Eukoenenia audax, Souza & Mayoral & Ferreira, 2020

Souza, Maysa F. V. R., Mayoral, Jaime & Ferreira, Rodrigo L., 2020, A new troglobitic palpigrade from Central Brazil, with notes on a new opisthosomal character (Arachnida: Palpigradi), Zootaxa 4869 (4), pp. 493-514 : 494-507

Eukoenenia audax sp. nov.

urn:lsid:zoobank.org:act:8741F9DE-6C56-430F-AF25-691687FBF9E7

Material examined. Holotype, male ( ISLA 47676) . Paratypes: 4 males ( ISLA 47677, ISLA 47678, ISLA 47679, IBSP 31 ) , 2 females ( ISLA 47680, ISLA 47681) , 2 immatures C ( ISLA 47682, IBSP 32 ), and 2 immatures B (ISLA 47683, ISLA 47684). All collected in Brazil, Goiás, Nova Roma, Gruta Cabeceira d’água (528 m. a.s.l, 13°52’53.57”S, 46°55’44.31”W), 08/VIII/2015, leg. R. L. Ferreira .

Diagnosis. Lateral organs with 9–11 finely reticulated blades. A single deutotritosternal seta present, 7 pairs of setae on propeltidium and 3 pairs of setae on metapeltidium, t 1> t 2, t 3. Cheliceral fingers with 9 teeth each. Coxae II–IV with 5, 5, 2 thick setae. Basitarsus of leg IV with 6 setae (grt, gla, r, esp and 2 esd). Opisthosomal tergites II–VI with two pairs of setae t between one setae s on each side. Opisthosomal sternites IV–VI with two pairs of a setae (a 1, a 2) flanked by a thinner seta (s) on each side. First lobe of male genitalia with 13 pairs of setae (2 st + 9 + 2 fusules on each half), second and third lobes with 5 and 4 pairs of setae, respectively. First lobe of female genitalia with 11 pairs of setae.

Description.

Body length without flagellum 1765 (1565–1770).

Prosoma. Frontal organ with two reticulated branches with rounded ends ( Fig. 2 ). Lateral organ with 11 (9–11) pointed and reticulated blades ( Fig. 1 ). Propeltidium with 7 + 7 setae ( Fig. 2 ) and metapeltidium, with 3 + 3 setae, t 1 135 (120–147) longer than t 2 92 (87–107) and t 3 95 (95–100) ( Fig. 3 ). Labrum with 5 + 5 setae. Sternum with one deuto-tritosternal seta ( Fig. 6 ). Basal segment of chelicera with 6 proximal setae, p 4 and p 6 thickened and densely barbed and p 1 longer and thicker than the remaining setae (as shown for the immature B in Fig. 7 ); three distal setae: d 3 162 (150–165) longer than d 1 65 (62–70) and d 2 67 (67–72); d 3 long, tapering and with small sparse setules; d 1 and d 2 thickened, with subparallel borders, tiny setules and a crown of spines on a truncated and expanded tip ( Fig. 8 ). Hand of chelicera with 7 setae, 6 dorsal and one ventral setae; one long dorsal seta 74 (67–87) projected forward and inserted in distal edge at the base of the fixed finger; fingers with 9 teeth each.

Coxal chaetotaxy. Pedipalp coxa with 19 setae of different lengths ( Fig. 9 ). Coxa I with 15 setae: 13 normal and 2 tiny and thin microsetae ( Fig. 10 ). Coxa II with 15 setae: 5 thick and 10 normal setae ( Fig. 11 ). Coxa III with 14 setae: 5 thick, 7 normal, a long macroseta and a microseta (proximal to the macroseta) ( Fig. 12 ). Coxa IV with 10 setae: 2 thick and 8 normal setae ( Fig. 13 ).

Palp ( Fig. 15–16 ). ta3 with fs, cs with a basal spine, 2 r, 11 m and 9 normal setae; ta2 with 6 m; ta1 with 2 m; bta2 with 5 m and 1 normal seta; bta1 with 2 m and 1 normal seta; ti with 1 m and 8 normal setae; fe with 2 m and 6 normal setae; tc with 9 setae (2 smaller than the others). Palp formula: ta3: fs, cs, 2 r, 11 m, 9n; ta2: 6 m; ta1: 2 m; bta2: 5 m, 1n; bta1: 2 m, 1n; ti: 1 m, 8n; fe: 2 m, 6n; tc: 9n, including 2 short setae (not ms).

Leg I ( Figs 14 , 17 ). ta3 with 5 fs with subequal branches, 2 r, rs, cs, 13 m and 5 normal setae; ta2 with 5 m, 1 tb and 1 fs; ta1 with 3 r and 2 normal setae; bta4 with 5 m, 1 tb and 1 fs; bta3 with 1 r, 1 grt and 1 short normal seta; bta2 with 3 m, 1 normal seta, 2 tb and 1 long fs; bta1 with 1 normal seta, 1 m, 2 tb and 1 fs (with the inner branch shorter than the outer); ti with 9 normal setae; pa with 9 normal setae and 1 tb; fe with 9 normal setae; tc with 11 normal setae (2 of them considerably smaller). Leg I formula: ta3: 5 fs, 2 r, cs, rs, 13 m, 5n; ta2: 5 m, 1 fs, 1 tb; ta1: 3 r, 2n; bta4: 5 m, 1 fs, 1 tb; bta3: 1 r, 1 grt, 1n (short); bta2: 3 m, 1 fs, 2 tb, 1n; bta1: 1 m, 1 fs, 2 tb,1n; ti: 9n; pa: 9n, 1 tb; fe: 9n; tc: 11n.

Basitarsus leg IV (IVbta) ( Fig. 19 ) with 6 setae (grt, gla, r, esp and 2 esd); seta r inserted most distally: dr/IVbta = 0.76 (0.71–0.76); pair esd inserted distally but below the r seta insertion level; gla inserted at the base of the segment and at the same level as the single esp present; grt inserted slightly above esp and gla; esp, gla and grt inserted one third from the base of the segment. Length of these setae are given in Table 1.

Opisthosoma. Tergites II–VI with 3 + 3 dorsal setae, two pairs of t setae (t 1, t 2) between a pair of slender setae (s). Sternite III with 2 + 2 setae, 70 (50–77) (external) and 83 (65–82) (internal). Sternites IV–VI each with 2 + 2 thickened setae (a 1, a 2) between a pair of slender setae (s 1); a 1 86 (65–87), a 2 90 (75–102), and s 63 (45–67). A pair of small orifices present between a 1 setae on sternites IV–VI ( Figs 20–21 ). Intersegmental furrows between sternites III–IV, IV–V, V–VI and VI–VII with paired cavities, one at each side of the opisthosoma ( Figs 18 , 38 ). Last pair (between sternites VI–VII) less conspicuous and not clearly visible in all specimens. Some of these cavities (i.e. in holotype) seem to be open to the exterior, and the border of the cuticle is clearly visible. However, it is difficult to determine whether the opening is natural or it is rather tore tissue. Segments VII–XI with 8 setae each.

Male genitalia ( Figs 22–23 ). First lobe with 13 + 13 setae: 2 + 2 anterior setae (st 1, st 2), 2 + 2 setae as part of the long fusules, 2 + 2 setae adjacent to each fusule and being part of the same fusule structure, 2 + 2 anterior setae on 2 independent prominent structures on each side, and 5 + 5 more setae of different lengths. Fusules separated from each other (within each side), wider at their bases, long, stylized and ending on a secretory seta. Second lobe with 5 + 5 setae (a, b, c, c’, d) and third lobe with 4 + 4 (x, y, z, w). Each half of the third lobe with at least 10 small orifices ( Fig. 22 ).

Female genitalia ( Figs 24–25 ). First lobe with 11 + 11 setae in six transverse rows: 2 + 2 sternal setae (st 1, st 2) followed by 2 + 2, 1 + 1, 1 + 1, 1 + 1 and 4+4 distal setae (a 1 = 20, a 2 = 22, a 3 = 30, a 4 = 40); inner surface of the first lobe with a group of 3 orifices on each side and a medial pair of smaller orifices. Second lobe with 3 + 3 setae (x = 25, y = 42, z = 37); there is a series of cuticular spines and a group of 4 orifices on each half of this lobe.

Measurements and ratios of the adult specimens are given in Table 1.

Flagellum ( Figs 28–31 ). Only the first nine segments preserved in adult male ISLA 47679; missing in all other adult specimens. Segments 1, 2, 3, 5, 7 and 9 with an apical crown of spines. All nine segments bear a row of long setae inserted in distal half (2 setae smaller than others on segments II and VI). The number of setae and the length of these flagellar segments are reported in Table 2.

Immature, types B and C. Frontal organ similar to the adults ( Fig. 4 ). Lateral organs with 7–9 blades ( Fig. 5 ). Metapeltidium with t 1 (87–95), t 2 (65–75) and t 3 (72–85). Labrum with 4 pairs of setae. Proximal ( Fig. 7 ) and distal setae (d 1 = 45–52; d 2 = 47–52; d 3 = 100–120) on basal segment of chelicera with shape and relative lengths similar to the adults. Hand of chelicera with 6 setae, 5 dorsal and one ventral setae, including one long dorsal seta projected forward and inserted in distal edge at the base of the fixed finger; fingers with 8 teeth each.

Coxal chaetotaxy: pedipalp with 18 setae; coxa I with 15 setae; coxa II with 4 thick and 10 normal setae; coxa III with 4 thick, 7 normal, a long macroseta and a microseta; coxa IV with 1 thick and 8 normal setae.

The chaetotaxy of the remaining body segments is similar to that of the adults, including the ventral cavities.

Genital area of immature B: first lobe with 4 + 4 setae and 1 + 1 on the second lobe ( Fig. 26 ); sternite III with 2 + 2 setae at each side of the second lobe.

Genital area of immature C: first genital lobe with 5 + 5 long setae, in addition of a st pair of setae; second lobe without setae, and third lobe with a pair of short setae; sternite III with 2 + 2 setae at each side of the third lobe ( Fig. 27 ).

Measurements and ratios of the immature specimens are given in Table 3.

Flagellum. Only the first seven segments are preserved in the specimen ISLA 47684; segments 1, 2, 3, 5 and 7 with an apical crown of spines, all seven segments with a row of long setae inserted in distal half (2 setae smaller than others on segments II and VI). The number of setae and the length of these flagellar segments are included in Table 2.

Etymology. The specific name audax comes from Latin and it means “audacious, daring”. It refers to the unusual distribution of this troglobitic species inhabiting the sandy sediments deposited by the water stream in the cave (see “Habitat and ecological notes” for details).

Habitat and ecological notes. Specimens of Eukoenenia audax were only found in the cave Cabeceira d’água, located in the municipality of Nova Roma, state of Goiás, Brazil ( Figs 32–33 ). Despite the efforts to sample other nearby caves in the area, no palpigrades were captured. The Cabeceira d’água is a limestone cave with 3,670 meters of horizontal projection and most part of its main passage runs along an autogenic stream that arises at the deepest portion of the cave ( Fig. 35 ). The cave has two entrances, both partially obstructed by big rocks and sandy sediments that make the access to the inner portions of the cave difficult. One entrance is blocked by medium sized rocks ( Fig. 36 ) and a spring pours out of the cave throughout these rocks. A second entrance, around 100 meters from the first one, leads to a dry creek bed that ends in a small lake. Although this way seems to be also blocked, it is possible to continue into the cave through a lateral opening by the side of the lake, which is normally filled with sediment. After unblocking this passage, a narrow corridor leads back to the main passage. There is a siphon around 200 meters from the “unblocked” access point (the water level reaches the cave ceiling), and the access to the inner portion of the cave is only possible during dry periods. Therefore, this last section of the cave is isolated from the exterior most of the time and it is extremely humid. The stream runs through the cave and deposits sand in different locations. There are also small deposits of plant debris and organic matter. A dry upper level with numerous chambers is accessible from certain points one dozen meters below in the main passage.

Remarkably, the natural habitat of E. audax seems to be the sand deposits near the water stream ( Fig. 34 ). All Brazilian troglobitic palpigrades described from caves with water streams in them were collected in their upper levels, away from the main watercourses, i.e. E. spelunca Souza & Ferreira, 2011 , E. sagarana Souza & Ferreira, 2012 or E. jequitinhonha Souza & Ferreira, 2016 . This may be explained because their small size limits their ability to escape from unexpected and fast water pulses (flash floods). In contrast, E. audax was observed only behind the siphon and close to the water level, mainly on the sand banks or the nearby walls. Despite a thorough search for this species in the upper chambers, palpigrades could not be found there, in contrast to other Brazilian troglobitic species. Several specimens were observed walking on the surface of water ponds near the stream. They seemed to be patiently looking for preys rather than being trapped on it, and this may indicate their ability to move on water. Springtails (Collembola) are quite common in the cave and were identified in the sand banks as potential preys.

Another interesting observation about E. audax is its population density. While most Brazilian troglobitic species are scarce (a cave visit yields a few specimens at the most), the density of E. audax is unexpectedly high: dozens of specimens are commonly observed all along the main passage behind the siphon. In the first visit to the cave, more than 50 specimens were observed in a single afternoon. Only a few were collected for conservation purposes and collecting permit restrictions. This distribution and density are certainly atypical, making this cave one of the most remarkable sites worldwide for the study of troglobitic palpigrades. The high number of specimens found offers unique opportunities to investigate biological and ecological aspects of these enigmatic arachnids in the future, as well as to collect samples for molecular work. A similar case has been reported for Ardovská cave, in Slovakia, that houses a big population of Eukoeneni a spelaea (Peyerimhoff, 1902) and that has been the target of several studies in the last 20 years ( Kovač et al. 2002; Smrž et al. 2013; Ballesteros et al. 2019). We also recommend to further study the reason for this high density, in addition to the behavioral mechanisms that prevents them from being washed away during flash floods.

The cave is rarely visited because of the difficulties described above. Only speleologists who enter the cave to run scientific studies or survey work can reach the cave sections where the palpigrades are found. Although the cave is well preserved, its surroundings are quite altered, especially the natural vegetation that was replaced by pastures. Native vegetation persisted only on limestone outcrops where farming is unfeasible ( Fig. 37 ).

Figures

FIGURE 17. Eukoenenia audax sp. nov., holotype, leg I: trochanter—tarsus 2. A—detail of the forked seta on basitarsus 1. Scale bar 100 μm.

FIGURES 1–3. Eukoenenia audax sp. nov., holotype. 1, lateral organ, left side (scale bar 25 μm); 2, propeltidium, dorsal view (scale bar 100 μm); 3, metapeltidial setae (scale bar 50 μm).

FIGURES 4–8. Eukoenenia audax sp. nov. 4, frontal organ, immature B ISLA 47683 (scale bar 20 μm); 5, lateral organ, im- mature B ISLA 47683 (scale bar 15 μm); 6, deutotritosternal seta, male ISLA 47677 (scale bar 20 μm); 7, proximal setae (p1 –p6) on basal segment of chelicera, immature B ISLA 47683 (scale bar 25 μm); 8, distal setae (d1 –d3) on basal segment of chelicera, male ISLA 47677 (scale bar 50 μm).

FIGURES 9–13. Eukoenenia audax sp. nov., holotype, coxae. 9, pedipalp; 10, leg I; 11, leg II; 12, leg. III; 13, leg. IV. The thickened setae are indicated in solid black. Scale bar 100 μm.

FIGURES 14–15. Eukoenenia audax sp. nov., holotype. 14, tarsus 3 of leg I; 15, tarsus 3 of pedipalp. Scale bars 50 μm.

FIGURE 16. Eukoenenia audax sp. nov., holotype, pedipalp: trochanter—tarsus 2. Scale bar 50 μm.

FIGURES 18–19. Eukoenenia audax sp. nov., holotype. 18, opisthosoma, ventral view showing the placement of paired cavities in the division of sternites III–IV, IV–V, V–VI and VI–VII (scale bar 200 μm); 19, basitarsus of leg IV (scale bar 50 μm).

FIGURES 20–22. Eukoenenia audax sp. nov. 20, sternite V, male ISLA 47679 (scale bar 25 μm); 21, sternite IV, female ISLA 47681 (scale bar 25 μm); 22, part of second and third lobes of male genitalia, male ISLA 47677 (scale bar 20 μm). White arrows in figures 20 and 21 indicate a pair of small orifices between a1 setae; arrows in figure 22 indicate some (only those in focus) small orifices in the third genital lobe.

FIGURES 38–44. Light (38, 39, 41–44) and SEM (40) micrographs of opisthosomal sternites in several Eukoenenia and Prokoenenia species. 38, Eukoenenia audax sp. nov., holotype, sternites IV–V; 39, Prokoenenia javanica, female holotype (MHNG), sternites IV–VI with dashed ellipses on right side indicating the ventral sacs; 40, E. cf. ferratilis, opisthosomal sternites; 41, Eukoenenia ibitipoca, female paratype (ISLA), sternites IV–VI; 42, Eukoenenia ibitipoca, male holotype (ISLA), sternites IV–V; 43, Eukoenenia navi, female paratype (ISLA12726), sternites IV–V; 44, Eukoenenia navi, male holotype (ISLA), sternites IV–VI. Dashed ellipses indicate the position of opisthosomal cavities. Scale bars: 60 μm.

FIGURES 24–27. Eukoenenia audax sp. nov. 24, female genitalia, first genital lobe, ISLA 47681; 25, female genitalia, second genital lobe, ISLA 47681; 26, Immature B, primordia of genital lobes, ISLA 47683; 27, Immature C, primordia of genital lobes, IBSP 32. Scale bars 50 μm.

FIGURES 28–31. Eukoenenia audax sp. nov., flagellar segments I–IX, male ISLA 47679. 28, segments I–II; 29, segments III–IV; 30, segments V–VI; 31, segments VII–IX. Scale bars 100 μm.

FIGURES 32–37. Cave Cabeceira d’água, location and habitat of the news species. 32–33, live specimens of Eukoenenia audax sp. nov.; 34, sampling efforts in the sand banks where the palpigrades were found; 35, main passage of the cave running along the subterranean stream; 36, spring at one of the cave entrances; 37, karst landscape in the municipality of Nova Roma (Goiás state, Brazil) where the cave is located.