Ploegia occulata, Published, 2007

Published, First, 2007, Chironomid midges from early Eocene amber of France (Diptera: Chironomidae), Zootaxa 1404, pp. 1-66 : 37-38

Ploegia occulata n. sp.

( Figs. 34, 35)

Etymology: This species is named to note the eyes without a distinct dorsomedial extension.

Diagnosis: As stated above for the genus.

Description: Head 0.26 mm long, deformed; ocelli absent; antenna 0.4 mm long, much longer than head, distinctly hairy (shortest setae 0.01 mm long, longest 0.24 mm long), pedicel broad and short, rounded; apex of terminal flagellomere rounded, without apical nipple, but with apical rosette of setae; eye bare, without dorsomedial extension; mouthparts lacking functional mandibles; 5 palpomeres with setae; frontal, postocular, inner and outer vertical setae absent. Thorax more than 0.4 mm long, 0.18 mm wide, 0.3 mm high; postnotum bare, with longitudinal median groove; surface of scutellum with 4 long setae in 1 row; scutal tubercle not visible; acrostichals absent, dorsocentrals uniserial; scutum with median longitudinal groove; 2 prealar setae, no supraalar setae; epimeron II and preepisternum bare. Wing macropterous, 0.58 mm long, 0.22 mm wide, hyaline, membrane bare; anal vein An 2 absent; radius with 3 branches R 1, R 2+3 and R 4+5, R 2+3 not divided into R 2 and R 3; only M 1+2 and M 3+4 present; cross­vein MCu absent; squama bare. Halter 0.3 mm long. Fore tibia 0.24 mm long, tarsus 0.42 mm long; mid femur 0.28 mm long, tibia 0.26 mm long, tarsus 0.28 mm long; hind tibia 0.24 mm long, tarsus 0.36 mm long; ta4 of all legs cylindrical, not cordiform; fore tibia with 1 long spur, mid and hind tibiae with 2 long spurs, hind tibial comb well developed. Abdomen 0.82 mm long, 0.1 mm wide; gonostylus 0.05 mm long, 0.008 mm wide, simple, elongate, with strong subapical megasetae, inner surface covered by numerous short setae, hinged to gonocoxite and folded inward; gonocoxite 0.09 mm long, 0.02 mm wide, without visible setae on outer surface; inferior volsella subtriangular with setae apically; anal point narrow and short, 0.05 mm long, 0.03 mm wide at base.

Discussion: Placement of this fossil in the Orthocladiinae is supported by the characters stated above. In the key to the Holarctic orthocladiine genera of Cranston et al. (1989), Ploegia n. gen. would fall near the recent genus Chasmatonotus . But Chasmatonotus differs from Ploegia by the following characters: male antenna short, plume reduced with only five flagellomeres; anepipreepisternals present; anal lobe strongly obtuse; squama without setae (but sometimes up to 5 setae present); pseudospurs present on tarsomeres 1 and 2 of mid and hind legs; and anal point prominent, short and with short fine setae. All these characters are absent or different in Ploegia . Parachasmatonotus differs from Ploegia by the following characters: dorsocentrals uniserial and biserial, gonostylus short and robust; and anal point narrow and elongate. The presence of setae on the wing membrane, a dorsomedian extension of the eye, and the bifurcate gonostylus in the genus Pseudochasmatonotus exclude affinities with our fossils. The eye with a dorsomedial extension and an anal point narrow and elongate in Chasmatonotoides exclude affinities with Ploegia . For these reasons we establish a new genus.

Material: Holotype PA 132 (3/12) (male), associated with two other paratypes, all females; paratype PA 9(1/6) and PA 2894, both males.

FIGURE 35. Ploegia occulata n. sp., holotype PA 132 (3/12), drawing of male genitalia (scale bar = 0.1 mm).