Pilogalumna tenuiclava ( Berlese, 1908 )

Seniczak, Anna & Seniczak, Stanisław, 2022, Morphological ontogeny of Pilogalumna tenuiclava (Acari, Oribatida, Galumnidae) and comments on Pilogalumna Grandjean, Zootaxa 5187 (1), pp. 95-120 : 97-103

Pilogalumna tenuiclava ( Berlese, 1908)

Oribates tenuiclavus Berlese, 1908 : Castagnoli and Pegazzano 1985.

Galumna tenuiclavus: Oudemans 1919 .

Galumna areolata Willmann, 1923 : Hammen 1952.

Galumna radiata Sellnick, 1928 : Willmann 1931.

Allogalumna atra Mihelčič, 1957 : Hammen 1952.

Pilogalumna tenuiclava ( Berlese, 1908) : Grandjean 1956; Sellnick 1960; Shaldybina 1975; Karppinen and Krivolutsky 1982; Golosova et al. 1983; Schatz 1983, 2020; Karppinen et al. 1986, 1987; Marshall et al. 1987; Mahunka 1992; Pérez-Iñigo 1993; Bernini et al. 1995; Olszanowski et al. 1996; Niemi et al. 1997; Mahunka and Mahunka-Papp 2000; Ryabinin and Pankov 2002; Weigmann 2006; Siepel et al. 2009; Bayartogtokh 2010; Norton and Ermilov 2014; Miko 2016; Murvanidze and Mumladze 2016; Ermilov and Klimov 2017; Behan-Pelletier and Lindo 2019.

Diagnosis

Adults brown to dark brown, of medium size (462–540), and with characters of Pilogalumna ( Ermilov & Klimov 2017) . Interlamellar setae short, bothridial seta fusiform, with long, narrow, finely barbed head. Notogaster with ten pairs of microsetae and five pairs of porose areas, including rounded Aa’ and Aa” of similar size, and elongated A3. Postanal porose area narrow and elongated.

Juveniles light brown, prodorsal setae of medium size or long and barbed, bothridial seta fusiform, with thick, barbed head. Larva with 11 pairs of gastronotal setae, including h 2; most setae short and smooth, except for mediumsized c 3, dp and h 1, and slightly shorter c 2 and h 2, most of these setae barbed, h 2 finely barbed. Nymphs with 15 pairs of these setae, most short and smooth, except for medium-sized and barbed c 3. Gastronotal shield poorly developed, with setae d -, l -series and h 1 in larva, and d -, l -, h -series and p 1 in nymphs; setae of c -series, p 2 and p 3 inserted on unsclerotized integument. In all juveniles, humeral organ present.

Morphology of adult

Adult ( Figs. 1–7 ) similar to that described by Berlese (1908) and investigated by Mahunka (1992), but see Remarks. Mean length (and range) of females 620.2±24.6 (553–650, n= 17) and males 552.5±46.6 (455–585, n= 13), mean width (and range) of females 461.8±25.7 (422–488) and males 411.5±22.3 (390–455). Notogastral microsetae 10 pairs, including c 2 on pteromorph, porose area Aa divided in Aa’ and Aa” of similar size, all porose areas small and oval, except for elongated A3 ( Figs. 1a , 3 , 4a , 5a–c , 6a, 6b ). Postanal porose area Ap narrow and elongated. All hypostomal setae short and smooth ( Figs. 2 , 5d ). Chelicera chelate, seta cha longer and thicker than chb, both barbed ( Fig. 4b ). Most palp setae smooth, except for finely barbed sup and inf on femur, and l” on genu and tibia ( Fig. 4c ), formula of palp seta 0-2-1-3-9(1). Leg femora oval in cross section, most leg setae barbed, seta v on paraxial side of tibiae, v’ on tarsus I and pv on all tarsi with longer barbs than those on antiaxial side ( Figs. 5 , 6c, 6d , 7 ). Solenidia ω 1 and ω 2 on tarsus I of similar length, seta ft” short. Formulae of leg setae [trochanter to tarsus (+ solenidia)]: I – 1-4- 2(1)-4(2)-20(2); II – 1-4-2(1)-4(1)-15(2); III – 2-2-1(1)-3(1)-15; IV – 1-2-2-3(1)-12. Leg tarsi heterotridactylous.

Remarks. The mean length and width of females of P. tenuiclava investigated herein are slightly larger than those described by Berlese (1908) – length 590, but smaller than those investigated by Sellnick (1960) – length 660, Pérez-Iñigo (1993) – length 620–690 and Weigmann (2006) – length 560–690 (in all papers sex not investigated). In our specimens, the porose area A3 is shorter than that drawn by Weigmann (2006), and longer than drawn by other authors. The distribution of porose areas and prodorsal setae are similar as in figures drawn by Berlese (1908) and Mahunka (1992). Only Mahunka (1992) showed the distribution of notogastral setae, which is similar to our adults, except for alveolus of seta la that is placed laterally to porose area Aa’ (vs. in our adults posterolateral to porose area Aa’), and dark point anterior to alveolus lm, which in our adults is absent.

Description of juveniles

Larva egg-shaped in dorsal view ( Figs. 8 , 9a , 10a , 11a–c ), and unpigmented, except for light brown prodorsal and gastronotal shields and legs. Prodorsum subtriangular, prodorsal setae barbed, in long, ro and le of medium size, and ex shorter ( Table 1 ). Mutual distance between setal pair le about 1.5 times longer than between pair ro, and distance between setal pair in about three times longer than between pair ro, pair le inserted closer to pairs in than ro. Opening of bothridium rounded, with anteromedial addition; bothridial seta fusiform, with thick, barbed head ( Figs. 8 , 10a , 11a, 11b, 11d ). Most palp setae smooth ( Figs. 10a , 12a ).

Gastronotum of larva ( Figs. 8 , 9a , 10a , 11a–c ) with 11 pairs of setae, including h 2 inserted lateral to medial part of anal valves; most short and smooth, except for medium-sized c 3, dp and h 1, and slightly shorter c 2 and h 2, most of these setae barbed, but h 2 finely barbed. Setae of c -series inserted on unsclerotized integument, length increasing from c 1 to c 3 ( Table 1 ). Gastronotal shield poorly developed, with seven pairs of setae (d -, l -series, h 1), seta h 2 on unsclerotized integument. Small porose areas present, Aa anteromedial to seta la, A1 anterior to seta lm, and A2 anteromedial to seta lp ( Fig. 8 ). Cupule ia posterior to seta c 3, cupule im posterior to seta lm, cupule ip between setae h 1 and h 2, cupule ih lateral to anterior part of anal valves. Opisthonotal gland opening gla lateral to seta lp, without dark sclerotized surrounding ( Figs. 10a , 12b ). Humeral organ located above insertions of leg II ( Figs. 10a , 12c ). Paraproctal valves (segment PS) glabrous. Legs of larva stocky, all femora oval in cross section, most leg setae barbed ( Fig. 11a–c , 13 ).

Shape of prodorsum of protonymph, prodorsal setae, bothridium and bothridial seta as in larva, but bothridial seta slimmer, and prodorsal setae relatively longer than in larva; in deutonymph and tritonymph le nearly as long as in. Gastronotum oval, with 15 pairs of setae because h 3 and p -series added, and retained in subsequent nymphs ( Figs. 9b , 10b , 14a, 14b ); all short and smooth, except for longer and barbed c 3. Setae of c -series inserted on unsclerotized integument. Gastronotal shield poorly developed, with ornamentation, well observed in lateral aspect ( Fig. 10b ), and 10 pairs of setae (d -, l -, h -series, p 1), setae p 2 and p 3 inserted on unsclerotized integument ( Figs. 9b , 14 ). Four pairs of porose areas present, Aa anteromedial to seta la, A1 posteromedial to seta lm, A2 posteromedial to seta lp and A3 anterior to seta h 1. In protonymph, one pair of genital setae inserted lateral to genital valves, two pairs added in deutonymph and in tritonymph each ( Figs. 9b , 14 ), all short and smooth. In deutonymph, one pair of aggenital setae appearing and three pairs of adanal setae, and remained in subsequent instars; all short and smooth. In protonymph and deutonymph, anal valves glabrous, in tritonymph two pairs of short and smooth anal setae present. In tritonymph, cupule ia as in larva, cupule im posterior to seta lp, and ip between setae p 1 and p 2, cupule iad lateral to anterior part of anal valves, cupules ips and ih displaced lateral to iad ( Figs. 10b , 11b , 14 ). Opisthonotal gland opening gla anterolateral to seta h 3 ( Figs. 10b , 12d ), without dark sclerotized surrounding, humeral organ located as in larva. Legs of tritonymph stocky, all femora oval in cross section ( Figs. 12d , 16 ), most leg setae barbed, but some setae on paraxial side of tibia (v’) and tarsi (v’, pv’) with longer barbs than those on antiaxial side (v’’ and v’’, respectively).

Summary of ontogenetic transformations

In all juveniles, the prodorsal setae le and in are longer than ro and ex, whereas in the adult seta ro and le are of medium size, and in and ex are short. The bothridium is rounded in all instars, but in the adult it is covered by anterior tectum of notogaster. In all instars, the bothridial seta is fusiform, with barbed head, which in juveniles has thicker head than in the adult, especially in the larva. The larva has 11 pairs of gastronotal setae, including h 2, the nymphs have 15 pairs (h 3 and p -series appearing in protonymph, and present in other instars), whereas the notogaster of adult loses setae c 1, c 3 and of d -series, such that 10 pairs of microsetae remain. The formula of gastronotal setae in P. tenuiclava is 11-15-15-15-10 (from larva to adult), the formula of epimeral setae are 3-1-2 (larva, including scaliform 1c), 3-1-2-1 (protonymph), 3-1-2-2 (deutonymph and tritonymph), and 1-0-1-1 (adult). The formula of genital setae is 1-3-5-6 (protonymph to adult), and formula of aggenital setae is 1-1-1 (deutonymph to adult), and setal formula of segments PS-AN is 03333-0333-022. The ontogeny of leg setae and solenidia of P. tenuiclava is shown in Table 2 .

Distribution, ecology and biology

Pilogalumna tenuiclava has a Holarctic distribution ( Subías 2004, updated 2022), and is hygrophilous, mucicol and tyrphobiotic ( Rajski 1968; Höpperger & Schatz 2013). This species is usually not abundant. For example, in mires of western Norway, P. tenuiclava occurred only in one sample, and only six specimens were found (out of almost 60,000 Oribatida studied). It was present only in Sphagnum riparium Ångstr. collected from poor carpet ( Seniczak et al. 2020a). It was found in feathers of herring gull ( Larus argentatus Pontoppidan ) ( Krivolutsky & Lebedeva 2004), and among fossil mites of the Quaternary Period ( Krivolutsky et al. 1990). It belongs to intermediate hosts of cestode tapeworms of the family Anoplocephalidae ( Denegri 1993) .

Note: structures are indicated where they are first added and are present through the rest of ontogeny; pairs of setae in parentheses, dash indicates no additions.

Based on ten samples of peat mosses collected on 18 June 2010 at the pond Zakręt 1 ( Poland), P. tenuiclava had a mean density of 34 individuals per 500 cm 3 (±SD = 45, range 0‒137 individuals per 500 cm 3), it occurred in 90% of samples and made 11% of oribatid mites. The juveniles were more abundant in this season than adults and made 83% of population ( Nowicka 2014) .

In the studies on the seasonal dynamics in the same pond, P. tenuiclava had similar abundance in four studied seasons (spring, summer, autumn and winter), and the juveniles were present all over the year. However, when we consider the mean value from two successive years, the participation of juvenile stages was the following: spring— 55%, summer—60%, autumn—34%, and winter—22% ( Seniczak et al. 2019a). In 30 randomly selected adults, the sex ratio (females to males) was 1:0.6, and 42% of females were gravid and carried 3–7 large eggs (211 x 132 each), comprising 34% of the length of females.

Figures

FIGURE 1. Pilogalumna tenuiclava, female. (a) Dorsal aspect, I pair of legs partially drawn, scale bar 50 μm; (b) shape of porose are A1 (enlarged).

FIGURE 2. Pilogalumna tenuiclava, female, ventral aspect, legs partially drawn, scale bar 50 μm.

FIGURE 3. Pilogalumna tenuiclava. adult, posterior aspect, scale bar 50 μm.

FIGURE 4. Pilogalumna tenuiclava. (a) Female with ejected ovipositor, lateral aspect, legs partially drawn; scale bar 50 μm; mouthparts, right side, scale bars 20 μm; (b) chelicera, Trägårdh organ in ‘transparent’ area), (c) palp.

FIGURE 5. Pilogalumna tenuiclava, adult, SEM micrographs. (a) Dorsolateral view, (b) frontal view, (c) lateral view, (d) ventral view.

FIGURE 6. Pilogalumna tenuiclava, adult, SEM micrographs. Dorsolateral view, (a) anterior part, (b) bothridial seta, (c) leg II, (d) leg III.

FIGURE 7. Pilogalumna tenuiclava, leg segments of adult (part of femur to tarsus), right side, antiaxial aspect, setae on the opposite side not illustrated are indicated in the legend, scale bar 20 μm. (a) Leg I; (b) leg II; (c) leg III, tibia (v’’), tarsus (pv’’); (d) leg IV; (e) part of tibia and tarsus I, ventral aspect.

FIGURE 8. Pilogalumna tenuiclava, larva. (a) Dorsal aspect, legs I and II partially drawn, scale bar 20 μm; (b) shape of seta c3 (enlarged).

FIGURE 9. Pilogalumna tenuiclava, ventral part of hysterosoma, legs III and IV partially drawn, scale bar 20 μm. (a) Larva, (b) protonymph.

FIGURE 10. Pilogalumna tenuiclava, lateral aspect, legs partially drawn, scale bars 50 μm. (a) Larva, (b) tritonymph.

FIGURE 11. Pilogalumna tenuiclava, larva, SEM micrographs. (a) Dorsal view, (b) lateral view, (c) ventral view, (d) bothridial seta.

FIGURE 12. Pilogalumna tenuiclava, SEM micrographs. Larva, (a) palp, ventral view; lateral view, (b) gla opening, (c) humeral organ, (d) tritonymph.

FIGURE 13. Pilogalumna tenuiclava, leg segments of larva (part of femur to tarsus), right side, antiaxial aspect, seta on the opposite side not illustrated is indicated in the legend, scale bar 10 μm. (a) Leg I, tarsus (pl’); (b) leg II, (c) leg III.

FIGURE 14. Pilogalumna tenuiclava, ventral part of hysterosoma, IV pair of legs partially drawn, scale bar 50 μm. (a) Deu- tonymph, (b) tritonymph.

FIGURE 16. Pilogalumna tenuiclava, leg segments of tritonymph (part of femur to tarsus), right side, antiaxial aspect, seta on the opposite side not illustrated is indicated in the legend, scale bar 20 μm. (a) Leg I, tarsus (pl’); (b) leg II; (c) leg III; (d) leg IV.