Xangoniscus ibiracatuensis, Cardoso & Bastos-Pereira & Souza & Ferreira, 2020

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 : 97-100

Xangoniscus ibiracatuensis n. sp.

Figs. 12–14 , 19D

Material examined. Holotype: Male ( ISLA 77516), Minas Gerais , Ibiracatu, Gruta São José III, 15.725886ºS, 44.205272ºW, 21 January 2015, leg. R. L. Ferreira . Paratypes: 3 males, 2 females, same data as holotype ( ISLA 47590).

Etymology. The specific epithet refers to the city of the type-locality (São José III cave), which is located in the municipality of Ibiracatu.

Diagnosis. Antennula with three aesthetascs; antennal flagellum with four articles; pereopods 5 and 6 merus sternal margin densely setose, dactylus with setae on sternal margin; pleopod 1 exopod triangular, with margin straight; pleopod 2 exopod subtriangular; pleopod 3 exopod with concave distal margin; uropod endopod and exopod subequal in length.

Description. Maximum length: male, 5 mm. Colorless, eyes absent ( Figs. 12A , 19D ). Dorsal surface smooth with scattered simple and fringed scale-setae. Cephalon ( Fig. 12B ) with small antennary lobes; profrons with Vshaped suprantennal line. 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. 12A ). Telson ( Fig. 12C ) with concave sides, round apex.

Antennula ( Fig. 12D ) with three articles, second article shortest, distal article with three aesthetascs, one subapical and two apical. Antenna ( Fig. 12E ) surpasses distal margin of pereonite 1 when extended backwards, fifth article of peduncle and flagellum subequal in length; flagellum with four articles. Left mandible with two penicils ( Fig. 1F ), right mandible with one penicil, lacinia mobilis leaf-shaped ( Fig. 1G ). Maxillula ( Fig. 1H ) outer branch with 4 + 5 teeth, apically entire, and two thick plumose stalks; inner branch with three penicils. Maxilliped ( Fig. 1I ) 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. 13A ) protopod longer than distal margin of telson; endopod and exopod subequal in length, exopod with proximal insertion.

Male. Pereopods 1–6 ( Fig. 13B, C ) merus longer than wide with fringed scales on sternal margin; pereopods 5 and 6 merus sternal margin densely setose, dactylus with setae on sternal margin. Pereopod 7 ( Fig. 13D ) basis with scales of water conduction system, merus margin with sparse setae. Genital papilla ( Fig. 13E ) lanceolate. Pleopod 1 ( Fig. 13E ) exopod triangular with fine setae on distal margin, straight margin; endopod longer than exopod, with narrow basal article and flagelliform distal article; protopod distal margin shorter than exopod. Pleopod 2 ( Fig. 13F ) exopod subtriangular, round distal margin, bearing one seta; endopod of two articles, basal article rectangular, shorter than exopod, distal article wrench-like, transverse pointed process on apex, directed outwards, with lateral membrane. Pleopod 3 exopod ( Fig. 13G ) ovoid, concave distal margin bearing setae. Pleopods 4 and 5 exopod ( Fig. 13H, I ) rhomboidal wider than long, with distal margin rounded and bearing setae.

Remarks. Xangoniscus ibiracatuensis n. sp. resembles X. ceci n. sp. in the pattern of modifications on pereopods 5 and 6, but are distinguished by the number of aesthetascs on antennula (three versus four or five in X. ceci n. sp.), the number of articles on flagellum of antenna (four versus six in X. ceci n. sp.), and the shape of male pleopod 1 exopod. The shape of male pleopod 3 exopod with concave distal margin is similar between these species, however in X. ibiracatuensis n. sp. the distal margin is round and the lateral margin is less developed.

Xangoniscus ibiracatuensis n. sp. also resembles X. lundi n. sp. by the number of aesthetascs on antennula (three, although with different size between the species) and the number of articles on flagellum of antenna (four), but can be distinguished by the shape of male pereopod 5 and 6 merus (longer than wide versus enlarged in X. lundi n. sp.). By the shape of male pleopod 2 exopod, this species resembles X. dagua n. sp., X. ceci n. sp. and X. lundi n. sp.

Habitat and threats. São José III cave is the only known habitat of X. ibiracatuensis n. sp. until the present. This cave is part of a set of three caves (closely located to each other: São José I, II and III) occurring in a karst valley in the municipality of Ibiracatu ( Fig. 11A ). Among the three caves, São José III cave is located in the uppermost portion of the intermittent drainage, which penetrates the cave through a secondary entrance ( Fig. 11B ), trespassing part of its main chamber, leaving the cave through its main entrance. The cave comprises a single voluminous chamber partially trespassed by two distinct intermittent drainages, one of them autogenic. There are visible signs that during strong rains a considerable part of this chamber is flooded (plant material deposits are widespread in different areas, Fig. 11C ). Specimens of X. ibiracatuensis n. sp. were only found within some travertine pools associated with a calcite flowstone connected to the cave ceiling, located in the inner portion of the cave chamber ( Fig. 11 C–E). Hence, such travertine can receive percolating water from the epikarst. During the dry seasons, it is likely that the travertine pools may be devoid of water, as occurs in many caves of the northeastern Minas Gerais state, especially considering the low amount of water inside the ponds. As observed for other species from this genus (e.g. X. itacarambiensis ), the end of the rainy season seems to signalize to the isopods that they should migrate to epikarst spaces. They may survive in such habitats during dry periods until the next rainy season, when the travertine pools are filled, allowing them to descent to the macro cave searching for additional food items. However, this is speculative, deserving further research on this species behavior ( Silva et al. 2018). Although the other two closely related caves (São José I and II caves) also present travertine pools, they were devoid of water and no specimens of Xangoniscus were found.

The external area surrounding those caves is quite preserved ( Fig. 11A ). Human visitors may enter the caves, but given the relatively difficult access to the karst valley, such tourism seems to be sporadic. Hence, the species seems not to be currently threatened, although this issue also deserves further research.

Figures

FIGURE 1. Xangoniscus lundi n. sp., male paratype. A, habitus, dorsal view; B, cephalon, frontal view; C, telson and uropod, dorsal view; D, antennula; E, antenna; F, left mandible; G, right mandible; H, maxillula; I, maxilla; J, maxilliped. Scale bars: A: 1 mm; B–J: 0.2 mm.

FIGURE 11. Xangoniscus ceci n. sp. A, Surroundings of Gruta Mãe Diná cave; B, entrance of the cave from the inside; C, entrance of the cave, view from the outside; D, collection site; E, specimen in the natural habitat.

FIGURE 12. Xangoniscus ibiracatuensis n. sp., male paratype. A, habitus, dorsal view; B, cephalon, frontal view; C, telson, dorsal view; D, antennula; E, antenna; F, left mandible; G, right mandible; H, maxillula; I, maxilliped. Scale bars: A: 1 mm; B–I: 0.2 mm.

FIGURE 13. Xangoniscus ibiracatuensis n. sp., male paratype.A, uropod; B, pereopod 1; C, pereopod 6; D, pereopod 7; E, genital papilla and pleopod 1; F, pleopod 2; G, pleopod 3 exopod; H, pleopod 4 exopod; I, pleopod 5 exopod. Scale bar: 0.2 mm.

FIGURE 14. Xangoniscus ibiracatuensis n. sp. A, Surroundings of São José III cave; B, entrance of São José III cave; C, entrance of São José III cave, from inside, red arrow indicating the collecting site, yellow arrow indicating organic matter and the water level; D, travertine pool where the specimens were collected; E, specimen in the natural habitat.

FIGURE 19. A, X. lundi n. sp.; B, X. dagua n. sp.; C, X. ceci n. sp.; D, X. ibiracatuensis n. sp.; E, X. santinhoi n. sp. Scale bar: 1 mm.