Diagnosis (Adults).

Chelicerae chelate-dentate in female, with fixed digit usually reduced in size; cheliceral digits of male subequal in length, with curved spermatodactyl slightly exceeding the tip of the movable digit. Dorsal shield entire, not covering the whole dorsal surface, and with hypotrichous setation (at most, 32 pairs of setae present). Sternal shield with three pairs of setae, metasternal shields and setae often absent. A pair of genital setae present or absent, usually placed on epigynal shield. Anal shield relatively small, elongate, bearing three circum-anal setae. Leg setation holotrichous to markedly hypotrichous.

Notes on the genus.

The genus Ljunghia was proposed by Oudemans [8], based on adults and deutonymphs collected from the theraphosid spider of the genus Selenocosmia Ausserer in Sumatra. Oudeman's genus Ljunghia has gained broad acceptance [9], [12], [15], [17], [20], mostly as a member of the subfamily Iphiopsinae within the family Laelapidae, and is currently divided into two subgenera, Ljunghia and Metaljunghia. We agree with Moraza et al. that this subgeneric structure is not useful, and it is not used here [17].

A new separate genus Arachnyssus was erected [16] to accommodate two mesostigmatic mite species associated with the mygalomorph theraphosid spider Selenocosmia huwena Wang, Peng & Xie ( = Haplopelma schmidti von Wirth, based on the newest taxonomic revision [21]) in China. The most important features that define the genus Arachnyssus, classified within the family Macronyssidae, are: (1) entire dorsal shield; (2) idiosomal setae very long, with tips reaching far beyond the insertions of following setae; (3) anus with anterior position to adanal setae; (4) coxae I–IV not armed with spines; (5) sternal shield saddle-shaped, with posterior margin deeply concave; (6) epigynial shield short, tongue-shaped; (7) anal shield drop-shaped; (8) epigynial and anal shields well separated [16].

It is obvious that the author who erected Arachnyssus neglected the existence of the genus Ljunghia because there is no reference to this genus in his paper [16] and all of the above characters enumerated for Arachnyssus can be found in Ljunghia [17]. Therefore Arachnyssus is here regarded as synonymous with Ljunghia, and the two species, namely A. guangxiensis and A. huwenae are therefore, newly transferred to the genus Ljunghia.

Material examined.

4 females, 2 males – on Pterinochilus chordatus (det. R. C. Gallon) kept in captivity in the Laboratory of Molecular Parasitology, School of Biological Sciences, Bangor University, Gwynedd, NW Wales. The mites were collected by one of the authors, MAP, following the technique described aboved; October 2006.

Description (Adults).

Female. Dorsal idiosoma (Figure 1A). Idiosoma oblong, egg-shaped, 810–860 µm long and 610–635 µm wide (650 µm long and 443 µm wide in freshly moulted and poorly sclerotized specimen). Dorsal shield entire, oblong, suboval, 560–595 µm long and 320–355 µm wide nearly at level of setae z5, usually not completely covering dorsal surface, with regularly rounded posterior margin and smooth surface. The shield free of anterior sections of peritremes, anterior ends of peritremes reaching close to paravertical setae z1. Podonotal region of the shield with 15 pairs of setae (j1–j6, z1, z2, z4–z6, s1–s4), opisthonotum with reduced complement of three setal pairs (J4, Z4 and Z5). Most dorsal shield setae simple, smooth, needle-like, sinuous and considerably elongated, the longest setae up to 270 µm in length and with thread-like distal part reaching far beyond the insertions of following setae; only setae j1, z1 and J4 short. Metric data for some selected dorsal setae as follows: j1 33–44 µm, j4 220–230 µm, j5 136–153 µm, j6 230–260 µm, J4 25–31 µm, z5 170–190 µm, Z4 142–152 µm, Z5 152–162 µm, the longest setae situated on soft membranous dorsal integument 220–255 µm. Dorsolateral membranous integument with 13 pairs of setae.

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Figure 1. Ljunghia pulleinei, female.

A, dorsal idiosoma (with setal notation of some dorsal setae); B, ventral idiosoma. Scale: 100 µm.

https://doi.org/10.1371/journal.pone.0039019.g001

Ventral idiosoma (Figure 1B). Presternal platelets absent. Sternal shield almost quadrangular, longitudinally narrowed, 30–40 µm long in midline, 120–132 µm wide at level of setae st2 and 149–158 µm at level of setae st3, smooth on surface, deeply concave posteriorly; anterolateral corners well developed, slender and obtusely acuminate; the shield bearing two pairs of lyrifissures and three pairs of setae, length of sternal shield setae slightly increasing posteriorly: st1 100–115 µm, st2 105–122 µm, st3 150–170 µm. Metasternal platelets and setae st4 absent, a pair of metasternal lyrifissures placed on soft membrane close to posterolateral corners of sternal shield. Endopodal sclerites absent. Epigynal shield tongue-shaped, elongated, slightly constricted between coxae IV, hyaline anteriorly, rounded posteriorly, 238–252 µm long, 75–83 µm wide at level of genital setae, with a pair of genital setae st5 (166–184 µm) inserted in posterior part and a pattern of weak longitudinal lines on medial surface; associate genital pores not detected. Peritrematal shields almost fully reduced, only short and narrow poststigmatic section present; peritremes well developed, long and with stigma between coxae III and IV. Exopodal sclerites absent, parapodal sclerites developed, crescent. A pair of small and suboval metapodal platelets present. Anal shield pear-shaped, rounded anteriorly and posteriorly, 74–82 µm wide, smooth, bearing rounded anus and three circum-anal setae; postanal seta (64–77 µm) shorter than adanals (80–90 µm); anus with posterior position on the shield. Ventral and ventrolateral membranous integument with 10 pairs of setae. All ventral setae similar to those on dorsal idiosoma.

Gnathosomal structures (Figures 2B, 2C, 2E). Anterior ventral part of hypostome as in Figure 2B, with three pairs of simple hypostomal setae h1–h3; posterior setae h3 longest; posterior surface bearing a pair of simple postcoxal setae. Deutosternal groove relatively narrow and difficult to examine posteriorly, with only three detectable transverse rows of denticles on its anterior section. Corniculi obscure and covered by hypertrophied, lobe-like projection. Chelicerae chelate-dentate (Figure 2C); fixed digit reduced in size, markedly shorter and thiner than movable digit, and armed with distal hook; movable digit relatively robust, with distal hook and two massive subdistal teeth. Epistome rounded and serrate on anterior margin (Figure 2D).

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Figure 2. Ljunghia pulleinei.

A, sternogenital shield of male; B, ventral hypostome of female (anterior part); C, cheliceral digits of female; D, cheliceral digits of male; E, epistome of female; F, tubular structures of insemination apparatus associated with coxae IV in female. Scales: a = 50 µm (Figs 2A, 2F), b = 25 µm (Figs 2B–E).

https://doi.org/10.1371/journal.pone.0039019.g002

Legs. All legs with a well developed pretarsus and ambulacral apparatus (including pulvillus and two claws), shorter than idiosoma. Leg segments without specific projections or macrosetae, with the chaetotactic pattern as previously described. Coxae IV associated with relatively thin and long tubular structures of insemination apparatus (Figure 2F).

Male (Figures 2A, 2D). Idiosoma 540–590 µm long and 360–395 µm wide, dorsal shield 490–515 µm long and 285–325 µm wide. Dorsum with a compact holodorsal shield. Metric data for some selected dorsal setae as follows: j1 23–29 µm, j3 177 µm, j4 200 µm, j5 110–115 µm, J4 12–19 µm, z5 134–158 µm, z6 184–207 µm, Z4 120–126 µm, Z5 126–132 µm. Venter with separate sternogenital (Figure 2A), and anal shields. Sternogenital shield oblong, subtruncate anteriorly, rounded posteriorly, 250–270 µm long in midline, 130–138 µm wide at level of setae st3 and 94–99 µm at level of setae st5, smooth on surface; the shield bearing three pairs of lyrifissures and four pairs of setae (st1–st3, st5), length of sternogenital shield setae slightly increasing posteriorly: st1 75–81 µm, st2 99–105 µm, st3 122–141 µm, st5 150 µm. Cheliceral digits subequal in length, without striking dentation; spermatodactyl hook-like, robust in basal part, curved distally (Figure 2D). Other characters almost identical as in female, including those on opisthogastric region.

Taxonomic notes.

The original description of Ljunghia pulleinei was inadequately illustrated, the description itself was insufficient [11]; therefore, amendments followed in the redescription of Domrow [12], especially in the dorsal shield setation. For example, Womersley stated only 14 pairs of setae on the dorsal shield instead of 17–18 pairs documented by Domrow who examined three series of specimens: (1) the type material collected from theraphosid spider Selenocosmia stirlingi Hogg in South Australia; (2) specimens from a nemesiid spider of the genus Aname L. Koch found in South Australia; (3) specimens from an unidentified diplurid spider in Queensland. All three series were keyed out together by Domrow and, despite the presence of some morphological differences, indicative of a mixture of three species, they were declared to be conspecific [12]. We now know that the specimens from the spiders of the genus Aname, which differ from the typical series mainly by the lack of the subterminal pair of setae on the dorsal shield, belong to the species Ljunghia aname, which was originally described as a new subspecies of L. pulleinei [13], [14]. A third unknown species is being described by Bruce Halliday (personal communication).

Unfortunately, the description and figures of adults given by Domrow [12] and of deutonymphs of Ljunghia pulleinei by Fain [14]) did not apply to the mites of the type series but to those of an unknown diplurid spider. The type specimens and specimens introduced by Domrow (and Fain) can be easily distinguished from each other by the length of setae situated on medial surface of the dorsal shield. They belong to two species, and show a certain degree of interspecific variability not only in the length of idiosomal setae but also in position of some dorsal shield setae (especially in J4 and Z4). So, two main patterns of chaetotaxy can be distinguished: (1) type species with longer idiosomal setae, e.g. setae j5 and z5 with tips reaching far beyond the insertions of j6, setae j6 beyond the insertions of J4, and setae z5 beyond the lateral margin of dorsal shield; (2) species illustrated by Domrow and Fain with shorter idiosomal setae, e.g. setae j5 and z5 with tips not reaching the insertions of j6, setae j6 hardly reaching to the insertions of J4, and setae z5 clearly not reaching the lateral margin of dorsal shield.

Ljunghia pulleinei bearing the longer setae cannot be reliably identified in the newest key of the genus [17]; where some statements are solely applicable to the form exhibiting short setae as described by Domrow [12]. In addition there is a mistake in their key in relation to both setal forms: “setae j4 do not reach the tips of j6”. With exception of this inaccuracy and a pair of additional setae present on the opisthogastric ventral surface in our individuals, our description generally agrees with most of the published morphological characters given by Womersley and Domrow [11], [12]. In addition, we have included in our redescription new metric data for some idiosomal setae, and the shields.

Ljunghia pulleinei s. str. has here been collected from the Kilimanjaro mustard baboon spider from East Africa and previously from the common whistling spider from Australia. This is the first time that one and the same Ljunghia species has been associated with two different host species suggesting that Ljunghia species are not strictly species-specific. Ljunghia is well known from mygalomorph spiders but has also been reported from a more primitive liphistiid Malaysian trap door spider belonging to the Mesothelae [10]. Recently, new Ljunghia species have been retrieved from more liphistiid spiders from Vietnam and Thailand [22]. The female spiders showed clear bite marks of the mites on their prosomata emphasising the parasitic nature of Ljunghia.