Agrenia falcula, Fjellberg, Arne & Bernard, Ernest C., 2009

Fjellberg, Arne & Bernard, Ernest C., 2009, Review of Agrenia Börner, 1906 with descriptions of four new species from North America (Collembola, Isotomidae), Zootaxa 2306, pp. 17-28 : 25-27

Agrenia falcula n. sp.

Figs. 1 E, F, H, N; 2B; 5A, B; 6C

Type material. Holotype (ethanol) and 43 paratypes, USA, North Carolina, Roan Mountain, Powers Branch, Southern Appalachian Highlands Conservancy, seep, elevation 1,423 m, 14.VI.2000, P. Jennings and A. Trently coll. Additional material examined: Two samples from USA, North Carolina, Haywood County, Great Smoky Mountains National Park, Purchase Knob, A. Fjellberg, coll., June 2007. Holotype and 25 paratypes deposited in the National Museum of Natural History, Washington, D.C.; remaining paratypes deposited in the University of Tennessee Entomology Collection.

Description. Size up to 1.4 mm, reproductive male 1.1 mm. Dorsal side of thorax and abdomen bluish or violet brown, usually pale ( Fig. 5 A). Broad midsections of Th. II-III and Abd. V-VI generally darkest. Posterior edges of tergites narrowly darkened. Tergites without sharp middorsal line. Head very pale, almost white, dark pigment present only as a middrosal occipital spot behind the dark eye fields ( Fig. 5 B). Area between eyes and antennal base diffusely darkened in large specimens. Mouth region and sides of head completely unpigmented. Head shape weakly prognathous ( Fig. 2 B). Antennae violet blue, 1.7–2.0 times length of head diagonal. Legs light blue, furca unpigmented. Maxillae with short, unmodified lamellae, lamella 1 slightly bypassing tip of capitulum ( Fig. 1 N). PAO oval, length about 1.4 times diameter of nearest ocellus. Setae on head and body short, thin, delicate, and sparse, of uniform length. Setae along frontoclypeal edge not differentiated. Ventral tube with 1–5 anterior setae on each side, 6–13 lateral setae, and more than 20 caudal setae. Retinaculum with 15–20 setae. Claws very slender, with small indistinct tooth at middle of inner edge; tunica short, claw index 3.0–3.9 ( Fig. 1 H). Mucro slender, with apical and subapical teeth of similar size; basal tooth strong ( Fig. 6 C); ventral edge straight, with broad lamella; mucronal seta absent; differentiated subapical seta on dens not reaching beyond tip of mucro ( Figs. 1 E-F). Reproductive males with unmodified setae on tip of abdomen.

Etymology. The name reflects the thin, slender claws ( falcula [L]: little sickle).

Discussion. The small body size, elongate mucro without lateral seta, short subapical seta on dens, and very slender claws with small tunica differentiate this species from other Agrenia . The mucro is similar to that of A. lamellosa , but in that species the lateral seta is present ( Fjellberg 1988). For separation from A. tarashchukae n. sp., see below. Only summer animals were seen. Winter samples may have specimens differing in characters of claws, mucro and antennae.

If the samples are representative, this species is the smallest Agrenia known. In particular, a reproductive male of only 1.1 mm is unusual. These small adults have "juvenile" traits, e.g., relatively short antennae, few setae on ventral tube, pale colour, and short subapical seta on the dens. We have considered the possibility that A. falcula n. sp. may be small A. parkeri that will develop typical characters of the latter (e.g., long subapical seta on dens) after continued growth. The existence of different reproductive "morphs" appearing during continued growth was described in A. polymorpha ( Fjellberg 1986) . Although we have no clear evidence that A. falcula and A. parkeri are conspecific, the case should be examined with molecular methods or with longterm studies of field/laboratory populations.

Distribution and ecology. This species is known so far only from high elevations of the southern Appalachian Mountains, in damp moss along cold streams, seeps, and springs.

Figures

FIGURE 1. A-G, mucro shapes of Agrenia spp. A. A. extrema n. sp., lateral view; B. A. extrema n. sp., dorsal view; C. A. parkeri n. sp., winter form; D. A. parkeri n. sp., summer form; E. A. falcula n. sp., ventral view showing the broad ventral lamella; F. A. falcula n. sp., lateral view; G. A. tarashchukae n. sp. H-K, claws of hind legs. H. A. falcula n. sp.; I. A. tarashchukae n. sp.; J. A. parkeri n. sp., winter form; K. A. extrema n. sp. L-N, maxillae. L. A. extrema n. sp., ventral side (left) and inner side (right); M. A. agilis, inner side; N. A. falcula n. sp., ventral side.

FIGURE 2. Head shape in Agrenia spp. A. A. parkeri n. sp.; B. A. falcula n. sp., reproductive male.

FIGURE 5. Agrenia falcula n. sp., holotype. A. Habitus; B. Dorsum of head. Scale bars = 500 μm.

FIGURE 6. Agrenia spp. A-C, mucrones. A. A. tarashchukae n. sp.; B. A. agilis; C. A. falcula n. sp.; D-E. Tips of Ant. IV. D. A. extrema n. sp.; E. A. agilis. Scale bars = 20 μm.