Paraplothrombium maketawa n. sp. (Acariformes: Parasitengona), the first member of the Johnstonianidae recorded in New Zealand

Paraplothrombium maketawa n. sp. is described from a female taken from native forest litter in a roadside ditch at the Maketawa river near Inglewood, Taranaki, New Zealand. This represents the first record of the Johnstonianidae in New Zealand.


Introduction
The cosmopolitan family Johnstonianidae comprised 46 species in nine genera, with nine species recorded as nomina dubia in Mąkol & Wohltmann (2012, 2013. Newell's (1957) monograph provides an introduction to the family and outlines why he thought their study was rewarding, "… this is perhaps the most primitive existing family, terrestrial or otherwise, within the Parasitengona". The family sits ecologically between the terrestrial trombidia and the water mites. Johnstonianids have always been found in moist habitats (Wohltmann 2001;Wohltmann et al. 2004). Newell (1957) was also attracted to their study because of the "very loose" nature of their parasitism as larvae. They do not attach firmly to their host as do the vast majority of the Parasitengona. The third fact of interest to Newell was the "generalized morphology" of these mites. They retain simple normal setae on the idiosoma and legs, while most Parasitengona frequently bear ornate setae.
However, Wohltmann et al. (2004) in their revision of the European Johnstonianinae point out that the assumed basal phylogenetic status claimed for the family is not supported by recent investigations.
This paper describes a new species of Paraplothrombium from New Zealand based on one female. Until now, the Johnstonianidae has not been recorded in New Zealand (Sirvid et al. 2009). Paraplothrombium is previously known from one species, P. problematicum Robaux, 1968 from Chile (Robaux 1968).

Materials and Methods
A Tullgren funnel extract was obtained from decaying mesic forest floor vegetation from under tawa/towai (Beilschmedia tawa/Weinmannia racemosa) forest from a roadside (SH 3A) storm-water ditch draining into the Maketawa river near Inglewood, Taranaki, S39.10°, E174.12°. The mite was initially stored uncleared in Hoyer's medium for 10 years. Then it was re-hydrated and cleared with acetic chloral hydrate. For microscopic examination, it was remounted in Hoyer's gum chloral for study with polarized light. Illustrations were aided with a camera lucida. Scanned drawings were labelled with GIMP software. An eyepiece graticule allowed measurements in micrometres (µm). Morphological nomenclature largely follows Newell (1957) and Wohltmann et al. (2004). Measurements taken from Robaux's (1968) illustrations of P. problematicum are indicated where used. Podomere length criteria are included as a note to Table 1. The system defining the place of insertion of specialized setae (relative to segment length) used by Newell (1957) is used here. e.g. ζ 0.6d means the seta ζ is inserted dorsally at 60% of the length of the segment from the proximal end. While usually possible to distinguish specialized setae from normal (n) seta, this author could not always distinguish different specialized setal types as did Newell (1957). Therefore his notation of labeling solenidia s (1-4) based on setal size and shape, is not used. Naming setae as n or specialized was informed from the setal position e.g., specialized leg setae are often dorsal, or at a particular location on the segment as well as birefringence qualities. Other characters used to assign setal type included the alveolus foramen size and shape and internal setal structure. Specialized setae were recognized from their larger tapered foramen through the exoskeleton (indicated in figures), than n setae foramen (open circles) as well as protoplasmic cores; distinctive curvature, blunt tips or their shape e.g., rod-shaped or spiniform.
Abbreviations: Standard abbreviations such as those in Wohltmann et al. (2004) are used.
Remarks -Robaux's description of P. problematicum does not describe or illustrate fin-like cuticle spurs. However, they are present (Mark Judson pers. comm. July, 2019). Diplothrombium Berlese, 1910 (probably a sister genus) possesses these cuticle spurs on palp and TiI but in D. longipalpe, they are present on Ta I -IV (Wohltmann et al. 2004). Newell (1957) illustrates them clearly on the palp tibia of D. micidium in his Fig. 153. The new species has these structures (labelled fs in figures) on the PaTi and Ta and dorsodistally on TiI and TaII, III and IV. However there is a gradation in size and shape of the spurs from a cuticle swelling on distodorsal TaI to rather square shaped cuticle swellings (viewed laterally), especially around ω and ζ, on all leg tarsi. These two forms have not been called fin-like spurs in this paper.

Differential diagnosis
The new species differs from P. problematicum in its larger idiosomal length and width (1400 x 1000 compared to 960 x 720); a slightly more inflated TaI (TaI H : TaI L 175:350 = 0.50 versus 130:290 = 0.45). The separation of the naso into an anterior and posterior part is at the n setae (replacing the ASens) in the new species (labelled ns in Fig. 1D) but c. 50 anterior to the n setae replacing the ASens in P. problematicum. Two pairs of straight acuminate setae, AL (anterolateral scutalae) and ML (middle scutalae), set adjacent and anterior to PSens are c. 50 long in P. problematicum (calculated from Robaux 1968 Table 1) -Colour when fresh not recorded; slide mounted, red brown. Idiosoma with shoulders giving a square outline; idiosoma with short bent smooth setae, some faintly barbed distally, imbricate to adjacent posterior setae insertions (Figs. 1A, 1B). Idiosomal setae each on small convex platelet in smooth cuticle. Sub-cuticle with distinct reticulate pattern (nerve net of Thor 1904; Fig. 1C) formed from intersection of three sets of straight parallel striae c. 12 apart with each set at 60°angle to the adjacent, intersections often form star of David pattern. They do not extend under scutum.
Anterior dorsal idiosoma -Eyes on pedicel of ocular sclerite either side of crista metopica, about level with base of PSens; ocular sclerite 38 in diameter; pedicels 425 apart; anterior eye lens 30 in diameter, posterior 25. Crista metopica posterior end to anterior tip of naso 387 long ( Fig. 1D) with unclear boundaries, extends anteriorly into broadly rounded naso that becomes narrower and pointed after clearing or as a result of flattening on slide (see discussion). At the time of remounting and clearing, one nude PSens measuring 70 long present, but may have been broken; both posterior sensilla now missing from specimen. Two n setae, 67 long, set in n alveoli in position of anterior trichobothria; distance between bases of these n setae and PSens 125. AL and ML 72 long, inserted on scutum edge just anterior to PSens (Fig.  1D), one of each pair is missing in the specimen. Seta PL off scutum and posterior to PSens. Anterior to the level of PSens and eyes on each side are 9 simple, curved setae set in round to oval convex platelets of 15 diameter.
Posterior dorsal idiosoma -Posterior to crista and extending to emergence of first pair of legs is a transverse strip of cuticle without setae or platelets (better seen ventrally). Posterior to it, mid-dorsal setae spine-tipped, diameter 4, 50-60 long, while posterior dorsal setae 60-70 long, diameter 5, set on convex, round or oval, platelets 25 in diameter; platelet edges 20 apart, setae set in middle or offset to the edge.

Legs (Table 1, Figs. 3C -D, 4A -F) -Specialized setae present on all podomeres except
Cx, Tr and bFe. Legs with exoskeleton mostly rugose, cuticle up to 20 thick. Legs terminate in pair of claws on I and II, 62-87 from tip to base measured across the span; on III and IV, that span is 100. Tarsal claw-retraction fossae poorly developed on all legs.
Leg IV: Ta (Fig. 4F), venter with 40 straight spines as on the medial and lateral faces. Dorsal ω tapered blunt semi-recumbent rods at 0.06d, 0.25d and 0.30d, 30 long on slightly Note: L measured between the dorsal condyles except for Tr and bFe where the distance is between the podomere's major proximal and distal condyles. CxIL excludes pars medialis. TaL excl. claws. *includes CxL; ** excludes CxL. The length of the pars medialis (paracoxal) field is 150 long; the TaI H (height) is 175. PaTi length includes odontus. raised pedicels; straight and curved ζ 75 long. Ti: with n straight setae, dorsum with four φ set at 0.20d, 0.65d, 0.70d and 0.90d with the three proximal raised and pointed 67 long and the distal one recumbent 25 long. Also dorsal surface bears > 15 ζ with fine tapered curved tips. Ge: venter unseen. Dorsum with seven stout erect ζ 65 long and c. 15 finely tapered ζ 50 long. tFe: venter with 2 stout n setae, laterodorsally 3 stout ζ 65 long and c. 12 finely tipped ζ. bFe: c. 10 n setae. Tr: c. 5 n setae.
Egg -Finely punctate shell (now broken) within holotype; 300 diameter ( Fig. 1A). Material examined -Holotype female with egg. Collected South of Inglewood, Taranaki, New Zealand, S39.10, E174.12., Alt. c. 210m, western side of State Highway 3A under tawa/kamahi native trees from roadside seepage/storm-water drain on the banks of the Maketawa River; J. M. Clark, 6th June 1997. Locality now removed by road realignment. Holotype on slide to be deposited in the Canterbury Museum, Rolleston Ave., Christchurch 8013, New Zealand.
Etymology -maketawa -Polynesian name probably referring to the tawa tree /ˈtaʊə/ /ˈtɑːwə/ once abundant in the area in pre-European times; 'make' also pronounced with long vowels. The mite was collected close to the Maketawa River.

Discussion
The author examined the three specimens identified as Paraplothrombium from Tasmania (Seeman in Driessen 2016). These specimens have richly branched dorsal setae: not the stiff rod-like setae of Johnstonianidae. They also lacked a projecting naso, fenestrated palp trochanter and pars medialis. They are excluded from Paraplothrombium.
The fin-like spurs, at least on the PaTa, are postulated here, to function as a support for the setae bases where those setae are used to apply a force such as holding prey. The PaTi dorsodistal fin-like spurs may also support the setal bases when they are used to push mesic substrate. The original generic diagnosis of Paraplothrombium (Robaux 1968: 463) mentions "La partie antérieure de la crête séparée de la postérieure par un étranglement, …" (The anterior part of the crista is separated from the posterior part by a constriction -author's translation). The constriction may be an artifact, i.e., the bending of the crista in the slide preparation makes the separation appear.
In the new species, there appeared to be a break or constriction in the crista separating the naso from the "2 poils simple non sensoriels". But by adding water to the mounting medium and releasing the coverslip pressure on the specimen, the apparent break became less obvious, presumably as the crista regained its more original shape. Newell (1957: 426) wrote: "The structure of the adult scutum as delineated by Berlese and reproduced by various authors is incorrect because of the very sharp downward flexure of the scutum between the posterior and anterior sensilla, …". Newell (1957) also pointed out that the naso anterior spine of Centrotrombidium is vertical so it cannot be seen in specimens unless laterally viewed.
This specimen is the only member of the family Johnstonianidae that the author has collected in more than 20 years of collecting forest floor mites in NZ. The species is most likely endemic to NZ and less likely to be recently transferred by humans, given the poor traveling record of the Johnstonianidae (Newell 1957: 441).