Arthrodamaeus reticulatus (Berlese, 1910)

Seniczak, Stanisław & Seniczak, Anna, 2011, Ontogenetic studies of three species of Gymnodamaeidae (Acari: Oribatida) with a focus on regressions of hysterosomal setae, Journal of Natural History 45 (5 - 6), pp. 361-391 : 363-369

Arthrodamaeus reticulatus (Berlese, 1910)

( Figures 1–6 , 7A , 8A )

Gymnodamaeus reticulatus Berlese, 1910 .

Arthrodamaeus rosarius L Subías, Arillo and J Subías, 1997 .

Diagnosis

Adults oval ( Figure 1 ), dark brown and of medium size (550–650 µm). Rostrum roughly triangular, distally rounded, lateral outline with large pedotecta I and II. Setae ro and le relatively long, curved, positioned anteriorly and covered thickly with granules of cerotegument; seta ex small, seta in minute. Bothridia well-developed, rounded, sensillus long, with narrow, barbed head. Transverse ridges between setae le, and from seta le to central part of prodorsum.

Notogaster almost flat, oval, with reticulate pattern of cuticle and cerotegument in central part, and six pairs of setae (h 1 – h 3 and p 1 – p 3) in posterior part. Formula of epimeral setae (I-IV) – 3-1-3-3. Seven pairs of genital setae positioned in two rows ( Figure 2 ). One pair of aggenital setae, three pairs of adanal setae and two pairs of anal setae present; all setae small. Formula of leg setae (trochanter to tarsus, solenidia in parentheses): I – 1-5-4(1)-5(2)-20(2); II – 1-5-4(1)-5(1)-16(2); III – 2-3-3(1)-4(1)-15; IV – 1-2-3-4(1)-12. Legs tridactylous.

Juveniles with general facies similar to adult, but cuticle less sclerotized and unpigmented. Prodorsal setae ro and le relatively long, pair ro further apart than le; seta ex short, seta in minute. Larva with 11 pairs of gastronotal setae (h 3 absent), and large d -series; nymphs with 10 pairs of these setae (d -series absent, h 3 and p -series present), with seta c 3 long, seta lp curved inwards, and large posterior excrescence bearing two pairs of setae curved anteriorly.

Description of juvenile stages. Larva oval, elongated ( Figure 3 ), without posterior excrescence, body unpigmented. Prodorsum triangular, with rounded rostrum. Lateral outline with depressions above level of legs I and II. Setae ro and le rather long and curved, seta ex shorter, seta in short; all setae with blunt barbs and granules of cerotegument. Seta ro positioned on lateral part of rostrum, distance between pair ro twice that between pair le. Bothridium well-developed, rounded, sensillus long, with narrow head and blunt barbs. Prodorsum with granules of cerotegument, lateral parts with longitudinal stria.

Gastronotum with 11 pairs of setae; h 3 absent, h 2 lateral to posterior end of anal opening ( Figure 4A ). Setae of d -series rather long, length increasing from anterior to posterior, other setae distinctly shorter, seta c 2 shortest; all setae curved, positioned on apophyses, with blunt barbs and granules of cerotegument. Paraproctal valves (segment PS) with two pairs of small setae. Cupule ia posterior to seta c 3, cupule im anterolateral to seta lm, cupule ip between setae h 1 and h 2, and cupule ih lateral to anterior part of anal opening. Gastronotum with few folds and granules of cerotegument.

Nymphs oval, unpigmented. Gastronotum of protonymph with 10 pairs of setae: seta h 3 present; three pairs of pseudanal setae (p 1 – p 3) appear on segment PS ( Figure 4B ) and remain in deutonymph ( Figure 5A ) and tritonymph ( Figure 5B ). Setae of d -series and setae la, lm lost in protonymph and remain absent through remainder of ontogeny. Protonymph forms large posterior excrescence bearing two pairs of setae: h 1 inserted dorsally and p 1 inserted laterally; all setae curved anteriorly, so excrescence remembers anchor; excrescence retains same form in deuto- and tritonymph. Genital valves of protonymph with one pair of short setae, two pairs added in deutonymph and three more pairs in tritonymph. One pair of small aggenital setae appears in deutonymph, lateral to genital valves, and remains in tritonymph. Number of genital papillae increasing from one pair in protonymph to three pairs in tritonymph. Paraproctal valves of protonymph (segment AD) and deutonymph (segment AN) bare, those of tritonymph with two pairs of small setae. In deutonymph three pairs of small and smooth adanal setae (ad 1 – ad 3) appear, and remain in tritonymph. Anogenital region with folds and granules of cerotegument, which often form lines.

In proto-, deuto- and tritonymph ( Figure 6 ) shape of prodorsum and prodorsal setae as in larva, except for seta in, which is minute. Bothridium well-developed, rounded, sensillus long, with slimmer head than in larva. Seta c 1 rather short and curved, seta c 2 shortest, seta c 3 extremely long ( Table 1) and directed posteriorly, usually lying on exuviae ( Figure 7A ); all setae with blunt barbs and granules of cerotegument, positioned on apophyses. Exuviae borne by nymphs reticulate, lightly fastened to gastronotum, often lost from specimens during preparation and handling. Setae lp, h 2, h 3 and p 1 positioned on lateral margin of gastronotum; seta lp curved inwards and covering exuviae. Cupule ia posterior to seta c 3, cupule im anterior to seta lp, cupule ip between setae h 2 and h 3, cupule ian lateral to anterior part of anal opening, cupules iad, ips and ih pushed laterally from cupule ian. Tarsus I with two solenidia, ω 1 slightly longer than ω 2, and pointed, while ω 2 blunt ( Figure 8A ); basal parts often with granules of cerotegument. Famulus ε short. Tibia I with two solenidia, ϕ 1 long, protruding beyond tarsal claw, ϕ 2 short.

Summary of ontogenetic transformations

During ontogeny, five pairs of setae are present on the prodorsum of A. reticulatus , including bothridial seta. Setae ro and le are rather long, seta ex is shorter, and seta in is short in the larva, but minute in the nymphs and adult. The bothridium is welldeveloped and rounded in all instars, and the bothridial seta (sensillus) is long, narrow, with barbed head, which is more slender in the nymphs and adult than in the larva. The larva has 11 pairs of gastronotal setae, while in the protonymph some setae appear (h 3, p -series) and some are lost (d -series, la and lm), so the 10 protonymphal pairs (lp, c -, h - and p -series) remain in deuto- and tritonymph. The adult loses all setae of c -series and seta lp, such that six pairs remain (h - and p -series). In the juvenile stages cupules ia, im and ip take a generally similar position, while cupules ih, ips, iad and ian appear in the successive instars lateral to the anterior part of the anal opening, and cupules ih, ips and iad are pushed laterally. In the adult, lyrifissures ia and im are situated in the anterior and medial part of the notogaster respectively, while lyrifissure ip lies anteroventral to seta h 2. Lyrifissures ih, ips, iad and ian are difficult to observe under the cerotegument.

The formula of gastronotal setae in A. reticulatus is 11-10-10-10-6 (larva to adult); formulae 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 Claparède’s organ. The formula of genital setae is 1-4-6-7 (protonymph to adult), and that of segments PS-AN is 23333-0333-022.

Distribution and ecology

Arthrodamaeus reticulatus is considered a Palaearctic species ( Subías 2004). In the dry steppe soil of East Tyrol ( Austria) it inhabits dry meadows and has been considered a xerophilic species ( Schuster 1960; Mihelčič 1964; Schatz 1996). It is common in different parts of Italy ( Bernini et al. 1995), has been recorded from several parts of Spain and is considered common in the Mediterranean region ( Pérez-Íñigo 1997). This species was relatively abundant in limestone quarries in Catalonia ( Spain), which were restored by different methods; A. reticulatus preferred planted shrubs and trees more than sown herbaceous species ( Pilar and Eduardo 2006). It has been recorded from pine litter and grasses in Andalusia ( Spain) at a low density (Seniczak and Seniczak 2010), but was more abundant in southern Italy in cypress and yew litter (Seniczak and Seniczak forthcoming). It was the most abundant gymnodamaeid mite in patches of mosses in the steppe of cape Tarhankut in the Crimean peninsula ( Ukraine), with a density of 95 individuals per 500 cm 3 and dominance index 15 ( Seniczak et al. 2009), but juveniles comprised a relatively small proportion (28.1%) of the population. Because of its greater size, A. reticulatus contributes more biomass to these patchy communities than small mites, and therefore probably participates more in transformation of soil organic matter.

Figures

Figure 1. Arthrodamaeus reticulatus, adult, dorsal aspect; scale bar 100 µm. Legs partially drawn. Explanation of labels in text.

Figure 2. Arthrodamaeus reticulatus, adult, anogenital region; scale bar 100 µm. Explanation of labels in text.

Figure 3. Arthrodamaeus reticulatus, larva, dorsal aspect; scale bar 50 µm. Legs partially drawn. Explanation of labels in text.

Figure 4. Arthrodamaeus reticulatus, scale bars 50 µm. (A) Anal region of larva; (B) anogenital region of protonymph. Explanation of labels in text.

Figure 5. Arthrodamaeus reticulatus, anogenital region; scale bars 50 µm. (A) Deutonymph; (B) tritonymph. Explanation of labels in text.

Figure 6. Arthrodamaeus reticulatus, tritonymph, dorsal aspect; scale bar 100 µm. Legs partially drawn. Explanation of labels in text.

Figure 7. Lateral aspect of tritonymph; scale bars 100 µm. (A) Arthrodamaeus reticulatus; (B) Gymnodamaeus bicostatus. Explanation of labels in text.

Figure 8. Part of tibia and tarsus I of tritonymph; scale bars 20 µm. (A) Arthrodamaeus reticulatus, paraxial aspect; (B) Gymnodamaeus bicostatus, paraxial aspect; (C) G. bicostatus, fragment of tarsus with solenidia; (D) Jacotella neonominata, paraxial aspect. Explanation of labels in text.