Xangoniscus dagua,

Cardoso, Giovanna Monticelli, Bastos-Pereira, Rafaela, Souza, Leila Aparecida & Ferreira, Rodrigo Lopes, 2020, New troglobitic species of Xangoniscus (Isopoda: Styloniscidae) from Brazil, with notes on their habitats and threats, Zootaxa 4819 (1), pp. 84-108: 89-93

publication ID

https://doi.org/10.11646/zootaxa.4819.1.4

publication LSID

lsid:zoobank.org:pub:AB417537-CE48-465A-8C23-5AF0B7602ADC

persistent identifier

http://treatment.plazi.org/id/E55C87AB-FFB1-1A25-C29F-F997FE81FE86

treatment provided by

Plazi

scientific name

Xangoniscus dagua
status

n. sp.

Xangoniscus dagua  n. sp.

Figs. 5–8View FIGURE 5View FIGURE 6View FIGURE 7View FIGURE 8, 19BView FIGURE 19

Material examined. Holotype: Male ( ISLA 77513), MG, Montes Claros , Parque Estadual da Lapa Grande, Lapa D’Água cave, 16.707038ºS, 43.920924ºW, 31 March 2015, leg. R. L. FerreiraGoogleMaps  . Paratypes: 1 male, 1 female, same data as holotype ( ISLA 14337)GoogleMaps  ; 3 males, same location as holotype, 20 December 2019 ( ISLA 77522)GoogleMaps  .

Etymology. The specific epithet means ‘from water’ in Portuguese. This refers to the name of the cave (Lapa D’Água cave) which represents the only known habitat of this species until the present.

Diagnosis. Antennula with four aesthetascs; antennal flagellum with five articles; pereopods 3 and 4 proximal margin of propodus concave, pereopods 5 and 6 with enlarged merus, pereopods 4–7 dactylus with setose sternal margin; male pleopod 1 exopod trapezoidal; male pleopod 2 exopod subtriangular; uropod exopod and endopod subequal in length.

Description. Maximum length: male, 9 mm. Colorless, eyes absent ( Figs. 5AView FIGURE 5, 19BView FIGURE 19). Dorsal surface smooth ( Fig. 5AView FIGURE 5). Cephalon ( Fig. 5BView FIGURE 5) with small antennary lobes; profrons with V-shaped suprantennal line, vertex with two transversal grooves. Posterior corners of pereonites progressively directed backwards, pereonite 7 not surpassing distal margin of pleonite 2; pleonites 3–5 epimera posterior point not developed; pleon narrower than pereon ( Fig. 5AView FIGURE 5). Telson ( Fig. 5CView FIGURE 5) with concave sides, round apex.

Antennula ( Fig. 5DView FIGURE 5) with three articles, second article shortest, distal article with four short aesthetascs, one subapical and three apical. Antenna ( Fig. 5EView FIGURE 5) reaches distal margin of pereonite 2 when extended backwards; fifth article of peduncle shorter than flagellum, with one long seta reaching haft length of first article of flagellum; flagellum with five articles. Left mandible with two penicils ( Fig. 1FView FIGURE 1), right mandible with one penicil, lacinia mobilis leaf-shaped ( Fig. 1GView FIGURE 1). Maxillula ( Fig. 1HView FIGURE 1) outer branch with 5 + 5 teeth, apically entire, and two thick plumose stalks; inner branch with three penicils. Maxilla ( Fig.1IView FIGURE 1) with bilobate apex, inner lobe wider than outer lobe with several setae on distal margin. Maxilliped ( Fig. 1JView FIGURE 1) basis enlarged on distal portion; palp apex with four tufts of setae; endite rectangular, outer and medial margins setose, apex with one triangular penicil between two teeth.

Pereopod 1 antennal grooming brush composed by serrated scale setae longitudinally on propodus and on sternal margin of carpus. Uropod ( Fig. 6AView FIGURE 6) protopod longer than distal margin of telson; endopod and exopod sub equal in length, exopod with proximal insertion.

Male. Pereopods 1–6 ( Fig. 6View FIGURE 6 B–E) merus with fringed scales on sternal margin; pereopods 3 and 4 propodus proximal margin concave, distal margin with fringed scales; pereopods 4–7 dactylus sternal margin setose; pereopods 5 and 6 merus enlarged, distal margin almost two times wider than proximal margin, wider than long. Pereopod 7 ( Fig. 6EView FIGURE 6) basis with scales of water conduction system. Genital papilla ( Fig. 7AView FIGURE 7) lanceolate. Pleopod 1 ( Fig. 7BView FIGURE 7) exopod trapezoidal, distal margin straight; endopod longer than exopod, with narrow basal article and flagelliform distal article; protopod distal margin shorter than exopod. Pleopod 2 ( Fig. 7CView FIGURE 7) exopod triangular, round distal margin, bearing one seta; endopod of two articles, basal article rectangular, as long as exopod, distal article wrench-like, transverse pointed process on apex, directed outwards, with lateral membrane. Pleopod 3 exopod ( Fig. 7DView FIGURE 7) ovoid, straight distal margin bearing setae. Pleopod 4 exopod ( Fig. 7EView FIGURE 7) rhomboidal wider than long, with distal margin rounded and bearing setae. Pleopod 5 exopod ( Fig. 7FView FIGURE 7) ovoid.

Remarks. Xangoniscus dagua  n. sp. resembles X. lundi  n. sp. by the modifications on pereopods, such as the proximal margin of propodus concave on pereopods 3 and 4, the enlarged merus in pereopods 5 and 6 and the setose sternal margin of dactylus on pereopods 4–7. However, these species can be distinguished by the number of aesthetascs on antennula (four versus three in X. lundi  n. sp.), and the shape of male pleopod 1 exopod (trapezoidal versus triangular in X. lundi  n. sp.). Xangoniscus dagua  n. sp. also resembles X. itacarambiensis  by the shape of male pleopod 1 exopod and the length of uropod rami (exopod and endopod subequal in length), but differs in the margin of pereopod 4 dactylus (only setose in X. dagua  n. sp.), the shape of pereopod 5 merus and pereopod 6 propodus (margin depressed only in X. itacarambiensis  ).

Habitat and threats. Lapa D’Água cave is the only known habitat of X. dagua  n. sp. until the present. This cave presents 1,234 m of horizontal projection and two distinct levels. The upper level (associated with the main entrance of the cave) comprises a predominantly linear conduit with heterogeneous floor substrates, varying from silt to collapsed rocks and dripstone floors ( Fig. 8AView FIGURE 8). At the innermost part of the upper level (approximately 400 m far from the entrance), there is a set of speleothems characterized by massive dripstones with several travertine pools ( Fig. 8C, DView FIGURE 8). Specimens of X. dagua  n. sp. were only found in this area, always associated with the travertine pools ( Fig. 8BView FIGURE 8). Despite the fact that there are some pools filled with water during the whole year, the population densities are higher during the rainy season and quite lower during the dry periods. This suggests the existence of vertical migrations between the macro cave and upper epikarstic habitats, as already observed for other species of this genus ( Silva et al. 2018). The lower level is trespassed by a drainage that enters the cave through a lower entrance located at the bottom of a sinkhole at the final portion of the cave. No specimens have ever been registered in this drainage probably due to the presence of (non-troglobitic) catfishes that may prey upon them.

The cave is located within the limits of Parque Estadual da Lapa Grande; hence it is currently inserted in a protected area. However, the cave receives human visitors, most of them unaware of the presence of the isopods. Therefore, there may be eventual risks of stepping, so that a management plan for the cave touristic use is highly recommendable.

MG

Museum of Zoology

R

Departamento de Geologia, Universidad de Chile