Palaeopetia dorsalis, Grimaldi, 2018

Grimaldi, David A., 2018, Basal Cyclorrhapha In Amber From The Cretaceous And Tertiary (Insecta: Diptera), And Their Relationships: Brachycera In Cretaceous Amber Part Ix David A. Grimaldi, Bulletin of the American Museum of Natural History 2018 (423), pp. 1-97 : 1-97

Palaeopetia dorsalis , new species

Figures 11 ; 38A, B, E, H ; 39 , 40B

DIAGNOSIS: Differs from P. terminus , n. sp., also in Burmese amber, by smaller size, wing shorter and broader (L/ W 1.77, vs 1.89), with microtrichia covering more of the wing membrane; arista situated dorso-preapically (vs. terminal); 1 (vs. 2) postalar seta; posteriormost notopleural seta slightly longer than others (vs. 2× the size); anteriormost scutellar seta nearly equal in size to adjacent one (vs. 0.3× the size); hind tibia with dorsal row of 3 strong setae (vs. 6, alternating with smaller, thick setae).

The Burmese amber species of Palaeopetia can be separated from all the compression-fossil species by the following venational differences: apical separation of Sc and R 1 ca. 0.5× their length (i.e., these two veins fused for greater distances in the amber species); cell cup is slightly shorter and wider, the apex less acute.

DESCRIPTION (based on unique female): Head: Eyes large, occupying most of dorsal and lateral portions of head, female dichoptic; eye bare, no differentiation of facets. Female frons: relatively narrow, sides parallel, width approximately equal to distance between outer margins of posterior ocelli; frons glabrous, without setae, possibly without setulae (obscure); presence/ absence of median furrow obscure. Ocelli well developed, raised above frons but not tuberculate; no ocellar setae; 2 short postocellars present. Occiput broad, gently and largely concave, lateral and dorsal margin near eye and vertex rimmed on each side with ca. 25 stout, stiff, flattened setae, lengths 6–8× diameter of eye facet. Occipital foramen very large, width ca. 0.3× occiput width. No vibrissa or genal setae. Antenna: Scape subcylindrical, short, with transverse row of 3 stout, black setulae dorsally; pedicel very short, rimlike, dorsal margin with row of 5–6 stout, short setae. Basal flagellomere large, laterally flattened, roughly drop shaped, with long groovelike seam on inner (mesal) surface, shorter seam on lateral surface, plus some apparent foveae (sacculi, sensu McAlpine, 2008). Arista bare; attachment dorsal-preapical, slightly lateral (not on dorsal edge), 3-articled, basal 2 articles small; total arista length 2.5× that of basal flagellomere. Mouthparts: Short, barely protruding beyond oral margin; palp 1-seg- mented, extended slightly past labellum; labellum small, prementum and clypeus not observable. Thorax: Brown, notum slightly convex (not dome shaped) in lateral view. Acrostichals numerous, fine, evenly scattered on notum (not in rows). One pair of dorsocentral setae, stout, close to scutellum, length ca. equal to that of apical scutellar setae; distance between dorsocentrals slightly greater than length of dorsocentral. Prescutellum well developed, lenticular, width almost equal to that of scutellum base. Scutellum with 4 pairs stout marginal setae, increasing in length apicad, apical pair upturned and slightly cruciate; dorsal surface of scutellum without fine setulae. One very long postalar seta, length ca. 1.8× the dorsocentral. Notopleural setae in row of four (entirely preserved on right side). No pleural setae present; prosternum not observable. Wing: Membrane entirely hyaline, no markings or infuscate areas; microtrichia absent except at wing margin between tips of R 2 +3 and CuA 2 +A 1. Wing short, broad, L/ W 1.77 (from tip of wing to level of crossvein h). Vein C ends at tip of R 4 +5. Sc long, joined to R 1 for 0.65× its length, separated at base and at apex, membrane slightly darkened between apical fork of Sc and R 1 . Stem of Rs short, fork of R 2 +3- R 4 +5 long, apices of Rs veins straddling tip of wing. Crossvein br-m very short, cell d present, L/ W 3.6, apically truncate (not acute) (dmcu perpendicular to M 2 and CuA 1). Basal cells bm and cup closed ; cell cup triangular; vein CuA 2 +A 1 complete, reaching wing margin; A 2 present, incomplete, anal lobe very shallow. Legs: Metafemur and metatibia slightly longer and thicker than in other two pairs of legs. Basitarsomere on all legs approximately equal in length to remaining, distal tarsomeres. All coxae with 2 setae (ventral on fore- and midlegs, dorsal on hind legs). Pro- and metafemur without setae; mesofemur with long, stout seta on anterior surface, ⅓ from femur apex. Protibia with short middorsal seta, 2 apical setae (lengths ca. equal to width of tibia). Mesotibia with 4 long setae: 2 midlength (anterior and posterior surfaces), 2 apical. Metatibia with 2 stout, long, lat- eral setae, row of 4 shorter fine ones on dorsal edge; 1 large ventroapical seta plus several smaller ones. Metabasitarsomere slightly expanded. Pretarsal claws well developed, strongly curved; pulvilli well developed, slightly shorter than claw; empodium not visible (probably small and setiform). Abdomen (female): Length ca. equal to that of head + thorax, width slightly greater than thorax; tapered apicad. Eight well-developed tergites visible, none with macrosetae, covered overall with decumbent setulae, no apparent color/pruinescence patterns; tergites extend laterally over pleural membrane. Sternites well developed, broad, lateral margins nearly touching tergites, 7 sternites visible (first one probably small, hidden). Female Terminalia: Largely membranous; terminal sternite (8?) divided medially into 2 small oval sclerites; hypoproct well developed, apically pointed; cerci well developed, 1-segmented, cercus broad, with apical half darkly pigmented. Spermathecae not visible.

SPECIMENS EXAMINED: Holotype, female, AMNH Bu-FB34, in Burmese amber. In good condition, largely well preserved except for loss/ damage of portions of thorax.

ETYMOLOGY: In reference to position of the arista on the basal flagellomere.

Figures

FIG. 11. Palaeopetia dorsalis, n. sp. (Ironomyiidae), in Burmese amber. A, B: Female holotype, AMNH Bu-FB34. A. Oblique dorsal habitus. B. Dorsal view of head. C. Paratype female, AMNH Bu-KL610.

FIG. 38. Palaeopetia n. spp. (Ironomyiidae) in Burmese amber. A, B, E, H. P. dorsalis, holotype male, AMNH Bu-FB34. C, D, F, G, I. P. terminus, holotype male, AMNH Bu-SE2/6. A, C. Midlegs. B, D: Portions of hind leg. E, F: antenna, lateral. G, H: Thorax, as preserved. I: Male terminalia, ventrolateral view.

FIG. 39. Palaeopetia dorsalis, n. sp. (Ironomyiidae) in Burmese amber, holotype female AMNH Bu-FB34. A. Female terminalia, ventral view. B. Antennae, oblique dorsal view.

FIG. 40. Wings of fossil Ironomyiidae in Burmese amber. A. Palaeopetia terminus, AMNH Bu-SE2/6. B. Palaeopetia dorsalis, AMNH Bu-FB34. C. Proironia gibbera, AMNH Bu-SE7.