Damaeus (Adamaeus) onustus C. L. Koch 1844

Damaeus (Adamaeus) onustus C. L. Koch, 1844

(Figs. 1–7, 8 A)

Damaeus onustus: Grandjean 1943; Hammen 1952; Sellnick 1960; Bulanova-Zachvatkina 1967; Marshall et al. 1987. Belba geniculata Berlese, 1887.

Damaeus geniculatus: Michael 1888; Trägårdh 1904; Bulanova-Zachvatkina 1957b. Oribata geniculata: Oudemans 1900.

O. geniculatus: Kulczyński 1902; Sellnick 1928.

Belba geniculosa: Oudemans 1929.

Damaeus (Adamaeus) onustus: Norton 1978; Balogh & Balogh 1992; Pérez-Íñigo 1997; Subías 2004; Miko 2006. Adamaeus onustus: Schatz 1983; Olszanowski et al. 1996.

Diagnosis. Adult of damaeid shape, large (1350–1600 μm), dark brown to almost black. Prodorsum subtriangular, notogaster strongly arched, almost spherical (Fig. 1), cerotegument with short vermicular excrescences. Seta in shorter than c 1 (Table 1), seta ex short (Fig. 2 A). Sensillus approximately as long as seta c 1. Apophyses P, Sp, Da, Ba and Bp well-developed, P large, Sp short, truncate, Da, Ba and Bp rounded, apophyses Dp and Sa weakly developed. Spinae adnatae (s. a.) relatively long, narrow, cone-shaped, and directed anteriorly, discidium (Dis) rather short. Notogaster with 11 pairs of strong setae, nine in two longitudinal rows; anterior pair directed anteriorly, approximately as long as sensillus, other setae curved outside, length decreasing from anterior to posterior, setae of p -series rather short (Fig. 2 B). Coxisternal apophyses E2a, Va and Vp well-developed, rounded, apophysis E2p weakly developed. Formulae of leg setae and solenidia given in Table 2, dorsal coupled setae d usually lost on genua I–III and tibiae I–IV. Legs monodactylous.

Juveniles slimmer than adult, elongated, unpigmented, legs slightly darker and approximately as long as body (Table 1). Prodorsal setae ro and le relatively long, le more widely spaced than ro; setae in and ex short. Bothridium large, rounded, with funnel-like rim, sensillus setiform, finely barbed. Gastronotum of larva slightly elongated, truncate posteriorly; gastronotum of nymphs oval, rounded posteriorly. Most dorsal gastronotal setae long, curved, finely barbed, with flagellate ends; in larva setae raised, and inserted on large apophyses, in nymphs setae curved ventrally, and inserted on small apophyses. Prodorsum and gastronotum covered with granular cerotegument, covering also legs and setae. Cornicle thick, short, anteromedial to setae la. Nymphs carry compact humus mass attached to exuviae of previous instars.

Species Morphological character L PN DN TN AD

D. onustus Body length 611 829 994 1271 1434 Body width 304 423 553 701 929 Length of: seta la 128 165 198 231 205 seta in 8 12 16 16 80 seta ex 8 12 16 16 12 seta c 1 295 289 290 292 239 seta c 3 93 106 116 119 lost leg IV 722 962 1174 1434 1712 genital opening nd 96 139 205 244 anal opening 133 169 195 264 248

D. clavipes Body length 410 462 631 848 962 Body width 198 205 324 449 644 Length of: seta le 96 112 129 172 191 seta in 46 42 40 40 86 seta ex 16 16 19 23 31 seta c 1 134 248 369 492 148 seta c 3 48 98 101 102 lost leg IV 520 650 1141 1630 1597 genital opening nd 58 79 139 190 anal opening 85 92 112 168 193

K. tecticola Body length 251 316 429 514 637 Body width 128 135 198 244 429 Length of: seta le 42 62 72 77 120 seta in 37 45 58 95 65 seta ex 35 62 40 88 48 seta c 1 166 212 286 343 81 seta c 3 38 40 87 136 lost leg IV 248 304 436 715 880 genital opening nd 25 52 80 106 anal opening 48 52 71 114 108 Description of juvenile stages. Larva elongated (Fig. 3), unpigmented. Prodorsum triangular, setae ro and le rather long (Table 1), curved, finely barbed; le slightly longer and more widely inserted than ro. Setae in and ex short. Bothridium well developed, rounded, protruding from surface, with funnel-like rim; sensillus setiform, finely barbed. Lateral depression present above leg I.

Gastronotum of larva with 12 pairs of setae, including h 2 and h 3 inserted lateral to posterior and middle part of anal opening, respectively (Fig. 4 A). Gastronotal setae inserted on large apophyses; most setae long, except for shorter seta c 3 (Table 1), curved, finely barbed and distally pliable, often twisted. Seta h 2 rather short, h 3 minute. Paraproctal valves (segment PS) with two pairs of vestigial setae. Cupule ia located posterior to seta c 3, cupule im posterior to seta lm, cupule ip between setae lp and h 2, and cupule ih lateral to posterior part of anal opening. Opisthosomal gland opening (gla) lateral to seta h 2. Gastronotum with granular cerotegument, and few folds.

Nymphs more oval and stocky than larva, unpigmented. Gastronotum of protonymph with 12 pairs of setae, as three pairs of pseudanal setae (p 1– p 3) appear on segment PS (Fig. 4 B), and remain in successive instars (Figs. 5 A, B), while setae of d -series absent, leaving central part of gastronotum bare. Setae of p -series finely barbed, length decreasing from p 1 to p 3. Genital valves of protonymph with one pair of short setae, two pairs added in deutonymph and two more pairs in tritonymph; all setae short. One pair of small aggenital setae appears in deutonymph, lateral to posterior part of genital valves, and remains in tritonymph. Genital papillae rather large. Paraproctal valves of protonymph (segment AD) and deutonymph (segment AN) bare, but those of tritonymph with two pairs of small anal setae (an 1 and an 2). In deutonymph three pairs of adanal setae (ad 1– ad 3) appear on segment AD, and remain in tritonymph; all setae slightly curved, and shorter than seta p 3. Anogenital region with granular cerotegument, and few folds.

Prodorsum of nymphs relatively shorter than in larva. Prodorsal setae of tritonymph (Fig. 6) as in larva, two lateral depressions present, posterior to seta le, and above leg I, and transverse ridge posterior to seta le. Bothridium rather large, rounded, protruding from surface, with funnel-like rim; sensillus setiform, with short, rare barbs. Prodorsum with granular cerotegument.

Gastronotal setae rather long, curved ventrally (Fig. 7), inserted on marginal parts of gastronotum, covered with exuviae of previous instars and humus mass. After removal of humus camouflage, dorsocentral part bare, with short, thick cornicle (k), situated midway between cupules ia (anteromedial to setae la). All setae pliable in distal part, fragile and often broken. Cupules ia and im located as in larva, cupule ip ventral to seta lp, cupule iad lateral to anterior part of anal opening, cupules ips and ih pushed laterally from cupule iad, gland opening (gla) posterior to cupule ih. Gastronotum with granular cerotegument.

Tarsus I of tritonymph long and thin, with two solenidia, ω1 longer and thicker than ω2, seta ft ’ long, seta ft ” short, posterior to solenidion ω1 (Fig. 8 A). Tibia I with two solenidia, φ1 long, with long coupled seta d, φ2 short.

Summary of ontogenetic transformations. Setae ro and le are rather long in all instars, and barbed, but in the juveniles setae ro are inserted closer to the rostrum than in the adult. Seta in is short in the larva and nymphs, and rather long in the adult, while seta ex is small in all instars. The bothridium is rather large, rounded in all instars, with a funnel-like rim, and the sensillus is long, setiform.

The larva has 12 pairs of gastronotal setae, but in the protonymph some setae appear (p -series) and some are lost (d -series), such that 12 pairs remain in all nymphs. The adult loses seta c 3, so 11 pairs of notogastral setae remain. The formula of gastronotal setae in D. onustus is 12-12-12-12 -11 (larva to adult), those of coxisternal setae are: 3-1-2 (larva), 3-1-2-1 (protonymph), 3-1-2-2 (deutonymph) and 3-1-3-3 (tritonymph and adult). In the larva seta 1c is scaliform and covers the Claparède’s organ (see Grandjean 1955). 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.

Distribution ecology and biology. Damaeus onustus is a widespread European species (Subías 2004; Miko 2006), including Spitsbergen (Lebedeva & Lebedev 2008). It was recorded from several parts of Poland (Olszanowski et al. 1996).

This species occurs in deciduous litter, mosses, bark and decaying wood (Willmann 1931; Sellnick 1960; Wood & Lawton 1973; Wallwork 1976; Maraun et al. 2004; Żbikowska-Zdun et al. 2006), but also in bushes and grasses, showing preference to loose accumulation of litter, with a great tolerance of humidity (Rajski 1967). In the Chiltern beech woods (South East England) this species was abundant in beach litter accumulated in sheltered depressions, but was less abundant on steep slopes Wallwork (1976). In Botanical Garden on the campus of the University of Life Sciences in Ås (Norway) it also occurs in Scots pine and shrub litter. Schatz (1983) considered it in forest, eurytopic, and microphytophagous species.

As D. onustus is relatively large, it was often cultured in the laboratory. Pauly (1956) investigated the development and biology of this species. When D. onustus fed on algae from tree bark, one female laid about 25 eggs in breeding season, whole development of species lasted about 140 days, and the adult lived about two years.

Madge (1964 a, 1964b, 1964c, 1965a, 1965b, 1965c) investigated the ecology of D. onustus in very detailed, and inventive laboratory experiments, which considered water-relations, humidity reactions, longevity, lethal temperatures and behaviour of this species. From all interesting results the most interesting seem to be those connected with bearing the exuviae of previous instars by nymphs. When D. onustus was exposed to temperatures 10–70o C, the critical temperature to waterproofing cuticular cover was lower for the juveniles (40o C) than for the adults (45o C), which may explain the ecological importance of bearing of exuviae and debris by nymphs. If debris was removed from the nymphs, evaporation of mites increased. Critical temperature for nymphs both with or without debris was then 40o C. This species controls well water-loss and temperature of body by well developed respiratory system. It also reacts well to air humidity by humidity receptors, which are probably located on forelegs, which is consistent with Pauly (1956). This species is more active in dry air than in moist air. As a matter of radiant heat, the tritonymphs chose lower temperature (11.5o C) than the adults (13o C).

Damaeus onustus is an intermediate host of Cittotaenia marmotae (Denegri 1993) and is a host of protozoan Apicomplexa— Erhardovina bisphaera (Purrini & Ormieres 1981) and Microspora – Nosema acari (Geest et al. 2000).