Scutogona minor, Enghoff, Henrik & Reboleira, Ana Sofia P. S., 2013

Enghoff, Henrik & Reboleira, Ana Sofia P. S., 2013, A new cave-dwelling millipede of the genus Scutogona from central Portugal (Diplopoda, Chordeumatida, Chamaesomatidae), Zootaxa 3736 (2), pp. 175-186 : 179-184

Scutogona minor n.sp.

Figs 1–13 .

Material studied: Holotype ♂ PORTUGAL, Sicó massif, Gruta da Arrifana (40°05’14.32”N; 8°30’59.00”W), 13.i. 2013, S. Reboleira leg. (ZMUC).— Paratypes: 2 ♂, 7 ♂, 1 juv., same data (ZMUC, 1 ♂, 1 ♀ DZUL). 1 ♂, 2 ♀ PORTUGAL, Sicó, Gruta de Santa Maria da Estrela (39°59'41.15"N, 8°32'59.40"W), 11.vi.2009, S. Reboleira leg. (ZMUC), 1 subad. 1 ♀ same data but, 29.viii.2009 (ZMUC). 1 ♂, Sicó, Gruta da Cerâmica (39°55'37.23"N, 8°31'3.99"W), 13.v.2013, S. Reboleira leg. (ZMUC).

Diagnosis: A species of Scutogona , characterized by

- small size (length of male 5.5 mm vs. 7-12 mm in other spp.)

- lack of eyes (≠ oculinigra )

- dorsum of body arched (≠ oculinigra )

- 3+3 macrochaetae on each body ring (≠ jeanneli )

- pregonopodal legs unmodified (≠ oculinigra )

- each angiocoxite with a deep longitudinal furrow (≠ vivesi )

- angiocoxites clearly overreaching syncolpocoxite (≠ mutica )

- syncolpocoxite mesally with a pair of caudad, broadly rounded lamellar lobes (≠ oculinigra and vivesi ).

Etymology: minor is a Latin comparative adjective. All Scutogona species are small, and whereas S. minor is smaller than the other known species, a still smaller one may be found in the future.

Description: Males and females completely unpigmented, with 29 pleurotergites (“30 segments”), body length 5–6 mm, vertical body diameter 0.45–0.5 mm.

Head ( Fig. 2 ) densely pilose, labrum tridentate, mandibular stipites (“cheeks”) subglobular, strongly protruding. Antennae stouter than in other species, ”antennal club” (“massue antennaire” = antennomeres 5+6+7– 8) ca. 4 times as long as broad.

Body subcylindrical, slightly tapering in both ends, lateral humps ( Fig. 3 ) situated high up on the flank, but leaving dorsum of body arched. Surface with polygonal microsculpture ( Fig. 3 ). Each pleurotergum with 3+3 macrochaetae situated on lateral humps, angle between them (MA) 120–130° on midbody rings, 160° on posterior 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 slightly (10–15%) longer than vertical body diameter.

Male sexual characters

Pregonopodal legs unmodified.

Anterior gonopods (P8) ( Figs 6–10 ): Angiocoxites (A) fused only at their base, curving backwards, covering tip of syncolpocoxite, each angiocoxite with a deep longitudinal furrow. Syncolpocoxite with a pair of stout, twopronged processes (KP) originating laterally and pointing disto-mesad, mesally with a pair of posterior laminar extensions (KL) (probably homologues of the ‘sac’ described by Ribaut (1913) for S. mutica and the ‘lame paire pectiné’ described by Mauriès & Vicente (1977) for S. vivesi . Telopodites (T) long, slender (but not as long as in S. vivesi ), with a terminal pore. Flagella (F) as in the other species.

Posterior gonopods (P9, ‘paragonopodes’) ( Fig. 11 ) with both telopodomeres of ca. equal length, telopodomeres without tubercles.

First and second pairs of post-gonopodal legs (P10 and P11) with coxal pores, P11 with a hook next to the pore ( Fig. 11 ).

Female sexual characters

Vulvae ( Figs 12–13 ) juxtaposed, operculum (O) ca. same length as valves, its distal margin slightly emarginated and with 2+2 setae; mesal and lateral valves (V) of same length, lateral valve with 5 setae, mesal valve with 4–7 setae; internal limit between valves strongly sclerotized, with a deep laterad notch. Post-vulvar organ (PV) with a short mesal process.

Distribution and habitat

Scutogona minor n. sp. has been discovered in three caves of Sicó karst: Gruta da Arrifana, Gruta da Cerâmica and Gruta de Santa Maria da Estrela, all shallow caves distributed along a highly dissected Jurassic karst ( Fig. 14 ). The distance between the extremes of the known distribution of the new species is 18 km. The specimens of Scutogona minor were only collected in the deepest and most thermally insulated parts of those caves. Humidity was 100% throughout the year, and temperatures ranged from around 16.4º C to 15.3ºC at soil level.

The new species shares its habitat with other detritivores hypogean species, such as the isopods Trichoniscoides broteroi Vandel, 1946 , a new species of Miktoniscus , and Porcellio cavernicolus Vandel, 1946 , together with the campodeid dipluran Podocampa cf. fragiloides Silvestri, 1932. This biocoenosis also includes hypogean predators: the pseudoscorpions Roncocreagris blothroides (Beier, 1962) and R. borgesi Zaragoza & Reboleira, 2013 , and the rove beetle Domene lusitanica Reboleira & Oromí, 2011 (Reboleira et al. 2010, 2011a, 2011b, 2013a, 2013b).

Some interesting troglophile species are common in this type of caves, such as the snail Oxychilus draparnaudi (Beck, 1837) , the centipede Lithobius pilicornis Newport, 1844 , the springtails Folsomia candida (Willem, 1902) , Proisotoma gisini Gama, 1964 , Oncopodura crassicornis Schoebotham, 1911 , Neelus murinus Folsom, 1896 , Arrhopalites elegans Cassagnau & Delamare, 1953 , Acherontiella xenylliformis Gisin, 1951 and Mesachorutes libycus (Caroli, 1914) , the ground beetle Trechus fulvus Dejean, 1831 , the guanobiont rove beetle Atheta subcavicola Brisout, 1863 , and the spiders Leptoneta conimbricensis Machado & Ribera, 1986 and Dysdera machadoi Ferrández, 1996 (Gama 1963, Reboleira et al. 2011b).

In the twilight area and near the entrances of these caves three species of non-hypogean millipedes are frequently observed, the chordeumatidan Haplobainosoma lusitanum Verhoeff, 1900 , the callipodidan Lusitanipus alternans (Verhoeff, 1893) and the julid Cylindroiulus propinquus (Porat, 1870) (Reboleira & Enghoff in press). The discovery of Scutogona minor increases the troglobiont diversity in the richest cave of central Portugal— Gruta da Cerâmica—which now counts 11 species of cave-adapted arthropods.

Discussion

The gonopods of Scutogona minor are particularly similar to those of S. vivesi , but also, surprisingly, to those of Meinerteuma lucasi (Silvestri, 1896) (= M. edoughense Mauriès, 1982 ). Mauriès (1982) compared Meinerteuma to Origmatogona and Coiffaiteuma , but also mentioned similarities with Scutogona . It is a question whether the distinction between these genera, and maybe all of the scutogonine genera, can be upheld. In his description of M. edoughense , type species of Meienrteuma, Mauriès stated that none of the walking legs had any particular structures. Re-examination of the holotype of M. edoughense (ZMUC) revealed, however, that although both P10 and both P11 are broken, enough remains of P11 to show that coxal hooks, similar to those seen in Scutogona and several other scutogonine genera, are actually present. Coxal hooks on P11 were also found by re-examination of the Tunisian male reported by Akkari et al. (2010)—these authors likewise didn’t notice this character, which contributes to the confusion about genus delimitations in Scutogoninae, clarification of which will require a much more comprehensive approach than lies within the scope of the present paper.

Figures

FIGURE 14. Location of the caves within the Sicó karst in central Portugal in which Scutogona minor n. sp. has been found. 1 — Gruta da Arrifana (type locality); 2 — Gruta de Santa Maria da Estrela and 3 — Gruta da Cerâmica.

FIGURES 1 – 5. Scutogona minor n. sp., female paratype from Gruta da Arrifana, SEM images. 1. Front end. 2. Head. 3. Lateral hump of midbody pleurotergum, right side. 4. Spinnerets. 5. Close-up of left spinneret, showing exuded thread. — Scales 100 µm (1, 2); 10 µm (3, 4); 1 µm (5).

FIGURES 6 – 10. Scutogona minor n. sp., male paratype from Gruta da Arrifana, anterior gonopods (P 8), SEM images. 6. Anterior view. 7. Oblique anterior-apical view. 8. Apical view. 9. Posterior view. 10. Lateral view (from right side). — A: right angiocoxite, F: flagellum, KP: two-pronged process, KL: laminar extension, T: left telopodite. — Scales 10 µm.

FIGURES 11 – 12. Scutogona minor n. sp., paratypes from Gruta da Arrifana, SEM images. 11. male, P 9 – 11. P 9: left posterior gonopod, P 10: left first post-gonopodal leg, P 11: right second post-gonopodal leg with coxal hook (arrow). — 12. Female, vulvae seen from the left. O: operculum, PV: post-vulvar organ, V: lateral valve. — Scales 10 µm.

FIGURE 13. Scutogona minor n. sp., female paratype from Gruta da Arrifana, vulvae in situ behind second pair of legs, posterior view. Insert: semi-diagrammatic drawing of left vulva, showing post-vulvar organ (PV) valves (V) with setae, and the internal separation of the two valves (dotted line). — Scale 50 µm.