Ixalidium Gerstäcker, 1869

Genus Ixalidium Gerstäcker, 1869 View in CoL

Ixalidium Gerstäcker, 1869: 220 View in CoL . Table III, figs 6 and 6a.

TYPE SPECIES. — Ixalidium haematoscelis Gerstäcker, 1869 by monotypy.

REDESCRIPTION

Small to medium size ( Tables 4-6). Males 16.5-20.2 mm; females 23.6-29, with body length up to 50% greater than males and with more robust habitus ( Fig. 11A). Integument rugose and punctate, variably setose.

Head

Antennae: 17-segmented, about as long as or slightly longer than head and pronotum together, basal segments (apart from scape and pedicel) dorso-ventrally compressed, 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 sometimes shallowly incurved between antennae; eyes ovoid, narrower above, oblique. Fastigium of vertex from above ( Fig. 4A) projecting over lateral ocelli and antennal bases, shorter than its maximal basal width, with obtusely rounded apex and median carinula continuing on occiput; foveolar area obsolete; frontal ridge in anterior view narrowest immediately below vertex, widening between antennae, then narrowing above median ocellus; lateral carinae widening below ocellus and becoming obsolete towards clypeus.

Thorax

Pronotum low tectiform, median carina crossed by 2-3 sulci; prozona 3-4 times longer than metazona; dorsum from above widening steadily from fore margin to hind margin. Prosternal tubercle transverse, spathulate, almost straight-sided, sparsely to densely setose, anterior face flat to slightly concave, posterior face flat to slight convex; apical margin straight or slightly uneven, with rounded angles. Meso- and metathorax tectiform, with median carina; mesonotum without visible tegminal rudiments; metathorax raised posteriorly and with distinct lateral carinae above robust lateral projections which stiffen its lateral lobes above hind coxae; Mesosternal interspace broader than its length, widening posteriorly; mesosternal furcal suture with deep medial and lateral pits. 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, 3.1-3.9 times as long as maximum depth, male; 3.3-4.1 times, female ( Tables 4-6); hind knee with upper and lower lobes bluntly or acutely rounded; hind tibia with 8 outer and 9 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

With median dorsal carina and with segments one and two distinctly raised, together with metathorax forming slight hump; tympanum large and sub-oval; tergites 9 and 10 fused laterally.

External terminalia ( Fig. 5 A-C) presenting nymph-like appearance, without specialised structures; supra-anal plate (epiproct) in two sections, articulating at transverse hinge; basal section forming roughly trapezoid area, narrowing anteriorly, on dorsum of tergite 10, and bounded anteriorly by tergite 9; its lateral margins formed by oblique cuticular ridges and its posterior margin carinate, undulating or straight, overlying a transverse groove adjoining movable triangular apical portion, with its sides slightly incurved, tip acutely rounded; supra-anal plate rugose and sculptured, with shallow median longitudinal groove; cerci straight, acutely conical, sometimes attenuated at apex, clothed with long sensory hairs; paraprocts triangular, partly exposed at lateral margins of supra-anal plate; subgenital plate conical, with apex varying from bluntly rounded to acute and attenuated; dorsal medial area usually membranous anteriorly, sometimes bounded by lateral carinae forming a distinct longitudinal groove.

Male genitalia

Epiphallus ( Figs 10G, H, I; 11E, F) much wider than endophallus ( Fig. 11C); bridge-shaped, without ancorae, but with distinct shoulders bearing sclerotised denticles along their anterior margin; bridge with large circular sensory pores, possibly campaniform or coeloconic sensilla, clustered in medial area ( Figs 10 G-I; 11F); lateral sclerites irregular in outline, laterally compressed and curved; lophi strongly developed, pointed, projecting caudad, hook-like in lateral view, weakly bilobate, with short externo-lateral spur near base ( Figs 10 GI; 11B); bridge with filamentous medial retractor apodeme situated antero-ventrally ( Fig. 11B, E).

Cingulum ( Figs 10A, B, E; 11B, C) with narrow, elongated and divergent apodemes, similar to those in Ommexechidae and Lentulidae , joined by narrow v-shaped zygoma carrying delicate anteriorly-directed lateral spurs (secondary apodemes) at ventrolateral margins ( Figs 10A, B, E; 11C); rami of cingulum forming pair of laterally compressed spoon-like plates, flanking apical valves of aedeagus, externo-laterally convex and internally concave, heavily sclerotised and denticulate along their dorsal surface (presumed to be homologous with dorso-lateral lobes in Mazaea ) but lightly sclerotised or membranous in their externo-medial part ( Figs 10E; 11B), with numerous sensory pores; their antero-ventral margins narrowly sclerotised.

Ventral lobe much reduced, present medially as narrow lightly sclerotised paired plates underlying apical valves of endophallus; homology of these structures with ventral lobe in other genera of Ixalidiidae Hemp, Song & Ritchie n. fam. confirmed by presence in each case of delicate whisker-like medial apodeme (residual ventral infold) ( Figs 10B; 11B) running forward from postero-ventral margin of ventral lobe below endophallus, dividing at node below spermatophore sac into two hair-like branches ( Fig. 11B).

Arch of cingulum formed by two separate struts, joining lateral margins of proximal end of apical endophallic sclerites to underside of zygoma at bases of cingular apodemes, rather than at centre of zygoma; supplementary pair of delicate narrow apodemes ( Fig. 10A; 11B, C) running capitad from point of origin of suprarami of cingulum, above spermatophore sac and between apodemes of cingulum, reaching as far forward as junction of spermatophore sac with fused section of endophallic apodemes; post-zygomal area overlain by lightly-sclerotised extension of dorsal fold (basal fold) of epiphallic membrane, covering anterior (basal) half of aedeagus, suprarami and rami of cingulum ( Figs 10A, D; 11C), and concealing additional shorter transverse fold of membrane, also covering bases of rami and aedeagus; main dorsal fold continuous laterally with pallium beneath rami and ventral lobe; pallium shown covering the whole aedeagus in Figure 11B, C, but folded back during copulation during eversion of the aedeagus and then forming ventral cushion below genitalia.

Endophallus ( Fig. 11D) elongated, in three sections; anterior section (endophallic apodemes) laterally flared anteriorly, convergent posteriorly; in lateral view ( Figs 10E, F; 11B, D) distal (posterior) ends of apodemes project caudad above spermatophore sac, well beyond junction of apodemes with medial sclerites of endophallus ventrally; paired medial sclerites fused, dorso-ventrally compressed, emerging from ventral surface of conjoined apodemes downwards and turning sharply caudad; ejaculatory sac situated antero-ventrally to point of fusion of endophallic apodemes; paired medially-directed flanges of endophallic apodemes flanking ejaculatory duct adjacent to gonopore, appear analogous (though perhaps not homologous) to gonopore processes of other Acridoidea (see discussion of that character below), but situated medially rather than ventrally; mid section of endophallus after flexure with transversely striated cuticle basally, with spermatophore sac situated above it, followed by break or “hinge” between medial sclerites and apical sclerites; aedeagus formed by slender, laterally compressed, distinctly paired apical sclerites of endophallus, with sheath of ectophallic origin ( Amédégnato, 1976), with dense denticulation on exposed apical portion ( Fig. 11D), narrowing distally, slightly flared at apex.

Female genitalia ( Fig. 8)

Spermatheca with simple robust duct, without bursa, with up to five loops and a short apical section, with flask-like preapical and short digitate apical diverticulum ( Fig. 8C, D).

Measurements

Tables 4-6.

Coloration ( Figs 2A; 11A)

Males, generally drab brown, more or less contrasted, varying from light to dark, with pale specks. Pronotum often marked by paired dorso-lateral pale striae (sometimes obsolete), starting behind eyes, converging towards median carina in anterior half of prozona before diverging and slanting obliquely downwards towards hind margin, continuing at a steeper downward slant onto lateral lobes of meso- and metanotum and coxae of hind femur; dorsum of meso- and metathorax and abdominal tergites with truncated dark triangles, narrowing capitad, on mid brown ground; hind margin of thoracic nota and abdominal tergites with paired black raised pustules bearing sensilla, less obvious in darker specimens; metathoracic pleura with triangular area of metaepimeron usually glossy black, bounded by lateral carina above, pleural suture and metaepisternum below and anteriorly and tympanum caudad; coxal joints ventrally blackish. Hind femur with internal medial area black at least in part, often extending onto upper and lower carinulae; lower internal carinula, lower internal carina and lower internal marginal area suffused with red, at least in basal area; upper internal marginal area in basal half with pale patch continuing on upper carina and outer upper marginal area; outer upper marginal and medial areas drab brown with faint dark patches before and after the pale patch; external medial area olivaceous, lower external margin blackish, greyish or olivaceous, with dense dark speckling; hind tibiae brownish to blackish basally becoming reddish in apical half. Abdominal tergites 2-4 laterally with glossy black longitudinal band above junction with sternites, extending dorsally as far as upper margin of tympanum, continuous with black triangle on metaepimeron, weakening progressively on tergites 5 to 8, often restricted to ventral and posterior margin of tergites, sometimes reaching only to tergite 5; this characteristic marking usually concealed by hind femur when at rest; thoric sterna and abdominal tergites largely pale brown, darkening at lateral margins to match colour of tergites. Females with more uniform, less contrasting coloration overall; dark banding on abdomen obsolete. Occasional green morph occurs ( Fig. 2B) with entire dorsum of head, thorax and abdomen, and dorsal and inner and outer lateral surfaces of hind femora yellowish green, apart from basal sixth and apical third; remainder of body shades of brown.

HISTORY

Although Gerstäcker had already briefly described Ixalidium and I. haematoscelis as new ( Gerstäcker 1869: 220), he repeated and extended his descriptions four years later ( Gerstäcker 1873: 46-47). We have designated the male syntype, labelled ambiguously as from “Bura, Endara” (DORSA BA000505 View Materials S01), as the lectotype of I. haematoscelis Gerstäcker, 1869 .

A second species, Acridium gabonense Brisout, 1851 from Gabon was later attributed to Ixalidium by Kirby (1910: 385), quite inexplicably, since Brisout himself had suggested that his new species was allied to Podisma . However, the original description of A. gabonense mentions the presence of elytra: “elytres trés courtes, oblongues-obovales” ( Brisout 1851: lxviii), which eliminates this taxon from Ixalidium . Its true identity and the current whereabouts of any type specimen are unknown. In 1929 three further species of Ixalidium were described from Tanzania: I. obscuripes Miller, I. transiens Ramme and I. usambaricum Ramme. These are here referred to the new genus Rowellacris Ritchie & Hemp n. gen. Uvarov (1941) described a further species, Ixalidium bicoloripes , from Kenya and Kevan (1950) reviewed Sjöstedt’s material from Kilimanjaro, originally determined as I. haematoscelis ( Sjöstedt 1909: 186, 190), referring it to a new species, I. sjostedti Kevan. Johnston (1956: 294) catalogued Ixalidium as a member of the Catantopinae , but Dirsh (1966) transferred the genus from the Catantopinae to the Hemiacridinae Dirsh, 1956 .

INCLUDED SPECIES

Ixalidium haematoscelis Gerstäcker, 1869 View in CoL

Ixalidium bicoloripes Uvarov, 1941 View in CoL

Ixalidium sjostedti Kevan, 1950 View in CoL