Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette, 2023

Campos-Filho, Ivanklin Soares, Sfenthourakis, Spyros, Gallo, Jéssica Scaglione, Gallão, Jonas Eduardo, Torres, Dayana Ferreira, Chagas-Jr, Amazonas, Horta, Lília, Carpio-Díaz, Yesenia Margarita, López-Orozco, Carlos Mario, Borja-Arrieta, Ricardo, Araujo, Paula Beatriz, Taiti, Stefano & Bichuette, Maria Elina, 2023, Shedding light into Brazilian subterranean isopods (Isopoda, Oniscidea): expanding distribution data and describing new taxa, Zoosystema 45 (19), pp. 531-599 : 553-554

Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette , n. sp.

( Figs 16-18 ; 21 )

urn:lsid:zoobank.org:act:873D2089-7918-4F1C-B7ED-071A64C3C351

TYPE MATERIAL. — Holotype. Brazil • ♂ (parts in micropreparations); Caverna Lagoa Azul, Nobres , state of Mato Grosso; 14°26’48.1”S, 56°1’33.2”W; 350 m a.s.l.; 24.IX.2017; J. E. Gallão, R. Machado & A. Chagas-Jr leg.; LES 27987 .

Paratype. Brazil • 1 ♀ (parts in micropreparations); same locality as holotype; 5.V.2015; M. E. Bichuette, A. Chagas-Jr & G. A. Nunes leg.; LES 27988 .

ETYMOLOGY. — The new species is named after the typical blue color of the water in the cave where the specimens were collected.

DESCRIPTION

Maximum body length: ♂ 3 mm, ♀ 6.5 mm. Animal without body pigments. Body ( Fig. 16A ) strongly convex; dorsal surface bearing small triangular scale-setae ( Fig. 16B ). Noduli laterales as in Figure 16A, G, I . Cephalon ( Fig. 16 CE) frontal shield rectangular, bent backwards over vertex, frontal margin broadly rounded; eyes composed of about 10-11 ommatidia. Pereonites 1 and 2 with ventral lobes; pereonites 1-4 with posterior margin straight, 5-7 gradually more concave; pereonite 1 epimera with anterior corners directed frontwards, those of 2-4 with outer margin rounded, and those of 5-7 subquadrangular ( Fig. 16A, E , G-J). Pleon ( Fig. 16A, K ) with epimera 3-5 well developed, directed backwards with acute apices; telson slightly broader than long, with slightly concave sides. Antennula ( Fig. 16L ) distal article longest, conical bearing about four lateral aesthetascs arranged in two rows and apical tip. Antenna ( Fig. 16M ) short and stout, not surpassing pereonite 1 when extended backwards; flagellum with subequal articles, distal article bearing two lateral aesthetascs; apical organ slightly longer than distal article of flagellum. Mandibles ( Fig. 17A, B ) with dense cushion of setae on incisor process, molar penicil consisting of about 10 branches. Maxillula ( Fig. 17C ) inner endite with two apical penicils, distal margin bearing outer tip; outer endite with 4+5 teeth, inner set with four teeth apically cleft. Maxilla ( Fig. 17D ) inner lobe rounded and covered with thick setae; outer lobe rounded, twice as wide as inner lobe, covered with thin setae. Maxilliped ( Fig. 17E ) palp with one strong seta on proximal article; endite subrectangular, medial seta short, not surpassing distal margin, distal margin covered with thin setae and bearing one seta on outer portion, rostral surface with setose sulcus ending with one short penicil. Pereopod 1 carpus with short antennal grooming brush; dactylus with two claws, ungual and dactylar setae simple, surpassing outer claw. Uropod ( Fig. 16K ) protopod enlarged, filling gap between pleonite 5 and telson, slightly surpassing distal margin of telson; exopod inserted on median margin, endopod twice as long as exopod and inserted proximally.

Male

Pereopod 1 ( Fig. 18A ) merus and carpus with sternal margin covered with short scales and sparse strong setae. Pereopod 7 ( Fig. 18B ) ischium elongated, sternal margin straight; merus bearing triangular lobe on rostral portion; carpus twice as long as merus. Pleopod 1 ( Fig. 18C ) exopod triangular, outer margin slightly concave on distal portion; endopod twice as long as exopod, distal portion bent outwards and bearing small setae on medial margin. Pleopod 2 ( Fig. 18D ) exopod triangular, outer margin concave; endopod flagelliform, slightly longer than exopod. Exopods of pleopods 3 and 4 as in Figure 18E and F , respectively. Pleopod 5 exopod ( Fig. 18G ) with outer margin sinuous, inner margin grooved to accommodate pleopod 2 endopod.

REMARKS

The genus Circoniscus comprises 10 species endemic to South America ( Schmidt 2007; Campos-Filho et al. 2018a). To date, Brazil holds the highest diversity in the genus, with nine species present in the country, i.e., C. bezzii Arcangeli, 1931 , C. buckupi Campos-Filho & Araujo, 2011 , C. carajasensis Campos-Filho & Araujo, 2011 , C. gaigei Pearse, 1917 , C. hirsutus Schmidt, 2007 , C. incisus Souza & Lemos de Castro, 1991 , C. intermedius Souza & Lemos de Castro, 1991 , C. ornatus ( Verhoeff, 1941) , and C. pallidus Arcangeli, 1936 (see Campos-Filho et al. 2018a).

Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette , n. sp. differs from all other species of the genus in having a triangular lobe on the rostral surface of the male pereopod 7 merus. Only one species of the genus is recorded from the state of Mato Grosso, C. intermedius ( Schmidt 2007; Campos-Filho et al. 2014), from which it differs in having the eyes composed of 10-11 ommatidia (vs 20 in C. intermedius ), pereonite 2 epimera with ventral lobe (vs absent in C. intermedius ), telson slightly wider than long (vs as wide as long in C. intermedius ), and male pleopod 1 exopod triangular, and as wide as long (vs heart-shaped, and slightly wider than long in C. intermedius ) (see Souza & Lemos de Castro 1991; Schmidt 2007).

This species is considered to be a troglophile. However, its body is pigmentless and the number of ommatidia is reduced, characters typically observed in troglobitic species. The species has a preference for highly humid places, composed of silt and guano substrates. Moreover, in the aphotic zone, its abundance is reduced, probably due to the lack of resources. More sampling efforts should be paid outside caves to confirm its classification as a troglophile.

Figures

FIG. 16. — Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette, n. sp., male holotype, LES 27987: A, lateral habitus; B, scale-seta; C, cephalon and pereonites 1 and 2, frontal view; D, cephalon, dorsal view; E, cephalon, and pereonites 1 and 2, lateral view; F, cephalon, back view; G, pereonite 1 epimera, dorsal view; H, pereonite 1 epimera, ventral view; I, pereonite 2 epimera, dorsal view; J, pereonite 2 epimera, ventral view; K, pleonites 4 and 5, telson, and uropods; L, antennula; M, antenna. Scale bar: A, 1 mm.

FIG. 17. — Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette, n. sp., male holotype, LES 27987: A, left mandible; B, right mandible; C, maxillula; D, maxilla; E, maxilliped.

FIG. 18. — Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette, n. sp., male holotype, LES 27987: A, pereopod 1; B, pereopod 7; C, pleopod 1; D, pleopod 2; E, pleopod 3 exopod; F, pleopod 4 exopod; G, pleopod 5 exopod.

FIG. 21. — Distribution map of Scleropactidae and Platyarthridae representatives: A, Circoniscus caeruleus Campos-Filho, Sfenthourakis & Bichuette, n. sp.; B, Trichorhina amplitelson Campos-Filho, Carpio-Díaz & Borja-Arrieta, n. sp. Abbreviations of states: MS, Mato Grosso do Sul; MT, Mato Grosso.