Allokoenenia canhembora, Souza & Ferreira, 2022

Souza, Maysa Fernanda Villela Rezende & Ferreira, Rodrigo Lopes, 2022, Two extraordinary troglobitic species of Allokoenenia (Eukoeneniidae: Palpigradi) from Brazil: first records of this initially monotypic genus more than a century after its description, European Journal of Taxonomy 789, pp. 11-48 : 17-26

Allokoenenia canhembora sp. nov.

urn:lsid:zoobank.org:act:F6B9B9E0-6B19-4FCB-82CF-A8B4F754F492

Figs 3–9

Diagnosis

Frontal organ formed by 2 reticulated and expanded branches; 5 blades finely reticulated in the lateral organs; 5 setae on deutotritosternum; 7 pairs of short setae on propeltidium; 3 pairs of setae with similar length on metapeltidium; cheliceral fingers with 9 teeth each; coxae II–IV with 3, 3, 1 thick setae, respectively; 5 setae (grt, r, esp and 2 esd) on basitarsus of leg IV; opisthosomal tergites II–VI with two pairs of setae t between one setae s on each side; opisthosomal sternites IV–VI with three pairs of a setae (a 1 shorter than a 2 and a 3) flanked by one s seta on each side; opisthosomal segment XI with 2 pairs of ventral setae arranged in 2 rows; first lobe of female genitalia with 10 pairs of setae; flagellum formed by 14 moniliform segments with setae of different lengths, including very long setae inserted in a V arrangement from the sixth flagellar segment onwards.

Etymology

The species ephitet is derived from a word of the Tupi language meaning ʻfugitiveʼ. The species received this name due to the difficulty of capturing the specimens, which quickly ran away and hid under the calcite plates on the cave floor as soon as they were discovered (see: Habitats and threats). The name is to be treated as a noun in apposition.

Material examined

Holotype BRAZIL • ♀; Bahia, Campo Formoso, Toca do Gonçalo Cave ; 10°30′40.94″ S, 40°53′42.10″ W; 527 m a.s.l.; 11 Jun. 2012; R.L. Ferreira leg.; ISLA 50394 .

Other material

BRAZIL • 1 ♀; same collection data as for holotype; 16 Mar. 2014; ISLA 50395 .

Description

Adult female

MEASUREMENTS AND RATIOS. See Table 2.

BODY LENGTH. Without flagellum: 1420 μm.

PROSOMA. Frontal organ formed by two reticulated and expanded branches (42 long), with blunt tips ( Fig. 3A ). Lateral organ with 5 blades pointed-lanceolate (32 long) and finely reticulated ( Fig. 3B ). Propeltidium with 7 +7 short setae ( Fig. 4B ). Setae t 1, t 2 and t 3 of metapeltidium 77, 75 and 77 long, respectively. Deuto-tritosternum with 5 setae in U-shaped arrangement ( Fig. 4A ). Labrum with 5+5 short setae. Basal segment of chelicera 195 long (dorsal length), with 6 proximal setae (p 4 and p 6 thickened and densely barbed; p 1 slightly thinner and barbed) ( Fig. 4C ), and 3 distal setae: d 3 (107) longer than d 1 (60) and d 2 (62); d 3 smooth near base and barbed in its distal half, d 1 and d 2 thin, flexible and with tiny projections in apex; and one apical seta. Hand of chelicera with 7 setae: 4 dorsal setae, 2 setae in its outer portion (1 close to articulation of movable finger and 1 on a tubercle close to teeth of fixed finger) and 1 seta inserted in its inner portion. Fingers with 9 teeth each.

COXAL CHAETOTAXY. Pedipalp coxa with 18 setae ( Fig. 3C ); coxa I with 13 ordinary setae and two microsetae ( Fig. 3D ); coxa II with 3 thick setae, 2 macrosetae and 8 ordinary setae ( Fig. 3E ); coxa III with 3 thick setae, 1 macroseta, and 8 ordinary setae (including 1 small seta adjacent to macroseta) ( Fig. 3F ) and coxa IV with 1 thick and 8 ordinary setae ( Fig. 3G ).

PEDIPALP. tc with 8 setae (2 considerably smaller than others); fe with 8 setae ( Fig. 5A ); ti with 8 setae; bta1 with 2 m and 1 normal seta; bta2 with 2 normal setae and 4 m; ta1 with 2 m; ta2 with 6 m ( Fig. 5B ); ta3 with 1 long fs, 1 cs with a conspicuous spine, 2 r, 10 m (one macroseta with basal denticle and conspicuous spine) and 10 normal setae ( Fig. 7A ).

LEG I. tc with 12 normal setae (1 considerably smaller than others); fe with 9 normal setae; pa with 9 normal setae and 1 tb ( Fig. 6A ); ti with 9 normal setae; bta1 with 1 m, 1 normal seta, 2 tb and 1 fs (with inner branch shorter than outer branch); bta2 with 4 m, 2 tb and 1 long fs ( Fig. 6B ); bta3 with 1 r, 1 grt and 1 short normal seta; bta4 with 5 m, 1 tb and 1 long fs; ta1 with 5 normal setae (2 considerably smaller than others); ta2 with 5 m, 1 tb and 1 long fs ( Fig. 6C ); ta3 with 5 fs (with subequal branches) arranged as fs 1 / fs 2 / fs 3 / fs, rs (rs / fs 1 =2.2), 2 r, 1 cs, 13 m and 5 normal setae ( Fig. 6D ).

4+5

LEG II. tc with 3 normal setae; fe with 1 m and 4 normal setae; pa with 2 m, 1 thick seta, and 2 normal setae; ti with 1 thick seta and 4 normal setae; bta with 6 normal setae; ta with 1 r, 1 m and 9 normal setae.

LEG III. tc with 2 normal setae; fe, pa, and ti with 1 thick seta and 4 normal setae each; bta with 6 normal setae; ta with 1 r, 1 m and 9 normal setae.

LEG IV. tc with 3 normal setae; fe with 1 m and 2 normal setae; pa and ti with 1 thick and 4 normal setae each; bta with grt, r, esp, and 2 esd; ta1 with 4 normal setae; ta2 with 8 normal setae.

IVBTA. 7.2 × longer than wide and with 5 setae (grt, r, esp and 2 esd). Seta r inserted in distal half (dr / IVbta =0.64) and grt inserted in proximal half of segment ( Fig. 7B ).

OPISTHOSOMA. Tergites II–VI with 3 +3 dorsal setae, two pairs of t setae (t 1 =35‒41 μm, t 2 = 37‒42 μm) between a pair of slender setae (s =27‒35 μm) ( Fig. 8A ). Sternite III with 2+ 2 setae. Sternites IV–VI each with 3+ 3 thickened setae (a 1 =30 μm, a 2 =41‒45 μm, a 3 =48‒53 μm) between a pair of slender setae (s = 36‒40 μm) (inserted caudal to thick setae); pair of pores present between a 1 setae on sternites IV‒VI ( Fig. 8B ). Presence of inconspicuous paired cavities in intersegmental furrows between sternites III–IV, IV–V, V–VI and VI–VII, one at each side of opisthosoma. Segments VII–X with 8 setae each (4 dorsal and 4 ventral). Segment XI elongated (1.15 × as long as wide), with dorsal row of 2+2 long setae (inner pair=160 μm; outer pair =117‒125 μm) inserted in its distal half and 2 pairs of ventral setae, 1 inserted around middle of segment (60 μm) and other inserted in apical region (75 μm) ( Fig. 8C ). Intermediate ring of flagellum reduced in size (11 μm) and bears 2 tiny setae (8 μm).

FEMALE GENITALIA. First lobe with 10 +10 setae in 5 transverse rows: 2+ 2 sternal setae (st 1, st 2) followed by 2+2, 1+1, 1 +1 and 4 +4 distal setae (a 1 =11 μm; a 2 = 12 μm; a 3 =20 μm; a 4 =30 μm); interior surface of the first lobe with a group of 3 orifices on either side and a medial pair of small orifices ( Fig. 7C ). Second lobe with 3+2 setae, asymmetry caused by lack of 1 y seta (x = 15 μm; y = 29 μm; z = 27 μm), and with cuticular spines; presence of group of 4 orifices on each half ( Fig. 7D ).

FLAGELLUM. Arched and formed by 14 short and moniliform segments. First flagellar segment with 4 short setae (21–44 μm); second with 2 short setae (27–30 μm); third with 2 long setae (75 μm) and 4 short setae (10 – 30 μm); fourth with 3 short setae (15–31 μm); fifth with 5 short setae (25–33 μm); sixth with 2 very long setae; seventh with 1 short seta (15 μm) and 4 very long setae; eighth with 3 short setae (10–15 μm) and 2 very long setae; remaining segments bear 1 short seta (10–23 μm) and 4 very long setae each ( Fig. 8D ). Very long setae inserted laterally on segments, being arranged in V along flagellum ( Fig. 9H ). Length (μm) and total number of setae (N) of flagellar articles available in Table 1 .

Male and immatures

Unkown.

Distribution

Known only from the type locality.

Remarks

Allokoenenia canhembora sp. nov. belongs to the genus Allokoenenia mainly because of the shape of the last opisthosomal segments and flagellum ( Figs 8C–D , 9F–H ). It shares with A. afra the presence of a short and arched flagellum formed by 14 moniliform segments, the chaetotaxy of opisthosomal sternites IV–VI (1 s +3 a +3 a +1 s), and the arrangement of the ventral setae of the last opisthosomal segment (in two rows) ( Figs 2 , 8C ). However, they can be distinguished by the shape of the frontal organ ( Figs 1C , 3A ), and by the number of blades on lateral organs (5 vs 1) and deutotritosternal setae (5 vs 1) ( Silvestri, 1913). Furthermore, we observed that the immature specimen of A. afra has 6 setae on basitarsus IV (grt, r, gla, esp and 2 esd). This feature was not visible in the adults and was not described by Silvestri (1913), but they probably have at least 6 setae, since in general the setation of this article is already complete in immatures of this stage or they have fewer setae than the adults. In the new species, the basitarsus IV bears only 5 setae (grt, r, esp and 2 esd). Some flagellar characters can also be useful to distinguish these two species: the flagellar segments 1–3, 5, 7 and 9 of A. afra bear the typical apical cuticular spines present in the flagellum of other palpigrades, as well as setae of uniform shape despite showing some variation in their lengths, as represented in Silvestri (1913: 216, fig. VI, 5) and confirmed by the study of the specimens ( Fig. 1B ); in A. canhembora sp. nov., the cuticular spines are absent and the flagellar segments carry setae of very different lengths and shapes, including very short (around 10–15 μm) to very long setae (longer than 100 μm).

Habitat and threats

The Toca do Gonçalo Cave is associated to carbonatic rocks from the Caatinga geological group, which comprises relatively young rocks deposited around three million years ago under a lacustrine condition. Such rocks are closely inserted to old carbonatic rocks from the Una geological group, from the Neoproterozoic. The cave is located in a semiarid biome (the Caatinga Formation), in the Campo Formoso Municipality, Bahia State, Northeastern Brazil ( Fig. 9A ). It presents around 500 m of topographed conduits and a single horizontal lenticular-shaped entrance ( Fig. 9B ), which connects to a descending conduit. This cave presents two distinct levels: the upper level (which corresponds to the left branch of the cave), is predominantly dry, and the lower level (corresponding to the right branch) is quite humid ( Fig. 9C ) ( Souza-Silva & Ferreira 2016). The lower level used to be mostly submerged by the water table, but it is currently accessible, since the water table reduced dramatically, as will be discussed further on. The main sources of organic matter for both terrestrial and aquatic species is the dissolved and particulate organic matter imported from the external habitats during strong rains, but also the small guano deposits and some root mats that can be used as food by invertebrates. The Toca do Gonçalo Cave is considered a hotspot of subterranean biodiversity (only three hotspots are currently known to South America), presenting 22 troglobitic species ( Souza-Silva & Ferreira 2016). Hostpots of subterranean biodiversity are those caves (or cave systems) with 20 or more cave-restricted species ( Culver & Sket 2000). However, most troglobitic species from this cave remain undescribed.

All individuals of A. canhembora sp. nov. were found at the lower cave level, always in very damp areas. In 2012, several specimens were observed, but only a single exemplar was captured since the cave substrata in the area prevented us to collect most of them. The water in karst systems usually presents high contents of dissolved calcium carbonates, which sometimes can form conspicuous deposits in the water surface inside caves. Such formations are usually called “calcite rafts” and are considered to be a kind of speleothem ( Fig. 9D ). Since the water table in Toca do Gonçalo Cave used to fluctuate in time, the areas devoid of water usually present a muddy substrate covered by many layers of calcite rafts ( Fig. 9E ). Most specimens of A. canhembora sp. nov. were found below those calcite rafts, so in most cases, as soon as we turned a piece of calcite, the specimen used to run away and hide in the uncountable small spaces between the layers, thus making their capture unfeasible. This is the reason why we decided to name the species “canhembora”, meaning ʻfugitiveʼ as explained in the etymology. A visit in 2013 revealed specimens (although in smaler number in comparison to 2012), but none could be captured. Finally, in 2014, we could find a single specimen that was successfully sampled ( Fig. 9F–H ).

All the cave visits from 2015 onward resulted in no further observations of specimens. Since the lower level of the cave was extremely dry, we believe that the specimens had probably migrated to inaccessible lower compartments. However, it is important to emphasize the fact that this species might be seriously threatened, as are other cave-restricted species from the Toca do Gonçalo Cave. This cave has been the target of several human impacts, which were highly intensified over the last years. In 1997, one of the authors (RLF) could attest that most part of the lower level was inaccessible due to the high level of the water table. In that period, the villagers of Gonçalo settlement used to draw water from the cave for their subsistence and this practice occurred during decades, by means of a diesel pump installed inside the cave. The villagers used to remove water from the cave once a week, thus the water table was persisting (although varying along the time), since the amount of water pumped out from the cave was negligible. However, an electric pump used by a local farmer for irrigation was installed in the cave in 2010 ( Prevorčnik et al. 2012; Souza-Silva & Ferreira 2016). According to the villagers, this pump remained active during the whole day. In one of our surveys in 2010, a pronounced decrease of the water table (at least two meters) was observed. In 2012, the equipments were removed from the cave since the National Cave Research and Conservation Center intervened and asked the municipal government to dig an artesian well for the villagers. In December 2018, a cave visit revealed that the water table was no longer observed. Hence, previously inaccessible areas could be explored, revealing the cave to be much longer than thought. However, from the 22 troglobitic species occurring in this cave, only two (an isopod and a springtail) were observed in this visit, in some moist areas located deep inside the cave. No specimens of A. canhembora sp. nov. were observed, despite the intense efforts employed by the team in searching for them. The villagers mentioned that the building of a reservoir some dozens of kilometers from the cave, has altered the water balance, so that eventual flooding that used to reach the area never occurred again. Therefore, the Toca do Gonçalo Cave is seriously threatened and it is crucial that the Brazilian government intervene, in order to ensure the protection of this unique habitat in South America.

Figures

Fig. 3. Allokoenenia canhembora sp. nov., ♀, holotype (ISLA 50394). A. Frontal organ. B. Blades of lateral organ. C. Coxa of left pedipalp. D. Coxa of left leg I. E. Coxa of right leg II. F. Coxa of left leg III. G. Coxa of right leg IV. Scale bars: A–B = 20 μm. C–G = 40 μm. Thickened setae on coxae II–IV indicated by arrows.

Fig. 4. Allokoenenia canhembora sp. nov., ♀, holotype (ISLA 50394). A. Deutotritosternal setae. B. Propeltidial chaetotaxy. C. Proximal setae (p 1–p 6) on basal segment of chelicera (p 5 out of focus). Abbreviations: see Material and methods. Scale bars: A= 20 μm; B = 50 μm; C = 45 μm.

Fig. 5. Allokoenenia canhembora sp. nov., ♀, holotype (ISLA 50394). A. Trochanter-femur of right pedipalp. B. Tibia-tarsus 2 of left pedipalp.Abbreviations: see Material and methods. Scale bar = 100 μm.

Fig. 6. Allokoenenia canhembora sp. nov., ♀, holotype (ISLA 50394). A. Trochanter-patella of right leg I. B. Tibia-basitarsus 2 of left leg I. C. Basitarsus 3-tarsus 2 of left leg I. D. Tarsus 3 of right leg I. Abbreviations: see Material and methods. Scale bars: A–C = 100 μm; D = 40 μm.

Fig. 7. Allokoenenia canhembora sp. nov., ♀, holotype (ISLA 50394). A. Tarsus 3 of left pedipalp. B. Basitarsus of right leg IV. C. First lobe of female genitalia. D. Second lobe of female genitalia. Scale bars = 40 μm. Dotted circles and ellipses in figures C and D represent cuticular orifices. Abbreviations: see Material and methods.

Fig. 8. Allokoenenia canhembora sp. nov., ♀, holotype (ISLA 50394). A. Chaetotaxy of opisthosomal tergite III.B. Chaetotaxy of opisthosomal sternite VI.C. Opisthosomal segments VIII–XI. D. Flagellum. Abbreviations: see Material and methods. Scale bars: A–B = 20 μm; C–D = 100 μm.

Fig. 9. Allokoenenia canhembora sp. nov. A. Map of Brazil showing the placement of the Caatinga Biome, delimited in yellow, and of Toca do Gonçalo Cave (red dot), the type locality of A. canhembora sp. nov. B. Entrance of Toca do Gonçalo Cave and its surrounding landscape, characterized by the semiarid climate. C. Gallery of the lower level (right branch) of Toca do Gonçalo Cave, where individuals of A. canhembora sp. nov. were observed. D. Puddle of water inside the Gruta do Gonçalo Cave, with numerous calcite rafts on its surface. E. Area of the cave devoid of water with muddy substrate covered by many layers of calcite rafts. F–G. Live specimens photographed on a tray before being captured. H. Habitus of the specimen (ISLA 50395) captured in 2014 under a stereo microcope.

Fig. 2. Allokoenenia afra Silvestri, 1913, immature, cotypus, ventral view of opisthosomal segment XI (the insertions of the dorsal setae are represented in dashed line). Scale bar = 40 μm.

Fig. 1. Allokoenenia afra Silvestri, 1913. A. Opisthosomal segments VIII–XI and first flagellar segment, ♀, typus. B. Flagellum (second to fourteenth flagellar segments), ♀, typus. C. Frontal organ, immature, cotypus. Scale bars: A–B = 100 μm; C = 10 μm.