Trachymolgus purpureus sp. n. is heavily armored with distinctive integument characteristic of Trachymolgus (Figs 1–2). Like Trachymolgus jesusi, the integument is dark purple, whereas Trachymolgus nigerrimus was described as black. Like Trachymolgus jesusi and Trachymolgus nigerrimus, there are two teeth on the fixed cheliceral digit. Like Trachymolgus nigerrimus, Trachymolgus purpureus has one tooth on the movable digit (Trachymolgus jesusi have three) and a serrated edge proximal to the tooth (undescribed in other species). All stages have two pairs of eyes, unlike the larva, proto- and deutonymphs of Trachymolgus jesusi, which lack eyes (tritonymphs and adults have two pairs). Trachymolgus purpureus pedipalpal basi- and telofemora are only fused dorsally. Trachymolgus jesusi pedipalp femora are completely fused, whereas Trachymolgus nigerrimus are completely divided. Trachymolgus purpureus, like other Trachymolgus, have undivided femora on legs I-II (femora III-IV are divided). All other Bdellidae have divided femora on all legs. Trachymolgus jesusi is the only bdellid reported to have undivided femora on legs II and III. The ontogeny of Trachymolgus purpureus differs markedly from that described for Trachymolgus jesusi, the only other species where ontogeny was investigated. Finally, there are many chaetotaxic differences on the appendages and venter between Trachymolgus purpureus and Trachymolgus jesusi. Most chaetotaxy of Trachymolgus nigerrimus remain to be investigated. See Remarks for discussion of Trachymolgus recki.

Females and males similar, except for genitalia, size, and chaetotaxic differences noted in Table 1. Color dark purple; occasionally immatures and adults were collected from the Buffalo National River (Arkansas) with an internally green coloration, which rendered the normally purple mite teal; teal specimens returned to purple after a few days in 95% ethanol, and were indistinguishable from normal specimens when slide-mounted (we also collected Penthaleus, a normally black to dark blue mite, from the same habitat exhibiting green internal coloration). Integument divided into heavily armored sclerites with foveolate sculpturing (Fig. 2a). The foveolate indentions (foveolae) are bordered with pits (Fig. 2b). Measurements in Tables 2–5.

Dorsal idiosoma (Fig. 3). Idiosoma dorsally armored with two large tergites: proterosomal and hysterosomal shields (see Terminology). Dorsal membrane (between proterosomal and hysterosomal shields and between dorsal and lateral shields) striated and accompanied with raised bumps similar in size to the foveolate indentions (Figs 4, 5a-b). Proterosoma ending anteriorly in a crenulated, tri-lobed shelf (crown) covering the stigmata. Two pairs of eyes present. Two pairs of minutely barbulate trichobothria: anterior (at) and posterior trichobothria (pt). Barbules are difficult to discern with light microscopy (Fig. 5c). Two pairs of barbulate setae are present: lateral proterosomal (lps) and median proterosomal setae (mps). Setae lps are oriented dorsomedially and lay in a groove posterior to the first pair of eyes (Fig. 5d); mps are the longest barbulate setae. Two pairs of heavily sclerotized, cylindrical, internally directed structures are apparent (Fig. 5e-f) that we interpret to be apodemes. Hysterosoma folding over posterior, shelf-like portion of proterosoma; with three lyrifissures (ia, im, and ip) and seven barbulate setae as follows: c1, c2, d1, e1, f1, f2, and h1. Posteriorly, the hysterosomal shield folds inward between the f1-2 and h1 forming a curved lateral furrow isolating h1 on a raised area.

Ventral idiosoma(Fig. 4). Lateral shieldseach posteriorly containing one lyrifissure (ih) and one barbulate seta (h2). Podocephalic canals lead from the posteriolateral edges of the gnathosoma and curve around coxal field I, and are visible externally (Figs 1a, 4). Ventral membrane is striated but lacks bumps. Genital region covered with one pair of genital shields each containing more than 20 barbulate setae. There are six pairs of paragenital setae; one unpaired median seta between coxal field IV; three pairs of genital papillae; one pair of genital tracheae associated with the genital papillae that leads into the body anteriorly from the anterior-most genital papilla, and ending in spoon-shaped platytracheae near coxal field I (Fig. 6a). Female with long, telescoping ovipositor that approaches body length (Fig. 6b); with 16 setae. Male amphoid sclerites each with nine setae. Unpaired median cylindrical structure interpreted as an apodeme between coxal field III (Fig. 8). Anal region with two pairs of sclerites: anal shields and paranal shields, each usually containing three pairs of barbulate setae. Either side of both anal and paranal shields may have one to two extra setae (symmetrically or asymmetrically). Legs(Figs 4, 7): coxal fields I-III distinct, coxal field IV indistinguishably fused medially with venter; sclerotized, inwardly directed cylindrical structures (interpreted here as apodemes) are readily apparent on coxal field II and III (Fig. 8). Trochanters, femora, and genua sclerotized, with pitted, sculptured armor, especially II and III (Figs 4, 9a); other podomeres unsclerotized with papillated striations (Fig. 9b). Podomeres with eight possible setal rows positioned ventrally (unpaired), medioventrally (paired), lateroventrally (paired), laterally (paired), laterodorsally (paired), and dorsally (unpaired). Base of the ambulacrum surrounded with two pairs of setae: prorals (p) and unguinals (u). Proximally, the dorsal setae are as follows: iterals (it), tectals (tc), and fastigials (ft). The tectals are paired on all legs except IV; fastidials are paired only on leg I, and are absent on leg IV. Other setal homologies remain to be investigated. Baculiform solenidia present on genua I-IV (σ), tibiae I and III (γ), and tarsi I, II, and IV (ω); short, ceratiform solenidia present on tibiae I and II (γ); and a short solenidion present on tarsi I that has the appearance of being raggedly broken, interpreted here as the famulus (ε). Trichobothria present on tibiae I and IV, and tarsus III. Apotele with barbulate ungues and pulvilli with tenant hairs (Fig. 9c-d). Leg arthrodial membrane is unsculptured.

Gnathosoma(Fig. 10). Subcapitulum (Fig. 10a) foveolate and armored posteriorly, longitudinally striated anteriorly (Fig. 11a); ventrally with two pairs of smooth adoral setae (ad), one pair of smooth anterior setae (avs), and one pair of barbulate posterior setae (pvs); dorsally with one pair of smooth, thin, straight setae (ds) that are hidden under the chelicerae in life; ending in three pairs of lateral lips (Figs 10a, 11d). Oral opening located midway between ventral setae (Fig. 11b). Gnathosomal membrane unsculptured. Pedipalps (Fig. 10b) entirely striated (Fig. 11e), becoming more papillated-striated distally (Fig. 11f); femora partially fused dorsally; terminal setae (ves and des) finely barbulate (Fig. 11f). Chelicerae (Fig. 10c) with foveolate armoring basally, and longitudinal striation distally (Fig. 11c); with two dorsal barbulate setae. Fixed digit ending in a hook, and with two teeth (one small and one large and triangular); movable digit with one small tooth and a serrated edge proximal to the tooth (Fig. 10d).

Measurements and chaetotaxy of immatures are given in Tables 1–6. Developmental stages are illustrated in Figures 13–16. Like other mites, developmental stages can be easily recognized by leg number (larvae have six legs) and genital development (Fig. 17). Chaetotaxic differences and femoral divisions are also helpful (Tables 1, 6). All immature stages appear soft bodied (despite dorsal sclerites) and vary in color from light green or purple to yellowish-white (Fig. 12).

Due to the unique armored morphology of Trachymolgus, other interesting developmental changes are present. These are discussed below.

Dorsal sclerites and setae.None of the immature stages of Trachymolgus purpureus have complete dorsal shields as seen in the adult. This is unlike Trachymolgus jesusi, which was described as having an armored tritonymph and unsclerotized proto- and deutonymphs. In Trachymolgus purpureus, all stages have dorsal sclerites. Shield sculpturingis underdeveloped in the larva with foveolate indentions absent but pits present (Fig. 13); protonymphs also lack foveolate indentions, but the pits are more organized, reminiscent of the indentions (Fig. 14); deutonymphs begin to develop foveolate indentions (Fig. 15), which are nearly complete in the tritonymph (Fig. 16). The proterosomal shield of the larva does not encompass the posterior pair of eyes, and the anterior crown is not developed, leaving the gnathosomal membrane appearing as a collar. The protonymph has a well-developed proterosomal shield that encompasses all eyes and has a complete crown. Hysterosomal shield of the larva only encompasses c1 and d1; nymphal stages also encompass e1. Small sclerotized regions containing pits, but not foveolate indentions, are present around c2 in the deuto- and tritonymphs. A posterior shield encompassing h1, contiguous with the hysterosomal shield in adults, is present in nymphal stages, but not larvae. Larvae completely lack f2.

Lateral shields.Lateral shields are present in deuto- and tritonymphs (Figs 15, 16), but do not encompass h2 or ih, as in adults (Fig. 3). Furthermore, in addition to lateral shields, larvae lack h2. Lyrifissure ih was not found in any immature stage.

Pseudotracheae.As described for Trachymolgus jesusi, pseudotracheae are lacking in the larva and protonymph, but are well-developed in the deutonymph (Fig. 17).

Membranes.As discussed above, adult Trachymolgus purpureus striations are accompanied with bumps (Fig. 5b), unlike other bdellid membranes that exhibit fingerprint-like striations. However, larvae and protonymphs lack bumps and have typical fingerprint-like striations (Figs 13, 14). Membrane bumps begin to develop on the deutonymphal dorsum (Fig. 15), and are well developed in the tritonymph (Fig. 16). All stages have normal, fingerprint-like striations on the venter.

In the early 1980s, Trachymolgus was collected by Cal Welbourn on a rocky bluff in the Buffalo National River (Arkansas). John Kethley recollected three specimens from the same bluff a few years later. Another specimen (one female) was collected by Evert Lindquist in the St. Lawrence Islands National Park, Canada (Smith et al. 1996), but the specimen has since been lost. Since then, we have collected this seemingly restricted, rare mite from a wide variety of microhabitats including litter, talus, rock outcrops and bluffs, moss, cedar stands, hardwood stands, and in both wet and dry conditions. Furthermore, the range is potentially not restricted to the Ozark highlands. Amusingly, we collected one tritonymph and one adult from leaf litter less than 200ft from where the Ohio State University Summer Acarology Course is taught (downtown Columbus, Ohio). Morphologically, these specimens cannot yet be distinguished from Trachymolgus purpureus, potentially extending the range to eastern U.S. We were able to extract DNA from one of these specimens and will publish our findings later.

The known distribution of North American Trachymolgus is Mexico (Trachymolgus jesusi), Ozark highlands (Trachymolgus purpureus), central Ohio (undet. species), and the northern Appalachian mountains (undet. species). Other groups have a similar distribution, and the biogeographic affinity between the Ozark and Appalachian mountains, and between Mexico and the eastern U.S. has been well documented. Examples include mosses (Crum 1952; Redfearn 1986), higher plants (Braun 1955; Dressler 1954; Miranda and Sharp 1950; Watson 1891), fungi (Miranda and Sharp 1950; Sharp 1948), snakes, flying squirrels, and plethodontid salamanders (see Martin and Harrel 1957). Recently, a mite was implicated as sharing this affinity (Skvarla et al. 2011). It is tempting consider Trachymolgus purpureus as representative of these biogeographic events, but much more sampling is necessary before this conclusion can be justified.

Trachymolgus purpureus seems to have extremely high temperature tolerances. They were found crawling on rock surfaces in direct sunlight during a drought in the hottest and driest time of year (August), and were collected near the surface during the winter. When preparing live specimens for LT-SEM, mites are set atop a metal bar that is subjected to liquid nitrogen fumes which freezes them mid-stride for imaging. When Trachymolgus purpureus was subjected to liquid nitrogen temperatures however, they would simply run, curl their legs, and roll off the plate (see Fig. 18a). This made imaging live specimens very difficult.

LT-SEM imaging illuminated another behavioral characteristic of Trachymolgus purpureus. Though other bdellids have been known to orally produce silk to tether prey (Alberti 1973, Krantz and Walter 2009), silk production in Trachymolgus was not previously known. When subjected to liquid nitrogen, Trachymolgus purpureus would charge its gnathosoma with silk, making investigation of chelae impossible on living specimens (Fig. 11d). One specimen tethered itself to the plate before rolling off (Fig. 18), potentially using silk as a dragline as has been described in many spiders.

Feeding behavior.We observed a tritonymph of Trachymolgus purpureus feeding on a small mite approximately 200–250m long. Unfortunately, the prey could not be retrieved for identification. The tritonymph fed with prey elevated from the ground. There seemed to be a droplet surrounding the bite site, interpreted here as silk seen in Figures 11d. We hypothesize that Trachymolgus purpureus uses a drop of silk at the bite site to act as a gasket when sucking prey fluids.

(27 individuals on slides). HOLOTYPE: female, collected from leaf litter, USA, Arkansas, Washington Co., Devil’s Den State Park (35°46.817 N, 94°14.750 W), 23 Sep 2009, by JR Fisher & MJ Skvarla, APGD 09-0923-006.

PARATYPES: Female (n=7): 2 individuals collected from leaf litter on rocky slope, USA, Arkansas, Washington Co., Devil’s Den State Park (35°46'50.1N, 94°14'45.9"W), 28 Aug 2008, by APG Dowling, APGD 08-0828-004 ● 2 individuals collected from leaf litter on rocky slope, USA, Arkansas, Washington Co. Devil’s Den State Park (35°46'50.1"N, 94°14'45.9"W), 30 Aug 2009 by JR Fisher, APGD 09-0830-001 ● 1 individual collected from leaf litter, USA, Arkansas, Newton Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W), 7 Sep 2009 by JR Fisher, APGD 09-0907-005 ● 1 individual collected from American beech leaf litter, USA, Arkansas, Newton Co., Buffalo National River, Boen Gulf (35°52.062 N, 093°24.092 W), 14 Mar 2010 by JR Fisher, APGD 10-0314-019 ● 1 individual collected from litter on rocky bluff, USA, Arkansas, Newton Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W), [date unknown] by Cal Welbourn, OSAL 0061853. Male (n=5): 1 individual collected from rocky overhang, USA, Arkansas, Washington Co., Devil’s Den State Park (35°46'50.1N, 94°14'45.9"W) by APG Dowling, APGD 08-0822-001 ● 1 individual collected from cedar litter, USA, Arkansas, Washington Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W) by JR Fisher, APGD 09-0802-006 ● 1 individual collected from leaf litter on rocky slope, USA, Arkansas, Washington Co. Devil’s Den State Park (35°46'50.1"N, 94°14'45.9"W), 30 Aug 2009 by JR Fisher, APGD 09-0830-001 ● 1 individual collected from leaf litter on rocky slope, USA, Arkansas, Washington Co. Devil’s Den State Park (35°46'50.1"N, 94°14'45.9"W), 30 Aug 2009 by JR Fisher, APGD 09-0830-003 ● 1 individual collected from leaf litter, USA, Arkansas, Newton Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W), 7 Sep 2009 by JR Fisher, APGD 09-0907-005. 1 individual collected from leaf litter, USA, Arkansas, Newton Co., Buffalo National River, Boen Gulf (35°52.062 N, 093°24.092 W), 10 Apr 2010 by APG Dowling. Tritonymph(n=6): 3 individuals collected from cedar litter, USA, Arkansas, Washington Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W) by JR Fisher, APGD 09-0802-006 ● 1 individual collected from oak litter, USA, Arkansas, Washington Co., Buffalo National River, Steel Creek trail (36°01'56.2"N, 93°20'01.5"W) by JR Fisher, APGD 09-0802-001 ● 1 individual collected from leaf litter, USA, Arkansas, Newton Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W), 7 Sep 2009 by JR Fisher, APGD 09-0907-005 ● 1 individual collected from litter on rocky bluff, USA, Arkansas, Newton Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W), [date unknown] by John Kethley, FMNH 2. Deutonymph (n=4): 3 individuals collected from cedar litter, USA, Arkansas, Washington Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W) by JR Fisher, APGD 09-0802-006. 1 individual collected from leaf litter on rocky slope, USA, Arkansas, Washington Co. Devil’s Den State Park (35°46'50.1"N, 94°14'45.9"W), 30 Aug 2009 by JR Fisher, APGD 09-0830-002. Protonymph (n=2): 1 individuals collected from leaf litter on rocky slope, USA, Arkansas, Washington Co., Devil’s Den State Park (35°46'50.1N, 94°14'45.9"W), 28 Aug 2008, by JR Fisher & MJ Skvarla, APGD 08-0828-004 ● 1 individual collected from cedar litter, USA, Arkansas, Washington Co., Buffalo National River, Roark Bluff (36°01'56.2"N, 93°20'01.5"W) by JR Fisher, APGD 09-0802-006. Larva (n=1): 1 individual collected from oak litter, USA, Arkansas, Washington Co., Buffalo National River, Steel Creek trail (36°01'56.2"N, 93°20'01.5"W) by JR Fisher, APGD 09-0802-001.

This species is named for the Latin "purpureus", meaning purple.