Coecobrya sirindhornae, Jantarit, Sopark, Satasook, Chutamas & Deharveng, Louis, 2019

Jantarit, Sopark, Satasook, Chutamas & Deharveng, Louis, 2019, Coecobryasirindhornae sp. n., the most highly troglomorphic Collembola in Southeast Asia (Collembola, Entomobryidae), ZooKeys 824, pp. 21-44 : 21

Coecobrya sirindhornae sp. n. Figs 1, 2, 3, 4, 5, 6, 7

Type material.

Holotype: male on slide, Thailand: Satun province: Manang district, Tham Rusri, altitude 58 m, nine specimens (one male, one female and three subadults in slides, three in ethanol), dark zone of cave, by aspirator, S Jantarit and A Nilsai leg. (sample # THA_SJ_STN09), 30/04/2016 (A Nilsai), six specimens (three subadults in slides, three in ethanol); 03/05/2016 (S Jantarit and A Nilsai), five specimens in ethanol; 25/07/2017 (S Jantarit and A Nilsai), three specimens in ethanol; 17/03/2018 (S Jantarit and A Nilsai), three specimens in ethanol. Holotype and 13 paratypes in slides deposited in NHM-PSU. Two paratypes in alcohol in MNHN. Three paratypes on slides and three in alcohol in NJAU. Tham = cave (in Thai).

Description.

Habitus (Fig. 1A‒D, G). Medium size Entomobryidae . Body length up to 2.6 mm (holotype 2.1 mm). No scales. Eyes absent. Colour: pale yellow to whitish in alcohol, without pigments. Four antennal segments (sometimes Ant. III and IV fused together). Body slender with very long antennae and moderately elongate legs and furca. Body not bent nor humped at level of Th. II. Th. II slightly longer than Th. III; Abd. IV 3‒4 times as long as Abd. III.

Pseudopores (Figs 2B, 3D‒E, 3H, 4A‒C, 5E‒G, 6F). Pseudopores present as round flat disks, smaller than mac sockets (Figs 3H, 4A‒C), except for the coxae and manubrium where psp are as large as mac sockets, present on various parts of the body: antennae, head, tergites, coxae and manubrium. On antennae, psp located ventro-apically between the tip of antennal segments and the chaetae of the apical row, or just below apical row of chaetae (two on Ant. I, 2‒3 on Ant. II, and 4‒7 on Ant. III) (Figs 2B, 3D‒E). On head, 1‒(2) psp located externally on each peri-antennal area (Fig. 4A). On tergites, 1+1 psp close to the axis from Th. II to Abd. IV (Fig. 4B, C). Coxae I, II, and III with 2‒ (3), 2‒ (3), and 1‒2 psp respectively, located close to longitudinal rows of chaetae (Fig. 5E‒G). On manubrium, 2+2 dorso-apical ones (Fig. 6F).

Mouthparts and ventral head chaetotaxy (Figs 2E‒J, 3F, 3K). Clypeal area with three long, smooth prefrontal and 6‒10 ciliated and two long smooth facial chaetae (Fig. 2E), sometimes asymmetric arrangement. Distal border of the apical non-granulated area of the labrum with a relatively narrow median U-form intrusion into the granulated area dorsally; apical edge not adorned with spines (Figs 2F, 3F). Ventro-distal complex of labrum well differentiated, asymmetrical, with 1+1 distal combs of 13‒21 minute teeth on the left side and 10‒11 strong and larger teeth on the right side, and an axial pair of long sinuous tubules, round apically (Fig. 2J). Prelabral and labral chaetae 4/5, 5, 4, all thin and smooth; three median chaetae of the first and second rows longer and slightly larger than those of the distal and proximal rows (35‒45 vs, 30 µm)(Figs 2F, 3F). Maxillary outer lobe with one papillate chaeta, one basal chaeta, and four sublobal hairs of which the upper one is three times shorter than the others (Figs 2H, 3F). Labium and ventral head (Figs 2G, K, 3G, K). Labial palp strongly modified for the genus, with 0, 5, 0, 4, 4 guards for papillae A‒E, like that described by Fjellberg (1999) for Entomobryidae or by Xu and Zhang (2015) for Coecobrya . Lateral process of labial palp subcylindrical, as thick as normal chaetae, with tip slightly beyond apex of labial papilla (Figs 2G, 3K). Five smooth and acuminate proximal chaetae. Chaetae of labial basis all smooth (m1m2rel1l2); chaetae m2 slightly larger and longer than m1, chaetae m1, e and l1 subequal, r thin and shortest, and l2 longest (Figs 2K, 3G). One short and smooth chaeta present in one individual between m2 and r, other two chaetae of the submentum smooth and acuminate, of similar size. Postlabial chaetae X2, X3, X and X4 smooth, long and acuminate, X1 absent; 2‒5 smooth and minute chaetae between H2 and H3. On each side of linea ventralis, 7‒9 smooth and 3‒7 ciliate chaetae, the anterior 6 always long, smooth and acuminate, the posterior ones either smooth or ciliated (Figs 2K, 3G). Mandible apex strong, asymmetrical (left with four teeth, right with five teeth); molar plate with three strong pointed basal tooth, and 3‒(5) smaller inner distal teeth, identical in both mandibles (Fig. 2I). Maxilla capitulum with a three-toothed claw and several stout ciliated lamellae; lamella 2 large and broad, lamella 3 well developed; several other lamellae present.

Antennae (Figs 1A‒D, 1G, 2A‒D, 3A‒E). Antennae extremely long, approximately 8.0-12.3 times as long as cephalic diagonal and 2.0‒2.2 times longer than (head + body). Antennal segment ratio as I: II: III: IV = 1: 1.3-1.9: 1.6-2.0: 8.1-11.3 (N = 5). Antennal segments not subdivided nor annulated. At least three specimens with asymmetrical antennae, one with four segments and the other one slightly shortened with three segments; two specimens with three antennal segments of both sides. Antennal chaetal types not analysed in detail. Ant. I dorsally with three mac (Fig. 3A) and a row of 2‒4 spear-like chaetae latero-dorsally (Fig. 3B). Ant. I ventrally with many smooth spiny mic of various sizes in its basal part, many subcylindrical, hyaline sens in its middle to apical part, and many long smooth straight chaetae. Ant. II dorsally with 10‒12 paddle-like chaetae (sensu Nilsai et al. 2017) in its distal part (Figs 2A, 3C). Ant. III organ with five sens; sens one and four subequal, hyaline; sens five acuminate, dark and shorter; sens two and three swollen resting in shallow groove (Figs 2B, 3D‒E), not clearly seen in most specimens. Ant. IV very long, not subdivided, without apical bulb (Fig. 2C‒D). Subapical organite not distinctly knobbed, swollen, slightly enlarged apically, inserted dorsally at 35‒45 µm from the tip (Fig. 2C).

Dorsal head chaetotaxy (Fig. 4A). Dorsal cephalic chaetotaxy with one antennal (An), without median (M) and five sutural (S) mac; Gr. II with only one mac; A0 as mes; 7+7 scale-like structures (2‒3 µm) present below sutural mac, probably inside the integument; a pair of short cephalic trichobothria, external and close to the middle of the head (Fig. 4A).

Tergites (Fig. 4 B–D). Th. II with three (m1, m2, m2i) medio-medial, two (m4, m4p) medio-sublateral and 15‒18 posterior mac; 1+1 ms and 1+1 sens antero-laterally. Th. III with 32‒35 mac; a1a as mac. 2+2 sens laterally. Abd. I with six (a3, m2-4, m2i, m4p) mac. 1+1 ms and 1+1 sens laterally. Abd. II with two (m3, m3e) central and one (m5) lateral mac. 2+2 tric without modified chaetae, 1+1 sens laterally and 1+1 mic near internal tric. Abd. III with one (m3) central and three (am6, pm6, p6) lateral mac. 3+3 tric not surrounded by modified chaetae, 1+1 sens laterally,1+1 mic near m3, ms not seen (Fig. 4B). Abd. IV with six central mac (I, M, A5-6, A5p, B6) and eight (D3, E2-4, E2p, F1-3) lateral mac, 2+2 tric and approx. 5‒7 long S-like chaetae anteriorly, without modified chaetae (Fig. 4C). Abd. V with 13‒15 mac and 2+2 sens (Fig. 4D). Abd. VI not analysed. S-chaetae formula from Th. II to Abd. V: 2+ms, 2/1+ms, 2, 2+ms, 1+ ≈5‒7, 2; as sens not seen and ps on Abd. IV 1/4 as long as S-like chaetae (Fig. 4C).

Legs (Figs 3I, 5A‒G) long; tita of leg III slightly longer than tita of legs I and II. Legs devoid of scales, covered with ordinary ciliated chaetae of various lengths, mic not seen. Coxa of leg I with three proximal psp and two chaetae posteriorly; coxa of leg II with 8-10 chaetae (5-6 mac) in anterior row, 3-4 chaetae (mac) in posterior row and 2-3 proximal psp in between; coxa of leg III with 13+15 chaetae (6-7 mac) in anterior row, and one proximal psp posteriorly. Trochanteral organ with 12‒18 smooth, straight, unequal spine-like chaetae (Fig. 5D). The distal whorl of tita with 10‒12 subequal ciliated mes, irregularly arranged, and a thin, acuminate, smooth dorso-apical tenent hair. Tenent hair of tita I longer (50‒65 µm) than that of tita II and III (30‒40 µm) (Fig. 5A‒C). Tita I-III with one smooth, thin and long chaetae close to tenent hair (25‒40 µm, N = 5) (Figs 3I, 5A‒C). Ventro-distal smooth chaeta of tita III thick, erected, pointed, rather short (35‒40 µm, N = 5). Pretarsal mic minute (2.5‒3.0 µm). Claw slender and elongated; claw I and II subequal (60‒98 µm long, 7‒12 µm wide at basis), claw III slightly longer (80‒100 µm long, 15‒17 µm wide at basis) (N = 5). All claw with one strong inner tooth at 50‒55% and a pair of basal inner teeth at approx. 22‒25% of inner edge from basis. Unguiculus approx. 3/5 as long as inner edge of claw, slightly swollen baso-internally, pointed apically, devoid of inner tooth, not truncated, with 2‒3 minute outer teeth, often inconspicuous, at 1/3 of its length (Figs 3I, 5A‒C).

Ventral tube (Fig. 6A‒D). Ventral tube four times longer than wide. Lateral flaps with 7‒8+7‒8 smooth chaetae (sometimes with 5+5 ciliated and 3+3 smooth) (Fig. 6C‒D). Anteriorly with 10+10 large chaetae, 3+3 ciliated and 7+7 smooth, two of them larger (Fig. 6B); posteriorly with 20‒30 mes, all serrated, arranged roughly asymmetrically, with 1+1 smooth, straight, distal mac close together (Fig. 6A).

Furcal complex (Figs 3J, 6E‒I). Tenaculum with four large teeth of decreasing size from the basal to the distal one of each ramus, on a prominent, irregular body, with a postero-basal strong serrated chaeta bent distally (Fig. 6E). Mucrodens 1.25‒1.60 times longer than manubrium. Furcula without smooth chaetae. Manubrium with a dense cover of ciliated chaetae both dorsally and ventrally. Manubrial plaque with two pseudopores and three ciliate chaetae (Fig. 6F). Distal part of manubrium ventrally with 8‒10 ciliate chaetae on each side, four of them mac (Fig. 6G). Inside the manubrium, two thin, straight longitudinal structure running on ¾ of manubrium length from its apex like in Lepidonella doveri (Carpenter, 1933) (after Deharveng et al. 2018) (Fig. 6H). Dens without spines, annulated and covered with ciliated chaetae on both sides. Distal smooth part of dens slightly shorter than mucro. Mucro strong and falcate, basal spine long, nearly reaching the tip of the mucronal tooth (Figs 3J, 6I).

Genital plate (Fig. 6J). Male genital plate with 3+3 genital mic, acuminate circumgenital mes not clearly seen, without modified chaetae. Spermathecal duct elongated and annulated (Fig. 6J). Female genital plate not clearly seen.

Ecology.

Coecobrya sirindhornae sp. n. is restricted to the dark zone of the cave where it has been found, in the oligotrophic environment of a small chamber, on muddy ground and wet rock walls. The chamber is connected to a narrow steep hole. Small puddles are present in the chamber and water is dripping from the ceiling. Muddy ground surface is flooded during rainy season. Some individuals were found feeding on a cricket corpse. They were quick jumping and moved rapidly. The species is found only in that chamber where humidity is at saturation, and temperature is constant (23‒24 degrees Celsius). The population seems rather limited (only 26 specimens were collected from five attempts, each time one hour collecting by 2 people). Small (young) individuals were less numerous and not collected.

Etymology.

This species is named to honour Her Royal Highness Princess Maha Chakri Sirindhorn, who is passionately interested in natural history and plays an important role in promoting the conservation of biodiversity and the environment of Thailand.

Remarks.

Coecobrya sirindhornae sp. n. differs at first from all other species of the genus by its highly troglomorphic characters. Diagnostic morphological characters of the new species and related troglomorphic Coecobrya are listed in Table 1. Coecobrya sirindhornae sp. n. is well characterised by the combination of large body size, extremely long antennae, all labial chaetae smooth, elongated lateral process of labial palp and four sublobal hairs on maxillary outer lobe, very elongated and slender claw, presence of 2‒3 minute teeth on outer edge on unguiculus, less chaetae on ventral tube and both sides of distal part of manubrium, and reduced dorsal chaetotaxy of both head and tergites. Head is without M row and with internal scale-like structures below the sutural mac. We have been unable to detect the third pair of sens on Abd. V, but we do not consider this absence as diagnostic as it would be a very unusual feature for a Coecobrya , and it is often difficult to observe or fallen down. Antennae of the new species are the longest known in the genus, longer than C. nupa Christiansen & Bellinger, 1992 from Hawaii, previously the species with the longest antennae; and C. polychaeta Zhang & Nilsai, 2017 and C. chumphonensis Zhang & Nilsai, 2017 (both in Nilsai et al. 2017) from Thai peninsula (Table 1). According to the three troglomorphic species of Thailand, C. polychaeta comes near to C. sirindhornae sp. n. in body length, colour, clypeus chaetae, elongated lateral process of labial palp and number of sublobal hairs on maxillary outer lobe, but can be clearly differentiated from it by the characters listed in Table 1. The other two taxa from Thailand are not close to the new species. Coecobrya nupa , the first report of highly troglomorphic species in the genus, differs from the new species mainly in shorter antennae length, labial basis chaetotaxy, claw morphology and mucronal spine exceeding the tip of the apical tooth (Table 1). The distribution map of C. sirindhornae sp. n. and the other two troglomorphic Coecobrya discovered in Satun province is shown in Figure 7.