Circoniscus xikrin López-Orozco, Campos-Filho & Carpio-Díaz, 2024

López-Orozco, Carlos Mario, Campos-Filho, Ivanklin Soares, Gallo, Jéssica S., Gallão, Jonas E., Carpio-Díaz, Yesenia M., Borja-Arrieta, Ricardo & Bichuette, Maria Elina, 2024, Iron-isopods: new records and new species of terrestrial isopods (Isopoda, Oniscidea) from Brazilian Amazon iron ore caves, European Journal of Taxonomy 921 (1), pp. 116-135 : 125-129

Circoniscus xikrin López-Orozco, Campos-Filho & Carpio-Díaz sp. nov.

urn:lsid:zoobank.org:act:A22A4823-7BC1-428A-AE59-39C00021300B

Figs 1 , 5–7

Diagnosis

Pigment and eyes absent; schisma on pereonite 1, pereonite 2 without ventral lobe; telson with acute apex; antennula bearing eleven lateral aesthetascs arranged in six sets; pleopod 1 and 2 exopods with respiratory areas; pereopod 7 ischium elongated, bearing semicircular lobe on rostral portion, merus bearing semicircular lobe on rostral portion; pleopod 5 exopod apex short and acute.

Etymology

The new species is named for the Xikrin native people, inhabitants of Terras Indígenas Cateté and Trincheira Bacajá, State of Pará.

Material examined

Holotype

BRAZIL – Pará, Canaã dos Carajás • ♂; SB_0049 cave (also registered as GEM 1460 and known as Samuel II by local people); 6°18′58.4″ S, 49°53′41.1″ W; 629 m a.s.l.; 16 Feb, 2022; J.E. Gallão, J.S. Gallo, D.F. Torres and V.F. Sperandei leg.; part in micropreparations; LES 0028772 .

Paratype

BRAZIL – Pará, Parauapebas • 1 ♀; N3_0026 cave; 6°02′40.3″ S, 50°13′10.6″ W; 18 Feb. 2022; same collectors as for holotype; LES 0028773 .

Description

MEASUREMENTS. Maximum body length: male 5.8 mm, female 6 mm.

BODY. Color pale yellowish, with typical muscle spots insertions. Exoantennal conglobation ( Fig. 5A ); body strongly convex ( Fig. 5A ); dorsal surface smooth, bearing small fan-shaped scale-setae ( Fig. 5B ). Noduli laterales not discernible at ×400 magnification.

CEPHALON. Wider than long, frontal shield obtuse on medial upper margin and straight lateral margins, lateral lobes and eyes absent ( Fig. 5C–E ).

PEREON. Pereonite 1 epimera with schisma, anterior corners directed frontwards ( Fig. 5A, E–F ); pereonite 2 without ventral lobes, epimera with outer margin rounded ( Fig. 5A, E–F ); pereonites 3–4 epimera with outer margin rounded ( Fig. 5A ); pereonites 5–7 epimera subquadrangular ( Fig. 5A ).

PLEON. Pleonites 3–5 epimera with outline continuous with that of pereonite 7, apex acute and directed backwards ( Fig. 5G ); telson triangular, broader than long, with slightly concave sides, acute apex ( Fig. 5G ).

ANTENNULA. Composed of three articles, distal article longest, conical, proximal portion protruding, bearing 11 lateral aesthetascs arranged in six sets plus apical tip ( Fig. 5H ).

ANTENNA. Short and stout, not surpassing pereonite 2 when extended backwards; flagellum consisting of two subequal articles, distal article bearing 17 lateral aesthetascs in two groups; apical organ short than distal article of flagellum ( Fig. 5I ).

MOUTH. Mandibles with molar penicil of seven branches; left mandible ( Fig. 6A ) with 2+ 1 free penicils, right mandible ( Fig. 6B ) with 1 + 1 penicils. Maxillula ( Fig. 6C ) inner endite with two apical penicils, distal margin bearing outer tip; outer endite with 4+ 6 teeth, inner set with four teeth apically cleft. Maxilla ( Fig. 6D ) inner and outer lobe rounded and covered with thick setae. Maxilliped ( Fig. 6E ) as in C. mendesi sp. nov.

UROPOD. Protopod flattened and enlarged, filling gap between pleonite 5 and telson, surpassing distal margin of telson; exopod inserted on median margin; endopod short, twice as long as exopod and inserted proximally ( Fig. 6F ).

PEREOPOD 1. Elongated, carpus short, transverse antennal grooming brush; dactylus with inner claw not surpassing median portion of outer claw, ungual seta, and dactylar organ simple not surpassing distal margin of outer claw ( Fig. 7A ).

PLEOPOD EXOPODS. Pleopod 1 and 2 exopods with respiratory areas.

Male

PEREOPOD 1. Without particular modifications ( Fig. 7A ).

PEREOPOD 7. Basis and ischium elongated, sternal margin straight, with one semicircular lobe on distal portion in rostral view; merus bearing semicircular lobe in proximal portion in rostral view ( Fig. 7B ).

GENITAL PAPILLA. Triangular ventral shield and subapical orifices ( Fig. 7C ).

PLEOPODS. Pleopod 1 ( Fig. 7C ) exopod ovoid, with semicircular apex; endopod about twice as long as exopod and bent outwards, apex acute and bearing small setae along inner margin. Pleopod 2 ( Fig. 7D ) exopod triangular, outer margin concave with one seta; endopod flagelliform, longer than exopod. Pleopod 3–4 exopods as in Fig. 7E–F , respectively. Pleopod 5 ( Fig. 7G ) exopod triangular, outer margin almost straight with one tiny seta, inner margin covered with small setae, apex short and acute.

Taxonomic remarks

Circoniscus xikrin sp. nov. is clearly distinguishable from C. buckupi , C. carajasensis , and C. mendesi sp. nov. in the semicircular lobe on the rostral surface of the male pereopod 7 ischium and merus, and telson with acute apex.

Ecological remarks

The specimens were collected in the aphotic zone, inhabiting very moist soil. This species is considered to be a troglobitic due to the absence of body pigments and eyes, and elongated pereopods.

Distribution

Presently known only from SB_0049 cave in PARNA dos Campos Ferruginosos, Canaã dos Carajás, and N3_0026 cave system, Parauapebas, Pará, Brazil ( Fig. 1 ).

Figures

Fig. 1. Study area. A. Distribution of the species. B. Vegetation of FLONA de Carajás. C. Mineral exploitation mine.

Fig. 5. Circoniscus xikrin López-Orozco, Campos-Filho & Carpio-Díaz sp. nov., ♂, holotype (LES 0028772). A. Habitus, lateral view. B. Dorsal scale-seta. C. Cephalon, dorsal view. D. Cephalon, back view. E. Cephalon and pereonites 1 and 2, frontal view. F. Pereonite 1 and 2 epimera, ventral view. G. Pleonites 3–5, telson and uropods. H. Antennula. I. Antenna, with flagellum detail.

Fig. 6. Circoniscus xikrin López-Orozco, Campos-Filho & Carpio-Díaz sp. nov., ♂, holotype (LES 0028772). A. Left mandible. B. Right mandible. C. Maxillula. D. Maxilla. E. Maxilliped, arrow illustrating the endite in caudal view. F. Uropod. Figure not to scale.

Fig. 7. Circoniscus xikrin López-Orozco, Campos-Filho & Carpio-Díaz sp. nov., ♂, holotype (LES 0028772). A. Pereopod 1, arrow illustrating the dactylus in rostral view. B. Pereopod 7. C. Genital papilla and pleopod 1. D. Pleopod 2. E. Pleopod 3 exopod. F. Pleopod 4 exopod. G. Pleopod 5 exopod. Figure not to scale.