Taxonomy of the Cryptopygus complex. III. The revision of South African species of Cryptopygus and Isotominella (Collembola, Isotomidae)

Abstract Species of the genera of the Cryptopygus complex in South Africa are morphologically revised. Five new species of the genus Cryptopygus Willem, 1902 s. s. and one new species of the genus Isotominella Delamare Deboutteville, 1948 are described. Cryptopygus abulbussp. nov. and C. bulbussp. nov. have only one chaeta on the anterior side of dens and no chaetae on the anterior side of manubrium, the latter species being characterized by the presence of a bulb at apex of antennae; C. inflatussp. nov. shows a rare combination of eight ocelli on each side of the head with a tridentate mucro; C. longisensillussp. nov. has five long s-chaetae on the fifth abdominal segment; C. postantennalissp. nov. is unique by having a very long and slender postantennal organ with strong inner denticles; Isotominella laterochaetasp. nov. is the second member of the genus and differs from the type species by many more anterior chaetae on the manubrium and the presence of chaetae on ventral side of metathorax. The genera are discussed and a key to all species of the Cryptopygus complex recorded in South Africa is given. The focus is on the Western Cape Province where the complex is the most diverse and sampling more complete than in other provinces of South Africa.


Introduction
Although poor compared to Europe, the diversity of South Africa Collembola is increasingly better understood due to international collaborations since 2008 (Janion et al. 2011a(Janion et al. , b, 2012Janion-Scheepers et al. 2013, 2015Potapov et al. 2011). The family Isotomidae, which include the dominant Collembola in soil and moss habitats of South Africa, has been particularly little studied, and currently consists of 19 confirmed described species (Janion-Scheepers et al. 2015). From samples collected over the last decade, especially in the Western Cape Province of South Africa, we found a large diversity of Cryptopygus species (Janion-Scheepers et al. 2011), which had not been recorded so far. Previous South African records of this genus include Cryptopygus caecus by Paclt (1959), now known as Mucrosomia caeca (Wahlgren, 1906), while Barra (1997) described Cryptopygus riebi Barra, 1997, now a synonym of Pauropygus caussaneli (Thibaud, 1996). We describe here the first five Cryptopygus species of South Africa and a new species of the genus Isotominella, monotypic up to this date. To summarize our data, we provide a key to all species of the Cryptopygus complex for South Africa. This is our second contribution to the taxonomy of the family Isotomidae of the country (Potapov et al. 2011) and the third piece of work on the Cryptopygus complex (Potapov et al. 2013;Potapov et al. 2017).
abdominal segments accp s-chaeta(e) situated near or within p-row of chaetae Ant.
Specimens were mounted on cavity or flat microscope slides using Gisin's solution or Marc André II mounting liquid, respectively. Specimens were studied using a Leica DM2500 microscope, while drawings were made using camera lucida.

Taxonomic part
In our understanding, the Cryptopygus complex includes all taxa of Anurophorinae s. l. having Abd. V well separated from Abd. IV and fused with Abd. VI, and lacking any special apomorphy (e.g., presence of true spines at the end of abdomen, loss of PAO, furca, etc.). Both genera studied below belong to the Cryptopygus complex. Number of s-chaetae on Th. III-Abd. II 1/1,1. Pleural fold on mouth cone with two finger-like processes (fig. 20 in Potapov et al. 2013 Discussion. Here we follow our simplified characterisation of the genus proposed formerly (Potapov et al. 2017) that is an expanded version of diagnosis of Rusek (2002). The latter diagnosis offers to be within the limits of the definite number of ocelli (6+6), "antarcticus-like" furca and clavate tibiotarsal hairs. We presume a wide variation of the main characters: the mucro may be absent, bidentate or tridentate; the manubrium with or without anterior chaetae; the dens short and smooth to long and crenulated; the ocelli absent to their full set, i.e. 8+8; tenent tibiotarsal hairs clavate or pointed; number of ms-chaetae from 1,0/0,0,0 to 1,1/1,1,1; maxillary outer lobe with changeable shape of palp and number of sublobal hairs. In our view, the splitting of Cryptopygus to groups, subgenera or genera will be probably necessary, but calls for preliminary morphological revisions and expanded molecular data of known species.
Etymology. The name is derived from the presence of apical bulb on Ant. IV. Distribution and ecology. Currently known to occur in the southern part of the Western Cape Province of South Africa, including Kogelberg, Franschoek and the Table Mountain area (Cape Town). All specimens were collected from leaf litter in indigenous vegetation.
Discussion. The species differs from other representatives of the Cryptopygus complex, if not from all Isotomidae of the Southern Hemisphere, by the presence of a globular bulb at tip of the antennae. The taxonomical value of this character is not fully clear. In the Northern Hemisphere several unrelated genera also possess an apical bulb which is embedded on the tip of the antennae, for example Anurophorus Nicolet, 1842 (most of the species), Sibiracanthella Potapov & Stebaeva, 1994, Tuvia Grinbergs, 1962and Vertagopus Börner, 1906. The antennal bulb of C. bulbus sp. nov. is set apart from the apex, which is unlike in the aforementioned taxa. The only exception found was in specimens observed from Orangekloof (Cape Town), where the apical bulb was less developed.
For other differences of the new species from congeners see the Discussion of C. abulbus sp. nov.  Diagnosis. Without globular retractile bulb on Ant. IV. Organite on Ant. IV chililike. 6+6 ocelli. Maxillary palp simple. Two sublobal hairs. Anterior side of manubrium without chaetae. Tenaculum with two chaetae.

Cryptopygus abulbus
Description. Body size 0.6-0.7 mm. Body with regular blue pigmentation, slender (Fig. 3). Abd. V well separated from Abd. IV and fused with Abd. VI (Fig. 15). Cuticle with orthogonal granulation. Ocelli 6+6 arranged as three in anterior and three in posterior group (Fig. 19). PAO more than twice as long as ocellus, 0.6-0.7 as long as width of Ant. I and 0.8-1.1 mm as long as inner unguis length. Maxillary outer lobe with two sublobal hairs, one individual with one sublobal hair on one side was found. Maxillary palp simple. Labral formula as 2/5,5,4. Labium with five usual papillae (A-E, Fig. 16) and labial formula as in C. bulbus sp. nov. Ventral side of head with 4+4 postlabial chaetae. Ant. I with eleven common chaetae, two ventral s-chaetae (s) and three small basal micro s-chaetae (bms), two dorsal and one ventral, Ant. II with three bms and one latero-distal s, Ant. III with one bms and five distal s (including one lateral). S-chaetae on Ant. IV weakly differentiated. Organite long, of chili-like shape, set apart from subapical micro s-chaeta (Figs 17,18). Tip of antennae without retractile bulb.
Etymology. The name is derived from the absence of apical bulb on Ant. IV to stress the difference from C. bulbus sp. nov. Distribution and ecology. Currently known from indigenous vegetation in the Jonkershoek Nature Reserve, Stellenbosch.
Discussion. Unlike C. bulbus sp. nov., the new species has no antennal bulb. Nevertheless, the two species form a rather well-defined group differing from almost all congeners by a simple maxillary palp, two sublobal hairs, chili-shaped organite on Ant. IV, and the absence of chaetae on the anterior side of the manubrium. Concerning the last character, only C. nivicolus (Salmon, 1965) and C. sverdrupi Lawrence, 1978 also lack this pair of chaetae, which is common to other species of the genus. Both mentioned species are inhabitants of Antarctic polar deserts and can hardly be conspecific to C. abulbus sp. nov. found in dry sites in a subtropical climate. These two Antarctic species are very dark and have two clavate tenent hairs (vs. one in C. abulbus sp. nov.) on tibiotarsi I. In addition, C. nivicolus has no mucro (vs. present in the new species) while C. sverdrupi has very small PAO (more than twice longer than ocellus in C. abulbus sp. nov.). Recently, Gressitacantha terranova Wise, 1967 was moved to Cryptopygus (Greenslade, 2015) adding another Cryptopygus species without anterior chaetae on the manubrium. The differences between C. abulbus sp. nov. and C. terranovus are more numerous than those from C. nivicolus and C. sverdrupi (in furca, arms of abdomen, length of macrochaetae, and others). Diagnosis. 1+1 ocelli. PAO very long and slender, with large inner denticles. MSformula 1,0/0,0,1 (ms). All s-chaetae of Abd. V in one dorsal group. Anterior side of manubrium with 1+1 chaetae. Dens of medium length. Mucro tridentate.

Cryptopygus postantennalis
Description. Body size 0.8 mm (only one adult female could be measured). Body mostly white, slender, with rare, scattered pigmentation and a distinct black eyespot (Fig. 23). Abd. V well separated from Abd. IV and fused with Abd. VI (Fig. 31). Cuticle with orthogonal and hexagonal granulation. One rudimentary ocellus, with a concentration of pigmentation. PAO very long and slender (Fig. 27), at least five times as long as ocellus, twice as long as width of Ant. I and 2.8 as long as inner unguis length. PAO constricted, with large "inner denticles". Maxillary head with unmodified lamellae. Maxillary outer lobe with four sublobal hairs, maxillary palp bifurcate. Labral formula as 4/5,5,4, edge of labrum not reduced. Labium with five usual papillae (A-E), guard chaetae e7 present, three proximal and four basomedian chaetae. Ventral side of head with 4+4 chaetae. Ant. I with two ventral s-chaetae (s), distal one much shorter than proximal one, and three basal micro s-chaetae (bms), of which a long dorsal one (Fig. 28), Ant. II with three bms and one latero-distal s, Ant. III with one bms and five distal s (including one lateral), without additional s-chaetae. S-chaetae on Ant. IV weakly differentiated. Organite hook-like, close to subapical micro s-chaeta, which is long and bent (Fig. 29).
Etymology. The species is named after its remarkable PAO.

Distribution and ecology.
Known only from type locality and Swellendam, from indigenous vegetation (fynbos and Afromontane forest).
Etymology. The name is derived from the swollen posterior part of abdomen. Distribution and ecology. Known from mostly dry, mountainous areas, from the Northern Cape (Sutherland), the Cederberg Wilderness area, and Franschhoek (not as dry as previous two sites).
Discussion. Considering all species in the Cryptopygus complex, the combination of 8+8 ocelli and tridentate mucro is unique. The only species resembling our species is Proisotoma (Isotomina) pseudominuta Schött, 1927, described from Cameroon. However, this species has clavate tenent hairs and a shorter dens, while Cryptopygus inflatus sp. nov. does not have clavate tenent hairs.
Some variation exists in the material examined and two forms of unclear status can be recognized; both have an ms on Abd. I (1,0/1,0,0) while C. inflatus sp. nov. does not. These two forms differ as follows: a. Specimens from Sutherland (SUT002) have an ms and two chaetae on the basal part of the posterior side of the dens. b. Specimens from Mont Rochelle (MR510) have an ms on Abd. I and three chaetae on the basal part of the posterior side of the dens like in C. inflatus sp. nov. Description. Body size 0.9-1.3 mm (Fig. 25). Body pale, with scattered black granules of pigmentation, more concentrated on head, eye spots and posterior of trunk. Body tubular. Abd. V well separated from Abd. IV and fused with Abd. VI ( Fig. 45). Cuticle with thin hexagonal primary granulation ("smooth"). Ocelli range from three to seven on each side (Figs 37-41) (see Discussion). PAO rather narrow, sharply constricted, with small inner denticles, longer than width of Ant. I (1.1-1.3) and inner unguis length (1.3-1.4). Maxillary head without modified lamellae. Maxillary outer lobe with four sublobal hairs, maxillary palp bifurcate. Labral formula as 4/5,5,4, edge of labrum not reduced. Labium with five usual papillae (A-E), guard chaetae e7 present, three proximal and four basomedian chaetae. Ventral side of head with 4-5+4-5 chaetae. Ant. I with three ventral s-chaetae (s) and two small basal micro s-chaetae (bms), dorsal and ventral, the former set together with long chaeta-like micro s-chaeta, Ant. II with three bms and one latero-distal s, Ant. III with one bms and six distal s (including two lateral), without additional s-chaetae. S-chaetae on Ant. IV weakly differentiated. Organite pin-like.
Etymology. The name is derived from the very long s-chaetae on Abd. V. Distribution and ecology. Cryptopygus longisensillus sp. nov. is currently known from Sutherland (Northern Cape) and Jonkershoek, Stellenbosch (Western Cape).
Discussion. The species belongs to a group of forms having ocelli, tridentate mucro and rather long dens (C. insignis Massoud & Rapoport, 1968, C. patagonicus Izarra, 1972, C. quadrioculatus (Wise, 1970, C. tricuspis Enderlein, 1909) (Table 1). Two species, C. insignis and C. tricuspis have 1+1 chaetae (vs. 0+0 in C. longisensillus sp. nov.) on ventral side of Th. III and common s-chaetae (vs. elongated in new species) on Abd. V. Due to insufficient descriptions the morphology of C. patagonicus and C. quadrioculatus is less understood. Both species differ from C. longisensillus sp. nov. in fewer chaetae (eight and nine vs. 10-12) on anterior and more chaetae (six vs. five) on posterior sides of dens. C. quadrioculatus shows specific position of ocelli with one anterior and one posterior at a distance.
Cryptopygus longisensillus sp. nov. shows a unique pattern of s-chaetae on Abd. V not found before in the genus: all five s-chaetae elongated while s-chaetae of dorsal triplet thin, two lateral ones slightly thickened, representing a s-pattern of type "4" according to the classification of Potapov et al. (2017). The variability in the number of ocelli is unusual: among six individuals of one population we recorded variants with three, four, five, and seven ocelli. Two ocelli near the PAO are always well visible, while the other ones are only recognizable by weak swellings of the cuticle. The nature of this variability is not fully clear and calls for further study. The only similar case is known in C. insignis ( fig. 4A in Massoud and Rapoport 1968). In the specimens from South Africa, Western Cape, Jonkershoek Nature Reserve, six posterior chaetae on dens were found. This variation also calls for further study. Morphological remarks on C. insignis Massoud & Rapoport, 1968 We had an opportunity to study two type specimens of this species kept in MNHN (Paris) labelled as "Lago Menendez 16.III.1959". It was possible to observe the following characters: s-formula as 4,3/2,2,2,3,5 (s), 1,0/0,0,0 (ms), five s-chaetae on abd.V short, as common for the genus (unlike in Cryptopygus longisensillus sp. nov.); four prelabral chaetae, maxillary palp bifurcate; e7 present on labial palp; ventral tube with 4+4 laterodistal chaetae; Ant. I with three s-chaetae (s) and three basal micro s-chaetae, with long and short in dorsal group (like in Cryptopygus longisensillus sp. nov.).
Reliable taxonomical decision on their status cannot be made at present and preliminary study of all known and unknown forms is underway.
Discussion. The genus Isotominella was described from Ivory Coast and was subsequently given a detailed diagnosis by Jordana et al. (2009) based on material of I. geophila from Algeria. The taxon was considered a member of the Cryptopygus complex and was said to differ from related genera mainly by the crenulation, which is developed only in the proximal half of the dens. According to Jordana et al. (2009), in other genera of the complex this crenulation is either absent (i.e., dens is "smooth"), or extends further along the posterior side of dens, as in Hemisotoma Bagnall, 1949. In our view, the crenulation is a flexible character within the genera of the Cryptopygus complex and depends on the length of furca, which can vary highly within a large genus, e.g., in Cryptopygus s. str., and particularly, among its representatives in South Africa (Figs 14,30,35,43). Two species of the genus Isotominella, I. geophila and I. laterochaeta sp. nov. share a remarkable s-chaetotaxy, particularly, the posterior position of medial s-chaetae on body tergites, a reduced s-formula (3,3/2,2,2,2,3), and differentiation of s-chaetae on Abd. V with two long dorsal and one short lateral s-chaetae. The mouth parts of the two species are uncommon: the terminal 'sensilla' of papilla A and B are rod-like, the number of basolateral chaetae of labium are increased, the labrum has two prelabral chaetae, the number of sublobal hairs of maxillary outer lobe is reduced (three in the new species and two in I. geophila), and the maxillary head is modified. The presence of 7-9 basolateral chaetae on the labium (vs. commonly five as determined by Fjellberg 1999) in I. laterochaeta sp. nov. have not been recorded so far for Isotomidae. This remarkable feature is less pronounced in I. geophila in which this number is variable (five or six). Six basolateral chaetae on the labium were found in the genus Pauropygus (Potapov et al. 2013) in P. projectus Potapov et al., 2013, P. caussaneli, P. pacificus Potapov et al., 2013, which also shows the posterior position of the s-chaetae on tergites. The two genera share other important characters and are probably closely related (Potapov et al. 2013). Labral chaetae are normally pressed to the labrum in Isotomidae, while they are projected forward in the new species (the character is unclear for I. geophila). Isotominella also resembles the blind genera Cylindropygus Deharveng et al., 2005 (Europe) and Dagamaea Yosii, 1965 (East Asia and North America) but reliably differs by the posterior (vs. mid-tergal) position of the s-chaetae on the body tergites. A table to compare all the genera of the complex Cryptopygus is given by Jordana et al. (2009 Diagnosis. Blind. Labium with 7-9 basolateral chaetae. Chaetae on ventral side of Th. III present. Labial palp with 16 guard chaetae. Three sublobal hairs on maxillary outer lobe. Anterior side of manubrium with 9-10+9-10 chaetae. Dens with 12-14 anterior and four posterior chaetae. Mucro bidentate. Description. Body size 0.8-1.0 mm. White, without pigmentation, appearance as Mucrosomia caeca (Fig. 47). Mouth cone projected forward. Abd. V well separated from Abd. IV and fused with Abd. VI (Fig. 53). Cuticle "smooth". Without ocelli. PAO small, not constricted, less than a half of width of Ant. I and 0.5-0.7 as long as inner unguis length. Maxillary head with slender lamellae and thin capitulum. Maxillary outer lobe with three sublobal hairs, maxillary palp simple (Fig. 52). Labral formula as 2/5,5,4, edge of labrum not reduced. Chaetae of labrum conspicuously projected forward (Fig. 50). Labral chaetae of middle and distal rows thicker than chaetae of proximal row. Inner chaetae of distal row shifted to more proximal position and integrated to middle row resulting the impression of 5,7,2 formula. Up to ten clypeal chaetae. Labium with five papillae (A-E), 16 guard chaetae (guard chaetae e7 present), and three proximal chaetae (Fig. 49). Terminal 'sensilla' of papillae A and B rod-like. All inner guard chaetae (b3, b4, d3, d4, e2, e3, e5, e6) strongly curved. With two curved and small accessorial hypostomal chaetae (h1, h2), main hypostomal chaeta (H) absent (Fig. 49). Basal part of labium with four basomedian and 7-9 Figures 47-53. Isotominella laterochaeta sp. nov. 47 appearance and macrochaetotaxy (some macrochaetae lost) 48 ventral side of head 49 labial palp (hypostomal chaetae shown separately) 50 labrum, lateral view (chaetae of distal row marked, three, three, and two chaetae shown for proximal, middle, and distal rows, respectively) 51 apical part of Ant. IV 52 basal parts of labium and maxillary outer lobe, lateral view 53 posterior edge of Abd. IV and fused Abd. V and VI. Abbreviations: A and B papillae of labial palp, blf basolateral field of labium, e7 guard chaeta e7, mp maxillary palp, h1 and h2 hypostomal chaetae, org organit, sms subapical ms-chaeta, ss s-chaeta, ms ms-chaeta. basolateral chaetae (Figs 48, 52). Ventral side of head with numerous chaetae (up to 13 on one side along ventral line), with numerous chaetae at base of labium (Fig. 48). Normal s-chaetae and basal micro s-chaetae hardly differentiated on antennae, their number difficult to ascertain. Ant. I with many chaetae and at least two ventral schaetae (s) mixed with normal chaetae (or thinner s-chaetae). Ant. III with five distal s (including one lateral), without additional s-chaetae. S-chaetae on Ant. IV weakly differentiated. Organite small, rudimental, close to subapical micro s-chaeta, which is long and bent (Fig. 51). mellae, 0.6-0.7 as long as unguis. All tibiotarsi with many additional chaetae: Tibiotarsal tenent hairs not clavate. Ventral tube with 5-8+5-8 laterodistal and 6-9 posterior chaetae (with two larger in distal position), anteriorly without chaetae. Tenaculum with 4+4 teeth and two chaetae (rarely more). Anterior furcal subcoxa with 19-23, posterior one with 11-15 chaetae. Anterior side of manubrium with 9-10+9-10 chaetae arranged in two symmetrical group (Fig. 58), with distal pair thickened. Posterior side of manubrium with 11-14+11-14 chaetae on main part, 4+4 laterodistal and 2(3)+2(3) lateral chaetae (Fig. 59). Dens of medium length, with weak crenulation at the middle, with 12-14 anterior and four posterior chaetae (Figs 55-57). One minute chaeta-like process often seen close to distal chaeta. Mucro bidentate. Ratio manubrium : dens : mucro = 3.0-3.9 : 3.2-4.3 : 1.
Etymology. The name is derived from its many lateral chaetae on the basal part of labium.
Distribution and ecology. Known only from type locality (Cape Point National Park).
Discussion. Isotominella laterochaeta sp. nov. and I. geophila (type species of the genus) differ by the number of anterior chaetae on the manubrium (9-10+9-10 vs. 1-4+1-4), chaetae on ventral side of Th. III (present vs. absent), number of guard chaetae on labial palp (16 vs. 13-14), and number of sublobal hairs (three vs. two) on maxillary outer lobe. Minute chaeta placed at the middle of posterior side of dens, numerous postlabial chaetae, and absence of hypostomal chaeta H are unique to I. laterochaeta sp. nov. The two last characters are unknown for I. geophila.

General discussion and conclusions
The six new springtails from South Africa described here, five Cryptopygus and one Isotominella, bring the total number of Isotomidae to 25 species for the country. Our study is a first contribution to the knowledge of the rich fauna of Cryptopygus of this high endemism country. The five new species described are strongly dissimilar with each other and belong to different groups within the genus, suggesting different colonization events. In addition, local geographic speciation is suspected within several of these species, as reflected in the forms of unclear status presented in species discussions. They call for more detailed variability analyses on more extensive material in order to establish the taxonomical value of the morphological differences that were detected, to reconstruct the distribution patterns of the recognized forms, and to better understand the origin of this local geographical diversification.