IXALIDIIDAE Hemp, Song & Ritchie, 2025

Family IXALIDIIDAE Hemp, Song & Ritchie n. fam.

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TYPE GENUS. — Ixalidium Gerstäcker, 1869 .

ETYMOLOGY. — Ixalidiidae Hemp, Song & Ritchie n. fam. takes its name from the root of the oldest genus name in the family, Ixalidium Gerstäcker, 1869 , which appears to have been derived from the Greek adjective ἴξαΛΟς meaning “bounding, springing”, combined with the final syllables of the old (and now suppressed) genus name Acridium Schaeffer, 1766 .

DESCRIPTION

Small to medium sized grasshoppers (males 16.5-27.6 mm; females 23.6-39 mm), females more robust. Integument rugose and punctate to tuberculate and granulose, variably setose. Antennae with 17-23 segments, from slightly shorter than to slightly longer than head and pronotum together, basal half excluding scape and pedicel dorso-ventrally compressed, widening somewhat from segment three, widest between 3 and 6, with 8-9 distinctly less compressed and terminal segments filiform.

Head width across eyes distinctly less than pronotum length and less than pronotum width at its hind margin; head in lateral view obliquely slanted, with vertex produced and frons in profile sometimes shallowly incurved between antennae; eyes of moderate size, ovoid, narrower above, oblique; fastigium of vertex from above rounded angular, with raised lateral margins, forming an angle less than or equal to 90° (in males), projecting over lateral ocelli and antennal bases; foveolar area obsolete; median carinula of occiput variably expressed, sometimes continuing on vertex; frontal ridge in anterior view narrowest immediately below vertex, widening between antennae, sometimes narrowing above median ocellus, obsolescent towards clypeus; lateral carinae widening below ocellus, sometimes becoming obsolete towards clypeus.

Pronotum low tectiform ( Ixalidium ) to inflated with projections ( Barombia ), median carina intersected by 2-3 sulci; prozona 3-5 times longer than metazona; dorsum from above widening from fore margin to hind margin. Prosternal tubercle conical ( Barombia , Mazaea ) ( Fig. 6B) to transverse, spathulate ( Ixalidium , Rowellacris Ritchie & Hemp n. gen., Tangana ). Meso- and metathorax shallowly tectiform to inflated ( Barombia ), with median carina; mesonotum usually lacking tegminal rudiments, but occasionally (in Rowellacris Ritchie & Hemp n. gen. species) with strap-like tegminal scars, just above lateral sutures separating dorsum from mesopleura. Metathorax raised posteriorly and with distinct lateral carinae above robust lateral projecting flanges which reinforce metapleura above hind coxae. Meso-sternal interspace medially slightly narrower than its length at outer margins, widening caudad (strongly in Barombia ); minimum width of metasternal interspace approximately equal to its length.

Fore and mid legs of typical acridoid appearance, unspecialized. Hind femur in lateral view stocky (length/max. depth, males: 3.1-4.0, females; 3.34-3.9), with upper basal lobe larger than lower lobe, upper carina serrate; hind knee with upper and lower lobes bluntly to acutely rounded; hind tibia with 8-9 outer spines and 9 inner spines; external apical spine present but of reduced size (West African genera) or absent (East African genera); arolium large, rounded, length in ventral view less than or equal to 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 to large hump; tympanum large, sub-oval, sclerotised. External terminalia ( Fig. 5 A-H) with tergites 9 and 10 fused laterally; tergite 10 dorso-medially excised, fusing with the roughly trapezoid basal section of supra-anal plate, the latter with its lateral margins defined by oblique ridges and grooves, their interspace narrowing forwards, bounded anteriorly by tergite 9 and posteriorly by hinged movable section of supra-anal plate (epiproct); this area unmodified in Ixalidium , symmetrically modified in Rowellacris Ritchie & Hemp n. gen. and West African genera, asymmetrically modified in Tangana ; cerci straight, unspecialised, narrowly 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 distal apex varying from bluntly rounded to acute and attenuated; dorsal medial area usually membranous anteriorly, often forming a distinct medial longitudinal furrow bounded by lateral carinae ( Fig. 5G).

Male genitalia. Morphology highly diverse (see figures). Epiphallus usually bridge-shaped (but with bridge elongated anteriorly into an apodeme in Tangana ); without distinct ancorae and with pointed lophi; lateral (oval) sclerites present. Cingulum highly variable, forming a sclerotised dorsal shell with or without paired apodemes ( Rowellacris Ritchie & Hemp n. gen.), less sclerotised ( Tangana ), or reduced to a narrow collar with elongated apodemes ( Ixalidium , Mazaea , Barombia ); zygoma present. Ventral lobe present as paired sclerotised plates below rami of cingulum, least developed and sclerotised in Ixalidium , massively developed and strongly sclerotised in Rowellacris Ritchie & Hemp n. gen. and Tangana , separated into elongated digitate lobes in Tangana ( Figs 16D; 17 G-L). Ventral infold present below endophallus, originating from anterior margin of ventral lobe, either forming a bi-layered sheet ( Fig. 7F) ( Mazaea , Barombia ) or reduced to a whisker-like apodeme ( Ixalidium , Tangana , Rowellacris Ritchie & Hemp n. gen.), sometimes bifurcating at a node anteriorly ( Fig. 11B). Endophallus tripartite (except in Rowellacris Ritchie & Hemp n. gen.), with paired basal, medial and apical sclerites separate but conjoined; endophallic apodemes of variable development and shape, lacking evidence of gonopore processes (but see Discussion), apart from small flanges (Ef) on inner surface adjoining gonopore in West African genera and Ixalidium ( Figs 7G; 9A; 10 A-D); sclerites of medial section (analogous to, though not necessarily homologous with lateral plates of Roberts (1941) elongated and dorso-ventrally flattened in all genera except Rowellacris Ritchie & Hemp n. gen. ( q.v.), with conjoined paired sclerites visible in West African genera ( Figs 7H; 9B) and Ixalidium ( Fig. 10E, F), but forming a single fused sclerite in Tangana ; medial section of endophallus obsolete in Rowellacris Ritchie & Hemp n. gen.; apical endophallic sclerites enclosed within a membranous or sclerotised ectophallic sheath, sometimes laterally compressed ( Rowellacris Ritchie & Hemp n. gen.), with a distinct arch arising basally and attaching to the cingulum, formed by a pair of sclerites in Ixalidium and W African genera, but with sclerites fused into a single pillar in Rowellacris Ritchie & Hemp n. gen. ( Fig. 14J, L). Ejaculatory sac either present as a free antero-ventral elastic sac ( Fig. 9B, C) ( Ixalidium , Barombia , Mazaea ) or reduced to a slight expansion of the ejaculatory duct ( Rowellacris Ritchie & Hemp n. gen., Tangana ). Spermatophore sac dorsal to the endophallus, of variable development.

Female genitalia. Spermatheca of diverse form, with two interconnected sac-like basal appendices or bursae, one short and one very long together with separate short narrow duct leading to well-developed apical diverticulum and ampullate or vermiform sub-apical diverticulum ( Rowellacris Ritchie & Hemp n. gen. and Tangana ) ( Fig. 12); or with a simple robust duct, without bursa, with up to five loops and a short apical section, with flask-like pre-apical and short digitate apical diverticula ( Ixalidium ); or with a very long repeatedly coiled vermiform duct ending in a vermiform subapical diverticulum and a much longer vermiform apical diverticulum in Mazaea ( Fig. 8A) and Barombia . Subgenital plate internally of typical acridoid form with floor pockets, postvaginal sclerites, egg guide and with or without medial pouch and columellae ( Fig. 6C). Ovipositor valves of normal acridoid type, unspecialised ( Figs 5C; 9), slenderer in Ixalidium and more robust in Rowellacris Ritchie & Hemp n. gen. and Tangana . Subgenital plate almost as wide as long in Mazaea ( Fig. 6C) and Ixalidium ; about 1.3 times as long as wide in Rowellacris Ritchie & Hemp n. gen. and 1.7 times as long as wide in Tangana .

General coloration typically drab brown (apart from Barombia which has lighter greenish yellow ground colour with reddish brown markings ( Fig. 3A); internal surfaces of hind femora with some dark patches, with or without reddish shading ventrally; tibiae straw-coloured, grey, violet or pink at least in part.

REMARKS

The genera assigned to the Ixalidiidae Hemp, Song & Ritchie n. fam. share few distinctive and consistent external morphological characters. Apart from their overall habitus, with matt and rugose cuticle, common to many ground-living acridoids across several families, the most distinctive external characters of Ixalidiidae Hemp, Song & Ritchie n. fam. are the absence of tegmina and wings, with the possession of a tympanum and the possession of a transversely divided supra-anal plate. These characters also occur in some genera across several other families, but only the Lentulidae are always apterous and they always lack a tympanum, while in Ixalidiidae Hemp, Song & Ritchie n. fam. the tympanum is always present and well-developed. A detailed comparison of the characters of both male and female internal genitalia reveals remarkable diversity across the family, with some unusual character states expressed in individual genera within the family, including the apparent loss of the medial sec - tion of the endophallus in Rowellacris Ritchie & Hemp n. gen. ( Figs 14 J-L; 15H-I), the fusion of the medial sclerites of the endophallus into a sclerotised casing enclosing the spermatic duct in Tangana ( Figs 16; 17) and the development of a massive blind-ending sac at the mouth of the spermatheca in both Rowellacris Ritchie & Hemp n. gen. and Tangana ( Fig. 12).

However, despite these unusual features expressed in individual genera of Ixalidiidae Hemp, Song & Ritchie n. fam., across the family as a whole there are no monomorphic character states that are not also found in one or more other families of Acridoidea ( Table 13). Instead, Ixalidiidae Hemp, Song & Ritchie n. fam. are ultimately distinguishable from other families by the external characters mentioned above, together with a unique combination of characters of the male genitalia. These are the possession of a bridge-shaped epiphallus with pointed lophi ( Fig. 7C, D), an arch sclerite or paired arch sclerites, a divided endophallus with basal and apical sclerites articulated ( Fig. 11D) and the spermatophore sac situated dorsal to the (ventral) endophallic sclerites ( Fig. 10E, F).

INCLUDED GENERA

The family Ixalidiidae Hemp, Song & Ritchie n. fam. comprises five genera, two from West and Central Africa: Mazaea Stål (including the former Eubocoana Sjöstedt n. syn.) and Barombia Karsch and three from the submontane and coastal forests of Tanzania and Kenya: Ixalidium Gerstäcker , Tangana Ramme and Rowellacris Ritchie & Hemp n. gen. These were all originally considered as Acrididae . Dirsh (1965) initially placed them all in the Catantopinae , but reassigned Barombia , Mazaea and Ixalidium to the Hemiacridinae ( Dirsh 1966: 97) .