Propolyxenus squamatus Nguyen Duy-Jacquemin , Uys & Geoffroy

Duy-Jacquemin, Monique Nguyen, Uys, Charmaine & Geoffroy, Jean-Jacques, 2011, Two remarkable new species of Penicillata (Diplopoda, Polyxenida) from Table Mountain National Park (Cape Town, South Africa), ZooKeys 156, pp. 85-103 : 86-89

Propolyxenus squamatus Nguyen Duy-Jacquemin, Uys & Geoffroy sp. n. Figs 1-5

Type material.

South Africa, Cape Town, Table Mountain National Park. Cecilia, Rooikat, site 12, felled pine, altitude 300 m, 33°59'43S, 18°25'22E, 4/X/2008, holotype adult female (no. 4); Cecilia, Rooikat, site 9, Afrotemperate forest, altitude 400 m, 33°59'34S, 18°25'12E, 4/X/2008, paratype adult female (no. 3); other paratypes: Kirstenbosch, Afrotemperate forest, site 5, altitude 400 m, 33°58'55S, 18°25'25E, 12/IX/2008, subadult female (12 pl) (no. 2); Cecilia, Spilhaus, Afrotemperate forest, site 13, altitude 400 m, 33°59'43S, 18°25'05E, 18/X/2008, larva with 8 pl (no. 5), all collected from leaf litter by Charmaine Uys and mounted on slides (MNHN).

Other material examined ( non–type).

Cecilia, Spilhaus, Fynbos, leaf litter, site 14, 33°59'53"S, 18°24'52"E, altitude 520 m, 18/X/2008, subadult male (12 pl) (no. 6), used for SEM.

Etymology.

The specific name refers to the scale–shaped tergal trichomes.

Diagnosis.

Differs from all other congeners by the position and structure of the tergal trichomes: these flat scale–shaped trichomes cover the tergites and are different from the barbate trichomes of the lateral tufts, pleurites and head. They are observed for the first time in the family Polyxenidae . As in the family Synxenidae , they lie close to the tergites and are all directed caudally, but differ from those of Synxenidae in their shape and structure.

Description of two adult females.

Measurements. Body length (without caudal penicil): 2.50 mm (holotype). Tarsus II length of 13th leg: 100 µm (holotype) and 105 µm (paratype).

Head (Fig. 2C). 6 ocelli on each side of which 1 antero–sternal (Figs 2D, 3F). Vertex with 1 pair of posterior tufts of 27+27 (holotype) and 24+25 trichomes (paratype), consisting of 3 rows, middle row with 12-13 trichomes (Fig. 3F); the distance between each tuft is about half their length.

Proportions of antennal articles as in Fig. 3A. Antennal article VI with 4 basiconic sensilla (Figs 2E, F, 3A): 2 anterior (a)shorter and thinner than the 2 posterior ones; the more posterior (p2)slightly thinner than the (p1)(Fig. 3B); 1 setiform sensillum (s) between anterior and posterior ones and 1 posterior coeloconic sensillum (c); antennal article VII with 3 basiconic sensilla, the anterior (a) slightly thinner than the others (Fig. 3C), 1 setifom sensillum (s) between the 2 posterior basiconic sensilla and 1 posterior coeloconic sensillum (c). The right antennal article VII of the holotype has 4 basiconic sensilla and 2 coeloconic sensilla, but this is recognizable as a regenerated antenna (as shown by Nguyen Duy–Jacquemin 1972) with 2 coeloconic sensilla on article VII and none on article VI (Fig. 3A).

3 trichobothria, arranged in a triangle, with the most internal (near posterior tufts of vertex) smaller than the 2 others (Figs 2C, D, 3F). Surface of labrum (Fig. 3G) with numerous small short cuspidate papillae; papillae of anterior 2 to 3 rows larger; 7+8 lamellate teeth on anterior margin (holotype: Fig. 3G), 8+8 (paratype); clypeo–labrum with 9 setae along posterior margin (Fig. 3G). Outer palp of gnathochilarium with 11 or 12 sensilla; middle palp with 19 or 20 sensilla (Fig. 3H).

Trunk (Fig. 2A): On each tergite (except collum, tergite X and telson) the trichomes are arranged in 3 rows and 2 lateral tufts (Figs 2B, 4A, B); each paired tuft connected by posterior and anterior rows of trichomes; middle row with more spaced trichomes (Fig. 4A). There are 2 types of trichomes. The flat trichomes, referred to as scales (sc) of the 3 rows are wider than barbate trichomes of lateral tufts (bt) and their shape and structure are different (Figs 2B, 4B, 5 A–C); they look like the scales of Synxenidae by their position: all are directed caudally and cover the tergites I (with only a posterior row) to X (Figs 4A, B). Their structure is different from scales of Synxenidae (Figs 5 A–E). The trichomes of the lateral tufts are longer and arranged in a bunch (Figs 2B, 4A, B (bt), C). Lateral protuberance of tergite I with 3 barbate trichomes (Fig. 4A).

Legs (Figs 4 D–H): Naming of leg segments is after Brolemann (1935). Coxae I with 1 seta and coxae II with 2 setae; all other coxae without seta. All trochanters and prefemora with 1 seta; these setae having an oval base furnished with acute process at apex (Fig. 4F). All tibias (except 13) have 1 small seta tapered apically as shown in Figs 4D, E; other articles without seta. Tarsus II spine (Fig. 4H) longer than telotarsus (Fig. 4G): length of spine to claw ratio about 1.80. Telotarsus bearing an anterior process (ap) with a spinous projection longer than claw, 2 latero–anterior and posterior spiniform processes (t), posterior larger than anterior; posterior lamellar process (plp) thickened and basally pleated (Fig. 4G).

Telson (Figs 1, 2A): typical of genera Propolyxenus , Polyxenus , Typhloxenus (subfamily Polyxeninae ). 21 (holotype) and 25 (paratype) dorsomedian barbate trichomes on caudal penicil. Hooked trichomes with 3 or 4 hooks.

Description of subadult female, 12 pl (no. 2).

Measurements. Body length (without caudal penicil): 2.40 mm. Caudal penicil length: 0.60 mm. Tarsus II length of 12th leg: 112 µm.

Head: 6 ocelli on each side. Antennal article VI with 3 basiconic sensilla (Fig. 3D); antennal article VII with 3 basiconic sensilla (Fig. 3E). Surface of labrum with numerous small short cuspidate papillae; papillae of anterior 2 rows larger; 9+9 lamellate teeth at anterior margin. Outer palp of gnathochilarium with 11 sensilla; middle palp with 19 sensilla.

Trunk: Scales on tergites I-IX. Lateral protuberances of tergite I with 3 barbate trichomes.

Legs: Coxae I with 1 seta and coxae II with 3 setae; all other coxae without setae. All trochanters and prefemora with 1 seta. All tibias (except 11 and 12) have 1 small seta tapered apically; other articles without seta. Telotarsus bearing an anterior process with a spinous projection longer than claw, 2 latero–anterior and posterior spiniform processes; posterior lamellar process thickened and basally pleated.

Telson: 22 dorsomedian barbate trichomes of caudal penicil. Hooked trichomes with 3 or 4 hooks.

Description of a larva 8 pl (no. 5).

Measurements. Body length (without caudal penicil): 1.80 mm. Tarsus II length of 8th leg: 110 µm.

Head: 6 ocelli on each side. Vertex with 1 pair of posterior tufts of 20+19 trichomes consisting of 3 rows, the middle row with 10 trichomes. Antennal article VI with 3 basiconic sensilla: 1 anterior shorter and thinner than the 2 posterior ones; the more posterior slightly thinner than the other; 1 setiform sensillum between anterior and posterior basiconic sensilla and 1 posterior coeloconic sensillum; antennal article VII with 3 basiconic sensilla, the anterior slightly thinner than the others, 1 setiform sensillum between the 2 posterior basiconic sensilla and 1 posterior coeloconic sensillum. 3 trichobothria, arranged in a triangle, with the most internal smaller than the 2 others. Surface of labrum as in adult females; clypeo–labrum with 10 setae along posterior margin. Outer palp of gnathochilarium with 12 sensilla.

Trunk: Trichomes arranged in 2 lateral tufts with 19 to 25 barbate trichomes connected by 3 rows of scales on tergites III–V and only 2 on other tergites. The tergites II–V have 22 to 31 scales, the collum 12 and the tergite VII 18. Lateral protuberance of tergite I with 3 (left) and 2 (right) barbate trichomes.

Telson: 18 dorsomedian barbate trichomes of caudal penicil. Hooked trichomes with 3 hooks (rarely 2 and 4).

Discussion.

Propolyxenus squamatus sp. n. is strongly distinguished from other species of the genus by the shape of the trichomes covering the tergites. Compared with the most closely related species Propolyxenus lawrencei Condé, 1949, from Natal (Champagne Castle, Drakensberg Mountains, alt. 6000 ft.), Propolyxenus squamatus sp. n. shares the following characters: 6 ocelli; internal trichobothrium shorter than the other 2; number and shape of sensilla on antennal articles VI and VII ( Condé 1949, p. 125-126, 1959); surface of the labrum with numerous papillae, the 2 or 3 anterior rows larger.

The new species shows the following important differences from Propolyxenus lawrencei :

Position and structure of trichomes on tergites: on each tergite (except collum and telson) the trichomes are arranged in 3 rows and 2 lateral tufts; each paired tuft being connected by posterior and anterior rows of trichomes; the middle row has more spaced trichomes. In Propolyxenus lawrencei , the trichomes are arranged in 3 or 4 irregular rows, forming 2 elongated lateral areas, slightly separated by a narrow medial space.

There are two types of trichomes: the trichomes of the three rows are wider and flatter than the trichomes of the lateral tufts, pleurites and head, and their shape and structure are different, being observed in the family Polyxenidae for the first time. They can be compared to the scale–shaped trichomes of Synxenidae : the trichomes of the rows are all directed caudally and cover the posterior half of tergites II–X and their internal structure is reinforced by differently distributed chitinous elements (Figs 5 C–E). The lateral trichomes are longer and arranged in lateral tufts. It is remarkable that the barbate trichomes of Propolyxenus squamatus sp. n. show a progressive transformation into scale–shaped trichomes in the posterior row of the tergite, representing a transition between the two types of trichomes as if, during the course of evolution, the former trichomes had changed into scale–shaped trichomes. These scale–shaped trichomes are thought to protect the animals from desiccation, abundant rain or other environmental disturbances.

In a key of the genus Propolyxenus , Propolyxenus squamatus sp. n. would be easily distinguished from all other congeners as is only species with scale-like trichomes. The other species of Propolyxenus are more difficult to identify using morphological characters such as the number of ornamental trichomes or coxal glands of the males. For instance, both Propolyxenus patagonicus (Silvestri, 1903) and Propolyxenus australis Short and Huynh, 2010, bear four pairs of coxal glands (cf. Condé and Massoud 1974, p. 227 for Propolyxenus patagonicus ) contrary to the first tentative key proposed by Short and Huynh (2010 p. 15). There is a difficulty in the limited nature of keys based (even partly) on characters such as coxal glands, requiring collection of adult males. More appropriate characters need to be determined for a more robust key for the genus.