Allokoenenia sp.

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 : 37-45

Allokoenenia sp.

Figs 20–25

Material examined

BRAZIL • 1 juvenile ♀; Bahia, Ourolândia, Toca dos Ossos Cave ; 10°55′51.31″ S, 41°3′27.22″ W; 571 m a.s.l.; 12 Jun. 2012; R.L. Ferreira leg.; ISLA 50396 .

Description

Immature female

MEASUREMENTS AND RATIOS. See Table 2.

PROSOMA. Frontal organ formed by two reticulated and expanded branches (33 μm long), with pointed tips ( Fig. 20A ). Lateral organ with 4 blades pointed-lanceolate (25 μm long) and finely reticulated ( Fig. 20B ). Propeltidium with 7 +7 short setae ( Fig. 20C ). Metapeltidium with 3 +3 setae of similar lengths (t 1 = t 2 =65 μm; t 3 =62 μm) ( Fig. 21D ). Deuto-tritosternum with 3 setae in U-shaped arrangement ( Fig. 21A ). Labrum with 4+4 short setae. Basal segment of chelicera 175 long (dorsal length), with 6 proximal setae (p 4 and p 6 thickened and densely barbed; p 1 slightly thinner and barbed) ( Fig. 21B ), and 3 distal setae: d 3 (85) longer than d 1 (47) and d 2 (50); d 3 smooth near base and barbed in distal half, d 1 and d 2 thin, flexible and with tiny projections in the apex ( Fig. 21C ); and one apical seta. Hand of chelicera with 6 setae: 3 dorsal setae, 2 setae in outer portion (1 close to articulation of movable finger and 1 on tubercle close to teeth of fixed finger) and 1 seta inserted in inner portion. Fingers with 8 teeth each.

COXAL CHAETOTAXY. Pedipalp coxa with 17 setae ( Fig. 20D ); coxa I with 13 ordinary setae and two microsetae ( Fig. 20E ); coxa II with 3 thick setae, two macrosetae, and 8 ordinary setae ( Fig. 20F ); coxa III with 3 thick setae, one macroseta, and 8 ordinary setae (including one small seta adjacent to the macroseta) ( Fig. 20G ) and coxa IV with 1 thick and 8 ordinary setae ( Fig. 20H ).

PEDIPLAP. tc with 8 setae (2 considerably smaller than others); fe with 8 setae; ti with 8 setae ( Fig. 22A ); bta1 with 2 m and 1 normal seta; bta2 with 1 normal seta and 5 m ( Fig. 22B ); ta1 with 2 m; ta2 with 6 m; ta3 with 1 long fs, 1 cs with conspicuous spine, 2 r, 14 m (1 macroseta with basal denticle and conspicuous spine) and 6 normal setae ( Fig. 22C ).

LEG I. tc with 12 normal setae (2 considerably smaller than others); fe with 9 normal setae; pa with 9 normal setae and 1 tb; ti with 9 normal setae ( Fig. 23A ); 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; 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. 23B ); ta3 with 5 fs (with subequal branches) arranged as fs 1 / fs 2+3 / fs 4+5, rs (rs / fs 1 = 1.8), 2 r, 1 cs, 13 m and 5 normal setae ( Fig. 23C ).

IVBTA. 5.5 × as long as wide and with 5 setae (grt, r, esp and 2 esd). Seta r inserted in distal half (dr / IVbta =0.66) and grt inserted in proximal half of segment ( Fig. 23D ).

OPISTHOSOMA. Tergites II–V with 3+3 dorsal setae, two pairs of t setae (t 1 =27‒35 μm, t 2 =27‒35 μm) between pair of slender setae (s = 20‒25 μm) ( Fig. 21E ). Tergite VI with 3+2 setae (asymmetry caused by lack of one t seta). Sternite III with 2+2 setae. Sternites IV–VI each with 2+ 2 thickened setae (a 1 =37 μm, a 2 =40‒45 μm) between pair of slender setae (s =25 μm) (inserted caudal to thick setae); pair of pores present between a 1 setae on sternites IV‒VI. It was not possible to observe paired cavities in intersegmental furrows between sternites III–VII. Since the opisthosoma of this specimen was ruptured during the mounting process, it is not possible to determine wether these cavities are absent or not interpretable. Segments VII–X with 8 setae each (4 dorsal and 4 ventral). Segment XI elongated (1.37 ×as long as wide), with dorsal row of 2 +2 long setae (inner pair=140 μm; outer pair= 100 μm) inserted in distal half and two pairs of ventral setae, one inserted around middle of segment (50 μm) and other inserted in apical region (55 μm) ( Fig. 24A ). Intermediate ring of flagellum reduced in size (11 μm) with membranous aspect, with cuticular spines and without setae ( Fig. 24A ).

PRIMORDIA OF GENITAL LOBES. Anterior genital lobe on sternite II with simple median indentation and 2 spines in its distal margin, and with 4+4 setae arranged in 3 transverse rows: proximal pair of setae, followed by 2+2 setae and more distally by pair of shorter median setae, corresponding to “ type 1” described by Condé (1984). Posterior lobe on sternite III formed by two rounded halves, each with 1 spine and 1 tiny seta laterally inserted ( Fig. 24B ).

FLAGELLUM. Not preserved.

Adults, immature male and larva

Unkown.

Distribution

Known only from Toca dos Ossos Cave.

Remarks

Allokoenenia sp. can be assigned to this genus by the relative width of the last opisthosomal segments. Unfortunately, the flagellum was lost during collection, which precludes to determine whether the arrangement of the flagellar features is in accordance with the diagnosis of the genus.

This species shares with A. afra the arrangement of ventral setae on the last opisthosomal segment (distributed in two rows). However, even though represented by a single immature specimen, it can be readily distinguished from A. afra by the shape of the frontal organ ( Figs 1C , 20A ), and by the number of blades on lateral organs (4 vs 1) and deutotritosternal setae (3 vs 1) ( Silvestri 1913), as well as by the chaetotaxy of basitarsus IV (5 vs 6 setae). The chaetotaxy of opisthosomal sternites IV–VI is an additional difference, since the immature of A. afra has three pairs of thickened setae, while this species has only two pairs.

Allokoenenia sp. is very similar to A. canhembora sp. nov., since they share most of their diagnostic features. The main differences observed in the specimens from these two localities are the number of thick setae (a) on opisthosomal sternites IV–VI (2 vs 3 pairs), the blades on the lateral organs (4 vs 5), the setae on the palpal coxae (17 vs 18), the setae on the cheliceral hand (6 vs 7), the deutotritosternal setae (3 vs 5), and the cheliceral teeth (8 vs 9). However, as the number of setae in these body parts and of cheliceral teeth tends to increase during ontogeny, these differences are presumably related to the fact that Allokoenenia sp. is represented by an immature specimen. Other characteristics that are most likely to actually correspond to morphological differences between these two specimens are the shape of the intermediate ring of the flagellum and opisthosomal segment XI. The intermediate ring of the flagellum is very rudimentary in Allokoenenia sp. , resembling more a membranous structure with cuticular spines, without any seta. In A. canhembora sp. nov. it is slightly more developed and bears two short setae. It is noteworthy that differences in the shape of this structure have never been reported in conspecific specimens in different stages of development. In addition, the last opisthosomal segment is slightly longer in Allokoenenia sp. than in A. canhembora sp. nov. (1.37 vs 1.15 × as long as wide).

The caves where Allokoenenia sp. and A. canhembora sp. nov. occur are located in the North of Bahia State (approximately 50 km bee-line from each other), in the domain of the Brazilian Caatinga, which is a semi-arid biome. Considering that palpigrades are fairly dependent on high humidity, the establishment of populations of these two species in endogenous habitats in this region is apparently unviable due to unsuitable climatic conditions. However, even with the previously mentioned morphological differences, and the low probability of connection between these two populations, the fact that the only specimen known from Toca dos Ossos is immature prevents us from ruling out conspeficity. Accordingly, we described the morphology of this immature specimen in order to register the presence of a troglomorphic species of this genus in Toca dos Ossos, since several visits to the cave after its discovery failed in finding additional specimens. We highlight the need of future efforts to capture new specimens, including adults. This will allow us to conclude whether or not this species is morfologically different from A. canhembora sp. nov.

Habitats and threats

The Toca dos Ossos Cave comprises the eighth largest cave in Brazil, with 14.2 km of topographed galleries. It is inserted in limestones from the Caatinga geological group (the same from the Toca do Gonçalo Cave), within the Caatinga Biome ( Fig. 25A ). The cave presents an extremely complex spongiform architecture, and although there are some vadose galleries conforming the main conduits of the cave ( Fig. 25B–C ), such galleries are connected to a complex of small labyrinthic conduids ( Fig. 25F ). The cave is extremely dry, and some water ponds are only formed during strong rains in the region, which are quite rare. The main organic resources occurring in the cave are guano piles deposited by bats, especially frugivorous and omnivorous species. Large bat colonies can persist for a long time in some areas inside the cave. One of the authors (RLF) observed such colonies sheltering at the same areas over the last 24 years, what indicates their fidelity to the roost sites.

The single specimen of Allokoenenia sp. ( Fig. 25G ) was found not far from one of the entrances, in a moistened area ( Fig. 25F ). It was sheltered below a fragment of speleothem deeply buried in the cave floor. During the speleothem displacement, lots of sediment was turned, what may have caused the specimen’s flagellum to detach. This area may be flooded during strong rains, but can also be dry in the peak of the dry seasons (although the exact place where the specimen was found is always moistened, even in the peak of the dry periods). As previously mentioned, several visits to the cave failed in finding additional specimens, even considering that all moistened habitats in other parts of the cave were also inspected, which indicates the rarity of this species. Furthermore, although it shares some common morphological traits with A. canhembora sp. nov., the harsh environmental conditions in the region are likely to prevent palpigrades from migrating between the two caves. The limestones from the Caatinga Formation are ʻthinʼ, rarely exceeding 20 meters in thickness. Considering the high aridity of the region, it is unlikely that suitable microhabitats would be kept along the whole extension between the caves, in such a thin rock layer. The moist subterranean habitats associated with the Caatinga limestones probably occur in patches (as observed in the macrocaves occurring in the area – most of them extremely dry and presenting only a few patches of moist substrates) which prevents migration across long distances. A fact that corroborates this hypothesis is that the few troglobitic species found in the Toca dos Ossos Cave were never observed at the Toca do Gonçalo Cave (and vice versa), so both caves do not share any troglobitic species.

The Toca dos Ossos Cave has been the target of intense impacts in the last decades. In addition to the uncontrolled visits to the cave, which is located close to the Ourolandia town, part of the limestone rock above the cave has been exploited over the last years ( Fig. 25D ). This mining has caused the transport of rock fragments to some parts of the cave, which were partially covered by them ( Fig. 25E ). Fortunately, the quarry above the cave has been interdicted, although the quarrying still occurs in other surrounding areas. Furthermore, no restoration project is currently in progress, and considering that part of the rock (and consequently the epikarst) was removed, the hydrological dynamics of part of this system are presumably altered.

Thus, we would like to highlight the speciesʼ rarity and the degree of threats to which Allokoenenia sp. is subject. According to the current national speleological laws, caves can be destroyed, and the conservation is only ensured to those considered to be of maximum relevance. Among the criteria for classifying a cave in this category, is the presence of a rare, endemic or relict troglobitic species, and Allokoenenia sp. certainly fits in all these attributes. Hence, the record of this species directly contributes to the conservation of its habitat.

Figures

Fig. 20. Allokoenenia sp., juvenile ♀ (ISLA 50396). A. Frontal organ. B. Blades of lateral organ. C. Propeltidial chaetotaxy. D. Coxa of right pedipalp. E. Coxa of right leg I. F. Coxa of left leg II. G. Coxa of right leg III. H. Coxa of left leg IV. Scale bars: A–B = 20 μm; C = 100 μm; D–H = 40 μm. Thickened setae on coxae II–IV indicated by arrows.

Fig. 21. Allokoenenia sp., juvenile ♀ (ISLA 50396). A. Deutotritosternal setae. B. Proximal setae (p – 1 p 6) on basal segment of chelicera. C. Distal setae (d 1 –d 3) on basal segment of chelicera. D. Metapeltidial chaetotaxy. E. Chaetotaxy of opisthosomal tergite III. Abbreviations: see Material and methods. Scale bars: A–B, D–E = 20 μm; C = 40 μm.

Fig. 22. Allokoenenia sp., juvenile ♀ (ISLA 50396), left pedipalp. A. Trochanter-tibia. B. Basitarsi 1–2. C. Tarsi 1–3. Abbreviations: see Material and methods. Scale bars: A = 100 μm; B–C = 40 μm.

Fig. 23. Allokoenenia sp., juvenile ♀ (ISLA 50396), left pedipalp. A. Trochanter-tibia of right leg I. B. Basitarsi 1-tarsus 2 of right leg I. C. Tarsus 3 of left leg I. D. Basitarsus of right leg IV. Abbreviations: see Material and methods. Scale bars: A–B = 100 μm; C–D = 60 μm.

Fig. 24. Allokoenenia sp., juvenile ♀ (ISLA 50396). A. Opisthosomal segments VIII–XI, ventral view (the dorsal setae of segment XI are also illustrated, with their insertions represented in dashed lines). B. Primordia of genital lobes of immature B. Scale bars: A = 100 μm; B = 30 μm.

Fig. 25. Allokoenenia sp. A. Map of Brazil showing the placement of the Caatinga Biome, delimited in yellow, and of Toca dos Ossos Cave (in red), habitat of Allokoenenia sp. B–C. Galleries of Toca dos Ossos Cave, showing its spongiform architecture. D. Surrounding landscape outside the Toca dos Ossos Cave, showing the limestone quarry that operated above the cave for many years. E. Area of Toca dos Ossos covered by rock fragments transported to the cave in consequence of the quarrying activities. F. Plan view of Toca dos Ossos, showing the structure of the cave with vadose galleries connected by a complex of labyrinthine smaller conduids; the palpigrade collecting site is indicated by a red star. G. Habitus of Allokoenenia sp., ♀ (ISLA 50396) under a stereo microcope before mounting.

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.