Allonothrus tuxtlasensis Palacios-Vargas & Iglesias 1997

Redescription of Allonothrus tuxtlasensis Palacios-Vargas & Iglesias, 1997 Taxonomy Family Trhypochthoniidae (sensu lato; see below) Genus Allonothrus van der Hammen, 1953 Type species: Allonothrus schuilingi Hammen, 1953; generic diagnosis: van der Hammen (1953), Wallwork (1960) Background Allonothrus tuxtlasensis is a Caribbean species, one of seven known from the Neotropics (Szywilewska-Szczykutowicz & Olszanowski 2006). It was described based on collections from the state of Veracruz, Mexico (Palacios-Vargas & Iglesias 1997) and its known distribution now includes the Mexican states of Quintana Roo, Chiapas, and Tlaxcala (Ermilov & Yurtaev 2023, and unpublished records from J.G. Palacios-Vargas). It probably occupies all the Antilles, having been reported from several islands, extending from Cuba in the north to Trinidad in the south (Prieto Trueba & Schatz 2004; Ermilov et al. 2016; Ermilov & Smit 2017). All collections have been from decomposing leaf litter, but the habitats range widely, from forests (natural jungle, secondary woodlands) to organic residues on sandy soil of an abandoned coconut grove. The original description of A. tuxtlasensis suffices for identification of the adult, but it lacks important details concerning the structure of gnathosoma and the chaetome of body and legs. These details are provided below, supported by line drawings, light photographs, and SEM images. Juveniles of A. tuxtlasensis are not yet known, so we present previously unpublished developmental data for an Indian species— A. giganticus Haq, 1978 —that was cultured by Palmer & Norton (1990), to allow inferences about leg setation. Diagnosis Based on the original description (Palacios-Vargas & Iglesias 1997) and supplemental data in our redescription we propose the following diagnosis for adult A. tuxtlasensis. Genus-level characters are mostly omitted. Allonothrus species with body length: 495–585. Rostral seta medium-sized, thickened, densely ciliate; lamellar seta longest on prodorsum, heavily barbed, thick basally, becoming sub-spatulate (phylliform) distally; interlamellar seta short, usually phylliform, densely barbed, at base of small tubercle; bothridial seta long, distal half weakly clavate, densely barbed. Dorsocentral part of notogaster foveolate except near setae; without distinct posterior concavity but pygidial region with slight semi-elliptical depression. Notogastral setae heavily barbed, widest distally, dimorphic; c 1, c 2, c 3, cp, d 1, d 2,e 1, e 2 short, phylliform (mostly sub-spatulate); f 2, h 1, h 2, h 3, p 1, p 2, p 3 long, with thick isodiametric basal half, gradually broadened distal half. Epimeral, genital and adanal setae slightly thickened, densely barbed; 10 or 11 pairs of homogeneous genital setae; anal setae attenuate, roughened by inconspicuous minute barbs. Pretarsi homotridactylous; genua I and II with minute setiform organ σ m in place of genual pore; genu III with genual pore. Redescription of adult (Figs 1–7) Measurements. Body length 495–585; width 255–315. Integument. Color of preserved specimens medium reddish to yellowish brown. Body and legs covered by encrusting cerotegument with weakly and irregularly microtuberculate surface (Figs 2a, b; 7a, f), including localized regions of more distinct, larger surface granules (diameter up to 4). With additional adherent debris, especially in posteromedial part of notogaster between longer setae. Exocuticle densely porose, most conspicuously on prodorsum, coxisternum, and subcapitulum (Figs 3a, f, 6a). Prodorsum (Figs 1, 2, 3a). Triangular in dorsal view; rostrum evenly rounded except for small, paired lateral tooth (lt). Middle third with two topographic features: pair of curved medial carinae (mc), nearly meeting to form inverted-V shape; and pair of marked lateral swellings (sw) underlain by muscle sigilla and delineated by sharp groove and strong contours (lc) in transmitted light. Posterior third of prodorsum slightly raised behind medial carinae, with small, sharply defined medial depression (md) overlying several muscle sigilla, and pair of bulging, almost capsular bothridial lobes. Bothridial opening surrounded by raised rim (Fig. 2b); internally with cluster of short brachytracheae opening into region just external to seta bs insertion (Fig. 3c). Bothridial seta (86–94; Figs 2b, c, 3c) slightly and gradually broadened by isotropic cuticle in distal third, forming weakly clavate-spatulate head; barbs minute near base, distally becoming larger and overlapping. Rostral (ro), lamellar (le), and interlamellar (in) setae all heavily barbed but differing greatly in size and form: ro (41–49) nearly isodiametric, curving ventromediad, pair separated by about half their length; le (90–105) inserted on strong tubercle, proximally thick, isodiametric, distal third sub-spatulate, gradually flattening and doubling in width, pair close together, directed almost straight anteriad; in (13–15) inconspicuous, phylliform (fan-shaped), approximately as broad as long, cupped, with dense barbs on outer face (Figs 2d, 3c), inserted at base of small, triangular tubercle. Exobothridial setae both represented by vestiges; ex 1 on rim of bothridial lobe lateral to opening, represented by simple, inconspicuous microseta (1) hardly emerging from alveolus (Figs 2b, 3c); ex 1 ventral to bothridial lobe, represented only by alveolus, larger than that of ex 1. Notogaster (Figs 1–3). About 1.1–1.3 x longer than wide in dorsal view, broadest in posterior quarter, at level of opisthonotal gland (Figs 1a, d, 2a, e). Anterolaterally concave above legs III, IV (Fig. 2e) and below suprapleural carina (Fig. 1d, spc) running approximately between levels of lyrifissures ia and im; spc variably expressed according to body distension. Central region mostly with strong, well-spaced foveolae, round but of various diameters (up to 10); foveolae absent in general vicinity of setae (Fig. 3d, e) and laterally, ventral to spc. Without distinct larger concavities but pygidial region with shallow, semi-elliptical depression between setal pairs h 1 and ps 1 observable in dorsal view of cleaned specimens. Notogastral setae heteromorphic, all heavily barbed; c 2 directed anteriad, others generally posteriad. Setae c 1, c 2, d 1, d 2 (37–49), c 3 (22–26), cp, e 2 (30–41), e 1 (45–56) strongly phylliform-spatulate (Figs 2a, 7a); narrow at base, gradually broadened, flattened and cupped distally; inserted on small tubercles. More posterior setae— f 2 (86–94), h 1, h 2, h 3, p 1 (123–139), p 2 (75–101), p 3 (71–94)—thick and isodiametric in basal half or two-thirds, gradually broadened, flattened and cupped distally to various degrees but often less conspicuously so than shorter anterior setae (Figs 2a, 7b); inserted on large tubercles. Seta f 1 represented only by small alveolar vestige in smooth cuticle, anterior to seta h 1 (Figs 3e, 4a; see R4). Opisthonotal gland opening on low protuberance, anterodorsal to seta f 2 (Figs 1a, b, 4a). Lyrifissures ia, im, ip, ih in normal positions and except for ih of normal size and slit-like shape; ih unusually short and inconspicuous (Fig. 1a, c, d), sometimes visible only as alveolus; ips inconspicuous (especially in contracted specimens), sub-cupular in form and located on softer cuticle of broad plicature region, seen directly or by transparency in distended or contracted specimens, respectively (cf. Figs 1c, 3h; see R5). Notes. Roman letters refer to normal setae (and famulus); Greek letters to solenidia; d σ and d φ indicate seta and solenidion coupled; prime (ʹ) designates seta on the anterior and double prime (ʺ) seta on the posterior face of a given leg segment; parentheses refer to a pseudosymmetrical pair of setae, collectively. Epimeral region. Coxisternum clearly in two units, with fused epimeres I/II separated from III/IV by narrow, but distinct ventrosejugal articulation (vsj, Figs 1c, 3f, g, 7d see R6). Apodeme ap.1 strongly oblique, ap.2 and ap.3 nearly transverse; all three meeting sternal apodeme (ap.st) at midline; ap.st inconsistently developed (Figs 1c, 3f), weakening posterior to ap.2, in mid-region of epimere II), and both anterior and posterior to ap.3. With narrow but distinct surface groove external to ap.2 and ap.3 (Fig. 7d). Epimeral setal formula 3-1-3-3 (I–IV); setae of different lengths (1a, 2a, 3a, 4b: 13–15; others: 30–34) but all slightly thickened, densely barbed throughout. Anogenital region (Figs 1c, d, 2a). Genital plates collectively trapezoid, 1–1.3 x wider than long; anteriorly with weak ridge along medial edge of each plate, effacing in posterior half. With row of 10–11 genital setae (30–37) aligned along medial edge but not isolated from rest of plate by sharply defined line or carina. Setae (30–37) slightly thickened, densely barbed throughout. Ovipositor (Fig. 6c) with general structure normal for family (Ermilov 2011a); length of distal part (beyond fold) 56, of which distal lobes comprise 19; setae ψ 1, and another (unidentified) τ-seta elongate, acute, narrowly spine-like (19); ψ 2 and two unidentified τ-setae short (7), thick, thorn-like, strongly bent in middle at nearly right-angle (Fig. 6e); six coronal setae (k) also short (9), thick, thorn-like, but nearly straight (Fig. 6d). Three pairs of adanal setae (22–26) setae appear slightly thickened by dense barbs; two pairs of anal setae (19– 26) attenuate, without conspicuous barbs. Lyrifissures iad and ian distinct, near anterior end of respective plates. Gnathosoma. Subcapitulum (Figs 4b, 6a. 8a, b) longer than broad: 90–101 × 71–86. With elements of both stenarthry and diarthry: oblique paired labiogenal articulation (scissure lgo) incomplete anteriorly, stopping just before reaching inferior commissure of mouth (Ji). Additional transverse articulation (scissure lgt) running laterally from Ji toward palp; genal seta m posterior to lgt (see R7). Rutellum atelobasic, with weak ventromedial expansion continuing distally as well-developed lamellate