Dixella intacta Greenwalt and Moulton

Greenwalt, D, 2016, The first fossil New World Dixidae with a critical discussion of generic definitions, Palaeontologia Electronica 19 (3), pp. 1-32 : 4-7

Dixella intacta Greenwalt and Moulton , new species

Figures 1 , 2 , 3.1 , 4.1 , 5

zoobank.org/ B50B1127-CA1E-4395-9A74-60B1AD5701CE

Etymology. The specific epithet is Latin for “untouched”, an indication of the intact nature of this fossil.

Holotype. Dixella intacta Greenwalt and Moulton , female; NMNH, USNM 546204 .

Type Horizon. Middle Eocene Coal Creek member, Kishenehn Formation.

Type Locality. Deep Ford site, Middle Fork of the Flathead River (Pinnacle, Montana) .

Differential Diagnosis. Distinguished from all other fossil Dixidae based on the presence of one or more of the following character states: distinct stylized spade-shaped cercus (similar to Dixa brevis Garrett, 1924 ), first flagellomere very slightly fusiform, antenna length much more than combined lengths of head and thorax, wing length/body length ratio equal to one, and apex of R 1 closer to C than to R 2.

Description. Adult female ( Figure 1 ), body length 4.5 mm.

Head. Black. Eyes dichoptic, large, oval with dorsal-ventral height (0.45 mm) greater than width (0.40 mm). Eyes separated by 0.12 mm. Maxillary palpus not visible. Antenna brown, 2.4 mm in length ( Figure 2.1 ). Scape barely visible, small, approximately 40 μm in width. Pedicel subspherical, 104 μm wide, 118 μm long. Antenna with 14 flagellomeres, each setose. F1 very slightly fusiform, 40 μm wide; F2–F4 widths gradually decrease to 30 μm. F5 (22 μm) more slender than F4. F5, subsequent flagellomere widths gradually decrease to 7 μm at F14. Flagellomere lengths/ widths (in mm) as follows: F1 (0.30/0.04), F2 (0.12/ 0.04), F3 (0.16/0.03), F4 (0.17/0.03), F5 (0.23/ 0.02), F6 (0.20/0.02), F7 (0.19/0.02), F8 (0.190.01), F9 (0.18/0.01), F10 (0.15/0.01), F11 (0.13/0.01), F12 (0.12/0.01), F13 (0.12/0.01), F14 (0.13/0.01).

Thorax. Length 1.3 mm. Dark brown medial, lateral vittae covering most of scutum except for posteromedial portion and four medial light brown spots connecting medial, lateral vittae ( Figure 2.2 ). Scutellum yellow. Acrostichal setae at lateral margin of medial vitta. Setae present along posterior margin of scutellum, lateral surface of mediotergite.

Wings. Length 4.28 mm, width 1.37 mm ( Figure 3.1 ). L/W ratio = 3.12. Vein R 2+3 arched. Sc apex even with Rs origin. Crossvein r-m single veinwidth distal to Rs bifurcation, slightly sigmoidal. Crossvein m-cu even with posterior point of r-m. A1 apex slightly basal to Cu bifurcation, distal to Sc apex and Rs origin. R 2+3 bifurcation basal to M bifurcation. Length ratios R 2 /M 2, M 2 /M 1, M 2 /M 1+2, R 2+3 /R 3 = 2.6, 0.61, 0.54, 0.49, respectively. Vein CuP present. Wing surface covered with microtrichae; veins, margin of wing with spiniform setae 55 ± 15 μm in length. Haltere dark brown, length 0.59 mm with setae on anterior margin of proximal end, knob; knob spherical, diameter 155 μm; base black.

Legs. All legs setose; hind tibia expanded distally. Foreleg femur, tibia, 5 tarsomeres lengths 1.38, 1.32, 0.9, 0.36, 0.23, 0.12, 0.14 mm, respectively. Midleg femur, tibia, 5 tarsomeres lengths 1.74, 1.58, 0.76, 0.42, 0.27, 0.14, 0.15 mm, respectively. Hind leg femur, tibia, 5 tarsal segments lengths 1.8, 1.83, 1.52, 0.53, 0.34, 0.18, 0.13 mm, respectively. Claws without teeth ( Figure 4.1 ).

Abdomen and genitalia. Abdomen brown, setose, length 2.84 mm (not including cercus); sternite 8, tergite 9 dark brown/black, more heavily setose than anterior portion of abdomen. With single sclerotized spermatheca, spherical, 0.17 mm in diameter. Cercus black, setose, shaped like stylized spade, length 0.12 mm ( Figure 5 ).

Male unknown.

Figures

FIGURE 1. Habitus of Dixa intacta, holotype. Scale bar equals 3 mm.

FIGURE 2. Morphological features of Dixa intacta. 1, Antennae with individual flagellomeres delineated; 2, Dorsal aspect of the thorax. Scale bars equal 0.5 mm for both figures.

FIGURE 3. Line drawings of wings. 1, Dixella intacta; 2, D. eomarginata; 3, D. curvistyla. Wing venation is from McAlpine (1981). Scale bar equals 1 mm.

FIGURE 4. Tarsal claw teeth of the Kishenehn Dixella. 1, Dixella intacta left metatarsal claw; 2, D. curvistyla left metatarsal claw; 3, D. spinilobata right metatarsal claw. Arrows point to teeth. Scale bars equals 50 μm.

FIGURE 5. The terminalia of Dixa intacta. 1, Posterior portion of abdomen including the spermatheca; 2, Cerci. Scale bars equal 0.5 mm (1) and 0.05 mm (2).