Gnathisotoma spinolabris Fjellberg, 2010, sp. n.

Gnathisotoma spinolabris sp. n.

(Figs. 78–92, 114, 115G)

Type material (all in alcohol, sex not checked). Holotype and 50 paratypes from "Alaska: Juneau. Mts. near Mendenhall Glacier, 58o29'N, 134o40'W, 13.VII.1980. On melt–water ponds, 975 m. alt., A. Fjellberg leg." (INHS).

Description. Body size up to 1.2 mm. Body shape slender, abdomen slightly pear-shaped, widening towards tip of abdomen, furca long (Fig. 115G). Head distinctly prognathous, with protruding mouth (Fig. 81). Abd. 5–6 fused without incision between the segments but with a clear gap in setal cover. Colour uniformly bluish black with white antennae, including the first segment. Tip of ant. 4 with a diffuse dark spot. Occipital area of head with a large crown-shaped white spot (Figs. 114, 115G). Legs pale beyond coxae, dens pale. Head with 6+6 large ocelli A–F, a small H ocellus also present. PAO elongated, slightly longer than diameter of nearest ocellus. Three setae associated with PAO (Fig. 83). Ant. 1 on ventral side with one short apical and three longer sensilla as well as 2–3 microsetae (Fig. 79). Ant. 2 with two lateral poorly differentiated setaceous sensilla near apex. Ant. 3 organ with two large pointed sensilla and two slender guards (Fig. 84). In lateral position on ant. 3 one small and one large sensillum near apex. Ant. 4 with bifurcate subapical pin seta, the subapical organite as a small peg in a pit. Labrum with 4 prelabral setae and 5,5,4 stiff spine-like setae inserted in distinct papillae (Fig. 80); apical edge with 4 low ridges; ventroapical ciliation very weak, in the shape of a simple irregular row. Central field of frontoclypeal area with 4–5 setae, two setae above posterior corner of labrum. Maxillary palp simple, with 4 stiff sublobal setae set close together. Labial palps modified, each split in two parts consisting of papillae A–B and C–E respectively (Fig. 90). Terminal sensilla of the papillae short; guards b3–b4 enlarged, strongly curved; guard e7 absent; lateral process (l.p.) on papilla E small, finger-like; four proximal setae present. Hypostomal papillae with a tiny seta-like H while h1–h2 are strong, curved (Fig. 91). Basal fields of labium with 4 median and 5 lateral setae. Head with 5–6 postlabial setae on each side of ventral line. Mandibles normal, with strong teeth. Maxillae strongly modified with a narrow 3-toothed capitulum and elongated lamellae passing tip of capitulum (Figs. 88–89); Lam.1 and 4 appear thin and transparent, without visible denticles or ciliations; Lam.2 and 5 have fine denticles like the short Lam. 3 and 6. Body integument smooth without visible granulation. Ground setal cover of body consists of rather long, thick, smooth setae. Macrochaeta strong, smooth, stiff (Fig. 82). Macrosensilla on tergites present as 55/55696, with some variation on abd. 3–5. All abdominal tergites with one or more (abd. 4) sensilla set in anterior position (Fig. 78). Posterior sensilla on abd. 1–4 inserted in the prow. Spine-like microsensilla as 10/000. Ventral tube 1+1(2) frontal, 3–4 lateral and 1–3 caudal setae. No ventral setae on thorax. Retinaculum with 4+4 teeth and 4–5 setae. Manubrium with blunt apical teeth and 0– 3 short ventroapical setae on each side; ventromedian part without or at most with 1–2 setae near base (Fig. 85). Dens dorsally crenulated, usually with 8 dorsal setae in basal 2/3 and one minute subapical setula (Fig. 87); ventroapical seta not differentiated. Mucro short and compact, with 4 sharp teeth and a large outer basal seta; inner lamella extends to tip of subapical tooth, not transformed to a secondary tooth (Fig. 92). Tibiotarsi with 11 apical setae (A1–7, T1–4), all acuminate. Inner side of tib.1–2 with 3+3 setae along the median line (as Fig. 72). Claws small, straight, inner tooth absent, lateral teeth very small or absent; unguiculus with a high dorsal lamella on last claw, less distinct on other claws (Fig. 86). Reproductive males without differentiated setal cover (nonepitokous).

Etymology. The name reflects the unusually "spiny" appearance of the labrum.

Discussion. Until the generic relationship of Gnathisotoma and Desoria is resolved, the present species is tentatively placed in the former genus due to similarity in maxilla and the small number of anterior setae on manubrium shared with the type species of the genus. It differs from the two Pyrenean species by presence of a mucronal seta and an increased number of tergal sensilla. The two South American species are not precisely described, but their colour is uniformly black including the antennae in patagonica Yoshii, and both are said to have a 3–toothed mucro apparently without lateral seta. Also one maxilla is figured with a very prominent 3-toothed capitulum, unlike other Gnathisotoma. Ocelli are said to be 5+5, although figured with 6 by Yoshii (1990, Fig. 4 I).

Distribution and ecology. Only known from the type locality in the coastal mountains above Juneau, Alaska, where a sample was "scooped" from the surface of water draining from the melting snow fields.