Rhysodesmus dasypus ( Gervais, 1847 )

Barrera, Ismael Eduardo Huerta-De La, Bueno-Villegas, Julián, Means, Jackson Cornelius & Cupul-Magaña, Fabio G., 2021, Redescription of Rhysodesmus dasypus (Gervais, 1847), the type species of the genus (Polydesmida: Xystodesmidae), Zootaxa 5040 (1), pp. 66-76 : 68-74

Rhysodesmus dasypus ( Gervais, 1847)

Figs 1–7 , Table 1

Polydesmus dasypus Gervais, 1847: 115 (type species by original designation).

Polydesmus (Fontaria) limax De Saussure, 1859: 322 (status changed by Cook in Cook & Colins, 1895).

Rhysodesmus limax —Cook in Cook & Colins (1895: 5), (synonymized by Hoffman 1970).

Polydesmus (Fontaria) limax — De Saussure (1860: 312, Pl. II, figs 10, 10a).

Rhysodesmus limax — Pocock (1910: 205, Tab. XV, figs 1, 1a); Attems (1931: 63; 1938: 140); Hoffman (1966: 10, fig. 4); Loomis (1968: 60).

Fontaria limax — Attems (1898: 264; 1899: 261).

Rhysodesmus dasypus —Bueno-Villegas & Rojas (1999: 75, fig. 28); Bueno-Villegas et al. (2004: 591); Hoffman (1970: 144; 1999: 330); Hollier et al. (2017: 213) ; Marek et al. (2014: 1, 53); Means et al. (2021: 2); Shelley & Whitehead (1986: 217).

Etymology: Although the epithet is not discussed in the literature, the word “ dasypus ” comes from the Greek for hare or rabbit and was used by Linnaeus (1758) for the only extant genus of armadillos (Dasyipodidae). Curiously, the Aztecs called the armadillos turtle-rabbits (ayotochtli in nahuatl; Cabrera 2002), and it is likely that Gervais (1847) was inspired by the similarity in shape or coloration with armadillos when choosing the epithet for Polydesmus dasypus . In addition, Means et al. (2021) have referred to R. dasypus in the literature as the armadillo millipede.

Synopsis: The type specimens are deposited in four collections: One syntype of Polydesmus dasypus is in the MNHN ( Gervais 1847; Hoffman 1970, 1999). Two type exemplars of Polydesmus (Fontaria) limax in MHNG, a male paralectotype in the dry collection, and the male lectotype placed in alcohol from the dry collection and designated by Hoffman (1966). Other two paralectotypes designated by Hoffman (1966) in the NHM and ZMHB ( Hoffman 1966, 1999; Hollier et al. 2017). Additional specimens are in the CNAC (four males and one female), My-UAEH (male and female) and the VMNH (four males and two females).

Material examined: MEXICO ● 1 ♂; Cerro El Vigía, Santiago Tuxtla , Veracruz, 18°27’28’’N, - 95°17’49’’W, alt. 280 m; 18 Feb. 1962; C.B. Rommel leg.; CNAC-DI000163 ● 1 ♂; same data as previous but 13 Sep. 1966; CNAC-DI000164 ● 1 ♂; same data as previous but 5 Jul. 1967; CNAC-DI000172 ● 1 ♂; same data as previous but 18 Feb. 1967; H.A. González leg.; CNAC-DI000165 ● 1 ♀; 3 km west from Ruíz Cortínez, San Andrés Tuxtla , Veracruz, 18°31’25’’N, - 95°08’28’’W, alt. 958 m; 12 Jan. 2012; R . Monjaraz , J. Cruz, O. Francke, G. Montiel leg.; CNAC-DI000750 ● 1 ♂; Estación de Biología Tropical Los Tuxtlas, San Andrés Tuxtla , Veracruz, 18°35’06’’N, - 95°04’26’’W, alt. 193 m; 18 Aug. 2007; J. Bueno-Villegas leg.; My-UAEH-6 ● 1 ♀; same locality as previous but 2011; J. Bueno-Villegas, E. Rodríguez-López leg.; (no catalog number) My-UAEH ● 1 ♂; Catemaco Lake, near to Coyame, Catemaco , Veracruz; 1–18 Jul. 1963; D. R . Whitehead leg.; (no catalog number) VMNH, (mentioned by Hoffman (1970)).

Diagnosis: Rhysodesmus dasypus is the largest (up to 8 cm long) known species of Xystodesmidae and has the highest number of antennal sensory cones (20) reported for the family ( Hoffman 1970). Male gonopods robust, with the telopodite almost straight and the prefemoral process acute; unlike other representatives of the genus the solenomere is strongly reduced, with a rounded apex and a sturdy parasolenomere. Geographically related to R. zapotecus ( De Saussure, 1860) , whose type locality was recorded in San Andrés Tuxtla, at the same as R. dasypus , but its length is close to 3 cm and width to 5 mm, with strongly flattened body, prominent prefemoral spines and lateral margins of paranota with a closed transition curve (as leaf shape). While in R. dasypus the body is dorsoventrally depressed, prefemoral spine discreet and the lateral margin with a constant transition curve (as an arch).

Redescription. Coloration ( Figs 1–5 ). Body black dorsally, paranota (Pa) and peritrema (Per) reddish-brown and yellow-brown ventrally (color and texture similar in all rings). Head reddish-brown, margins of clypeus (Cly) and vertex (Ve) darker than rest of head, tip of the tentorial transverse bar (Ttt) and antennal sockets pale; antennae light yellow except distalmost two articles, which are brown. Walking legs light yellow in all articles, nails amber color. Gonopods similar in color to legs, light yellow in gonocoxa (Gc)-prefemoral region (Pfr), and amber in prefemoral process (Pp)-acropodite (Ac) region.

Body shape and size. With 20 rings. Body depressed dorsoventrally ( Fig. 1 ), fusiform in dorsal view (tapering anteriad and posteriad, widest at the middle). Total length 73–81 mm, collum (Col) width 12.11–13.41 mm, ring 11 width 21.53–24.9 mm, ring 19 width 6.34–7.05 mm. Curvature of paranota (Pa) and sharpness of caudolateral corners giving side margins of body a serrated appearance ( Fig. 2A ); ozopore (O) formula 5, 7, 9, 10, 12, 13, 15, 16, 17, 18, 19 (usual in Polydesmida ). Paranota (Pa) with ozopores (O) with thickened peritrema (Per) ( Fig. 2B ), except in rings 18 and 19 with reduced paranota (Pa) ( Fig. 2C ). Prozonite (Pro) smooth and metazonite (Me) slightly rugose, metazonite (Me) with two or three transverse rows of metatergal pores (Mp) ( Fig. 2B, D ).

Head capsule ( Fig. 3 ). Globose, length 6.26–6.85 mm, and width 7.26–8.25 mm, with the incisura lateralis (Ila) strongly marked; genae (Ge) prominent, not exceeding head margin, with shallow longitudinal groove; clypeus (Cly) with highly convex arch, with marginal setae. Sulcus (Su) strongly impressed, starting from epicranial margin and extending ventrad between antennal bases, bifurcating ventrad. Cardo and mandibular stipes not visible in frontal view, not contacting paranota (Pa) of collum (Col), interantennal socket width (Isw) 1.93–2.11 mm.

Rhysodesmus dasypus as in the rest of order Polydesmida , lacks Tömösváry organ, but the tip of the tentorial transverse bar (Ttt) is often misinterpreted as such ( Moritz & Koch 2020). The tip of the tentorial transverse bar (Ttt) conspicuous, the surrounding cuticle forming an elevated margin with the anterior region rounded and slightly obtuse, and the posterior region ending at an acute angle and appressed to the incisura lateralis (Ila).

Antennae ( Fig. 3 ). Total length 10.37–11.98 mm. Except for the first (Fa) and ultimate antennomere (Ua), each one about twice as long as it is wide; length of the second antennomere 2.02–2.48 mm. ultimate antennomere (Ua) with 20 small sensory cones (Sc) mainly distributed around the margin, but typically with two or three central cones.

Collum ( Fig. 3 ). Small with respect to rest of body, length 5.09–5.79 mm, and width 12.11–13.41 mm, with strongly marked paranota (Pa) and rounded apex; paranota (Pa) exceeding those of second ring in length by 2 mm in lateral view.

Tergal plates ( Figs 1 , 2 , 4D ). Stricture between prozonites (Pro) and metazonites (Me) strongly impressed and peritrema (Per) conspicuous, except in 19th ring ( Figs 2D , 4D ). Length of the 11th ring prozonite (Pro) 2.87–3.95 mm, smooth, polished, and hidden within metazonite (Me) of preceding ring, same in all body rings except collum (Col) and telson. Length of the 11th ring metazonite (Me) 4.07–4.36 mm, visible, not as polished as prozonite (Pro) and slightly rugose, with two or three transverse rows of metatergal pores (Mp); posterior margin with small protuberances. Lateral margin of the paranota (Pa) with a transition curve as an arch, caudolateral corners of paranota (Pa) acute, projecting caudally on body rings 1–18, becoming rounded posteriorly on body ring 19. Ozopores (O) located anterolaterally on paranota (Pa).

Sternal plates ( Fig. 4A, B ). Reniform shaped spiracles conspicuous, the 11th ring spiracles length 1.10–1.23 mm, and width 0.89–0.94 mm. Sterna with a strongly-impressed medial transverse suture and a longitudinal suture posteriorly; posterior margin with two conical projections, gradually becoming more acuminate on posterior rings. From the 8th ring, each one with anterior leg coxae set wider apart than posterior leg coxae, with intercoxal distance reduced on posterior rings, where coxae are almost in contact. Spiracles located ventrolaterally on body rings, set near anterolateral margin of coxae; reniform, set horizontally on body ring.

Walking legs ( Fig. 4A, C ). Leg articles short, robust, coxae lacking spines, prefemur with small ventrodistal prefemoral spine, femur the longest article; claws translucent amber.

Telson ( Fig. 5 ). Preanal ring (Par) with blunt, triangular epiproct (Ep), length 2.60–2.68 mm, beset apically with four inconspicuous spinneret setal sockets. Paraprocts length 4.69–5.05 mm, globose, smooth, with distal thickening. Each paraproct with two apical setae. Hypoproct (Hyp) rounded, with two medial setae and a small projected tip, length 1.68–1.72 mm, width 3.24–3.73 mm.

new locality records.

Gonopods ( Fig. 6 ). Gonopod aperture (Gap) fusiform, lateral margins slightly curved anteriad; rim of aperture thick, conspicuous gonopod aperture projection (Gpr); rim of gonopod aperture (Gap) extended laterally above spiracles of leg pair 9 ( Fig. 6A ); length 1.51–2.06 mm, and width of aperture 3.2–4.03 mm (measured between internal margins). Gonocoxa (Gc) depressed, with two large setae medially on posterior face; gonopod apodeme (Ga) long and slender, emerging basally from gonocoxa (Gc); cannula (Ca) arising distad from gonocoxa (Gc) in medial view, inserting basad into telopodite (Te), tapering distad and forming base of prostatic groove (Prg). The prostatic groove (Prg) continues through the telepodite (Te) to the solenomere (So) ( Fig. 6B, D, E ). Telopodite (Te) straight, forming almost 90° angle with gonocoxa (Gc); lateral margin with slight curvature; telopodite (Te) length 3.77–4.57 mm, from base of telopodite (Te) to apex of parasolenomere (Pas). Prefemoral region (Pfr) with slender setae; prefemoral process (Pp) arising from posterior margin of the basal third of the telopodite (Te) as a thin projection directed anteroposteriad, dorsal margin almost straight, slightly curving; ventral margin strongly curved, connecting to telopodite (Te) at an almost 60° acute angle, apex acuminate, slightly undulate ( Fig. 6C–D ). Gonopod acropo- dite (Ac) comprising about a third of the telopodite (Te), distal portion curving mediad. Acropodite (Ac) apex with an acuminate, slightly sharp and hooked parasolenomere (Pas), occasionally rounded tip (probably broken during collection), arising dorsad. Solenomere (So) strongly reduced, with the rounded apex ( Fig. 6E ). At the base of the acropodite (Ac) a characteristic and large seta (As) emerges from the medial portion ( Fig. 6C–E ).

Distribution. Known only from the “Los Tuxtlas Region” in the municipalities of Catemaco, San Andrés Tuxtla and Santiago Tuxtla, in Veracruz State, Mexico. Albeit, previously Córdoba was considered in the distribution of R. dasypus , we think that De Saussure (1860) mentioned Córdoba as a geographical reference to easily locate San Andrés Tuxtla ( Fig. 7 ).

Figures

FIGURE 1. Female of Rhysodesmus dasypus (Gervais, 1847) on a tree root from Los Tuxtlas Tropical Biology Station. Photo by Julián Bueno-Villegas.

FIGURE 2. Rhysodesmus dasypus (Gervais, 1847), male (MyUAEH-6). A. Habitus, dorsal view. B. Right paranota of body rings 5 and 6, dorsal view. C. Right posterior region (rings 17–19, and epiproct), dorsal view. D. Body ring 11, dorsal view. Abbreviations: Ep = epiproct; Me = metazonite; Mp = metatergal pores; O = ozopore; Pa = paranota; Per = peritrema; Pro = prozonite. Scale bars: 5 mm (A), 1 mm (B, C), and 2 mm (D).

FIGURE 3. Frontal view of cephalic region of Rhysodesmus dasypus (Gervais, 1847), with magnified inset of ultimate antennomere, male (MyUAEH-6). Abbreviations: Cly = clypeus; Col = collum; Fa = first antennomere; Ge = genae; Ila = incisura lateralis; Isw = interantennal socket width; Sc = sensory cones; Su = sulcus; Ttt = tip of the tentorial transverse bar; Ua = ultimate antennomere, Ve = vertex. Scale bar: 1 mm. The scale bar does not include the magnified square.

FIGURE 4. Midbody region of Rhysodesmus dasypus (Gervais, 1847), male (MyUAEH-6). A. Body rings 11–13, ventral view. B. Enlargement of the red square in Fig. 4A, the arrows indicate the spiracles C. Diagram of transverse section of body ring 11, posterior view. D. Diagram of tergal plate of body ring 11, dorsal view. Abbreviations: Me = metazonite; Pa = paranota; Per = peritrema; Pro = prozonite. Scale bars: 2 mm (A, C, D), and 0.5 mm (B).

FIGURE 5. Caudal region of Rhysodesmus dasypus (Gervais, 1847), male (MyUAEH-6). A. Telson, lateral view. B. Telson with magnified spinneret setal sockets, frontal view. C. Telson, ventral view. Abbreviations: Ep = epiproct; Hyp = hypoproct; Par = preanal ring. Scale bars: 1mm. The scale bar does not include the magnified square.

FIGURE 6. Gonopods of Rhysodesmus dasypus (Gervais, 1847), male (MyUAEH-6). A. Gonopods in situ, anterior view. B. Gonopods ex situ, posterior view. C. Left gonopod, lateral view. D. Left gonopod, mesal view. E. Tip of left gonopod, mesal view. Abbreviations: Ac = acropodite; As = acropodite setae; Apr = aperture projection; Ca = cannula; Ga = gonopod apodeme; Gap = gonopod aperture; Gc = gonocoxa; Pas = parasolenomere; Pfr = prefemoral region; Prg = prostatic groove; Pp = prefemoral process; So = solenomere; Te = telopodite. Scale bars: 1 mm (A-D), and 0.25 mm (E). The scale bar does not include the magnified squares.

FIGURE 7. Distribution of Rhysodesmus dasypus (Gervais, 1847). Veracruz State highlighted in green. Red dot indicates the Córdoba “record”. Los Tuxtlas Region records in yellow (from literature), and cyan (new records).