Pachymerium mundus Chamberlin 1955

Plateurytion mundus (Chamberlin, 1955)

(Figs. 1–53)

Chilerium mundum Chamberlin, 1955: 23, 24.

Eurytion mundum: Crabill, 1968:231; Foddai, Pereira & Minelli, 2000:75, 182. Eurytion mundus: Pereira, 2006:167 (in key).

Plateurytion mundus: Bonato, Pereira & Minelli, 2007:6; Pereira, 2008:56.

Diagnosis. A species of Plateurytion characterized by having one cluster of coxal organs in each coxopleuron of the ultimate leg-bearing segment. Of the other South American species currently included in the genus, only the present species and P. zapallar (Chamberlin, 1955) share the same character. Plateurytion mundus can be confidently differentiated from P. zapallar by means of the following selected traits (the corresponding ones in the latter are given in parentheses): body length of female 35–45 mm (28 mm, female; 27 mm, male); female with 49, 51 leg-bearing segments (female with 47, 49, probably 51, 53; male with 47, 49, 51); dorsal side of a.a. XIII with ca. 14 type b and ca. 6 type c specialized sensilla, Fig. 4 (with ca. 3 type b and ca. 1 type c, Fig. 59); teeth of labrum midpiece short, slightly sharp-pointed, Fig. 8 (similar to the long filaments of the side-pieces, but thinner and smaller, Figs. 63, 64); second article of telopodite of first maxillae with ca. 12–13 setae (with ca. 4–7); ventral pore-fields undivided on metasternite 1, divided in two areas on metasternites 2 to penultimate, Figs. 15–29, 45–51 (undivided on metasternites 1 to ca. 15, divided in two areas on remaining metasternites including penultimate, Figs. 73–85); with ca. 20–25 organs in each cluster of coxal organs in the coxopleura of the ultimate leg-bearing segment, Fig. 39 (with ca. 8–11 organs in each cluster, Figs. 96, 104).

Other morphological traits included in Table 1 differentiate P. mundus from P. zapallar.

Remarks. P. mundus can be separated from the other South American members of Plateurytion using the identification key below.

Type material examined. CHILE: 35 km E of Temuco, winter of 1951, M. G. Smith col., three syntypes here designated as lectotype ♀ with 49 l. -b.s., b.l. 45 mm (head capsule, dissected mouth parts, leg-bearing segments 44–49, and postpedal segments in an original permanent slide; forcipular segment, and leg-bearing segments 1–43 in alcohol); paralectotype A ♀ with 51 l. -b.s., b.l. 35 mm (in alcohol); paralectotype B ♀ with 51 l. -b.s., b.l. 37 mm (in alcohol). All specimens labeled as Chilerium mundum Chamberlin (CAS Entomology type No. 9173).

Remarks. Chamberlin (1955) stated that the syntypical series comprised four specimens, but actually comprises three (apparently one of these is now missing). Left forcipular telopodite, pretarsus of left ultimate leg, and last three apical articles of right ultimate leg, missing in lectotype ♀.

Depository of types. CAS.

Redescription. Female lectotype. Forty nine leg-bearing segments, body length 45 mm, maximum body width 1.9 mm. Maximum width of cephalic plate 1.08 mm, length of cephalic plate 1.74 mm, maximum width of forcipular coxosternite 1.70 mm. Color (of preserved specimen): head and forcipular segment light chestnut, rest of the body yellowish light orange.

Antennae. About 2.95 times as long as the cephalic plate, distally attenuate (Fig. 1). Ratio of width of a.a. II/ width of a.a. XIV ca. 2.08: 1, all a.a. longer than wide. Ventral chaetotaxy: setae on a.a. I–VI (VII) of various lengths and relatively few in number; those of remaining a.a. progressively shorter and more numerous towards the tip of the appendage (Fig. 1). Dorsal chaetotaxy: setae on a.a. I–VI (VII) similar to the ventral side, setae on remaining a.a. a little longer and slightly less numerous. A.a. XIV with ca. 29 claviform sensilla on the external margin and ca. 16 on the internal margin (Fig. 2: a); distal end of this a.a. with ca. 5–6 very small hyaline specialized sensilla, having about half the length of the claviform sensilla and not split apically (Fig. 2: b). Ventral and dorsal surface of a.a. II, V, IX and XIII (Figs. 3, 4) with very small specialized sensilla. On the ventral side these sensilla are restricted to an internal latero-apical area and are represented by two different types (a and b). Type a sensilla very thin and not split apically (Fig. 3: a), type b sensilla (Fig. 3: b) very similar to those of the apex of a.a. XIV. Specialized sensilla on dorsal side restricted to an external latero-apical area and are represented by three different types: a and b respectively similar to a and b of ventral side (Fig. 4: a, b) and type c sensilla, similar to type b, but a little bigger and darker (ochreous in color) (Fig. 4: c). Position of specialized sensilla on ventral and dorsal surface of a.a. XIII as in Figs. 3, 4 respectively. Number and distribution of specialized sensilla on ventral and dorsal sides of a.a. II, V, IX and XIII, as in Table 2.

Ventral Dorsal Figs. a b a b c

II – 2–3 – 2–4 –

V 1 4 1 5–6 –

IX 1 7 1 3 7

XIII 1 5 1 14 6 3, 4 Cephalic plate. Distinctly longer than wide (length/width ratio ca. 1.53: 1), without a distinct frontal sulcus. Posterior region somewhat narrower than the anterior; sides nearly straight to slightly convex, curving in at the ends; anterior margin convex at middle, slightly concave at level of bases of the antennae; posterior margin straight. Shape and chaetotaxy as in Fig. 5.

Clypeus. With one central seta in front of the clypeal area, one seta located on it (Fig. 7), and posterior to the latter 3 + 2 setae distributed at both sides of the middle line (Fig. 6). Clypeal area well developed with surface minutely punctuate or granulate, not areolate (Fig. 7).

Labrum. Mid-piece unpigmented, small, with ca. 8 short slightly sharp pointed teeth; side-pieces with 21 + 20 hyaline filaments of variable sizes (Fig. 8).

Mandible. With shape as in Fig. 9, pectinate lamella with ca. 31 hyaline teeth.

First maxillae. With well developed lappets on coxosternite and telopodites, relative size as in Figs. 10, 11. Coxosternite devoid of setae; coxal projections subtriangular, round tipped and provided with 11 + 8 setae (Fig. 10). Apical article of telopodites with 12 + 13 setae on ventral side (Fig. 10), and 2 + 2 small sensilla on dorsal side.

Second maxillae. Coxosternites medially joined through a narrow, hyaline and non-areolate membranous isthmus only (Fig. 10), provided with 12 + 12 setae distributed as in Fig. 10. Metameric pores accompanied by a sclerotized rim (Fig. 10: c; Fig. 12: a). Apical claw of telopodites well developed (Figs. 10, 13, 14). Chaetotaxy of coxosternites and telopodites as in Figs. 10, 13.

Forcipular segment (similar to paralectotype A female). When extended the telopodites attaining the end of the a.a. II (Fig. 40). Forcipular tergite trapeziform, with anterior and posterior margins respectively covered by the cephalic plate and the tergite of the first leg-bearing segment (Fig. 41: a); chaetotaxy represented by 16 + 19 setae with relative size and distribution as sin Fig. 41. Coxosternite without chitin-lines, middle part of anterior border slightly concave, provided with 1 + 1 slightly pigmented denticles bearing one dorsal seta; aspect and relative size as in Figs. 40, 42. Telopodites: medial edge of trochanteroprefemur with two teeth, both deeply pigmented, the proximal one smaller than the distal (Figs. 40, 42). Femur and tibia without denticles. Tarsungulum basally with a well developed and deeply pigmented subtriangular tooth (Figs. 40, 43); medial edge of tarsungulum not serrate (Figs. 40, 43). Relative size of poison glands as in Fig. 40: a, calyx of poison gland subtriangular in shape (Fig. 43: b; Fig. 44: a). Chaetotaxy of coxosternite and telopodites as in Fig. 40.

Metasternites of leg-bearing segments 1 to penultimate. With a distinct median longitudinal sulcus along all the body length, areolation of its surface as in Figs. 19, 23. Pores present in an uninterrupted series from metasternite 1 to penultimate inclusive. Metasternite 1 with only one pore (Fig. 15); remaining metasternites with well developed pore-fields divided in two main areas, which are subsymmetrical on metasternites 2, 4–8, 11–48 (Figs. 16, 18, 19, 22–29), and asymmetrical on metasternites 3 (Fig. 17), 9 (Fig. 20), 10 (Fig. 21). Metasternites 4 (Fig. 18), and 25 (Fig. 24) with an additional small group of pores located on the posterior left side; metasternites 8 (Fig. 19), and 45 (Fig. 26) with a similar group of pores on the posterior right side. Number of pores on selected metasternites as follows: metasternite 1 (1); 2 (51 + 46); 3 (27 + 54); 4 (77 + 69); 8 (8 + 98 + 97); 9 (50 + 185); 10 (136 + 33); 11 (88 + 100); 13 (100 + 109); 25 (28 + 41 + 9); 35 (35 + 42); 45 (4 + 24 + 40); 46 (42 + 45); 47 (43 + 37); 48 (35 + 36). Chaetotaxy of metasternites, shape and relative size of pore-fields as in Figs. 15–29.

Legs (pair 1 to penultimate). First pair shorter than the second in the proportion ca. 0.88: 1. Chaetotaxy similar throughout the whole body length (Figs. 30–34). Each claw with an anterior and a posterior spine, the anterior (Figs. 35, 36: a) bigger and similar in color to the claw; posterior spine (Figs. 35, 36: b) minute and pale in color.

Ultimate leg-bearing segment. Intercalary pleurites absent at both sides of the ultimate pretergite; ultimate presternite not divided along the sagittal plane; length/width of metatergite 0.76: 1; length/width of metasternite 0.55: 1. Shape and chaetotaxy of metatergite and metasternite as in Figs. 37, 38. Coxopleura slightly protruding at distal-internal ventral ends, setae small and numerous distributed on the internal ventral area, the remaining coxopleural surface with few larger setae (Figs. 37, 38). Each coxopleuron with all coxal organs grouped in a cluster opening on the membrane between coxopleuron and metasternite, partially or totally covered by the latter (Figs. 38, 39). Each cluster with ca. 20–25 organs arranged as in Figs. 38, 39. Ultimate legs moderately inflated, telopodites composed of six articles. Ratio of length of telopodites of ultimate legs/length of metasternite ca. 4.65: 1. Shape and chaetotaxy of ultimate legs as in Figs. 37, 38. Ultimate pretarsus unguiform, relatively smaller than those of the preceding legs, bearing a single internal very small, and hyaline spine ventro-basally (similar to paralectotype A female, Fig. 53: a).

Postpedal segments. Intermediate tergite with posterior margin strongly convex, bearing numerous setae (Fig. 37); intermediate sternite distinct, with posterior border concave, posterior border of first genital sternite convex (Fig. 38). Gonopods uniarticulate, relatively small, not separated on the middle line (Fig. 38). Anal organs absent.

Male. Unknown.

Variation. Disposition of ventral pores in lectotype female and paralectotype A female reveals the following intraspecific variation (traits in the latter are given in parentheses): Metasternite of first leg-bearing segment with a single pore, Fig. 15 (with a group of three pores, Fig. 45); most of pore-fields on metasternites 2 to penultimate divided in two subsymmetrical areas, Figs. 16, 18, 19, 22–29, and a few divided in two asymmetrical areas, Figs. 17, 20, 21 (all divided in two subsymmetrical areas, Figs. 46–51); a few metasternites bearing an additional small group of pores located on their left or right posterior sides, Figs. 18, 19, 24, 26 (all metasternites devoid of additional groups of pores, Figs. 45–51). (Shape of divided pore-fields of paralectotype B female similar as to paralectotype A female).

All other characters without significant variation.

Remarks. Plateurytion mundus was inadequately described by Chamberlin. The original description does not refer to a specimen in particular, nor does it specify the sex of the studied specimens. It only includes three not accurate drawings (cephalic plate; first maxillae; coxopleura and metasternite of ultimate leg-bearing segment showing coxal organs); and completely lacks information on pilosity of the antennae; kind and number of specialized sensilla of a.a. II, V, IX and XIII; shape of mandibles; anterior and posterior limits of ventral pore-field series; shape and relative size of pore-fields; shape of postpedal segments; etc.

In his original description Chamberlin states “coxae of second maxillae broadly and completely united at middle”, but the coxosternites are medially joined through a narrow, hyaline and non-areolate membranous isthmus only (Fig. 10). About the labrum, the author says “median piece small, transversally subelliptic, without teeth on caudal margin”, but ca. 8 distinct short teeth are present.

The adult (and mated) condition of the three female type specimens is indicated by the presence of spermatozoa in both spermathecae, located at level of the antepenultimate leg-bearing segment.

In the preceding redescription, the forcipular segment is described after the paralectotype A female, because in the lectotype the left forcipular telopodite is missing. Both ultimate legs are incomplete in the lectotype, therefore an ultimate leg of the paralectotype A is illustrated including a detail of the claw-like ultimate pretarsus.

Type locality. CHILE: Region IX (Araucanía region): Cautín province: 35 km E of Temuco.

Known range. Only known from the type locality. (See Fig. 110).

Remarks. According to the biogeographical regionalization of the Andean Region proposed by Morrone (2015), the geographical distribution of this species corresponds to the "Maule province" (Sub-Antarctic subregion).