Folsomia sedecemoculata Salmon, 1943

Anurophorinae with all abdominal segments clearly separated and a Proisotoma-like furca: manubrium with few anterior chaetae (1+1-3+3), dens slender, crenulated, with rather numerous anterior and posterior chaetae, mucro clearly set off from dens, with two or three teeth. 7+7-8+8 ocelli in known species. With simple or bifurcate maxillary palp and four sublobal hairs, two or four prelabral chaetae. Macro s-chaetae 22235 on Abd.I-V. Tergal macro s-chaetae on abdomen situated in front of p-row of chaetae. B-row of chaetae on Ti.1–2 complete (both B4 and B5 present). Ventral chaetae on Th.III present or absent. Sexual dimorphism present or absent.

To date an appropriate generic name did not exist for the small group species related to Proisotoma Börner, 1901 sensu lato which were discussed in the monograph of Potapov et al. (2006). This group, so-called “Proisotoma tenella, ripicola, biseta”, consists of forms sharing characters such as: the three last abdominal segments separated, manubrium with anterior chaetae, four prelabral chaetae, and presence of three and five s-chaetae on Abd.IV and V, respectively.

Recently, one more species, Proisotoma sedecimoculata (Salmon, 1943), became a probable candidate to belong to this group (Potapov and Janion-Scheepers 2017). This species was described by Salmon (1943) as Folsomia sedecimoculata and was afterwards proposed as a generotype for the new genus Bagnallella Salmon, 1951. Bagnallella was erected based on three last abdominal segments fused, bidentate mucro and eight ocelli. Later, Bagnallella was lost in the taxonomy of the subfamily and was mostly treated as a junior synonym of either Folsomia or Proisotoma. After the examination of the type specimen, it was discovered that the three last abdominal segments were actually separated (Potapov and Janion-Scheepers 2017). Here, we suggest restoring Bagnallella for the group of species mentioned above, rather than erecting a new generic name. Several other forms described under different generic names also fit to Bagnallella at lesser or larger degree of accuracy. For these species, the two Bagnallella key characters were mentioned in the associated descriptions or were seen by us, apart from three forms with unknown sensillar chaetotaxy. Nevertheless, we suppose the last ones (notated with question marks in the list of species of Bagnallella below) belong to the genus. Among these species, Bagnallella sedecimoculata is poorly described and so is not the best to be a generotype, but we prefer to keep a generic name already created by John Salmon.

The incertae sedis genus Bagnallella combines the characters of two large generic groups by the separation of its two last abdominal segments and the presence of three and five s-chaetae on Abd.IV and V respectively in characteristic position. The former character is a diagnostic feature of the Proisotoma Börner, 1901 complex, the latter indicates basic set of s-chaetae in Cryptopygus Willem, 1902 and related genera belonging to Cryptopygus complex (Potapov et al. 2006, 2013, 2020). The latter complex is characterized by the fusion of the two last abdominal segments. The genus Bagnallella takes a neatly intermediate position between Cryptopygus (Cryptopygus complex, Southern Hemisphere) and Scutisotoma (Proisotoma complex, Northern Hemisphere). The three genera share, apart from the characters of the subfamily, the presence of a furca, a mid-tergal position of macro s-chaetae on body tergites, and the absence of any specific apomorphy. The combinations of the two key characters mentioned above are shown in Figure 1. After the separation of the two last abdominal segments, we suggest treating Bagnallella in the Proisotoma complex.

Figures 1–4. 

S-patterns of Abd. IV–VI in the genera Cryptopygus Bagnallella and Scutisotoma (1) B. sedecimoculata (2) and B. dubia (3, 4) 2, 3 furca, anterior view 4 macrochaetae and s and ms-chaetae on body. s = s-chaetae, ms = ms-chaetae.

Bagnallella. The genus is distributed worldwide. More local species (B. davidi, B. douglasi, B. mishai, B. biseta, B. koepckei) are distributed in the Southern Hemisphere that indicates further relation to the “austral” genus Cryptopygus. Due to apparent ruderal B. tenella and pioneer B. ripicola, the genus also occurs in the Northern Hemisphere. The ecology of the former species is especially remarkable, as B. tenella is often recorded in mass abundances (Agrell 1939; Arle 1970; Neves and Mendonça 2016). We speculate that B. davidi has an unusual biology and ecology due to its morphological modifications (described below).

Below we give the diagnosis, description, remarks, and distribution, with, if possible, ecological remarks of all species of Bagnallella. Some sections may be omitted if the associated species have good morphological descriptions in the literature.

Adult male from Argentina under label “Tucuman, 19/4/59, entre maderas ...”, deposited in the Museum national d’Histoire naturelle (MNHN), Paris, France. This individual was obviously among the material the original description was based on by E.H. Rapoport.

Maxillary palp bifurcate, four prelabral chaetae. Dens with ~50 anterior chaetae. Mucro bidentate. Anterior side of manubrium with 3+3 chaetae. 33/22235 s and 11/111 ms on body. Ventral chaetae absent on Th.III.

Maxillary outer lobe with four sublobal hairs, maxillary palp bifurcate. Labral formula as 4/5,5,4. Guard chaeta e7 present on labium. Ant. III without bms and with five distal s (including one lateral), without additional s-chaetae. Th. I, II, and III without ventral chaetae. S-formula as 33/22235 (s), 11/111 (ms). Tibiotarsal tenent chaetae (1,1,1) clearly clavate. Tibiotarsi 1–2 with more than 24 chaetae. Ventral tube with 6+5 chaetae (in the adult male studied). Retinaculum with 4+4 teeth and two chaetae. Dens long and slender, with numerous crenulations, many (~50) anterior and 17 (in the adult male studied) posterior chaetae. Anterior side of manubrium with 3+3 chaetae. Mucro bidentate.

Our redescription is based on one individual of E. Rapoport, and more material is needed to complete the understanding of B. biseta. The species obviously belongs to the genus Bagnallella by separation of two last abdominal segments and s-chaetotaxy of Abd.IV and V. After chaetotaxy of tibiotarsi, ventral tube, and dens, B. biseta appears to be a more polychaetotic species than its congeners. The close relation of B. biseta and B. tenella (sharing 3+3 manubrial chaetae) is doubtful due to difference in maxillary palp (bifurcate vs simple). The independence of B. koepckei and B. paronai from B. biseta call for further verification. Bagnallella paronai is not included in the key due to the incomplete diagnosis.

Argentina and Chile (see Mari Mutt and Bellinger 1990 for details).

New Zealand, South Island, Central Otago, Pisa Range and Old Man’s Range, high alpine zone, different sites, 17.02.2014, M. Minor leg.

Maxillary palp bifurcate, two prelabral chaetae. Dens with 12–16 anterior chaetae. Mucro bidentate. Anterior side of manubrium with 1+1 chaetae. 33/22235 s and 10/100 ms on body. 2+2 ventral chaetae on Th.III.

Colour grey. Cuticle, ocelli, outer mouth parts, and antennae as in B. sedecimoculata. PAO as long as 0.8–0.9 Ant. I and as 1.4–1.5 as long as Claw III. Ventral side of head with 4+4 postlabial chaetae. Th.III with 2+2 ventral axial chaetae.

Macrochaetae weakly differentiated, medial ones on Abd.V about as long as 0.4–0.5 of tergal midline. S-chaetae weakly differentiated. S-formula as 43/22235 (s), 10/100 (ms) (Fig. 4). S-chaetae on Abd.I–III in mid-tergal position. Tibiotarsi 1–2 with 21 chaetae, Tibiotarsi 3 with few additional chaetae. Tibiotarsal tenent chaetae not developed. Ventral tube with 4+4 laterodistal and usually with five posterior chaetae. Retinaculum with 4+4 teeth and two chaetae. Anterior furcal subcoxae with 13–15 chaetae, posterior ones with 7–9. Anterior side of manubrium with 1+1 distal chaetae. Dens with 12–16 anterior chaetae, posterior side of dens with crenulation and seven chaetae (Fig. 3). Mucro bidentate. Ratio of manubrium : dens : mucro = 6.0–6.7 : 5.0–6.0 : 1. Males present, with two thin spurs on Tibiotarsi I.

This species was named after its dubious position in generic system of Proisotoma/Cryptopygus (Deharveng 1981). It resembles B. sedecimoculata (see the Discussion below) and apparently belongs to the genus Bagnallella by separation of two last abdominal segments and s-chaetotaxy of Abd.IV and V. Our specimens from New Zealand match the first description.

Bagnallella dubia was described from Marion Island and recorded in Macquarie Island (Greenslade and Wise 1986) and alpine sites of New Zealand (Babenko and Minor 2015). The species is possibly widely distributed in cold sites of high altitudes of the Southern Hemisphere. Its occurrence in Australia (Greenslade 2006) needs to be verified.

The species can be attributed to Bagnallella by the two key characters of the genus. It is characterized by 33/22235 s, 11/111 ms, bifurcate maxillary palp, long polychaetotic dens (34-35/14), and bidentate mucro. The presence of seven ocelli and 2+2 chaetae on anterior side of manubrium are two unique characters among members of the genus.

This species is currently only known from SE Brazil.

It is an easily recognizable species by 43/22235 s, 11/111 ms, simple maxillary palp, dens (15-16/12-13), and tridentate mucro.

One locality in southeastern Brazil.

Maxillary palp bifurcate, four prelabral chaetae. Ant. I with many additional chaetae. Dens long and slender, with 20–30 anterior chaetae or more. Mucro bidentate. Anterior side of manubrium with 1+1 chaetae. 33/22235 s and 11/111 ms on body. Lateral s-chaetae on Abd.IV shifted to ventral side. Without ventral chaetae on Th.III.

The full redescription is given by Fjellberg (2007).

Europe. It prefers sandy places along the edge of water.

South Africa, Western Cape, Stellenbosch, Jonkershoek Nature Reserve, canyon to waterfall, SAF-086, 34.005570°S, 18.992067°E, 15/03/2008, forest litter, Berlese, L.D. and A.B. leg.; Somerset, Helderberg, SAF-107, SAF-109, SAF-116, 34.040883°S, 18.873649°E, alt. 600 m, 04/03/2009, native forest litter, L.D. and A.B. leg.; Cape Town, Wynberg, Table Mountain, second collapse, SAF-141, 33.987637°S, 18.405750°N, alt. 725 m, 10/03/2009, native forest litter, L.D. and A.B. leg.; Constantia, Silvermine, in a small forest patch above Tokai, SAF-235, 34.038273°S, 18.395478°E, alt. 390 m, 06/11/2010, dead wood, D. Porco leg.; Kalk Bay, Echo Valley, Spes Bona forest, SAF-555, 01/03/2019, Afromontane forest, moss on rock, L.D. and A.B. leg.

New Zealand. NZL-049, Rotoiti: Lakes Rototongata and Rotoatua, 08/01/1996, primary forest, litter, L.D. and A.B. leg.

Australia. Victoria, July 2010, University Ballarat, St. Helens, 37.629979°S, 143.890801°E, Eucalyptus plantation, moss, P. Greenslade. leg.

Macquarie Island, Bauer Bay, 54.5549°S, 158.8760°E, April 2016, Turf sample, Berlese extraction, L. Phillips leg.

Maxillary palp bifurcate, two prelabral chaetae. Dens slender, with 16–20 anterior chaetae. Mucro bidentate. Anterior side of manubrium with 1+1 chaetae. 33/22235 s and 10/100 ms on body. Without ventral chaetae on Th.III.

Colour grey. Cuticle outwardly smooth. 8+8 ocelli, G and H smaller. PAO about as long as 0.8 Ant. I and as 1.1–1.3 Claw III. Maxillary outer lobe with four sublobal hairs and bifurcate maxillary palp. Labral formula as 2/554. Labium full set of guards (e7 present), three proximal and four basomedian chaetae. Ventral side of head with 4–5+4–5 postlabial chaetae. 11 chaetae on Ant.I, with three basal micro s-chaetae (bms), of which one bms large, and two ventral s-chaetae (s), Ant.II with three bms and one laterodistal s, Ant.III with one bms and six distal s (including two lateral). Thorax without ventral axial chaetae.

Macrochaetae weakly differentiated, medial ones on Abd.V as long as 0.4–0.5 of tergal midline. S-chaetae weakly differentiated. S-formula as 43/22235 (s), 10/100 (ms). S-chaetae on Abd.I–III in mid-tergal position. General pattern of chaetotaxy as in B. dubia (Fig. 4). Ti.1–2 with 21 chaetae, Ti.3 with few additional chaetae. Tibiotarsal tenent chaetae not developed. Ventral tube with 4+4 laterodistal and usually with six posterior chaetae (four in a transversal row). Retinaculum with 4+4 teeth and two chaetae. Anterior furcal subcoxae with 11–15, posterior ones with 7–9 chaetae. Anterior side of manubrium with 1+1 distal chaetae (Fig. 2). Dens with 17–19(16–20) anterior chaetae, posterior side of dens with crenulation and seven chaetae (Fig. 2). Mucro bidentate. Ratio of manubrium : dens : mucro = 5.3–6.3 : 5.9–6.7 : 1.

Bagnallella sedecimoculata was described from New Zealand and was designated as type species for the genus Bagnallella (see the discussion to the genus above). The type specimen from New Zealand was studied (Potapov and Janion-Scheepers 2017), although only one generic character (separation of two abdominal segments) was proven. The redescription given above is based mostly on the South African material which looks conspecific to one individual in hand from New Zealand (L.D. and A.B. leg.). Bagnallella sedecimoculata resembles B. dubia and differs by ventral chaetae on Th.III (absent vs present) and a few more anterior chaetae on dens (16–20 vs 12–16). The latter character is not stable enough to separate the two species.

Probably widely distributed. So far with scattered records in the South Hemisphere (New Zealand, Australia, South Africa, Macquarie Island).

South Africa, Western Cape, Haarwegskloof, Swellendam, 34.3425°S, 20.3167°E, 18.vii.2017, litter trap (R17) with Dicerothamnus rhinocerotis litter, O. Cowan leg.; Haarwegskloof, Swellendam, 34.3444°S, 20.3225°E, 18.vii.2017, litter trap (A17) with Medicago sativa litter, O. Cowan leg.; Eastern Cape, Baviaanskloof, 33.7311°S, 23.9655°E, 24.iv.2013, BAV_F_49, A. Liu leg.; Free State Province, Bankfontein Farm, 30.0567°S, 24.8942°E, 24.iv.2019, Berlese-Tullgren, tree leaf litter, H. Badenhorst leg.

Figures 5–8. 

Bagnallella tenella 5 chaetotaxy of posterior part of Abd. IV, Abd.V and VI 6 ocelli, PAO, and Ant. I 7 furca, lateral view 8 macrochaetae and s and ms-chaetae on body. s = s-chaetae, ms = ms-chaetae.

Cuba, Cienfuegos Province, 1984, J. Banasco-Almenteros leg.

Indonesia, Lombok Island, vic. Toko Nusa Sari, marine beech, 8.7411° S, 116.0011° E, 4.IV.2017, V. Makarov leg.

Brazil, Espirito Santo, Domingos Martins, Arace, 4.VII.2000, M. Culik leg.

Maxillary palp simple. Four prelabral chaetae. Dens slender, with ca 20–30 anterior chaetae. Mucro bidentate. Anterior side of manubrium with 3+3 chaetae. 33/22235 s and 11/111 ms on body. No ventral chaetae on Th.III.

Colour grey of different intensity. Cuticle outwardly smooth. 8+8 ocelli, G and H smaller. PAO (Fig. 6) about half as long as width of Ant.I and 0.8–0.9 as long as Claw 3. Maxillary outer lobe with four sublobal hairs and simple maxillary palp. Labral formula as 4/554. Labium without guards e7, with three proximal and four basomedian chaetae. Ventral side of head with 4-5+4-5 postlabial chaetae. With several additional chaetae on Ant.I. Ant.I with three basal micro s-chaetae (bms), one dorsal large, Ant.II with three bms, Ant. III without bms. Thorax without ventral axial chaetae. Macrochaetae rather long, differentiated (11/3334), medial ones on Abd.V about as long as tergal midline. S-chaetae on tergites slightly shorter than ordinary chaetae. S-formula as 33/22235 (s), 11/111 (ms) (Figs 5, 8). S-chaetae subequal, on Abd.I–III in mid-tergal position. Micro s-chaetae on Abd.I–II in front of lateral s-chaetae, on Abd.III between medial and lateral s-chaetae (Fig. 8). Tibiotarsal tenent chaetae (1,1,1) often present, weakly clavate (see Discussion). Retinaculum with 4+4 teeth and 1–2 chaetae. Furca long. Anterior side of manubrium with 3+3 chaetae arranged in two lines (Fig. 7). Dens with more than 20 anterior chaetae, posterior side of dens with crenulation and 7–10 chaetae (Fig. 7). Mucro bidentate. Ratio of manubrium : dens : mucro = 7–8 : 9 : 1.

The species belongs to the genus Bagnallella by having two last abdominal segments separated and three and five s-chaetae on Abd. IV and V. It shares 3+3 anterior chaetae on manubrium with B. biseta, B. koepckei, and B. paronai from South America from which it differs by fewer chaetae on dens.

Number of posterior chaetae on dens, clavate tibiotarsal chaetae, and chaetae on retinaculum vary. We treat all this variation within one species, but further study is needed. The independence of Proisotoma nigromaculosa (Hawaiian Islands) is doubtful.

Although we have no material from Europe, Stach’s (1947) concept of P. tenella based on the specimens from Poland is accepted by us (for details see Potapov 2001; Fjellberg 2007). Our tropical material fits Stach’s (1947) descriptions.

Widely distributed cosmopolitan species. Common in tropics. In higher latitudes only in protected soils.

. Typical form: South Africa, Free State Province, Bankfontein Farm, 30.0567°S, 24.8942°E, 24.iv.2019, Berlese-Tullgren: tree leaf litter, H. Badenhorst leg.; South Africa, Western Cape, Haarwegskloof, Swellendam, 34.3422°S, 20.3169°E, 18.vii.2017, litter trap (G18) with Pentameris eriostoma litter, O. Cowan leg., South Africa, SAF 583 (11.m CJ SWB); Prince Albert: Swartberg North: road to Swartberg Pass, 11/03/2019, meadow, moss, C.J. leg.

Short-haired form: South Africa, Western Cape, Haarwegskloof, Swellendam, 34.3534°S, 20.3042°E, 18.vii.2017, litter trap (A4) with Medicago sativa litter, O. Cowan leg.; Cederberg Wilderness area, Litter trap CED588; South Arica, Western Cape, Cederberg Wilderness area, Litter trap CED394; Jonkershoek Nature Reserve, 33.9891°S, 18.9575°E, 05.ix.2011, Litter trap (J4, 124); Jonkershoek Nature Reserve, 33.9891°S, 18.9575°E, 30.vii.2009, Litter trap, C.J. leg.; J2, 32.1; Landdroskop, Jan. 2012, H. Basson leg.; Prince Albert, Swartberg North, Swartberg crest, 12/03/2019, SAF-612, SAF-618, meadow, litter and soil, L.D., C.J. and A.B. leg.

Intermediate form: South Africa, Western Cape, Haarwegskloof, Swellendam, 34.3345°S, 20.3187°E, 18.vii.2017, litter trap (R24) with Dicerothamnus rhinocerotis litter, O. Cowan leg.; Prince Albert, Swartberg North, Swartberg crest, SAF-612, 12/03/2019, meadow, litter, L.D., C.J. and A.B. leg.; Prince Albert, Swartberg North, Swartberg crest, SAF-618, 12/03/2019, meadow, soil, L.D., C.J. and A.B. leg.; Prince Albert, Swartberg North, road to Swartberg Pass, SAF-601, 12/03/2019, meadow, litter and soil, L.D., C.J. and A.B. leg.; Prince Albert, Swartberg North, Swartberg crest, SAF-614, 12/03/2019, moss on rock, Berlese, L.D., C.J. and A.B. leg.

“Clasping supermales”: SAF-601, South Africa: Western Cape: Prince Albert: Swartberg North: road to Swartberg Pass, 12/03/2019, meadow, litter and soil, L.D., C.J. and A.B. leg.

“Spiny supermales”: SAF-554; South Africa: Western Cape: Kalk Bay: Echo Valley: Spes Bona forest, 01/03/2019, Afromontane forest, moss and lichen on rock, L.D. and A.B. leg.

3+3 postlabial chaetae. Maxillary palp simple. Dens with four anterior and four posterior chaetae. Mucro tridentate, teeth arranged in a line. Anterior side of manubrium with 1+1 chaetae. 43/22235 s and 10/100 ms on body (Figs 9–11). No ventral chaetae on Th.III. Typical form of species with long macrochaetae (Fig. 10).

Figures 9–14. 

Bagnallella davidi, normal long-haired (9–11) and short-haired form (12–14) 9, 12 macrochaetae and s and ms-chaetae on body 10, 13 posterior part of abdomen 11, 14 Abd.I. s = s-chaetae, ms = ms-chaetae.

Maxillary outer lobe with four sublobal hairs, maxillary palp simple. Labral formula as 4/5,5,4. Labium with five usual papillae (–Е) and labial formula A1B4C0D4E6, guard chaeta e7 absent, three proximal and four basomedian chaetae. Ventral side of head with 3+3 chaetae. PAO shorter than Ant.I width (0.6–0.8). Ant. I with 11 common chaetae, two ventral s-chaetae (s) and three bms, of which one dorsal long, chaeta-like (this ms was calculated together with common chaetae in first description, 12 at whole); Ant. II with three bms and one latero-distal s; Ant. III with one bms and with six distal s (including two lateral), without additional s-chaetae. Organite pin-like, not very small. Empodial appendage about half as long as Claw. Anterior and posterior furcal subcoxae with 9–14 and 7–8 chaetae, respectively. Male spurs on tibiotarsi 3 thin, stick-like. Th. I–III without ventral chaetae. Ratio manubrium : dens : mucro as 4.4-5.0 : 3.3-3.8 : 1; dens : Claw as 3.3–3.6 (for the typical form).

Bagnallella davidi is a rather peculiar species of the genus due to few chaetae on dens (vs many more chaetae both on anterior and posterior sides), tridentate mucro (shared with B. mishai only), and 3+3 postlabial chaetae (vs 4+4 or more in other species). The first description is almost complete and, therefore, we made very few additions concerning mouth parts. The species exhibits high variation in length of macrochaetae and show different modifications of males. All the forms (described below) can indicate either high plasticity of a single species or the complex of separate although closely related species, calling for further morphological, biological, ecological, and molecular investigations.

Eastern Cape, Amatola Mountains (type location) and widely in the Western Cape and Free State (our material) provinces of South Africa.

Polymorphism of Bagnallella davidi

1. “Typical “ form (Figs 9–11). B. davidi was described in this form (Barra 2001). Macrochaetae on body segments are long. Ratios: Mac on Abd.V as long as 0.7–1.0 of tergal midline. Mac : Abd.V width = 0.7–1.0; Mac : mucro = 3.3–4.1; Mac : dens = 0.8–1.1 (Fig. 9). In Proisotoma complex, so long macrochaetae is a unique character among species of Bagnallella and sometimes occur in the genera Weberacantha Christiansen, Narynia Martynova and Folsomides Stach. This form was found in juvenile and fully adult specimens, both in females and males.
2. “Short-haired” form (Figs 12–14). Macrochaetae are short, shorter than common chaetae on most abdominal segments. Ratios: Mac : Abd.V Mac on Abd.V as long 0.2–0.3 of tergal midline; Mac : mucro = 0.9–1.4; Mac : dens 0.2–0.3. In spite of their small size, macrochaetae are erect and stiff and so well recognized indicating their possible ecomorphic nature although the integument and mouthparts are not modified. Head and furca appear to be relatively larger than in typical form. Ratio manubrium : dens : mucro as 5.1–6.6 : 4.1–5.8 : 1; dens : Claw as 3.3–4.5. All other significant characters (s-chaetotaxy, mouth parts, chaetotaxy of extremities) are as in typical form. All instars and both sexes can belong to this form.

We also found individuals with middle-sized macrochaetae (as in Fig. 15), which is on Abd.V twice as long as mucro (vs 3.3–4.1 in typical form and 0.9–1.4 in short-haired form) and half as long as dens (vs subequal to dens in typical form and 0.2–0.3 as dens in short-haired form).

Figures 15–19. 

Bagnallella davidi, the “clasping supermale” 15 subadult individual, dorsal view 16, 17 adult, dorsal 16 and lateral 17 views 18 posterior part of abdomen in adult male, ventral view 19 mandible. Man = Manubrium.

Each studied population consists of only one of the forms, and we have not found a continuous range of macrochaetae variability, apart from short-haired clasping adult supermales occurring in “normal” populations.

1. “Clasping supermales” (Figs 15–20). Ant.I–III expanded and partly fused. Antennae joints probably lost mobility. Inner side of Ant.II and III is armed with thickened, flame-shaped, and bifurcate chaetae which probably form a clasping organ. Front of head have chitinized tubercles. Anal valves are armed with spines. Mandibles without apical teeth. Macrochaetae short. Subadult clasping supermales, i.e., males without fully developed genital plate and without developed ejaculatory duct, have also expanded antennae although without modified chaetae on inner their side. They show normal (longer than on adult supermales) macrochaetae and normal mandibles and have no spines on anal valves (Fig. 15–20). The females of the same population belong to the form with middle-sized macrochaetae.
2. “Spiny supermales” (Figs 23–25). One of the males has a row of spiny p-chaetae on Abd.IV and strong thickened macrochaetae on lateral parts of Abd.VI. Other macrochaetae on the body are weakly developed. Common chaetae on dorsum of Abd.IV–VI curved at apex (Fig. 25). Mandibles without apical teeth and molar plate (Fig. 24). Outer mouth parts (labrum, maxillary outer lobe, and labium) not fully developed.

Unmodified males are much more frequent than the two male forms described above. In most populations, only unmodified males are known. They can show all possible length of macrochaetae and belong to associated forms (Figs 21, 22).

Figures 20. 

Bagnallella davidi, anterior part of head and antennae in adult “clasping supermale”.

Figures 21–25. 

Bagnallella davidi unmodified (21, 22) and “spiny supermale” (23–25) 21–23 lateral view 24 mandible 25 posterior part of abdomen, lateral view. s = s-chaetae, M = macrochaetae.