Folsomia najtae, Potapov & Fjellberg & Bokova, 2017

Potapov, Mikhail B., Fjellberg, Arne & Bokova, Anna, 2017, Folsomia najtae n. sp. (Collembola: Isotomidae) - a new species with ‘ mobile’ forms from the Far East of Russia, Zoosystema 39 (1), pp. 95-102 : 96-100

Folsomia najtae n. sp.

(Figs 1; 2; 3A-D)

TYPE MATERIAL. — Holotype. Adult ♀. Russia, Far East , southern spurs of Sikhote-Alin Range , Ussuriysky District , Ussuriysky State Nature Reserve , Komarovskoye Forest , Turova Nipple, Khripunovsky Pass, Pinus sibirica (Ledeb.) Turcz forest on slope, rotten wood, 22.VII.2016, coll. N. Kuznetsova and M. Potapov. deposited in MSPU.

Paratypes. Five (adult and subadult individuals of normal form) from nearby the holotype location, Grabovaya Nipple, mixed forest on slope, rotten wood, 23.VII.2016, coll. N. Kuznetsova and M. Potapov ; two (juveniles of mobile form) – from Ussuriysky District , Ussuriysky State Nature Reserve, mixed forest, litter, 05.X.2004, coll. M. Potapov. ; three paratypes from Far East , Sikhote-Alin Range , Shkotovsky District, Khualaza Mt., forest, litter, 19.IX.2004, coll. L. Deharveng and A. Bedos. Seven paratypes are deposited in MSPU, three paratypes in MNHN .

OTHER MATERIAL. — Russia, Far East, Sikhote-Alin Range, Shkotovsky District, Pidan Mt., mixed forest, rotten wood, c. 800 m alt., 20.IX.2004, coll. M. Potapov; ibidem, coniferous forest ( P. sibirica , Taxus L.), 21.VII.2016, coll. M. Potapov; Far East, Lazovsky District, State Reserve of Laso, nearby Preobrazheniye, valley of Sokolovka River, mixed forest, rotten wood, 21.IX.2011, coll. M. Potapov. deposited in MSPU.

DIAGNOSIS. — Species with eight anterior and four posterior chaetae on dens, 6 + 6 ommatidia, short chaetae covering, full set of ms-chaetae (1,1/1,1,1) on body tergites, long accp3 s-chaetae on Abd.V, and two s-chaetae on Ant.1.

ETYMOLOGY. — The species is named in honor of Judith Najt, the famous taxonomist of Collembola.

DESCRIPTION

General characters

Body size from 0.8 to 1.1 mm (based on five adult ♀ and one adult ♂), with whole range probably wider since subadult ♀ of 1.4 mm seen. Colouration as in Fig. 1A. Pigment grains form transversal bands, intersegmental areas and appendages unpigmented, anterior half of body darker. Body stout, antennae short, 0.8-0.9 as long as head diagonal.Abd. IV, V and VI clearly fused. Cuticle ‘smooth’, granules much smaller than chaetae bases, forming a mixture of hexagonal and orthogonal pattern.

FIG. 1. — Folsomia najtae n. sp.: A, appearance of subadult ♀ of normal form (1.4 mm); B, Abd. IV-VI. Abbreviations: see Material and methods. Scale bars: A, 0.3 mm; B, 0.1 mm.

Head

Ocelli 6+ 6, size of cornea strongly variable (see the dimorphism part below). PAO narrow, constricted, longer (1.1- 1.3) than width of Ant.I and 1.3-1.6 as long as inner unguis length ( Figs 2 E-G; 3A). Its anterior and posterior edges often with chitinized wrinkles (‘setulae’ or ‘denticles’ in use, auct.): though the variation of the character is high, from factually smooth to wrincled, even in our not so abundant material. Maxillary outer lobe with 4 sublobal hairs, maxillary palp bifurcate (few specimens found with simple palp at least on one side). Labral formula as 4/5,5,4. Labium with 5 papillae (A-E), guard e7 absent, with 3 proximal, 4 basomedian, and 5 basolateral chaetae. Ventral side of head with 4 + 4 postlabial chaetae. Ant.1 with 2 ventral s-chaetae (s) and 3 small basal ms-chaetae (bms), 2 dorsal and 1 ventral ( Fig. 2E ), normally with 13 chaetae. Ant.2 with 3 bms and a laterodistal s. Ant.3 without bms and with 6 distal s (including two lateral), without additional s-chaetae. Ant.4 with several tubular s-chaetae. Organite rather big and roundish, set together with subapical ms.

Body

S-formula 4,3/2,2,2,3,5 (s) and 1,1/1,1,1 (ms) ( Fig. 3B, C ). Tergal s-chaetae short, much shorter than common chaetae, longer on Abd.V. Medial s-chaetae on Th.II-Abd.III situated in mid-tergal position, on Abd.I-III between Mac1 and Mac2. Abd.V with 5 s-chaetae arranged as 3 dorsal ones (as, accp1, accp2), of middle size, almost as long as common chaetae, one dorso-lateral accp3, longer and thicker than in dorsal group, and one ventro-lateral short (‘3+1+1’ pattern) (Figs 1B; 3B). Common chaetae short. Macrochaetae rather short and smooth, 2,2/3,3,3 in number, medial pair hardly

Potapov M. B. et al.

visible on thorax, especially on Th.II. Medial macrochaetae on Abd.V shorter than dens (0.4-0.7, see also dimorphism) and 1.6-2.1 times longer than mucro. Foil chaetae at the tip of abdomen absent. Axial chaetotaxy abundant. Thoracic sternites without ventral chaetae. Unguis with lateral teeth ( Fig. 3D ). Empodial appendage about half as long as inner edge of unguis. Tibiotarsi normally with 1-2 additional chaetae on Leg 1 and 2, and with several additional chaetae on Leg 3. Tibiotarsal tenent chaetae pointed. VT with 4 + 4, more rarely 3+ 4 or 3 +3 laterodistal and 6-7 posterior chaetae, anteriorly without chaetae. Tenaculum with 4+ 4 teeth and 1-2 chaetae. Anterior furcal subcoxae with 7-12, posterior one with 2-4 chaetae. Anterior side of manubrium with two pairs of chaetae, as 2 + 2 (rarely 1 + 2 or 3+ 2) ( Fig. 2C ). Posterior side of manubrium with 4 + 4 (4+ 5) laterobasal, 1+ 1 apical (a1), 2+ 2 distal chaetae (M1, L1, without ml1). Lateral chaetae (l2) present or absent ( Fig. 2C ). Dens with 8 anterior chaetae arranged as 1,1,1,2,3. Posterior side of dens with few distinct crenulations at the middle, with 3 chaetae on proximal half and 1 at the middle. Length of dens and crenulations on its posterior side affected by dimorphism (see below). Mucro bidentate. Ratio of manubrium: dens: mucro = 3.8-4.4: 2.8-4.6: 1 (considering both normal and ‘mobile’ forms).

REMARKS

F. najtae n. sp., F. setula (eastern areas of USA), and F. orientalis (North of Far East of Russia) form a compact group of species which is characterized by the presence of 6+6 ommatidia, full set of ms-chaetae on body tergites, long accp3 s-chaetae on the fifth abdominal segment (Figs 1B; 4A, B), short chaetae covering, two s-chaetae on Ant.1.

Normally F. najtae n. sp. does not show such a prominent PAO as in F. setula , but its variability prevents ( Fig. 3A ) reliably separating the two species with this key character. After our study the only steady character is the number of chaetae on the posterior side of the dens: 4 ( F. najtae n. sp.) vs 3 ( F. setula ) (see Figs 2C ; 3E ). Apart from this, F. setula has 12 common chaetae on Ant.1 (vs 13 in F. najtae n. sp.) but the character is not very stable in the new species. Folsomia orientalis has 8-10/5 chaetae on dens ( Fig. 3G , vs 8/ 4 in F. najtae n. sp.) and 6-8+6-8 laterodistal chaetae on ventral tube (vs 4(3)+4(3) in F. najtae n. sp.), labial palp with guard e7 present (vs absent in F. najtae n. sp. and F. setula ), chaetae ml1 present on the manubrium ( Fig. 3G , vs absent in F. najtae n. sp. and F. setula ), and basal ms present on Ant.3 (vs absent in other two species).

ECOLOGY AND DISTRIBUTION

The new species is known from four localities within the southern spurs of the Sikhote-Alin Mt. Range (Far East of Russia). It often inhabits rotten wood that may explain its stout body shape, large head and short antennae being usual characteristics of xylophilous species of springtails.

Folsomia setula Christiansen & Tucker, 1977 ( Figs 3E, F ; 4A )

Folsomia setula Christiansen & Tucker, 1977: 376 .

MATERIAL. — Several juveniles, adult ♂ and ♀: USA, North Carolina, Swain, Blue Ridge Parkway , Thomas Divide , 35°31.241’N, 83°14.840’W, c. 3.800 ft. alt., red rotten hardwood, 29.V.2007 ; North Carolina, Graham, Cherohala Skyway, Unicoi Crest , 35°20.668’ N, 84°02.103’ W, 27.V.2007, soil under large hardwood lump. c. 4.600 ft. alt .; Tennessee, Monroe, Cherohala Skyway, Charles Hall Bridge , 35°20.996’N, 84°04.055’W, c. 3.700 ft. alt., hardwood, damp litter at seep. 27.V.2007, coll. A. Fjellberg.

ECOLOGY AND DISTRIBUTION. — F. setula is probably distributed only in the East of USA.

REDESCRIPTION

Colouration from almost white (often in juveniles) to blue fumose. Body stout, antennae short. Corneas of ocelli hardly marked, their number (6 + 6) defined by form of eye pigment which often weakly developed in juveniles. PAO narrow, constricted, longer (c. 1.3) than width of Ant.I and 1.8-1.9 as long as inner unguis length ( Fig. 3F ), its anterior and posterior edges with chitinized wrinkles. Outer mouth parts as in F. najtae n. sp. Labial palp without guard e7 (present on one side of one individual). Ventral side of head with 4+ 4 postlabial chaetae. Ant.1 with 2 ventral s and 3 small bms, 2 dorsal and 1 ventral, with 12 (rarely 11) common chaetae. Ant.2 with 3 bms and a latero-distal s. Ant.3 without bms and with 6 distal s (including two lateral), without additional s. Ant.4 with big and roundish organite. S- and ms-formula as in F. najtae n. sp. Abd.V with 3 dorsal s (as, accp1, accp2) of middle size, one longer and thicker dorso-lateral accp3, and one short ventro-lateral accp4 ( Fig. 4A ). Common chaetae very short. Macrochaetae short and smooth, ‘2’,2/3,3,3 in number, medial pair rudimentary on Th.II. Medial macrochaetae on Abd.V shorter than dens (0.6-0.8) and 1.8-1.9 times longer than mucro. No foil chaetae. Axial chaetotaxy abundant (9,7/6,5,5 seen in one individual). Unguis with lateral teeth. Empodial appendage about half as long as inner edge of unguis (0.5-0.6). Tibiotarsi with few additional chaetae. VT with 3-4+3-4 laterodistal and 5-6 posterior chaetae. Tenaculum with 4+4 teeth and 1-2 chaetae. Anterior furcal subcoxae with 5-7, posterior one with 3-4 chaetae. Anterior side of manubrium with two pairs of chaetae (rarely 1+2). Posterior side of manubrium with 4 +4 laterobasal, 1 +1 apical (a1), 2+ 2 distal chaetae (M1, L1, without ml1), and 4+4 central chaetae. Lateral chaetae (l2) present. Dens with 7-8 anterior and 3 posterior chaetae, basal chaeta larger ( Fig. 3E ). Ratio of manubrium: dens: mucro = 3.5-3.7: 2.6-3.0: 1.

REMARK

After Christiansen & Bellinger (1998), F. setula is recorded from Illinois and Kentucky and can be easily separated from the related species by a striking PAO with prominent inner ‘setulae’ ( Fig. 3F ). Our material from neighboring states (North Carolina and Tennessee) fits well to the available descriptions ( Grow & Christiansen 1976; Christiansen & Tucker 1977) and therefore makes the detailed comparison between F. setula and F. najtae n. sp. possible (see the Remark part to F. najtae n. sp.).

Figures

FIG. 2. — Folsomia najtae n. sp.: A, B, appearance of juvenile specimens of normal (A) and mobile (B) forms (both of about 0.9 mm); C, D, furca of normal (C) and mobile (D) forms; E, G, anterior half of head in normal (E), mobile form (F), and juvenile individual (G) of 0.6 mm length. Abbreviations: see Material and methods. Scale bars: A, B, 0.3 mm; C-G, 0.05 mm.

FIG. 3. — A-D, Folsomia najtae n. sp.: variability of PAO (A); s-chaetae and macrochaetae on tergites of Abd.II-VI (B) and Th.II,III and Abd.I (C), apical part of leg 3 (D); E, F, F. setula Christiansen & Tucker, 1977, dens, lateral view (E), PAO (F); G, F. orientalis Martynova,1977 furca, lateral view. Abbreviations: see Material and methods. Scale bars: A, D-F, 0.03 mm; B, C, 0.02 mm; G, 0.05 mm.

FIG. 4. — s-chaetae and macrochaetae on Abd. IV-VI of F. setula Christiansen & Tucker, 1977 (A) and F. orientalis Martynova, 1977 (B). Abbreviation: see Material and methods. Scale bar: 0.1 mm.