Xangoniscus itacarambiensis, Bastos-Pereira & Souza & Ferreira, 2017

Bastos-Pereira, Rafaela, Souza, Leila Aparecida & Ferreira, Rodrigo L., 2017, A new amphibious troglobitic styloniscid from Brazil (Isopoda, Oniscidea, Synocheta), Zootaxa 4294 (2), pp. 292-300 : 293-297

Xangoniscus itacarambiensis sp. nov.

( Figs 1 D–5)

Etymology. The specific epithet refers to the city of the type-locality (Olhos D’Água cave): Itacarambi.

Material examined. Holotype male, body length 10.5 mm (ISLA19131), March 2003, Olhos D’Água Cave (15°06'47"S 44°10'11"W), municipality of Itacarambi, Northern Minas Gerais, Brazil, Ferreira, R. L. coll.

Paratypes: 3 females ( ISLA 19133), body length 8.59 ± 0.33 mm, same data as holotype. Additional material examined: MZUSP 29423 (3 individuals), MZUSP 29426 (3 individuals), MZUSP 29435 (1 individual), MZUSP 29459 (2 individuals), MZUSP 29463 (1 individual), MZUSP 29467 (3 individuals), all of them collected by Chaimovicz, F. in travertine pools in the same cave as holotype, April 1985.

Description. Body ( Fig. 2 A) unpigmented and smooth with tiny scale-setae, pereonites 1–7 width subequal. Eyes absent.

Cephalon quadrangular in dorsal view when considering the antennal lobes, with posterior margin slightly concave, well-detached from pereonite 1; antennal lobes slightly elevated in relation to the vertex; profrons with supra-antennal line V-shaped, with point directed to the projected clypeus; furrows on inner side of "V" formed by supra-antennal line.

Pereonites separated when the body is stretched, posterior tips more developed from pereonite 5–7. Pleon narrower at pleonites 1 and 2. Telson strongly depressed in relation to pleon and uropod protopods, laterally concave with truncated apex.

Antennula with 3 articles, proximal article longer than second, second subequal in length to third, second article with 1 small set of short setae on outer margin, distal article with six short apical aesthetascs. Antenna ( Fig. 2 G) fifth article of peduncle longer than flagellum; flagellum with 4 articles, first article longest, second and third articles subequal in length, fourth article shortest, tenuous division between third and fourth articles; when stretched antennae reach the posterior border of pereonite 2.

Right mandible with 1 penicil between pars incisiva and lacinia. Left mandible with 2 penicils; molar process more projected than in right mandible. Maxillula outer lobe with 5 + 5 teeth, 2 slender plumose setae present; endite with 3 penicils, inner penicil is the longest. Maxilla setose with 2 lobes: one bigger and rounded and other smaller and narrower. Maxilliped basis triangular enlarged on distal portion; endite narrow, densely setose, with 1 large rounded apical penicil between 2 triangular teeth; palp with 3 projections, each of them with 1 tuff of setae.

Uropod endopod and exopod subequal in length inserted at same level.

Male. Pereopods 1–2 ( Fig. 4 B–E) merus, carpus and propodus, pereopods 3–6 ischium, merus and carpus, and pereopod 7 ischium and merus with tiny fringed scales on sternal margin. Pereopods 1–4 propodus curved, curvature more pronounced on pereopod 4. Pereopods 4–6 carpus concave on distal half of sternal margin more evident on carpus 5 and 6. Propodus 5 and 6 longer and slender than others (P1–7 length at proportions 1: 1.3: 1.5: 1.5: 2.4: 2.4: 2.0, respectively, and length: width ratio of P1=4.1, P2=4.6, P3=5.9, P4=6.0, P5=10.3, P6=10.4, P7=8.2). Pereopods 6 and 7 ischium tergal face with short spiny scales. Genital papilla lanceolate with roughness apically.

Pleopod 1 ( Fig. 5 A) exopod trapezoidal with fine setae on inner and outer distal margin; endopod 2-jointed, longer than exopod; protopod without short setae on distal margin and long setae on distal margin. Pleopod 2 ( Fig. 5 C) exopod subtriangular, longer than proximal joint of endopod, margin with several short setae laterally; endopod robust, 2-jointed, distal joint about threefold longer than first, apical part with rounded margin with one narrow transverse pointed process (wrench-like structure) and outer triangular lobe, longitudinal ridge laterally reaching lobe basis.. Pleopod 3 ( Fig. 5 D) exopod triangular, slightly longer than wide, with short marginal setae. Pleopod 4 ( Fig. 5 E) exopod semi-circular and pleopod 5 ( Fig. 5 F) exopod trapezoidal, both wider than long with several short marginal setae.

Remarks. Xangoniscus itacarambiensis sp. nov. was placed in Xangoniscus due to the (1) cephalon with large antennal lobes, (2) absence of penicil on the molar process of the right mandible, (3) presence of lines of scales on pereopods, (4) male pleopod 1 exopod shorter than endopod 5, (5) complex apical part of the male pleopod 2 endopod, (6) unbranched dactylar seta of the pereopods and (7) genital papilla not enlarged distally. The new species shares more morphological traits with X. odara than with X. aganju , like the number of antennal flagellum, shape of male pleopod 2 exopod, absence of concave distal margin, presence of a large rounded penicil between two triangular teeth in the maxilliped endite and type of dorsal scale-setae. The morphological data suggest that X. odara and X. itacarambiensis are putative sister taxa. The new species presents the cephalon well-detached from the first pereonite, while in X. odara the head is more thickset. Furthermore, differences are observed in the proportion of antennula articles, number of aesthetascts in the antennula and in the distal lobe of the pleopod 2 endopod. Further characteristics comparing the Xangoniscus species are presented on Table 1.

Habitat and threats. Currently there are four already described troglobitic species for Olhos D’Água cave: Trichomycterus itacarambiensis Trajano & de Pinna, 1996 ( Siluriformes , Trichomycteridae ), Charinus eleonorae Baptista & Giupponi, 2003 ( Amblypygi , Charinidae ), Iandumoema uai Pinto-da-Rocha, 1996 ( Opiliones , Gonyleptidae ) and Endecous peruassuaensis Bolfarini & Bichuette, 2015 ( Orthoptera , Phalangopsidae ). Furthermore, there are at least three species of Colembola, Polydesmida and Styloniscidae to be described (Ferreira, personal communication). Therefore, the cave presents at least eight potentially troglobitic species, most of them endemic of this cave, what enhances its biological relevance.

The Olhos D’Água cave is inserted in a conservation unit of integral protection opened to visitation, the National Park Cavernas do Peruaçu, but the access is not allowed for all the caves. Olhos D’Água cave is not included in the touristic route, what somehow ensures the conservation of the species and the cave community as a whole. Other caves in the region were inventoried in the last 20 years and any other population of X. itacarambiensis sp nov. was recorded. Despite of the favorable condition of the cave, which is protected within a Conservation Unit, the endemism of X. itacarambiensis , as well as of other rare troglobites, represents a risk by itself.

The cave is inserted in a region of transition between the biomes Cerrado (Brazilian Savannah) and Caatinga, a semi-arid biome (Ab’Saber 1977). Since X. itacarambiensis presents an amphibious habit, as its con-generics, the species depends on both the aquatic and terrestrial habitats, therefore long dry periods may represent a natural disturbance for the population, which individuals probably migrate inside the cave searching for wet and aquatic microhabitats. It is important to mention that given the presence of a predator in the stream (the troglobitic fish Trichomycterus itacarambiensis ) it is unlike that the individuals of X. itacarambiensis migrates to the stream when the travertine dams dries. In this sense, specimens of X. itarcarambiensis have never been found in the stream. Accordingly, it is probable that specimens migrates to epikarstic compartments during dry seasons, returning to the cave in the subsequent rainy periods, searching for food (as bat guano or plant debris deposited in the travertine dams during cave flooding). However, more studies with X. itacarambiensis sp nov. regarding its ecology and behavior are encouraged to elucidate this issue.

Figures

FIGURE 1. A: Itacarambi municipality, Northern Minas Gerais, Brazil, and Olhos D’Água Cave localization within the limits of National Park Cavernas do Peruaçu; (B – C) Travertine dams along the Olhos D’Água stream; (D) Xangoniscus itacarambiensis sp nov. in the travertine dams, dorsal view; (E) lateral view.

FIGURE 2. Xangoniscus itacarambiensis sp nov., holotype male, Olhos D’Água Cave (15 ° 06 ' 47 " S 44 ° 10 ' 11 " W), municipality of Itacarambi, Northern Minas Gerais, Brazil (ISLA 19131). A, habitus; B, frontal view of head; C, laterial view of head; D, antennula; E, antenna; F, dorsal scale-setae. Scale bars A – C = 1 mm; D = 100 µm; E = 0.2 mm.

FIGURE 4. Xangoniscus itacarambiensis sp nov. A – G: pereopods 1 – 7. Scale bars A – G: 0.2 mm.

FIGURE 5. Xangoniscus itacarambiensis sp nov. A, pleopod 1; B, genital papilla; C, pleopod 2 exopod; D, pleopod 3 exopod; E, pleopod 4 exopod; F, pleopod 5 exopod; G, uropod. Scale bars A – G = 0.2 mm.