Chilon robustus Sorensen 1896
Creators: name: Bauer, Christian
name: Prieto, Carlos E.
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Opiliones
Assamiidae
Chilon
Chilon robustus

description: Chilon robustus Sørensen, 1896
Figs 1–2, 9–14, 36–43, 68, table 1
Chilon robustus Sørensen, 1896: 188 [Kitta, Cameroon]. Roewer, 1923: 278 [Bibundi, Cameroon]; Roewer, 1927: 364 [Basilé, Musola and Baja de S.Carlos, Bioko island]; Roewer, 1935: 57 [Bibundi, Edea and Fernando Poo (=Bioko Island)]; Starǫga, 1992: 300 [synonymisation of Chilon undulatus Sørensen, 1896, Monorhabdium singulare Loman, 1902, Chilon armatus Roewer, 1912, Chilon ferrugineus Roewer, 1912, Monorhabdium echinatum Roewer, 1912, Chilon atroluteus Roewer, 1916, Tsadsea picta Roewer, 1935, Parachilon bistriatus Roewer, 1940, Parachilon bicolor Roewer, 1942, and listing of recorded localities for each synonym].
Material studied. 4 3, 5Ƥ syntypes of Chilon robustus (NHRS): Kamerun, W. Sjöstedt leg., 1891. 3 3, 3 Ƥ (MRAC /135327): Buea (Cameroun), 4º9’N, 9º14’E (UTM: 32NNK25), J. J. van Mol leg., 9.02.1968. 1 3 (MRAC /148230): Mieri (Cameroun), 4º15’N, 13º58’E (UTM: 33 NUE 87), F. Puylaert leg., 23.01.1976.
Description. MALE (MRAC/148327): Total body length, 4.0; maximal width, 3.25 (at 2nd area of scutum). Scutum length, 3.5 (carapace/scutum ratio, 0.34).
Coloration (Figs 1–2). Ground colour dark yellow. Carapace with brown frontal margin, bright yellow at lateral margins and in post-ocular area. Opisthosomal part of scutum with light brown lateral and posterior margins; brown anterior areas separated by a light median stripe; posterior areas light yellow; spines with dark brown bases. Free tergites and anal operculum light brown. Coxae and coxosternal-complex light yellow, with pigmented area behind the genital operculum and along the posterior border. Free sternites dark yellow. Appendages yellow.
Carapace (Figs 1, 9, 11). Frontal tubercle system with outer lateral projections half the size of inner ones. Frontal margin with sparse granules. Ocularium with a central pair of large tubercles, 2–3 pairs of granules on the frontal surface and a pair at the rear, a lateral pair at level of eyes, a paramedian pair just between the ocularium and the rear of the carapace, and a lateral row of small tubercles from the corner of intercoxa II/III to area III of scutum.
Opisthosomal part of scutum (Figs 1, 9, 11). Strongly convex, broadening progressively until area III and then narrowing. Area I divided by a median groove. Areas I–III with pairs of spines on convex protuberances, those in area I and II of similar length whereas those in area III longer and robust; pairs in areas II and III slightly curved posteriorly. Area I with a pair of granules on anterior surface of spine-bearing protuberances. Area IV smooth. Area V with a large medial spine, two smaller on each side of it and small denticles between them. Lateral margin with a row of small tubercles, one of them on area III larger than the others. A small tubercle on lateral margin between area IV and V.
Free tergites (Figs 9, 11). First tergite with a row of granules and a spine on each lateral corner. Second tergit with a pair of median spines and a smaller spine on each lateral corner, with interspersed granules. Third with a median spine flanked by a pair of smaller ones.
Ve n te r (Figs 2, 10). Granulose. First coxa with three tubercle rows arising in a tubercle field on basal part of coxa; frontal row ending in a packed group of 4–5 tubercles on prolateral border. Middle row formed by large and small interspersed tubercles, gently curved and reaching prolateral corner. Back row formed by large granules along the border with coxa II. Retrolateral corner with a large tubercle and two smaller tubercles, these posteriorly and medially to the large tubercle. Surface between tubercle rows and prolateral surface finely granular. Coxa II with two tubercle rows, first along anterior margin and second, more irregular, along midline. Coxa III with irregular tubercle rows along distal half of coxal margins. Distodorsal margin of coxae I–III with isolated tubercles on both prolateral and retrolateral corners, opposing tubercles of contiguous coxae touching each other. Coxa IV with a robust, acute dorsolateral tubercle (at level of area II) dividing external margin into two zones, anterior zone occupying two-thirds of coxa length parallel to the scutum contour, posterior zone diverging from scutum contour and being covered by sparse granulation. Ventral surface of coxosternal plate with sparse granulation, a granule row along posterior margin and tubercle groups formed by 3–4 sternal and 1–2 coxal tubercles partly covering spiracles; a pigmented pentagon behind genital operculum pointing backwards (in males vertex lengthened by a dark median stripe reaching posterior margin). Genital operculum with anterior granulation. Free sternites with sparse granules in loose rows.
Chelicera (Fig. 13). Basal segment with elevated distal part, row of granules along ectodistal margin, and an inflated, granulose bulla covered with ectobasal and ectodistal tubercles. Second segment with tiny granules and a tubercle on ectodistal margin.
Pedipalp (Fig. 14). Trochanter with ventral spur and sparse dorsal and lateral granules. Femur with a ventral row of 8–11 irregular denticles, dorsal and mesodistal surfaces with sparse granules. Patella with two granules on mesodistal edge and some granules on dorsal surface. Tibia with IiiI on mesal and iiiIi on ectal edges. Tarsus with iiIiI on mesal and iiIiI on ectal edges.
Legs (Table 1). Surface with small granules and setae. Trochanter, femur and tibia of leg IV enlarged. Calcaneus I 12 % of metatarsus length. Tarsal formula 5(2)/11(3)/6/7.
Penis (Figs 36–43). Penis head separated from stalk by a neck, head heart-shaped, with long translucent keels on both sides and two setose bulges separated by a median groove and enclosing the glans. Ventral side with three pairs of small setae; partners of two distal pairs pointing towards each other (the inner one shorter), third pair situated on lateral bulges and pointing proximad. Lateral side with three close pairs of large and foliate setae pointing proximad. Dorsal side with three pairs of setae, two of them smaller than others and situated more apically, the third one larger, situated more proximally and pointing proximad.
FEMALE (MRAC/135327): Total body length, 4.16; maximal width, 2.77 (at 3rd area of scutum). Scutum length, 3.17 (carapace/scutum ratio, 0.36). Different from male in outline of body, with scutum and coxosternal plate more delicate, free tergites elongated, opisthosomal region inflated, dark median stripe behind genital operculum absent, and more slender legs. Measurements of pedipalp and legs, see table 1.
Ovipositor (Fig. 68). Bilobed; inner lobe convex; apical edge and distal inner surface denticulate; outer surface lacking denticles except on ventral margin. Each lobe with five setae, two ventral and three dorsal; setal tips with ramus; ramus shorter than axial tip.
Comments. Our specimens are conspecific with the type material: External features and penial morphology of the syntype (Figs 40–43) are nearly identical and differences are attributed to individual variation. Chilon robustus has a wide distribution area along the Gulf of Guinea coasts between Ivory Coast and Gabon (Roewer, 1923, 1927), Monorhabdium echinatum Roewer, 1912 was recorded from both areas and a high level of variability is expected. Staręga (1992) compared C. robustus and nine other ‘species’ of four genera ‘with respect to their genital morphology’ and concluded that they are synonyms of C. robustus. Unfortunately, Staręga did not draw the penis of C. robustus (previously undescribed) or of any of those synonyms, with the result that the penial variability range remains unknown and the synonymisation rests solely on his authority. We do not accept his synonymisation of Chilon undulatus (see below) because the penial morphology of its syntypes differs from that of all other specimens examined, including syntypes of C. robustus. A revision of the remaining species in synonymy could reduce the geographical range of C. robustus sensu Staręga.
description: Published as part of Bauer, Christian & Prieto, Carlos E., 2009, Three new Assamiidae (Arachnida: Opiliones) from Cameroon, with a redescription of Chilon robustus and comments on related species, pp. 1-22 in Zootaxa 2059 on pages 3-4, DOI: 10.5281/zenodo.186783