Sireuma nobile, Reboleira, Ana Sofia P. S. & Enghoff, Henrik, 2014

Reboleira, Ana Sofia P. S. & Enghoff, Henrik, 2014, Sireuma, a new genus of subterranean millipedes from the Iberian Peninsula (Diplopoda, Chordeumatida, Opisthocheiridae), Zootaxa 3785 (1), pp. 79-86 : 80-83

Sireuma nobile n. sp.

Figs. 2–22

Material studied. Holotype, Portugal, Alentejo province, Alandroal, Algar de Santo António, S. Reboleira leg., 10.X.2008, ♂ ( ZMUC). Paratypes: same data as holotype but 30.XII.2009, 1 ♀, ( ZMUC); same data as holotype but 30.III.2009, 5 ♀, ( DZUL); same data as holotype but 22.V.2009, 1 ♀ coated for SEM, 1 ♂, 5 ♀, 1 juv (SR).

Etymology. nobile = noble, cf. etymology of genus name.

Description. Male and females unpigmented, with 29 pleurotergites (“30 segments”), body length 5–6 mm, vertical body diameter 0.5–0.6 mm ( Fig. 2 ).

Head ( Fig. 3–4 ) pilose, mandibular stipites (“cheeks”) subglobular, strongly protruding. Antenna slender, “antennal club” (“ massue antennaire ” = antennomeres 5+6+7–8) ca. 5 times longer than broad; area behind antennal insertion with cobblestone paving-like microsculpture ( Fig. 4 ). Gnathochilarium with a divided mentum ( Fig. 3 ).

Body subcylindrical, slightly tapering at both ends, lateral humps ( Fig. 2 ) very small, situated high up on the flank, but leaving dorsum of body arched. Surface with polygonal microsculpture ( Fig. 17 , as in Scutogona minor Enghoff & Reboleira, 2013 ). Each pleurotergum with 3+3 macrochaetae situated on lateral humps, angle between them (MA) ca. 135° on midbody rings. Distance between external and middle macrochaetae = distance between middle and internal ones (i.e., CIX (midbody) = 1), = ~ 1/3 of distance between middorsal suture and internal macrochaeta (i.e., MIX (midbody) = 3), = 1/3 of macrochaeta length.

Legs ca. 1.4x as long as body diameter. First two pairs of legs with modified, knifelike setae on ventral surface, similar to those exhibited in other Chordeumatida , shown for males by Shear (2011) and Shear & Krejca, (2007), but also present in the females of this new species ( Fig. 3 ).

Male sexual characters. Pregonopodal legs unmodified and incrassate. Anterior gonopods ( Fig. 5–9 and 12– 16 ) composed of: an undivided, bilobed angiocoxite (A, ‘synangiocoxite’) (the apparent separation of the angiocoxite seen on Fig. 6 is due to an artificial break); a pair of two-segmented, approximately L-shaped colpocoxites (K) with the apex strongly curved backwards; a pair of large, robust telepodites, wide at the base, each telopodite with two branches; main branch (Ta) strongly arched posteriad, mediobasal branch (Tb), directed obliquely mesad, the two branches ‘embracing’ distal segment of colpocoxite. Posterior gonopods (P9, ‘paragonopodes’) ( Fig. 10–11 ) two-segmented, both podomeres of ca. equal length, unspecialised, without any kind of processes. First pair of post-gonopodal legs (P10) with three stout setae in a tight group near coxal gland opening, no prefemoral process ( Fig. 11 ). Second pair of post-gonopodal legs (P11) with coxal gland and no prefemoral process ( Fig. 11 ).

Female sexual characters. P2 coxae fused ( Fig. 19–20 ). Vulvae ( Figs 17–22 ) juxtaposed; operculum (Op) longer than the bursa (LV+mV), its distal margin slightly emarginated and with 3+3 setae; bursa globular, connected to operculum with two hinges (h), one mesal and one lateral; lateral valve of bursa (LV) slightly broader than mesal valve (mV), both valves of same length, lateral valve with 4–5 setae, mesal valve with 6–8 setae; bursa with a sclerotized zipper-like internal structure between valves (z) and a pair of irregularly shaped receptacula at base. No postvulvar organ.

Distribution and habitat. Sireuma nobile n. gen. n. sp. has been discovered in the cave Algar de Santo António, located at 350 m. a.s.l. in Alandroal town, Alentejo province of Portugal. Santo António Cave is one of the few caves known in the Estremoz-Cano paleokarst ( Almeida et al. 2000). The cave consists of two entrance pits from the surface, interconnected at their bases and then one single pit reaches the maximum depth - 52 m, ending in fallen rock debris previously filled with water and now dried. The new species was collected at -20 and -52 meters depth, corresponding to the deepest and most thermally insulated parts of the cave. Although Alentejo is the driest province of Portugal, with an annual precipitation of 647.3 mm in Alandroal, humidity in the cave is 100% throughout the year, and temperatures range from 17.7–18.9º C at soil level. At the base of the entrance pit, we are able to sample directly deep soil layers, about - 20 m depth. This is where highest diversity is found, strongly linked to endogean habitats.

Sireuma nobile is the first hypogean species described from the Alentejo province, a region located outside the main karst areas of Portugal, which are in the oriental and southern border of the country ( Reboleira et al. 2011, 2013).

The new species shares its habitat with other subterranean detritivore species, such as the isopods Trichorhina anophthalma Arcangeli, 1936 , a new genus and species of trichoniscid isopod, several unidentified species of Collembola, a new species of Zygentoma , genus Coletinia , and Coleoptera Carabidae and Histeridae ( Reboleira 2012) .

Figures

FIGURES 1 – 2. Sireuma nobile n. gen. n. sp. 1. Sampling locality in the Iberian Peninsula. 2. Female habitus, SEM image. Scale bar: 100 µm.

FIGURES 3 – 4. Head of Sireuma nobile n. gen. n. sp., female 3. Gnathochilarium and first pair of legs, ventral view. 4. Detail of microsculpture behind the antennae. Scale bars: 10 Μm.

FIGURES 5 – 11. Sireuma nobile n. gen. n. sp., male paratype, gonopods, SEM images. 5. Anterior gonopod (P 8), posterior view. 6. P 8, anterior view. 7. P 8, oblique anterior-apical view. 8. P 8, lateral posterior view. 9. P 8, apical view. 10. Posterior gonopod (P 9), P 10 and P 11. 11. Detail of P 9, P 10 and P 11. The arrow indicates the three stout setae near the coxal gland opening of P 10. Scale bar: 10 Μm.

FIGURES 12 – 16. Sireuma nobile n. gen. n. sp., male paratype, diagrammatic drawings of anterior gonopods (P 8). 12. Posterior view. 13. Anterior view. 14. Oblique anterior-apical view. 15. Lateral posterior view. 16. Apical view. A: Angiocoxite, K: colpocoxite, T: telopodite, Ta: apical branch, Tb mediobasal branch.

FIGURES 17 – 20. Sireuma nobile n. gen. n. sp., female paratype, vulvae. 17. Front end of specimen, showing position of vulvae behind second pair of legs. 18. Lateral right view. 19. In situ behind second pair of legs, apical view. 20. Posterior view. Scale bars: 17: 100 Μm, 18 – 22: 10 Μm.

FIGURES 21 – 22. Sireuma nobile n. gen. n. sp., female paratype, vulvae. 21. In situ behind second pair of legs, cleared in lactic acid, posterior view in optical microscope. 22. Diagrammatic drawing of vulvae. Op: operculum. LV: lateral valve. mV: mesal valve. Rec: receptaculum. Z: zipper-like structure. h: hinge. Scale bar: 50 Μm.