Prokoenenia sarcodactylica, Bu & Souza & Mayoral, 2021

Bu, Yun, Souza, Maysa Fernanda Villela Rezende & Mayoral, Jaime, 2021, New and interesting palpigrades (Arachnida, Palpigradi) of the genera Koeneniodes Silvestri, 1913 and Prokoenenia Börner, 1901 from Asia, Zootaxa 4990 (1), pp. 45-64 : 54-62

Prokoenenia sarcodactylica sp. n.

( Figures 7–12 , Table 2 )

Material examined: Holotype ♀, juvenile B (slide no. BJ-2018001 ) ( SNHM), China, Beijing, Fangshan District, Fozizhuang town, Xiayingshui village , Jinhua cave , 295 m a.s.l., 39°48'N / 115°54'E, 22-XI-2018, coll. Ze-Gang Feng and Chen Zhang.

Diagnosis. Frontal organ with two cylindrical branches with blunt apex and fine reticulation; a cluster of 18 finger-shaped blades with hexagonal reticulation in the lateral organs; 7 pairs of setae on propeltidium; 2 pairs of setae on metapeltidium; cheliceral fingers with 8 teeth each; 7 setae (grt, gla, r, 2 esp and 2 esd) on basitarsus of leg IV; primordium of the first lobe of the immature B female genitalia with four pairs of proximal setae and two pairs of shorter distal setae; second lobe with two smaller and simple rounded primordial structures without setae.

Description. Body length without flagellum 2150 μm.

Prosoma. Frontal organ 30 long, 6 wide, composed of two cylindrical branches with blunt apex and reticulation ( Fig. 9A ). Lateral organ with 18 finger-shaped blades in a cluster (25–28 long, 5 wide), with fine reticulation ( Figs. 7A, B ; 9B–D ). Propeltidium with 7 + 7 setae, 25–30 long. Metapeltidium with 2 pairs of setae (t 1 and t 2) (only insertions visible, setae lost). Labrum with 5 + 5 short setae (18–20 long). Basal segment of chelicera 350 long (dorsal length) and 160 wide, with 6 proximal setae (p 6 the thickest and densely barbed, 140 long; p 4 thicker than the remaining setae and densely barbed on most of its length, 115 long); p 1 = 120, p 2 = 65, p 3 = 80, p 5 = 60 long ( Figs. 7E , 9F ); 3 distal setae with similar shape and thickness, with pointed apex and tiny projections more densely arranged in distal half: d 3 longer (82) than d 1 (75) and d 2 (80) ( Figs. 7D , 9E ). Hand of chelicera, length 230 (excluding fingers) and 135 wide, with 6 slender setae: 5 dorsal and 1 ventral. Fingers with 8 teeth each ( Figs. 8A , 12B ). Deuto-tritosternum with 8 long setae (45–48) arranged in two rows: 3 anterior and 5 posterior ( Fig. 7C ).

Coxal chaetotaxy. Pedipalp coxa with 19 setae ( Fig. 9G ); coxa I with 13 setae (including two tiny setae) ( Fig. 9H ); coxa II with 4 thick, 8 normal and 2 macrosetae ( Figs. 7F , 10A ); coxa III with 6 thick, 8 normal and one macroseta ( Figs. 8F , 10B ); coxa IV with 4 thick and 8 normal setae ( Figs. 8F , 10C ).

Pedipalp. tc with 11 normal setae ( Fig. 10D ); fe with 8 normal setae ( Fig. 10E ); ti with 9 normal setae ( Fig. 10F ); bta1 with 3 m; bta2 with 3 normal setae and 3 m ( Fig. 10G ); ta1 with 2 m; ta2 with 6 m; ta3 with 9 m, 2 fs, r, cs, and 11 normal setae ( Fig. 10H ); claw length 25 with barbed unguiculus (15) ( Fig. 10H ).

Leg I. tc with 13 normal setae ( Fig. 11A ); fe with 9 normal setae ( Fig. 11B ); pa with 10 normal setae and tb ( Fig. 11C ); ti with 2 m and 8 normal setae ( Fig. 11D ); bta1 with 2 m, 2 tb and fs; bta2 with 4 m, 2 tb and fs ( Fig. 11E ); bta3 with r, grt and a small normal seta ( Fig. 11F ); bta4 with 5 m, tb and fs ( Fig. 11F ); ta1 with r, 2 normal setae and 2 other smaller normal setae ( Fig. 11F ); ta2 with 5 m and tb ( Fig. 11F ); ta3 with 5 fs (fs 1 / fs 2+3 / fs 4+5) (all with branches with similar lengths), 11 m, cs, rs, and 8 normal setae ( Fig. 11G ), claw 30 long with barbed unguiculus (15) ( Fig. 11G ).

Legs II and III with nearly identical chaetatoxy. tc with 3 (leg II) or 2 (leg III) normal setae; fe with 2 m and 3 normal setae; pa with 2 m and 3 normal setae; ti with 5 normal setae; bta with 7 normal setae; ta with 10 normal setae.

Leg IV. tc with 3 normal setae; fe with 3 normal setae; pa and ti each with 5 normal setae; bta with grt, gla, r, 2 esp and 2 esd ( Fig. 12A ); ta1 with r and 4 normal setae; ta2 with cs and 6 normal setae.

IVbta. 205 long, 30 wide, with 7 setae (grt, gla, r, 2 esp and 2 esd) and a suture approximately in the middle of the segment. Seta r short, about 0.4 of the tergal edge of segment and inserted distally (dr/ IVbta = 0.78); gla and grt inserted at the same level as esp setae, in proximal half ( Fig. 12A , Table 2 ).

Opisthosoma. Tergite II with 7 setae: 2 pairs and a middle t setae (t 2, t 1, t, t 1, t 2) between a pair of slender setae (s). Tergites III–VI with 3 + 3 setae each: two pairs of t setae (t 1, t 2) between a pair of slender setae (s). Sternite III with 3 + 3 setae (40–45) ( Fig. 8B ). Sternites IV–VI each with one pair of sacs and 6 pairs of setae, four l setae, one ω and one s ( Figs. 7G–J ): l 1 (68–70), l 2 (70–75), l 3 (75–77), l 4 (70–73), ω (47–50), s (50). Segments VII–XI with 10, 10, 10, 8, and 8 setae, respectively ( Figs. 8D, E ). Two dorsal setae on the intermediate ring of the flagellum are smaller than two ventral setae. Pubescence of the opisthosomal segments IX–XI evenly short and dense. Flagellum lost.

Primordia of genital lobes (Juvenile stage B). First lobe with 6 + 6 setae arranged in rows: 1 + 1, 1 + 1, 2 + 2 and 2 + 2 shorter distal setae (a 1 = a 2 = 32 long) ( Figs. 8B, C ). Second lobe with two rounded and rudimentary primordia without setae ( Figs. 8B, C ).

Measurements (in μm) and ratios are given in Table 2 .

Distribution: The species is only known from the type locality—Jinhua cave (Beijing, China).

Etymology. The new species is named after the shape of the multi-lobulated lateral organs that resembles the fruit of Citrus medica var. sarcodactylis , commonly known as a Buddha’s hand.

Remarks. The palpigrade captured in Jinhua cave belongs to the family Prokoeneniidae , mainly by the presence of a pair of ventral sacs on each of the opisthosomal sternites IV–VI ( Condé 1996). This new species is morphologically closer to the other six species in the genus Prokoenenia than to the single species in the genus Triadokenenia, especially if compared to the congeneric species described from Asia. Furthermore, it does not share important characters with Triadokoenenia , like the absence of a frontal organ or the presence of four setae on basitarsus IV ( Condé 1991).

Despite being represented by an immature specimen, Prokoenenia sarcodactylica sp. n. can be readily distinguished from all other species in the genus (immatures and adults) by presenting 18 blades in the lateral organs, and a total body length of 2150 (without flagellum). The adults of P. californica Silvestri, 1913 , P. asiatica , and P. celebica are the species in this genus with the most blades (5) in the lateral organs ( Silvestri 1913; Condé 1994). Furthermore, all other six species of Prokoenenia have a body length ranging from 0.9 mm in the single specimen of P. chilensis ( Hansen, 1901) (an immature B) to 1.69 mm in the adult female of P. celebica ( Hansen 1901; Condé 1994).

A comparison of the new species with the three American Prokoenenia species is difficult. They were described at the beginning of the last century, and their descriptions generally lack most characters used in modern taxonomy and a detailed description of the immature individuals. The only specimen known for P. chilensis is an immature female, but since its description is very incomplete, it is only possible to conclude that the new species and P. chilensis share the same number of deuto-tritosternal setae (8) ( Hansen 1901).

On the other hand, the three Prokoenenia species from Asia— P. javanica , P. asiatica , and P. celebica —were described by Bruno Condé in the 1990s with very detailed morphological information, including the description of the immature females. Several similarities between our Chinese specimen and the immatures of the same stage of the three Asian species were found: two pairs of metapeltidial setae, seven pairs of propeltidial setae, eight teeth in the chelicerae, seven setae and the presence of a pseudo-articulation on basitarsus IV, and six pairs of setae on the primordium of the first genital lobe (four pairs of long setae in its anterior portion and two pairs of shorter setae in its posterior margin). This configuration of the genitalia corresponds to “type 3” described by Condé (1984). In addition to the differences in body length and number of blades in the lateral organs, Prokoenenia sarcodactylica sp. n. can be distinguished from the immature of these three species by the chaetotaxy of the opisthosomal sternites IV–VI, the number of deuto-tritosternal setae, and the absence of a trichobothrium on IVti ( Condé 1990, 1994). The immatures of P. celebica and P. javanica also differ from the new species by the presence of a single pair of t setae on tergites III–VI and II–VI ( Condé 1990, 1994).

In palpigrades, particularly in Eukoenenia , morphological characters and ratios were used to assess the level of troglomorphism. Ratios that reveal elongation of appendages, such as B/IVbta and IVbta/ti suggested by Condé (1996, 1998), may or may not apply to Prokoenenia species. In fact, edaphic adult Prokoenenia specimens show values similar to that of many troglobitic Eukoenenia species (B/IVbta = 1.94–2.5; IVbta/ti = 0.9–0.97) ( Condé 1990, 1994). For this comparison only two species of Prokoenenia ( P. asiatica , and P. javanica ) were available, but more data is needed for substantial conclusions.

The increased number of blades in the lateral organs, as well as the large body size indicate that this new species is the first undoubtedly cave-adapted Prokoenenia . In fact, Prokoenenia sarcodactylica sp. n. exhibits the highest number of lateral organ blades ever recorded—all the more remarkable as the specimen is an immature. The second largest number of blades in the lateral organs (12–13) was found in the adult female of Eukoenenia thais Condé, 1988 ( Condé 1988) . Blade numbers and body size often increase over the course of development, as was shown also for the other three Asian Prokoenenia . Therefore, the adult stages of the new species may have a greater number of blades in the lateral organs and a larger body size. Although immature, the specimen of Prokoenenia sarcodactylica sp. n. is the third largest palpigrade ever recorded (L = 2150), topped only by E. draco (Peyerimhoff 1906) (L = 2010–2356) and E. florenciae (Rucker, 1903) (L = 2000–2300) ( Mayoral & Barranco 2013).

The description of a new species based on a single specimen is not ideal, especially if this specimen is immature. However, the remarkable morphology of the Chinese cave Prokoenenia and the poor knowledge of the genus justify the description of a new species. In addition, Jinhua cave is very difficult to access and to explore. The cave is accessible only to experienced speleologists with vertical techniques, and it is not likely that new specimens will be collected in the near future.

Figures

FIGURE 7. Prokoenenia sarcodactylica sp. n. A, lateral and frontal organ; B, lateral organ, detail; C, deuto–tritosternal setae; D, distal setae (d1–d3) on basal segment of chelicera; E, proximal setae (p1–p6) on basal segment of chelicera; F, coxae II–IV, left side, arrows indicate thick setae; G, sternites IV–VI; H, sternite IV, sac and setae; I, sternite V, sac and setae; J, sternite VI, sac and setae. Scale bars: 20 μm (A–C), 50 μm (D–J).

FIGURE 8. Prokoenenia sarcodactylica sp. n. A, hand of chelicera; B, immature B, genitalia; C, immature B, detail genital lobes; D, tergites VII–XI; E, sternites VII–XI; F, coxae III and IV. Arrows show thick setae. Scale bars 50 μm.

FIGURE 9. Prokoenenia sarcodactylica sp. n. A, frontal organ, lateral view; B, lateral organ; C, blade of lateral organ, detail; D, insertions/sockets of blades, lateral organ; E, distal setae (d1–d3) on basal segment of chelicera; F, proximal setae (p1–p6) on basal segment of chelicera; G, pedipalp coxa, right side; H, leg I coxa, right side I. Scale bars: 20 μm (A–F), 50 μm (G–H).

FIGURE 10. Prokoenenia sarcodactylica sp. n. A, coxa of right leg II; B, coxa of right leg III; C, coxa of right leg IV; D, trochanter of left palp; E, femur of left palp; F, tibia of left palp; G, basitarsus 1–2 of left palp; H, tarsus 1–3 of left palp. Arrows indicate thick setae. Scale bars: 50 μm.

FIGURE 11. Prokoenenia sarcodactylica sp. n. Leg I. A, left trochanter; B, left femur; C, left patella; D, left tibia; E, left basitarsus 1–2; F, right basitarsus 3—tarsus 2; G, left tarsus 3. Scale bars: 50 μm.

FIGURE 12. Prokoenenia sarcodactylica sp. n. A, basitarsus IV, right side. B, hand of chelicera. Scale bars: 50 μm.

Tables

TABLE 2. Prokoenenia sarcodactylica sp. n. Measurements (in μm) and ratios.

L	2150	Ibta3–d r	50	IVbta	205
B	400	Ibta3– r	110	IVbta– a	30
Seg.	350	Ibta3– a	30	IVbta– r	80
Pcx	195	Ibta3– grt	93	IVbta–d r	150
Ptc	245	Ibta3–d grt	25	IVbta– gla	105
Pfe	150	Ibta3/ a	2.2	IV–d gla	65
Pti	210	r /Ibta3	1.7	IV– grt	95
Pbta1	85	d r /Ibta3	0.8	IV–d grt	67
Pbta2	80	grt /Ibta3	1.4	IV– esp	105
Pta1	50	d grt /Ibta3	0.4	IV–d esp	55
Pta2	72	Ibta4	70	IV– esd	90
Pta3	125	Ita1	60	IV–d esd	143
Icx	205	Ita2	70	IVbta/ a	6.8
Itc	280	Ita3	240	IVbta/ r	2.6
Ife	165	IVcx	170	d r /IVbta	0.7
Ipa	230	IVtc	195	IVta1	85
Iti	270	IVfe	220	IVta2	95
Ibta1+2	235	IVpa	190	IVbta/ti	0.95
Ibta3	65	IVti	215	B/IVbta	1.95