Oribatella quadricornuta ( Michael, 1880 )

Seniczak, Stanisław & Seniczak, Anna, 2013, Differentiation of external morphology of Oribatella Banks, 1895 (Acari: Oribatida: Oribatellidae), in light of the ontogeny of three species, Journal of Natural History 47 (23 - 24), pp. 1569-1611 : 1571-1584

Oribatella quadricornuta ( Michael, 1880)

( Figures 1 , 2A–C , 3A , 4–9 , 10A )

Oribata quadricornuta Michael, 1880 .

Oribatella calcarata Willmann, 1931 .

Oribatella quadricornuta: Hammen 1952 ; Krivolutskiy 1975; Bernini 1978; Behan- Pelletier and Hill 1983; Subías 2004; Weigmann 2006; Schatz 2008; Behan-Pelletier 2011.

Diagnosis

Adult of medium size (460–550 µm), dark brown, with characters of Oribatella (see Bernini 1974, 1975, 1977, 1978; Bernini and Avanzati 1983; Weigmann 2006; Shtanchaeva and Subías 2009). Sexual dimorphism weakly expressed. Lamellae broad, without lateral dens, outer cusp longer than inner cusp ( Figure 1 ). Apical end of seta in reaching that of le in dorsal aspect; all protruding beyond rostrum. Integument of prodorsum, notogaster and ventral plate micropunctate. Notogaster almost spherical, usually with 10 pairs of setae, including c 2, rarely with seta c 3 inserted unilaterally. Notogastral setae curved ventrally, except raised seta h 1 ( Figure 2A ). Porose areas roundish, Aa slightly larger than others, A3 located closer to seta h 1 than to seta p 2. Seta 4c thicker than other coxisternal setae ( Figure 3A ). Seta l” on tibia I thick, solenidion ω 1 on tarsus I longer than ω 2, famulus ε short ( Figure 2B, C ). Formulae of setae (+solenidia) of legs (trochanter to tarsus): I – 1-5-(3 + 1)-(4 + 2)-(20 + 2), II – 1-5- (3 + 1)-(4 + 1)-(15 + 2); III – 2-3-(1 + 1)-(3 + 1)-15; IV – 1-2-2-(3 + 1)-12. Tarsi tridactylous.

Juveniles light brown, with long, rather thick, curved and barbed prodorsal and gastronotal setae, except smaller setae in anal or anogenital region. Sensillus shorter than seta ex. Larva with 12 pairs of gastronotal setae, nymphs with 15 pairs. Nymphal pair dm inserted twice as wide as pair da, and pair dp inserted more than twice as wide as pair dm; nymphal seta dp slightly shorter than seta dm and more curved. Nymphs carry exuvial scalps of previous instars.

Description of juvenile stages

Larva light brown, with relatively long, subtriangular prodorsum, and rounded rostrum ( Figure 4 ). All prodorsal setae long ( Table 1), rather thick, curved and barbed; ro shortest, ex longest. Bothridium rounded, sensillus long, fusiform, with barbed head. Sensillus shorter than seta ex.

Gastronotum with 12 pairs of setae, including seta h 3 ( Figures 5A , 6A ), positioned lateral to medial part of anal opening. All gastronotal setae long ( Table 1), rather thick, curved and barbed, except shorter setae h 2 and h 3; h 3 small, h 2 longer and barbed, but distinctly shorter than h 1. Paraproctal valves (segment PS) glabrous. Humeral organ (oh) anterior to seta c 3, cupule ia posteroventral to seta c 3, cupule im posteroventral to seta lm, cupule ip lateral to seta h 2, cupule ih lateral to anterior part of anal opening. Opisthonotal gland opening (gla) between setae lm and h 3. Ventral parts of gastronotum with several folds. Seta l” on tibia I and seta pl” on tarsus I slightly thicker than other setae, solenidion ω 1 on tarsus I directed anterior, famulus ε short ( Figures 7A, B ).

Protonymph with 15 pairs of gastronotal setae, because setae of p -series (p 1 – p 3) appear on segment PS ( Figure 6B ), and remain in deutonymph ( Figure 8A ) and tritonymph ( Figure 8B ); length increasing from p 3 to p 1; all setae barbed. Genital valves of protonymph with one pair of short setae, two pairs added in deutonymph and two more pairs added in tritonymph; all setae small. One pair of small aggenital setae appears in deutonymph, lateral to posterior part of genital valves, and remains in tritonymph. Paraproctal valves of protonymph (segment AD) and deutonymph (segment AN) glabrous, those of tritonymph with two pairs of small setae (an 1 and an 2), inserted in anterior and medial parts of paraproctal valves, respectively. In deutonymph three pairs of adanal setae (ad 1 – ad 3) appear on segment AD, and remain in tritonymph; all setae smooth and shorter than p 3, but longer than anal setae. Anogenital region with several folds.

Prodorsum of nymphs relatively shorter than in larva. Prodorsal setae of tritonymph, bothridium and sensillus ( Figure 9 ) as in larva. All gastronotal setae long ( Table 1) and rather thick, curved and barbed; pair dm inserted twice as wide as pair da, while pair dp inserted more than twice as wide as pair dm. Cupules ia and im as in larva, cupule ip between setae h 2 and p 2, cupule iad lateral to anterior part of anal opening, cupules ips and ih pushed anterolaterally from cupule iad ( Figure 8B ). Gland opening gla between setae lp and p 3 ( Figures 5B , 8B ). Anogenital region with several longitudinal folds. Seta l” on tibia I hypertrophied, seta pl” on tarsus I thicker than other setae, solenidion ω 1 on tarsus I longer than ω 2, famulus ε short ( Figure 10A ).

Summary of ontogenetic transformations

The five pairs of setae are present on the prodorsum during ontogeny, including the sensillus. In all juveniles the prodorsal setae are long, whereas in the adult, seta in remains long, setae le and ro get shorter than in the nymphs, while seta ex remains short. In all instars the bothridium is rounded, and the sensillus is rather long and fusiform. The larva has 12 pairs of gastronotal setae, whereas the nymphs have 15 pairs (p -series present); most setae are long, rather thick, curved and barbed. The adult usually loses notogastral setae c 1, c 3 and d -series, so 10 pairs of setae remain; these setae are inserted on lateral and posterior parts of notogaster, and are short, thin, smooth, and curved outside and ventrally. In some individuals seta c 3 is present unilaterally, and is shorter than seta c 2.

The formula of gastronotal setae in O. quadricornuta is usually 12-15-15-15-10 (larva to adult), and those of coxisternal setae are: 3-1-2 (larva), 3-1-2-1 (protonymph), 3-1-2-3 (deutonymph) and 3-1-3-3 (tritonymph and adult). In the larva seta 1c is scaliform and covers Claparéde’s organ. The formula of genital setae is 1-3-5-6 (protonymph to adult), and that of aggenital setae is 1-1-1 (deutonymph to adult). The formula of segments PS–AN is 03333-0333-022. All formulae of setae are consistent with those given by Grandjean (1949).

Distribution and ecology

Oribatella quadricornuta is considered a Holartic species ( Subías 2004). This species is dioecious, and in its populations females dominate ( Domes et al. 2007). It is considered a silvicolous and xerophilous species ( Schatz 2008), abundant in spruce litter ( Starý 2005), a strictly microphytophage ( Behan-Pelletier and Hill 1983; Wunderle 1992), which strongly prefers dark pigmented fungi, like Alternaria sp. and Ulocladium sp. ( Schneider et al. 2004; Schneider and Maraun 2005). Krivolutskiy and Lebedeva (2004) found O. quadricornuta in bird feathers of tree sparrow [ Passer montanus (L.)]. This species is considered an intermediate host of Anoplocephalid species Aprostatandrya macrocephala (Douthitt, 1915) and Paranoplocephala variabilis (Douthitt, 1915) ( Denegri 1993) .

In municipal Scots pine forest in the Marcelin quarter of Poznań ( Poland, 52 ◦ 23.43’ N, 16 ◦ 49.12’ E; 84 m above sea level), O. quadricornuta was not abundant, and the adults dominated in its population, with distinctly higher frequency in thuja litter than in pine ( Pinus sylvestris L.) and spruce litter ( Picea abies (L.) H. Karst).

Figures

Figure 1. Oribatella quadricornuta, adult, female, dorsal aspect, legs partially drawn, scale bar 100 µm.

Figure 2. Adult, female. (A) Oribatella quadricornuta, lateral aspect, legs partially drawn, scale bar 100 µm; (B) O. quadricornuta, part of tibia I and tarsus I, scale bar 20 µm; (C) O. quadricornuta, region of solenidion ω1; (D) Oribatella superbula, part of tibia I and tarsus I, scale bar 20 µm.

Figure 3. Adult, female, anogenital region, legs partially drawn, scale bars 50 µm. (A) Oribatella quadricornuta; (B) Oribatella superbula.

Figure 4. Oribatella quadricornuta, larva. (A) Dorsal aspect, legs partially drawn, scale bar 100 µm; (B) medial part of seta c2.

Figure 5. Oribatella quadricornuta, lateral aspect, legs partially drawn, scale bars 100 µm. (A) Larva; (B) tritonymph.

Figure 6. Oribatella quadricornuta, legs partially drawn, scale bars 50 µm. (A) Anal region of larva; (B) anogenital region of protonymph.

Figure 7. Oribatella quadricornuta, part of tibia I and tarsus I, some setae are not illustrated, scale bars 10 µm. (A) Larva, antiaxial aspect; (B) larva, region of solenidion ω1; (C) protonymph, region of solenidion ω1; (D) protonymph, antiaxial aspect.

Figure 8. Oribatella quadricornuta, anogenital region, legs partially drawn, scale bar 100 µm. (A) Deutonymph; (B) tritonymph.

Figure 9. Oribatella quadricornuta, tritonymph, dorsal aspect, legs partially drawn, scale bar 100 µm.

Figure 10. Part of tibia I and tarsus I of tritonymph, antiaxial aspect, some setae are not illustrated, scale bars 20 µm. (A) Oribatella quadricornuta; (B) Oribatella superbula.