Geodiscelis (Thaumoediscelis) Packer and Dumesh

Packer, Laurence & Dumesh, Sheila, 2014, Two new species of Geodiscelis Michener & Rozen (Hymenoptera: Apoidea: Colletidae) with a phylogenetic analysis and subgeneric classification of the genus, Zootaxa 3857 (2), pp. 275-291 : 286-287

Geodiscelis (Thaumoediscelis) Packer and Dumesh , new subgenus

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Type species. Geodiscelis thaumaskelos Packer, 2009 . Here designated.

Diagnosis. This is the only xeromelissine with a single metatibial spur. This character works for both sexes but the male has a truncate process where the outer metatibial spur would be, this process is immovably fused to the tibia. Each sex has additional diagnostic characteristics: the male hind leg is enormously modified and the metabasitarsus in particular is uniquely modified, being as wide as it is long, deeply concave on the anterior surface and trilobed—no other bee known to us has such an unusually modified metabasitarsus; the female S2 is almost glabrous, which is unique among the xeromelissines.

Description. Both sexes with extensive yellow on lower paraocular area. Male protibia black basally. Metasomal terga mostly pale, dark areas mostly maroon; lacking basal bands of appressed squamose pubescence, minute silvery hairs present. Clypeus and lower paraocular area shiny, lacking distinct imbricate microsculpture. Frontal area and mesoscutum with punctures crowded, dull. Galeal comb with a few teeth. Mandible with well developed subapical tooth. Malar space absent. Anterior tentorial pit elongate, almost attaining apex of clypeus. Supraclypeal area strongly concave in profile. Metasternum between metacoxae broad, as wide as long (both measurements>2MOD) widening posteriorly in male, narrower in female (L:B 1.2:1 both <1.5MOD). First abscissa of M+Cu of hind wing subequal in length to 2nd. Male hindleg considerably modified, femur and tibia strongly swollen, basitarsus with complex structure. Both sexes lacking inner metatibial spur; male with robust process where inner metatibial spur might be expected but this immovably fused to tibia. Horizontal surface of metapostnotum shorter than scutellum, longer than metanotum. Sclerotized portion of proctiger, widely separated, not extending mesad. Male S6 with apex rounded. S7 apicodorsal lobe narrowly extended posteriorly, margin with row of hairs, bearing hair tuft anteriorly. S8 apical process narrowly oval; posterior margin of lateral lobe transverse with posteriorly oriented convexity laterad. Gonobase with apicoventral rim with large median process broadening from base to apex. Gonoforceps without subapical medial angulation. Gonostylus moderately long, broad, curved posteromesad; retrorse lobe large, broad. Female sternal scopa considerably reduced, S2 almost glabrous.

Included species. Geodiscelis thaumaskelos Packer 2009 .

Etymology. The subgeneric name is a combination of the specific epithet— thaumaskelos and Oediscelis, a genus-group name within the Xeromelissinae that means “swollen thighs”: a descriptor that applies only to this species within the genus.

Comments. This subgenus is known only from an arid valley in western Argentina and contains the southernmost species in the genus.

An interesting observation not previously made concerning this taxon is sexual dimorphism in the form of the metasternum. In the male it is considerably broadened posteriorly and almost on the same plane as the mesopleuron immediately in front of it ( Fig. 36 ). In the female, it is much narrower, not considerably expanded posteriorly, and recessed dorsad ( Fig. 37 ). The metasternum of the female is most similar to that of related species and genera and the unusual modification of the male is undoubtedly an autapomorphy associated with the extreme modifications of the hind legs.

Figures

FIGURES 36 − 37. Geodiscelis thaumaskelos mesosomal venter to show sexual dimorphism in metasternum. 36. Male; 37. Female. Scale bar = 0.5 mm. Note that the magnification differs between the two images.