Chilexenus rosendinus ( Silvestri, 1903 )

Duy-Jacquemin, Monique Nguyen, 2009, Revision of the genera of Polyxenidae bearing pseudoarticulated gnathochilarial sensilla (Diplopoda, Polyxenida, Polyxenidae), with the description of two new species, Zoosystema 31 (4), pp. 829-848 : 831-832

Chilexenus rosendinus ( Silvestri, 1903)

( Figs 2 ; 3 )

Polyxenus rosendinus Silvestri, 1903: 16 , 17.

MATERIAL EXAMINED. — Chile. S. Rosendo, adult ♀ syntype, mounted on slide in Canada balsam (Museo civico di Storia Naturale di Genova). The label reads “ Polyxenus rosendinus Silv. Cotypus !!, S. Rosendo”. The thick microscope preparation does not allow a detailed observation of the ventral face.

REVISED DESCRIPTION

Coloration:Body and some trichomes pale yellowish; other trichomes varying from clear greyish to dark brown; pigmentation only present around ocelli.

Measurements:Body length (without caudal penicillus) 2.70 mm; caudal penicillus length 0.90 mm. Length of tarsus II of 13th leg: 160 µm.

Head: Eight ocelli on each side. Vertex with one pair of posterior tufts consisting of two rows: anterior row with 18 (right) and 19 (left), posterior row with 10 trichomes. The small distance between each tuft and the length of the trichomes as shown in Figure 3F .

Length of antenna 0.50 mm; proportions of antennal articles as shown in Figure 3A ; length of article VI twice its diameter. Antennal article VI with three, thick, dorsal sensilla basiconica: posterior sensillum slightly longer than the subequal anterior and median ones ( Fig. 3C, E ); one posterior sensillum coeloconicum. Antennal article VII with two dorsal sensilla basiconica: posterior one slightly shorter than anterior on left article ( Fig. 3D ); on right article, anterior sensillum is broken ( Fig. 3B ); one posterior sensillum coeloconicum. Three trichobothria of equal size, with cylindrical funiculi.

Clypeo-labrum with12 setae along posterior margin and 12 lamellar teeth on anterior margin. External structure of labrum not visible. Lateral expansion of gnathochilarial palp with 18 pseudoarticulated sensilla on the right and 14 visible on the left; middle palpus with 20 (21? on left) visible ( Fig. 3G ).

Trunk: Tergal trichomes arranged in two, long, oval tufts separated by a short space – sometimes occupied by two or more trichomes directed towards the telson ( Figs 3H ; 11A ) – and one, uninterrupted, sinuous posterior row of trichomes directed towards the telson, running along posterior margin of tergite ( Fig. 11A ); about 146 trichomes on tergite VIII.

Legs: ( Fig. 3I ). Trochanter and prefemur bearing one seta, coxa with one to three setae with slightly oval base. It is not possible to observe the small setae on femur and tibia. Second tarsus with a spine longer than the claw. Posterior lamellar process longer than claw; other process of telotarsus not visible.

Telson: Type II ( Condé 1970) characteristic of the subfamily: two latero-dorsal penicilli of hooked trichomes joined side by side; dorsal face of telson with a row of ten and 11 barbate trichomes a on each side of median plate ( Fig. 3K ); two subcircular groups composed of 10 barbate trichomes c, and one barbate antero-internal trichome b ( Fig. 3K ); on ventral face the usual subrectilinear row of barbate trichomes located at edge of penicillus of hooked trichomes is not visible. A large part of caudal penicillus is lacking; the left hooked trichomes have two hooks ( Fig. 3J ).

REMARKS

Tarsi II of Chilexenus rosendinus each bear one spine (as in Macroxenus ), hence Chilexenus differs from Macroxenodes and Afraustraloxenodes , both of which have a seta rather than a spine on tarsus II. Chilexenus differs from Macroxenus in the different arrangement of the tergal trichomes: long oval lateral tufts separated by a short space and reduced anterior and posterior rows in Chilexenus ( Fig. 11A ), long space between lateral tufts connected by an anterior row and a posterior row in Macroxenus ( Fig. 11B ).

Figures

FIG. 2. — Chilexenus rosendinus (Silvestri, 1903), adult female syntype from S. Rosendo, dorsal view.Drawing by M. Bertoncini. Scale bar: 0.50 mm.

FIG. 3.— Chilexenus rosendinus (Silvestri,1903):A, right antenna;B, C, details of sensilla basiconica and coeloconica on articles VII and VI of antenna A; D, E, detail of the same sensilla on left antennal articles VII and VI;F, head,dorsal view;G, palpi of gnathochilarium;H, left part of tergite II; I, right leg XI;J, distal part of hooked trichome;K, end of telson with posterior part of its tergite.Abbreviations:a1-a11, insertions of barbate trichomes a; b, insertion and trichome b; c, groups of trichomes c. Scale bars: A, F-I, K, 50 μm; B-E, J, 25 μm.

FIG. 11. — Insertions of trichomes on tergite VIII in adult females: A, Chilexenus rosendinus (Silvestri,1903),lectotype; B, Macroxenus rubromarginatus (Lucas, 1846), from Ifrane; C, Macroxenodes meinerti (Silvestri, 1898), cotype; D, Afraustraloxenodes namibiensis Nguyen Duy-Jacquemin, 2003, paratype. Scale bars: 50 μm.