Kunstidamaeus arcticus, Miko & Monson, 2013

Miko, L. & Monson, F. D., 2013, Two Interesting Damaeid Mites (Acari, Oribatida, Damaeidae Berlese, 1896) From The British Isles And Svalbard (Spitsbergen, Norway), With A Description Of Kunstidamaeus Arcticus N. Sp., Acarologia 53 (1), pp. 89-100 : 90-94

Kunstidamaeus arcticus n.sp. ( Figs. 1-3 )

Diagnosis — Kunstidamaeus with a short, slightly dilated sensillus covered distally by cerotegument; tubercle Ba absent; with a set of variably developed small tubercles present at the basis of prodorsum; and with weakly developed spinae adnatae. Ventral side with a paired anterior ventromedial apophyse, with most epimeral setae inserted on distinct tubercles; only 5 pairs of genital setae present.

Description of the adult.

Material examined — Holotype and four paratypes, collected by S. Coulson from soil of tundra heath in Svalbard ( Spitsbergen , Norway), sample number OR 804, 1991 - 1993. More detailed information about the collected material is not available to us.

Measurements — Body ventral length 470 – 500 µm (n=5), body length in dorsal view about 500 – 530 µm. Length of prodorsum 180 – 210 µm, width (between the tips of P apophyses) around 200 µm (n=2), width of notogaster 260 – 320 µm (n=5).

Integument — Surface of body and legs, except distal parts of tarsi, covered mostly by filamentous and columnar cerotegument, which has, on prodorsum, anterior and central part of notogaster and on ventral plate, a very characteristic appearance: individual, rather short and distinctly attenuated filaments each with a slightly expanded, buttonlike base. Lateral part of sejugal area, propodolateral apophyse and parastigmatic apophyses with granular cerotegument. Distal part of sensillus with a very specific, short, but distinct, fine "leaflike" cerotegument ( Fig. 2J ). Body surface under cerotegument finely granulated, with the granulation well visible on the prodorsum and the ventral plate.

Prodorsum ( Figs. 1A , 2 A-B, D-G, J) — Shape of prodorsum triangular, with well developed, blunt apophysis P, perpendicular to body. Lateral tubercles La small, distinct, but hardly visible beneath a layer of cerotegument. A series of 3 – 4 small tubercles present at the basis of the prodorsum, replacing postbothridial or centrodorsal tubercles, partly merging and creating a tuberculate ridge. In some individuals, however, the ridge only weakly developed and basis of the prodorsum just with a rugged and an irregularly thickened cuticle ( Fig. 2B ). Parastigmatic apophyses strong and distinct, Sa longer, sharp, ’thorn-like’, perpendicular to body, Sp shorter, dentiform, with broader basis than Sa ( Fig. 2A ). Rostrum with a slightly projecting central lobe, partly separated from the rest of the prodorsum by short, distinct and slightly arched ridges anterior to insertion points of the lamellar setae, projecting anteromediad. Bothridium ’funnellike’, with an expanded, round rim, sometimes with an indistinct, blunt, antiaxial projection ( Fig. 2J ). Sensillus relatively short (110 – 130 µm), slightly dilated in distal part, and attenuated towards tip; sparsely, but distinctly scabrose distally. The distal, dilated portion covered by specially formed, leaf-like cerotegument, giving the sensillus an overall fusiform appearance. Rostral (ca 75 µm) and lamellar (ca 83 µm) setae subequal in length, arched, smooth and relatively fine ( Fig. 2 D-E). Interlamellar setae relatively short (about 50 µm), strong, dilated at the base, with a finely dentate posterior edge, projecting posteriad or posterolaterad ( Fig. 2G ). Exobothridial setae very fine, smooth, strongly curved or almost curly, with an attenuated tip ( Fig. 2F ), about as long (45 – 50 µm) as the interlamellar setae.

Notogaster ( Figs. 1A , 2 B-C, H-I) — Oval or subglobular in dorsal view. Spinae adnatae very weakly developed, small and almost invisible in the layer of cerotegument, unpigmented and transparent, variable in shape - either small and triangular ( Fig. 2B ), or narrowly ceratiform ( Fig. 2C ). Notogastral setae in two subparallel rows, medium long, posterior ones slightly shorter (c1 and c2 around 65 – 70 µm, la 65 µm, h1 55 µm). Setae ps1-ps3 finer and shorter (ps1 45 – 50 µm, ps3 40 – 45 µm). Lyrifissures normally developed.

Ventral characters ( Fig. 1B ) — Gnathosoma relatively broad, cuticle with characteristically fine transverse ridges. Mouthparts and palps as usual in Kunstidamaeus , setae h and a quite long (around 35 µm), with setae a shorter. Tectum of podocephalic fossa slightly projecting posteriad into a blunt, ’beak-like’ tip. Epimeral tubercles E2a, E2p absent, in medial part of sejugal area with distinctly paired tubercle VM; tubercles Va and Vp absent (see remarks for potential analogies). Discidium strong, pointed, triangular or ’beak-like’ projecting laterad or slightly anteriolaterad. Anterior part of epimeral region laterally with a longitudinal, more sclerotised ridge, bearing epimeral seta 1c. Epimeral setal formula 3-1-3-4, setae of epimeres 1-3 and seta 4a on distinct tubercles, these most pronounced around insertions points of 3a, 4a, 2a and 3b. Length of all ventral setae around 25 – 35 µm; setae 3c the longest (ca 40 µm), oriented anteriad. Genital plates, in some individuals, posteriorly with a fine longitudinal striation, and with only 5 genital setae of medium length (18 – 24 µm). From the position of genital setae, it is assumed seta g2 or g6 is reduced (absent). Otherwise, normal set and positions of setae (5g, 1ag, 2an, and 3ad) in anogenital area. Posterior end of ventral plate behind anal plates with postanal sclerite, developed as a short, transverse, sclerotised lath or indistinct ridge. Notogastral margin behind postanal sclerite possibly undulate or indented axially.

Legs ( Fig. 3 ) — Only leg IV distinctly longer than body; legs I and III almost as long as or only slightly longer than body, leg II distinctly shorter than body. Tibiae I and IV longer than their respective genua, with trochanter IV and femur IV subequal in length. Proximal part of tarsus II and IV before bulb, ventrally with strongly thickened cuticle ( Fig. 3C ). Leg setation (famulus included, with solenidia in parenthesis): leg I 1-7- 4(1)-4(2)-21(2), leg II 1-6-4(1)-4(1)-17(2), leg III 2-5-3(1)-3(1)-17, leg IV 1-4-3-3(1)-14. Dorsal setae of femora, particularly of femur I, strong, unilaterally with fine ’saw-like’ dentation or with dark scales. Tarsus I with accessory ventral seta v2’, which is absent on tarsus IV. Famulus normally developed, emergent, setiform. Genual solenidia σ on leg I-II slightly longer than coupled seta. Tibial solenidia of leg I (’1) and leg IV (’) tactile, very long, fine, about 160 – 170 µm long, solenidion ’2 of tibia I setiform, but much shorter. Both solenidia of tarsus I (ω1, ω2) also fine, setiform, relatively long (75 – 85 µm).

Remarks — The species has several unusual characters distinguishing it from all other Kunstidamaeus (and Epidamaeus ) species. The most unusual being the presence of only 5 genital setae per plate, whilst, the normal number for both genera and all Damaeidae is 6 setae per plate. The combination of the presence of a typical apophyse P perpendicular to the body axis together with prodorsal tubercles La and Ba is typical for Kunstidamaeus , and the similar combination of apophysis P and tubercle La let us to assign the species to this genus. However, in K. arcticus n.sp., postbothridial tubercles are absent, whilst a row of 3-4 small tubercles at each side of prodorsum base has developed instead, in some individuals. One could speculate about the homology of this structure with tubercles Ba or Da. However, this structure is variable in our material, and in some individuals is only weakly developed. This suggests that the homology is questionable and the structure may have evolved independently. The idea is, in our view, supported also by the very unusual presence of paired tubercles VM in the medial part of the ventrosejugal groove. The single, unpaired ventromedial tubercle VM is known from this area in only a few species of Epidamaeus eg. E. fortispinosus Hammer, 1967 and E. hastatus Hammer, 1967 . The latter of the two species shares some more similarities (see Behan-Pelletier and Norton, 1985 for details), e.g. shape of spinae adnatae, exobothridial setae and partly also the relatively short, lanceolate sensillus, and, more importantly, a thickened cuticle at the basis of prodorsum. To our knowledge, unique to K. arcticus n.sp. is also the presence of a distinctly thickened cuticle at the ventral part of the proximal end of tarsi III and IV. Another unusual character belonging to the new species is the presence of a second antiaxial accessory seta, ventral to seta v2’ on tarsus I, whilst the same seta on tarsus IV is absent. Absence of this seta on tarsi I and IV is a typical character shared by most of the species of Epidamaeus and Kunstidamaeus within the Damaeus (sensu lato) complex, and, if occasionally present, they are developed always on both legs. On the other hand, the weak development of the spinae adnatae is not sur- prising - the tendency of minimization and weakening of spinae adnatae seems to be quite common within the Damaeidae from northern Arctic areas, as demonstrated by Behan-Pelletier and Norton (1983). This unique combination of characters, combined with the very characteristic shape of the cerotegument, sensillus and presence of only 5 genital setae clearly differentiates this species from all other known species. Based on the presence of short sensillus (appearing distally slightly dilated), shape and size of the notogastral setae and presence of granular cerotegument, the new species shows similarities to the species-group "tenuipes", but given the specific characters described above, it should be considered as self-standing within the Kunstidamaeus .

Figures

FIGURE 1: Kunstidamaeus arcticus n.sp.: A – dorsal view, legs only partly depicted; B – ventral view, legs and gnathosoma only partly depicted (scale bar = 200 µm).

FIGURE 2: Kunstidamaeus arcticus n.sp.: A – lateral part of prodorsum with apophyses P, Sa and Sp, and tubercle La; B – dorsosejugal area with tubercles at posterior end of prodorsum and spinae adnatae; C – spina adnatum of another individual; D – lamellar seta; E – rostral seta; F – exobothridial seta; G – interlamellar seta; H – notogastral seta c1; I – notogastral seta lm; J – sensillus and bothridium (scale bar = 50 µm).

FIGURE 3: Kunstidamaeus arcticus n.sp.: A – leg I; B – trochanter, femur and genu IV; C – tibia and tarsus IV; D – femur and genu IV, axial view; E – tibia IV, axial view; F – trochanter III; G – genu and tibia III (scale bar = 50 µm).