Oxelytrum selknan, Oliva, Adriana, 2012

Oliva, Adriana, 2012, A new species of Oxelytrum Gistel (Coleoptera, Silphidae) from southern Argentina, with a key to the species of the genus, ZooKeys 203, pp. 1-14 : 4-5

Oxelytrum selknan sp. n.

Oxelytrum biguttatum : Oliva & Di Iorio, 2008. Tierra del Fuego, forensic sample.

Description.

Large (13-16,5 mm in length), sturdy beetles, black in color, with a pair of subquadrate reddish spots on the margin of the pronotum. Antennomere 8 expanded into a disk (Fig. 1A). Eyes small, not prominent (Fig. 1A). Dorsum of pronotum and of elytra densely punctate. Pronotum flat, bearing two pairs of indistinct longitudinal costae, the outer pair basal, short, the medial pair about two thirds of the pronotal length, not reaching the anterior or the posterior margins. Elytra bearing each three longitudinal costae, the two inner ones reaching the posterior margin, the outer one interrupted about two thirds of elytral length. Elytral apices broadly rounded, in males a little produced at the sutural angle or at the segment of the margin comprised between the two innes elytral costae (Fig. 1B); in females expanded outwards. Protarsi of males with the four basal tarsomeres dilated, bearing thick adhesive hairs forming soles. Female styli short, wide, truncate at apex (Fig. 6A). Outer appearance entirely similar to Oxelytrum biguttatum (Philippi) (Fig. 5).

Male genitalia. Paramera narrow, weakly broadened in apical ⅓, apices blunt, turned inwards. Median lobe distinctly longer than paramera, in dry material triangular, narrowing evenly to the acuminate apex (Fig. 2A). Rehydrated material shows a spindle-shaped median lobe (Fig. 4A, 4B). Everted internal sac with apical cylinder covered in brown microtrichia, slightly constricted about the middle of its length; small rounded lobes basal to apical cylinder, large semi-globular lobe basal to smaller ones (Fig. 4A, 4B, 4C, 4D; small lobes marked by arrows).

Material examined.

Holotype, male. "Argentina/Tierra del Fuego". 14,5 mm. Two male paratypes: Male. "Valle Túnel /Dr. Witte/ Hyponecrodes/biguttatus Phil." 15,5 mm. Male. "Tierra del Fuego/Ushuaia/XII 1967" Leg. A. O. Bachmann. Four female paratypes: Female. “República Argentina/ Gob. Tierra del Fuego/190-/C. Bruch." 17 mm. Female. "Tierra del Fuego" 13 mm. Female. "Argentina/Tierra del Fuego" “32938” 16,5 mm. Female. “República Argentina/Santa Cruz/ II-190-/C: Bruch." “20959” "Hyponecrodes biguttatus". All in the collection of the MACN.

Etymology.

The name alludes to the Native American people, Selk’nan (also called Ona), who inhabited the land part of the Isla Grande de Tierra del Fuego until the end of the nineteenth century.

This species can be recognized by the male genitalia. This is the only species of Oxelytrum known so far that has the median lobe longer than the paramera. The general shape of the internal sac is similar in Oxelytrum selknam sp. n. and in Oxelytrum biguttatum Philippi, but in the latter the apical cylinder is not constricted and bears no microtrichia apparent under 25 ×, there are no smaller lobes at the base of the cylinder and there are two large basal semi-globular lobes, one ventral and the other dorsal (Fig. 4E, 4F). The paramera of Oxelytrum biguttatum are not broadened at the apex, and the median lobe is distinctly shorter than the paramera, parallel-sided (Fig. 2AB, 2D; 3B).

No other differences were found between Oxelytrum selknan sp. n. and Oxelytrum biguttatum . The latter species was described from Valdivia in S Chile. I have examined material from several localities in Magallanes and they all have a parallel-sided median lobe shorter than the paramera. The geographical barrier between the species appears to be the Magallanes strait. Oxelytrum biguttatum is found in S Chile, in the Patagonian tabl eland in Argentina, and in some mountain localities in SW Argentina. This species may have spread across the Andes through the present-day province of Neuquén. On the the other hand, Oxelytrum selknan sp. n. could have evolved in the main island of Tierra del Fuego (Isla Grande). Although the distances may appear small in the map, the straits are actually an effective barrier for flying insects. The presence of some specimens in the mainland could be explained by recent man-aided dispersion.