Barydesmus nangaritza, Recuero & Sánchez-Vialas, 2018

Recuero, Ernesto & Sánchez-Vialas, Alberto, 2018, A new distinctive species of Barydesmus (Diplopoda, Polydesmida, Platyrhacidae) from Ecuador, with an annotated bibliographical checklist of the American Platyrhacidae, Zootaxa 4482 (2), pp. 245-273 : 247-250

Barydesmus nangaritza , new species

( Figures 2 , 3 )

Material. Male holotype (251005 QCAZI, Museo de Zoología de la Pontificia Universidad Católica del Ecuador, sección de invertebrados) from Ecuador, Provincia Zamora-Chinchipe, Cantón Nangaritza, Las Orquideas ( Fig. 1 ), 1040 m, 4°14'57''S 78°39'50''W, 8 December 2016, A. Sánchez leg.

Etymology. The species name, a noun in apposition, refers to the region where the type locality occurs.

Diagnosis. This new species differs from any other species in the genus by the deeply notched paraterga ( Fig. 2 ), giving the appearance of having two pairs of lateral teeth in each trunk segment.

Description. Adult male holotype, ca. 60 mm long, width, at collum = 4.8 mm, at 2nd segment = 7.5 mm, at 10th segment = 8.7 mm, at 19th segment = 3.8 mm. General habitus slender, with W/L ratio ca. 14.5%, with convex dorsum and paranota set high and slightly upturned ( Fig. 2 ).

Color: Head, body, legs and antennae black; collum and metaterga decorated with transverse rows of large, rounded, grey tubercles. Paraterga covered with smaller, greyish tubercles. Margins of paranota greyish. Labrum yellowish.

Head ( Fig. 2a ) granulated, except for labrum and a semicircular area of the clypeus with coriaceous texture just above labrum, and glabrous, except for a few large setae on gnathal lobes (18+ 18 in frontal area and a few more irregularly dispersed elsewhere), and a few compound setae (7+7 labral, 4+4 prelabral, 2+2 clypeal). Labrum tridentate, deeply offset from level of clypeus. Epicranial sulcus deep. Antennae robust, extending up to the third segment when stretched backwards. Antennomeres covered with long setae. Relative lengths of antennomeres 6>3>5=4=2>1>7. Four apical sensory cones. Antennomere 4 of left antenna with a teratological extra antennomere ( Fig. 2a ).

Collum glabrous, elevated caudad, with frontal and posterior margins almost straight; paranota progressively narrowed laterad, broadly rounded, but margin with 7 small indentations. Surface irregularly granulated, less marked in the middle, and with one anterior and one posterior transverse row of medium to large grey tubercles, the former with 9 tubercles, the latter with 10. Paraterga also covered with granulations and small grey tubercles.

Second segment also clearly elevated caudad, following segments ( Fig. 2b, c ) increasingly levelled. Surface of postcollum metaterga without setae, granulated in posterior third and next to paranota, the rest being coriaceous. A conspicuous transverse row of 8 large grey tubercles, rarely with 9 or 10, near caudal margin. These tubercles present in every segment, but increasingly reduced towards terminal segments. There are also one (segments 2–9) or two (segments 10–19) additional irregular transverse rows of much lower, weaker, dark tubercles. Prozonae uniformly and very finely punctured.

Paranota ( Fig 2a, b, d ) well-developed, profusely covered dorsally with small to medium-sized grey tubercles. Posterior corners of paranota 2 projected laterad; both anterior and posterior corners of following paranota projected laterad, thus looking deeply notched laterally and forming two large teeth in each paratergum, posterior tooth being more slender than anterior one. Notch smaller in segment 18 and vestigial in segment 19. Anterior and posterior margins finely serrulated, the former with a defined whitish rim. Lateral margins also covered with irregularly sized grey tubercles. Ventral surface granulated. Pore formula normal, ozopores opening dorsally at base of notch.

Epiproct ( Fig. 2d ) granulated, flattened and rounded, fringed by four long setae (three of them missing in the preserved holotype), with two additional dorsal setae (one missing). Paraprocts ( Fig. 2e ) slightly convex and granulated, with two pairs of setigerous tubercules. Hypoproct ( Fig. 2e ) small, longer than wide, granulated and with two large paramedian processes at rear edge.

Sternites elevated, without processes, with rugose surface and sparse long setae, more abundant at front margins of segments 6 and 8. Sides of metazonae finely granulated. Legs uniformly covered with erect setae, with no traces of spines or processes. Gonapophyses opening on swollen, blunt coxae 2.

Gonopod aperture ( Fig. 2f ) transversely oval, fitting closely with width of gonopodal coxae. Posterior edge elevated. Gonopods ( Fig. 3 ) slender, extended forward between legs of segment 6, coxa brown in external half, white inside and around articulation, with no trace of setae; telopodite brown over most of its lower half, yellow in distal part, except at tip which is brown again. Base of telopodite with dense setation, this part shorter than glabrous one. Both solenomere and apical lamina (tibiotarsus) acute and directed dorsad.

Comments. The form of the paranota in Barydesmus nangaritza sp. nov. is unique among the American Platyrhacidae . Checking all descriptions and published figures, only Barydesmus exsul ( Cook, 1896a) leaves some doubt about its possible similarity to the paranota of B. nangaritza sp. nov., as in the original description it is said: "lateral carinae usually deeply excised opposite to the pore" ( Cook 1896a: 54). We have examined photographs of the type specimen of B. exsul and the form of the paranota is highly variable among segments. Only paranota 5 and 12 appear clearly excised opposite to the pore (even if not as deeply as in B. nangaritza sp. nov.), but most paranota of B. exsul have 3–4 blunt teeth providing the rough, irregular external margins typical of several other species of the family. Gonopod structure among Barydesmus species, as in other Platyrhacidae , is highly homogeneous and peripheral characters should be considered as major diagnostic features in this group ( Hoffman et al. 2011; Martínez-Torres 2016). Given the available information, it is not feasible to postulate solid hypotheses regarding the affinities among species of Barydesmus without a full review of the genus.

Barydesmus nangaritza sp. nov. comes from the Nangaritza River Basin, an area characterized by the presence of isolated sandstone mountains named "tepuyes", and a humid subtropical climate ( Guayasamín and Bonaccorso 2011). The habitat has a sandy soil covered by a thin layer of leaf litter, with dispersed stones and rotten logs. Most trees are covered with dense epiphytic vegetation. The holotype of B. nangaritza was found active by night, walking on a vertical trunk of a living tree, in a dense piedmont forest located on the eastern slope of a tepuy ( Fig. 1 ).

The biodiversity in this region has remained largely unexplored for a long time. Recent investigations, focused on regional diversity, have resulted in the description of at least four species of Amphibia, one of Reptilia, 10 of Phasmida and 13 of Tettigoniidae ( Guayasamín and Bonaccorso 2011) . This suggests that more effort is still needed to attain a better knowledge of the biodiversity and biological history of this remarkable region and its unique geological formations.

Figures

FIGURE 1. Location of the type locality of Barydesmus nangaritza sp. nov. and view of the habitat.

FIGURE 2. Habitus of Barydesmus nangaritza sp. nov. A: Head and collum; B: 5 th to 7 th segments; C: 10 th to 12 th segments; D: 18 th and 19 th segments and epiproct; E: Hypoproct and paraprocts; F: Gonopods in situ. Scales = 1 mm.

FIGURE 3. Left gonopod of Barydesmus nangaritza sp. nov. A: ectal view; B: mesal view; C: tip of telopodite, dorsal view.