Bagnallella davidi (Barra, 2001) Potapov & Deharveng & Janion-Scheepers, 2021

Potapov, Mikhail, Deharveng, Louis & Janion-Scheepers, Charlene, 2021, Taxonomy of the Proisotoma complex. VI. Rediscovery of the genus Bagnallella Salmon, 1951 and epitoky in Bagnallella davidi (Barra, 2001), comb. nov. from South Africa, ZooKeys 1072, pp. 185-204 : 185

Bagnallella davidi (Barra, 2001) comb. nov.

Figures 9-14 , 15-19 , 20 , 21-24

Proisotoma davidi Barra, 2001

Material examined

. 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 .

Diagnosis.

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 ).

Description.

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).

Discussion.

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.

Distribution.

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

"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.

“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).

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.

"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.

"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

Figures 20. Bagnallella davidi, anterior part of head and antennae in adult " clasping supermale ".

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.

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.

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.