsal one thin tubular, uncoiled, shorter than dorsal ovipositor valves, with apical and subapical diverticula, one ending in an apical ampulla, the other swollen vermiform ( Fig. 12 E-G); vestibule with a wide lenticular cleft ventrally between ventral valves of ovipositor ( Fig. 12 E-G).

Measurements

Table 12

Coloration ( Fig. 2 F-H)

Males with similar patterning to Ixalidium , as illustrated by Hemp (2017, fig. 42 A). Lateral dark bands on flanks of thorax and abdomen strongly marked up to and including tergite 8; abdominal segments 9 and 10 distinctly paler than rest of body, with contrasting dark longitudinal striae on expanded tergite 9 and darkly pigmented spots around setae on tergite 9 and subgenital plate. Venter pale, mottled, or with darker patches in medial area of sternites 1-5, reaching hind margin of sternites, but leaving fore margins pale. Hind femur with lower internal area, lower carinula and lower carina light red in basal three fifths. Tibiae violet to dirty grey brown, sometimes with pinkish tinge on internal surface. Females with more uniform, less contrasting coloration. Occasionally with contrasting blocks of rufous brown on upper body (from head to abdominal segment 1) and pale buff (abdominal segments and wide band across hind femora) ( Fig. 2H and Hemp 2017, fig. 42B) resembling dead leaves.

HISTORY

The genus Tangana was created by Ramme (1929: 309) for his species T. asymmetrica described from material collected by A. Karasek from “ Tanga ”. Though it was presumably collected from the lowland coastal forest zone, the exact location(s) and date(s) of collection are unknown. Tangana was synonymised under Ixalidium by Uvarov (1941) on the grounds that there were no generic characters which separated females. This synonymy was tacitly ignored but not formally recalled by Dirsh (1965). This position was followed by later catalogues and checklists ( Johnston 1968; Otte 1995) but the synonymy was explicitly contradicted by Johnsen & Forchhammer (1975) whose paper was not catalogued by Otte (1995).

DISTRIBUTION

T. asymmetrica and undescribed species of the genus are now found in isolated populations in remnants of lowland and sub-montane forest in northeast Tanzania and eastern Kenya from close to sea level up to around 880 m (at Sanje Falls, Udzungwa Mountains, Tanzania). There is significant variation in morphology between populations ( Fig. 17) which most probably represents as yet unrecognised vicariant speciation. However, there is also a high degree of morphological variability within populations, as shown by dorsal and lateral views of the epiphalli of two individuals from Mchelelo Forest ( Fig. 17M, O, P, Q) and various views of the genitalia of two individuals from the Nguru Mountains, Tanzania ( Fig. 17 A-D and H-K). There are further species of Tangana from Tanzania, Kenya and Somalia awaiting description ( Ritchie et al. pers. comm.) which have similar internal genitalia to T. asymmetrica , but with an intermediate level of asymmetric development of the external terminalia and inflation of the endophallic sclerites.

REMARKS

The female spermathecae ( Fig. 12) of Tangana and Rowellacris Ritchie & Hemp n. gen., not previously studied, are here shown to be radically different from those of Ixalidium species, as here defined, or of any other acridoid, and the status of Tangana as a valid genus is confirmed, based both on molecular evidence and on striking divergence in characters of the genitalia in both sexes from those in Ixalidium .

This account of the morphology of Tangana is based on the only described species, Tangana asymmetrica Ramme ( paratype male, Fig. 16). The crumpled appearance of the tip of the aedeagus of this paratype, shown in dorsal view in Figure 16B may be a result of trauma sustained by the living insect. Other specimens seen, from a wide range of localities ( Fig. 17), do not show this wrinkled effect. The male terminalia in Tangana are the most heavily modified and specialised in the family Ixalidiidae Hemp, Song & Ritchie n. fam. In addition to the unique asymmetry of the external terminalia, the most striking features of the male genital complex in T. asymmetrica are its overall size in relation to body length (up to 5.6 mm out of around 23 mm), the inflated and fused distal endophallic sclerites (apical valves of endophallus), the epiphallic apodemes and the finger-like paired arms of the ventral lobe. The homology of the modified ventral lobe in Tangana with the same paired sclerite in Ixalidium and all other members of the family is largely proven by the consistent presence of the ventral lobe apodeme, representing the reduced ventral infold which arises from the anterior ventro-internal margin of the lobe. The anterior dorsal positioning of the genital pore at the base of the inflated aedeagus, rather than at its tip, is an autapomorphy of the genus Tangana .

The epiphallus with its long asymmetrically placed apodemes, differs from that of all other Acridoidea, including its nearest relatives in Ixalidiidae Hemp, Song & Ritchie n. fam. Males typically adopt a dorsal mating position and copulate from the left side of the female. Since the male abdominal apex is turned upwards and forwards to connect with the underside of the female abdominal tip at a slight angle, the asymmetric form and alignment of the epiphallus allows the male to achieve the correct alignment to grip the female subgenital plate and egg-guide from the left side. During mating, when the epiphallus grasps the female subgenital plate, the egg guide probably slides over the sensory cushion on the posterior surface of the epiphallic bridge and docks within the dorsal epiphallic pouch. Fusion of the normally separate lateral sclerites of the epiphallus with the lateral plate ( Fig. 17 P-S) presumably gives the epiphallus greater rigidity to resist bending when the lophi are under tension, grasping the female subgenital plate. Given the considerable force with which the lophi would be inserted into the female genital cavity, their flattened button-like tips ( Fig. 16A) may be an adaptation to prevent damage to the internal surface of the female subgenital plate.

Although the hinged endophallus seems quite rigid in alcohol-preserved specimens, it appears that in life considerable mobility is possible. In lateral view the long axis of the aedeagus (apical endophallic sclerites) may form an obtuse angle of about 135° to the basal valves, such that the aedeagus is depressed to lie close to the ventral lobe ( Fig. 17I). However in some cases the aedeagus is found to have become flexed upwards and forwards (capitad) to an acute angle of between 80° and 60° with the endophallic apodemes ( Fig. 17G). When the fused apical sclerites are flexed upwards, a large space is created between the aedeagus and the two upcurved arms of the ventral lobe. Membranes folded below the inflated tip of the aedeagus in its lowered position ( Fig. 17I) are unfurled and drawn taut when it is fully raised ( Fig. 17G). In dead specimens this variation in relative angle between cingulum and aedeagus and in the angle of flexion of the endophallus at its hinged break can present a strikingly different appearance. This may give a false impression of taxonomically significant character differences, where in reality none exist.

During mating it is likely that the tips of the ventral lobe arms are thrust upwards and forwards between the ventral ovipositor valves of the female as the epiphallic lophi pull downwards and backwards against the tip of the subgenital plate and egg guide, opening up the female genital chamber between the lower surface of the ventral ovipositor valves and the dorsal surface of the subgenital plate; the domed aedeagus could then be driven forward into the genital chamber; vertical rotation of the genitalia would mean that the spermatophore would be extruded ventrally onto the floor of the female genital chamber. It would then need to move upwards and forwards to reach the vestibule of the spermatheca.

The presence of the asymmetric prong arising from the right side of the massively reinforced supra-anal plate ( Fig. 5H) narrows the space available for the aedeagus and ventral lobe arms to be everted for copulation. It is unclear whether during mating the prong ends up pointing vertically upwards or forwards over the male abdomen. If it was near vertical, it could perhaps be inserted upwards between the ovipositor ventral valves, or even between both ventral and dorsal valves, to keep the male and female locked together during mating. If it can be deployed horizontally it could perhaps enter the genital chamber. Whichever is the case, the genitalia must be everted past it and rotated upwards and forwards over the male abdomen to perform spermatophore transfer to the female genital chamber.

GENITAL ASYMMETRY IN TANGANA

Bilateral asymmetry is common in the male genitalia of insects ( Huber et al. 2007) and a few striking examples of internal genital asymmetry occur in Acridoidea, most notably in the aedeagus of the Central American acridid genus Rhachicreagra Rehn, 1905 ( Ommatolampidinae Brunner von Wattenwyl, 1893 ) ( Jago & Rowell 1981) and the epiphallus of the genus Stolzia Willemse, 1930 ( Oxyinae Brunner von Wattenwyl, 1893 ) ( Hollis 1975: 212). However, pronounced external asymmetry within the Acridoidea appears to be restricted to the genus Tangana . Huber et al. (2007) proposed that one major evolutionary driver of asymmetry is sexual selection in males for the capacity to adopt a dorsal mating position which requires asymmetric contact between male and female genitalia. In Tangana , the development of novel structures is predominantly to the right side of the male (dextral), corresponding to a leftsided approach to the female genitalia. Only one example is known of a Tangana asymmetrica male with sinistrally asymmetric terminalia. This is a paratype specimen in the Museum für Naturkunde Berlin, mentioned by Ramme (1929) in his original description of T. asymmetrica . This sinistral paratype male has a prong on the left side, but it is not a mirror-image of the dextral morphotype since it also has traces of a short process at the corresponding point on the right side of the abdomen ( Fig. 16E). The extreme rarity of sinistral variants in Tangana suggests that either the morphological change itself or a concomitant change in mating position are highly disadvantageous for mating success. The condition of the internal genitalia in this sinistral specimen is unknown. The functional morphology of the male and female genitalia in Tangana asymmetrica in relation to mating and spermatophore formation and transfer requires further research using the methodology employed by Woller & Song (2017).