Spinaethorax adamantis, Schneider & Deharveng & Umr & Umr, 2017

Schneider, Clément & Deharveng, Louis, 2017, First record of the genus Spinaethorax Papáč & Palacios-Vargas, 2016 (Collembola, Neelipleona, Neelidae) in Asia, with a new species from a Vietnamese cave, European Journal of Taxonomy 363, pp. 1-20 : 4-13

Spinaethorax adamantis sp. nov.

urn:lsid:zoobank.org:act:B0F131AB-279A-4890-A33B-ED70D437828D

Figs 1–8 , 9A, D ; Table 1

Diagnosis

Postero-dorsal area of head with 12 + 12 chaetae including 5 + 5 lanceolate chaetae. Antero-dorsal area of head with two unpaired chaetae. Ant. III with 14 chaetae; S-chaetae S2, S3, S4 long and tubular. Dorsal area of Th. II with 4 + 4 thickened or lanceolate chaetae. Abd. I–V terga without spine-like microchaetae. Abd. VI tergum with thickened chaetae. Subcoxa 2 III and coxa III with thickened chaetae. Dens proximal part with one strong chaeta.

Differential diagnosis

Spinaethorax adamantis sp. nov. differs from S. spinotricosus and S. tonoius in several characters, summarized in Table 1 . Most notably, S. adamantis sp. nov. has only one proximal chaeta on dens (instead of two in the other species), long and tubular S-chaetae S2, S3 on Ant. III (vs short in the other species) and a long and tubular S-chaetae S4 (vs short and globular in the other species). S. adamantis sp. nov. and S. tonoius differ most strikingly from S. spinotricosus by the absence of the numerous spinelike microchaetae (reduced number of ordinary chaetae instead).

Etymology

The name is derived from the Latin adamas (diamond) and is inspired by the local name for the cave Hang Kim Cuong, “Diamond Cave”, in which the new species was collected. The name emphasizes that one of its richnesses lies in the biodiversity instead of actual diamonds.

Material examined

Holotype

VIETNAM: ♂, on slide ( MNHN-EA040281 ), Kien Giang Province, Kien Luong, Hon Chong karst, Nui Hon Chong hill (also called Nui Chua Hang ), Hang Kim Cuong ( Diamond Cave ), 28 Nov. 2006, X=104.639784 E, Y=10.137582 N, elevation about 15 m, extracted with Berlese funnel from soil in the dark zone of the cave, L. Deharveng and A. Bedos leg. (sample Vn 06-088) ( MNHN).

Paratypes

VIETNAM: 3 ♀♀, 1 ♂, 1 specimen of unknown sex on 3 slides, same data as the holotype, three paratypes deposited in the collection of the MNHN ( France), two paratypes in the collection of the HCMU ( Vietnam).

Description

SIZE. Length from labrum to anus of largest specimen ~ 550 µm.

PIGMENTATION. Whitish in alcohol.

GENERAL SHAPE AND BODY SEGMENTATION ( Fig. 1 ). Orthognathous. Antennae directed laterally with a slight curve toward the anterior direction, slender. Ant. III and IV fused. Total length of antenna ~ 148 µm; max width (Ant. III) ~ 18 µm; ratio width: length ~ 0.12; relation of length of Ant. I: Ant. II: Ant. III: Ant. IV 0.15: 0.5: 1: 1. Point of insertion of head on Th. I aligned with antero-posterior axis of the head. Diameter of Th. I slightly reduced without steep curve between Th. I–head and Th. I–II. Th. I in one part, neck missing. Th. I–head articulary folds not observed. Terga from Th. II to Abd. V fused. Posterior granule T of the dorso-median line missing, replaced by a small unpaired patch devoid of secondary granules (T, Fig. 4A ). Wax rod secretory elements of sf3 (dorsal area of Th. II) and of sf6 (dorsal area of abdomen) standing on strong, protruding processes ( Fig. 1 ). Precoxal area of Th. II and III without clear anterior lobe. Each coxa long and bent. On leg I and II length of coxa> tibiotarsus> femur> trochanter. On leg III length of coxa> tibiotarsus ~ femur> trochanter.Abd. VI sternum clearly separated posteriorly from Abd. VI tergum by large anal aperture, separated anteriorly from Abd. V sternum by a steep curve, Abd. VI sternum distinct laterally from the great abdomen terga by the absence of secondary granulation. Abd. IV sternum enlarged, creating a large ventro-posterior side bearing the furca. Abd. I–III sterna reduced with tenaculum close to ventral tube. Manubrium/dens articular processes: manubrium with weak process bearing hardened peg with convex tip that connects to concave tip of strong, projecting process of dens ( Fig. 6C ). Dens proximal part wider than the distal part with a steep curve between the two. No suture line or articular process between proximal and distal part of dens ( Fig. 6D ). Relation of length of manubrium: dens proximal part: dens distal part: mucro ~ 0.90: 0.32: 1: 0.82.

INTEGUMENT. With a simple secondary granulation made of fine granules. Secondary granulation present on posterior part of Th. II to Abd. V terga ( Fig. 4A ), absent on head, antennae, Abd. VI tergum, furca, legs, thoracic and abdominal sterna. Dermastra missing. Integumentary channels missing.

CHAETAE. Seven morphological variations of chaetae on head and trunk:(i) ordinary chaetae; (ii) s-chaetae, short and swollen chaetae (s1–s3, s3’) found on trunk; (iii) τ-chaetae, long and flexible chaetae shaped as trichobothria with basal ring implanted in a small depression of the integument and weakly contrasted in light microscopy, found on trunk (~ 30–35 µm, Fig. 4B ); (iv) wax rod secretory crypts associated with a sensory field; (v) free wax rod secretory crypts (wrc1–8); (vi) inner swollen chaetae of sensory fields; (vii) neosminthuroid chaetae. Ordinary chaetae size ranging from microchaetae [1–6 µm], mesochaetae [7–15 µm] to macrochaetae [16 µm– 42 µm]. Ordinary chaetae morphology ranging from simple to lanceolate; including spectacular lanceolate macrochaetae on head and thorax ( Figs 2A , 4A ).

SENSORY FIELDS AND WAX RODS. Six pairs of sensory fields (sf1–6) on head and trunk, each field associated with a wax rod secretory crypt ( Figs 2A , 4A ). On head: sf1 preantennal without special inner chaeta ( Fig. 2A ); sf2 postantennal without special inner chaeta ( Fig. 2A ). On trunk: sf3 dorsally on Th. II with three short candlelight-shaped inner chaetae ( Fig. 4A ); sf 4 in precoxal area of Th. II with two short candlelight-shaped inner chaetae ( Fig. 4A ); sf 5 in precoxal area of Th. III and sf6 dorsally on posterior part of abdomen, each with a short candlelight-shaped inner chaeta ( Fig. 4A ). sf6 well developed ( Fig. 4A ). Eight pairs of free wax rod secretory crypts (seven in Th. III tergum area, eight in abdominal terga area) ( Fig. 4A ). Edges of sf5 and wrc5 separate, wrc 8 in antero-ventral position and close to sf6 ( Figs 4A , 9D ). Tertiary wax rod secretory elements apparently missing.

LABRUM. Labrum without clearly differentiated anterior process, a-row of chaetae very close to labral ridge ( Fig. 2C ). a-row consisting of two pairs of smooth, slightly thickened and strongly curved mesochaetae (a1, a2). m- and p-rows of chaetae each with five mesochaetae ( Fig. 2C ). Labral ridge without apical hairs or spines ( Fig. 2C ).

LABIUM. Basomedian fields with 4 + 4 mesochaetae ( Fig. 2B , D–E). Basolateral fields with 3 + 3 mesochaetae (lateral chaetae on weak tubercles) and with small antero-lateral integumentary processes ( Fig. 2B , D–E). Proximal field with four mesochaetae ( Fig. 2E ). Palp with six papillate chaetae and six guard hairs as (H, h1, h2), (A), (B), (b2, b4), (C), (D, d2), (E, e) (lettering sensu Fjellberg 1999). Hypostomal papilla (H) with a strong, apically enlarged chaeta, other papillae with acuminate, straight or slightly curved chaetae ( Fig. 2D, F ).

OTHER MOUTHPARTS. Oral fold with two chaetae and a microspine, ventral chaeta enlarged and strongly curved near the base, lateral chaeta of ordinary morphology ( Fig. 2 A–B, J). Maxilla outer lobe with sub-basal mesochaeta and apical papilla bearing a mesochaeta ( Fig. 2 J–K), apical papilla without annex hair ( Fig. 2 J–K), sublobal plate with strong hair ( Fig. 2 J–K). Left and right mandibles each with four apical, rounded teeth ( Fig. 2I ). Maxilla with at least four cilliated lamellae, capitulum with two hooked teeth ( Fig. 2 G–H).

HEAD CHAETOTAXY. Postero-dorsal area with 12 + 12 chaetae: 5 + 5 macrochaetae, 6 + 6 mesochaetae in f.p–pa.a-rows, 1 + 1 mesochaetae on the border of sf2 ( Figs 2A , 7A ). Postero-lateral area with 3 + 3 mesochaetae ( Figs 2A , 7A ). Antero-dorsal area with 10 + 10 mesochaetae and two unpaired mesochaetae ( Figs 2A , 7A ). Antero-lateral area with 1 + 1 macrochaetae and 4 + 4 mesochaetae ( Figs 2A , 7A ). Ventral area with 3 + 3 post-labial mesochaetae ( Figs 2B , 7B ).

ANTENNAL CHAETOTAXY. Ant. I with three dorsal chaetae ( Fig. 3A ). Ant. II with six chaetae in two whorls, one in basal whorl, five in apical whorl ( Fig. 3 A–B). Ant. III with 14 chaetae in 4 rough whorls distributed as 1, 2, 4, 7 ( Fig. 3 A–B), of varied morphology, ranging from thin ordinary chaetae to “S-chaetae S -like”; five S-chaetae (S1–S5). S1 as a plump, stalked chaeta, possibly with four folds ( Fig. 3A, D ), S2–S4 long and tubular with blunt apex, S5 short with pointed apex ( Fig. 3 A–B). Ant. IV with 14 chaetae, 14 S-chaetae (12 S, Sx, Sy), one organite (Or) and two apical and subapical sensory rods (a, sa) ( Fig. 3 A–C). Five chaetae slightly departing from the ordinary morphology in a large and contrasted basal ring, a subtly more tubular aspect (vs conical aspect) and outward curving (vs inward curving) ( Fig. 3 A–B). S-chaetae S scarcely differentiated from ordinary macrochaetae, with apex finely rounded. Sy thick and tubular with round apex, Sx as long as Sy but slender with round apex ( Fig. 3A, C ). Organite apparently bifid with two thin arms apically converging, one perceptibly larger than the other ( Fig. 3A, C ). Ornamentation of S-chaetae not seen with light microscopy.

TH. II–ABD. V TERGA CHAETOTAXY. Th. II–Abd. V terga with a minimum of 52 + 52 chaetae, 12 + 12 τ-chaetae, 4 + 4 s-chaetae (s1, s2, s3, s3’) and 8 + 8 wrc ( Figs 4A , 7C ). Dorso-lateral areas of Th. II with 5 + 5 macrochaetae, 4 + 4 mesochaetae and 2 + 2 τ-chaetae ( Figs 4A , 7C ), lengths of the 5 macro- and 4 mesochaetae 13 40 µm: a4 (13 µm)<a1, p1, p4 <a2 <p3 <a5, p2 <a3 (40 µm); a2, a3, a5 and p2 thickened. Precoxal areas of – Th. II with 5 + 5 macrochaetae, 1 + 1 s-chaetae s1 and 1 + 1 τ-chaetae ( Figs 4A , 7C ); lengths of chaetae a8, a9 (22 µm) <p7 <p8 <a7 (42 µm); a7, p7 and p8 thickened. Dorso-lateral areas of Th. III–anterior abdomen with 16 + 16 chaetae, 2 + 2 s-chaetae (s3, s3’) 5 + 5 wrc (wrc1–4, wrc7) and 7 + 7 τ-chaetae ( Figs 4A , 7C ); chaetae consisting of 1 + 1 macrochaetae (p7, 35 µm), the others as mesochaetae; p2 and p3 slightly thickened, p7 strongly thickened; wrc3 thickened. Precoxal areas of Th. III with 3 + 3 chaetae, 2 + 2 wrc (wrc5–6) and 1 + 1 τ-chaetae ( Figs 4A , 7C ); chaetae including 2 + 2 thickened macrochaetae (a 8 –45 µm, p 8 –22 µm); wrc5 thickened. Posterior area of the abdomen (until Abd. V included) with chaetae in variable numbers and tendency to asymmetrical distribution (range seen 19 + 19 to 23 + 24 chaetae), 1 + 1 s-chaetae (s2) and 1 + 1 wrc (wrc8) ( Figs 4A , 7C ); chaetae including 8 + 8 macrochaetae (17–34 µm) and 13 + 13 mesochaetae. s1 tubular, s2 bean - shaped ( Fig. 4C ), s3, s3’ light bulb-shaped ( Fig. 4A ).

LEG CHAETOTAXY. Leg I ( Fig. 5A ) subcoxa 1, subcoxa 2 and coxa each with one chaeta; trochanter with four chaetae (2 proximal, 2 distal); femur with nine chaetae; tibiotarsus with 13 chaetae in five rough whorls distributed as 2, 2, 1, 3, 5; one of the apical anterior chaetae slightly different (weak contrast, thin and with subtly blunt apex). Leg II ( Fig. 5B ) subcoxa 1, subcoxa 2 and coxa each with one chaeta; trochanter with three chaetae; femur with eight chaetae; tibiotarsus with 14 chaetae in four rough whorls distributed as 3, 4, 3, 4. Leg III ( Fig. 5C ) subcoxa 1 with two chaetae; subcoxa 2 with one chaeta; coxa with two chaetae in proximal position; trochanter with four chaetae; femur with 8 chaetae; tibiotarsus with 13 chaetae in four rough whorls distributed as 2, 4, 3, 4. Each pretarsus with two microchaetae, one on anterior side and one on posterior side, the anterior chaeta larger than the posterior chaeta ( Fig. 5 D– G).

CLAWS. Ratio unguis length: pretarsus width on leg I–III, respectively ~3.5, 3.3, 2.8. Ratio of unguiculus: unguis for claw I, II, III ~0.5, 0.55, 0.45 ( Fig. 5 D–G). Unguis with basal narrowing ( Fig. 5 D–G). On claw I lamella la moved in anterior position, shaped as a thin spine ( Fig. 5D ); on claw II and III lamella la missing ( Fig. 5F, G ). On each claw lamellae lp and Bp well developed ( Fig. 5 D–G). On unguiculus basal tubercle reduced to very small posterior integumentary process, lamella of the unguiculus with slender, conical aspect, without perceptible crests and with smooth edges reduced to apical part ( Fig. 5 D–G). Ratio of unguis length: tibiotarsus length on leg I–III ~0.38, 0.4, 0.4.

ABD. VI AND GENITAL CHAETOTAXY. Abd. VI tergum with 3 + 3 macrochaetae, two unpaired mesochaetae (a0, av) and 1 + 1 microchaetae (µ.av) ( Figs 4A , 7C ). Abd. VI sternum with 5 + 5 chaetae (including av), 2 + 2 microchaetae µ.av and 1 + 1 small basal rings without visible chaetal element ( Figs 4A , 7C ). No clear delimitation between anal valves and rest of Abd. VI tergum and sternum. Male genital plate either with 6 + 6 circumgenital chaetae or 5 + 5 and one unpaired circumgenital chaetae and 7 + 7 eugenital chaetae ( Fig. 6A ). Immature male observed with 8 + 8 or 9 + 9 chaetae or microspines ( Fig. 6B ). Female genital plate not observed.

ABD. IV STERNUM AND FURCA. Abd. IV sternum with 4 + 4 chaetae and 1 + 1 neosminthuroid chaetae ( Fig. 4A ). Neosminthuroid chaetae flame-shaped, with very minute teeth ( Fig. 4A, D ). Manubrium with 4 + 4 chaetae ( Fig. 6D ). Posterior side of dens with a strong proximal chaeta with minute external teeth, two subdistal conical spines with basal ring, a distal chaeta and two lobe-like distal spines without basal ring; anterior side distally with small acute spine and two lobes (blunt spines) without basal ring ( Fig. 6 D–E). Mucro with thin lamellae, posterior lamellae serrate (15–17 teeth), apex rounded ( Fig. 6 F–G).

TENACULUM AND VENTRAL TUBE. Tenaculum with 3 + 3 large teeth, basal tubercle produced as 1 + 1 well-developed processes ( Fig. 6 G–H). Ventral tube with 2 + 2 apical chaetae, without clear posterior lobe ( Fig. 6I ).

Ecology and distribution

The presence of a species of Spinaethorax in Vietnam indicates that this genus has a much larger distribution than thought when it was described. The species is likely to be cave-restricted, in spite of its weak troglomorphic characters (the claws appear thinned in their distal part, but this may be phyletic rather than adaptive), as we never encountered it in the numerous surface samples we examined in this small region of southern Vietnam. Spinaethorax may have been overlooked because of its cave habitat, but also because it could be a rare species inside caves. The presence of the genus was confirmed in two other caves of the Hon Chong karst (one cave yielding a species new to science, the other yielding juveniles of an unidentified species). Many caves sampled in Southeast Asia contained unidentified Megalothorax , but Spinaethorax remains so far restricted to the Hon Chong karst. However, thorough re-examination of cave Neelidae from the region as well as new sampling may change the figure.

Figures

Fig. 1. Spinaethorax adamantis sp. nov., habitus, with enlargement of the protuberance bearing wax rod secretory element of sf6.

Fig. 2. Spinaethorax adamantis sp. nov. A–B. Chaetotaxy of the head. A. Dorsal side. B. Ventral side, anterior part. C. Labrum dorsal side. D–F. Labium. D. Focus on papillate chaetae of the palp. E. Focus on chaetae in proximal field. F. focus on papilla H. G–H. Maxilla, different views. I. Left mandible. J–K. Maxilla outer lobe. J. Lateral side. K. Ventral side. Abbreviations: blf = basolateral field of labium; bmf = basomedian field of labium; mol = maxilla outer lobe; of = oral fold. Labial palp lettering after Fjellberg (1999).

Fig. 3. Spinaethorax adamantis sp. nov. A–D. Chaetotaxy of the antenna. A. Dorsal side. B. Ventral side. C. Focus on S-chaeta Sx and Organite Or with enlargement of the latter. D. S-chaeta S1, different aspects. Asterisks indicate modified chaetae. Chaetae implanted on the other side represented with gray stroke.

Fig. 4. Spinaethorax adamantis sp. nov. A. Chaetotaxy of the trunk. B. Focus on the τ-chaetae (asterisks link τ-chaetae in A and B). C. Focus on s-chaeta s2. D. Focus on the neosminthuroid chaeta. Secondary granulation of Th.II–Abd.V terga partially shown (anterior, ventral and posterior limits, also limits near sensory fields and wrc1–8).

Fig. 5. Spinaethorax adamantis sp. nov. A–C. Chaetotaxy of legs. A. Leg I with focus on apical chaetae of tibiotarsus, asterisk indicates a special chaeta. B. Leg II (also with sf4 on Th. II precoxal area). C. Leg III (also with sf5 on Th. III precoxal area). D–G. Morphology of claws. D. Claw I posterior side. E. Claw I anterior side. F. Claw II posterior side. G. Claw III posterior side.

Fig. 6. Spinaethorax adamantis sp. nov. A–B. Male sexual apparatus. A. Male genital plate (asterisk indicates a chaetanot seen on otherside, possiblyunpaired).B. Immature male genital plate.C. Manubrium/ dens anterior articular process. D. Chaetotaxy of manubrium and dens posterior side. E. Distal part of dens and mucro anterior side. F. Mucro posterior side. G–H. Tenaculum. H. Focused on apical teeth and basal process. I. Ventral tube lateral side.

Fig. 7. Spinaethorax adamantis sp. nov. A–B. Diagram of the chaetotaxy of the head: A dorsal side, B ventral side. C. Diagram of the chaetotaxy of the trunk. Enlarged or lanceolate chaetae with thicker line. Nomenclature of chaetotaxy after Schneider & D’Haese (2013), Schneider et al. (2016) and Schneider (2017), partial equivalence with head nomenclature of S. tonoius (Palacios-Vargas & Sánchez 1999) is given in A (IL1–5 chaetae).

Fig. 8. Spinaethorax adamantis sp. nov., partial diagram of the chaetotaxy of the antenna (Ant. III/Ant. IV).

Fig. 9. A. Schematic interpretation of the labrum of Spinaethorax adamantis sp. nov. B–F. Chaetotaxic organization of sf6. B. Neelus murinus. C. Megalothorax minimus. D. Spinaethorax adamantis sp. nov. E. Megalothorax granulosus. F. Acanthoneelidus pratensis. G–L. Outline of claw III, normalized in length, of representatives of the six genera of Neelipleona. G. Spinaethorax adamantis sp. nov. H. Neelus murinus. I. Megalothorax minimus. J. Zelandothorax novaezealandiae. K. Neelides folsomi. L. Acanthoneelidus pratensis. H, I, K, L after Schneider (2017), J after Bonet (1947).