Azana akarenos Kerr and Greenwalt, 2022

Greenwalt, Dale E., Amorim, Dalton De Souza, Hauser, Martin, Kerr, Peter H., Fitzgerald, Scott J., Winterton, Shaun L., Cumming, Jeffrey M., Evenhuis, Neal L. & Sinclair, Bradley J., 2022, Diptera of the Middle Eocene Kishenehn Formation II, Palaeontologia Electronica (a 22) 25 (2), pp. 1-52 : 14-17

Azana akarenos Kerr and Greenwalt sp. n.

Figures 6-7

zoobank.org/ 465EEEB4-8583-4425-8878-FF79F8A4D252

Type species. Azana scatopsoides Walker, 1856 , by monotypy (= Azana anomala Staeger, 1840 ).

Holotype. Female, USNM 625099 , deposited in the Paleobiology collections of the National Museum of Natural History in Washington, D.C.

Locality and horizon. Spring site, Middle Fork of the Flathead River (Pinnacle, Montana, USA). Middle Eocene Coal Creek Member, Kishenehn Formation.

Etymology. The species epithet is derived from the Greek term akarenos , meaning headless.

Diagnosis. Head is either not present or barely visible on left side of thorax below anterior margin of wing; thorax arched; costa produced beyond tip of R 4+5; subcosta short, ending free; r-m long, arising near base of wing; Rs essentially absent as R 1 and r-m veins touch; M 1 obsolete at its base, M 4 faintly present at wing margin.

Description (female). Body length 2.05 mm (from terminus of genitalia to middle of scutum); scutum, scutellum, abdomen and terminalia dark brown, legs light brown ( Figure 6 ). Wings 1.61 mm (right) and 1.66 mm (left) in length, 0.64 mm wide, lightly infuscate without markings, membrane densely microtrichose, veins thick and brown (except base of M 1 obsolete); costal vein extends beyond R 4+5, approximately 0.18 of distance between R 4+5 and M 1; Sc short; R 1 reaching C at 0.47 times length of wing; Rs imperceptible, R 1 touching longitudinal rm/R 4+5; ratio of R 1 to R 4+5 0.27 (given difficulty of locating Rs, this value could range from 0.24 to 0.27); r-m long and longitudinal; M 1 obsolete at base, but well defined in apical 2/3, extending straight to wing margin far beyond apex of wing; M 2 absent, M 4 present at right wing margin, about 0.2 mm in length (about twice the distance between M 4 and CuA), delaminated and very faint in left wing; CuA strong, more angled than smoothly curved (i.e., with defined inflection point) ( Figure 7 A-C); halter relatively small, 0.19 mm long, knob 0.07 mm wide, stem and knob light brown. Femur covered in short, light brown setae;

PALAEO- ELECTRONICA.ORG all tibial setae shorter than width of tibia; mid and hind tibiae with row of several larger spines; abdomen 1.3 mm long, 0.62 mm wide; tibial spurs 1:2:2 ( Figure 7D ). Gonostylus absent; abdomen suggestive of a female ( Figure 6 ).

Male. Unknown.

Synimpressions. Chironomidae (32, one at mideclosion), Parasitica ( Hymenoptera ) (1), Corixidae (2), Hemiptera (1), Dipteran pupae (6), unidentified larvae (2), Diptera (2)

Remarks. Mycetophilidae is a diverse group of small nematocerous Diptera with approximately 4,900 described species including 403 described fossil species ( Evenhuis and Pape, 2021). However, the Sciophiline genus Azana contains only 13 extant species, although it is widely distributed ( Kerr, 2010). Species of the genus are easily distinguished by reduced wing venation; Sc short, ending free; M 1 obsolete at its base; M 4 vestigially present, near wing margin. The habitus of extant species of Azana provides a rationale for the missing head of A. akarenos . The middle of the scutum is the anterior-most aspect of the bodies of these flies, with the entire head tucked below the ventral aspect of the thorax. From a dorsal view, therefore, the head is typically not visible. In the fossil, the head is probably mostly buried in the shale matrix although a portion of it may be seen to the left, near the base of the wing (computed tomography using a GE Phoenix micro CT failed to image the specimen.). Azana akarenos is distinct from the single fossil known for the genus, A. rarissima Meunier , described from Baltic amber by Meunier (1904). Meunier (1904) described the antenna of A. rarissima , figured its wing and stated that the 2.0 mm-long insect had tibial spines and setose tarsi. The two Eocene species are distinguished from one another based on the ratio of R 1 to R 4+5, 0.22 in A. rarissima and 0.24-0.27 in A. akarenos . More obvious, however, is the difference in the length of Rs. In A. akarenos , this vein – in both the left and right wings – is short to the point of not existing; R 1 and the junction of r-m and R 4+5 touch oneanother. In contrast, the length of Rs in A. rarissima is 80% of the distance between R 1 and C, at that point.

Given that differentiation of the various species of the genus are based mostly on characteristics of the head and male terminalia, and color, it would be futile to attempt a detailed comparison of A. akarenos with extant members of the genus. However, the four extant species of Azana from North America differ from A. akarenos with respect to the same character states used to distinguish the two fossil species of the genus. Azana malinamoena Kerr, 2010 , A. frizzelli Kerr, 2010 and A. sinusa Coher, 1995 (= A. pilosa Taber ) have distinctly longer R 1 veins relative to the length of R 4+5 (ratios = 0.37, 0.34, 0.39 and 0.36, respectively). In addition, all three of these species have a distinct Rs vein, although in A. sinusa the length of Rs is only about the width of the vein itself ( Coher, 1995; Taber, 2017). In A. atlantica Oliveira and Balbi, 2008 (in Amorim et al., 2008a), collected in Brazil, Rs and r-m are separated by slightly more than a vein width but the base of r-m is absent and “r-m indistinct from Rs” ( Amorim et al., 2008b). Again,

PALAEO- ELECTRONICA.ORG the ratio of R 1 to R 4+5 is large, in this case 0.37 (vs. 0.27 in A. akarenos ).

Figures

FIGURE 6. Azana akarenos Kerr and Greenwalt sp. n. female, USNM 625099. Habitus; Insert: Terminalia. Scale bar equals 2.0 mm.

FIGURE 7. Azana akarenos Kerr and Greenwalt sp. n. USNM 625099. A, Left wing, arrow denotes vestigial M4; B, Sc, right wing; C, Left wing macrotrichia; D, Row of spines on right mid tibia (small arrows), tibial spur (large arrow). Scale bars equal 0.5 mm (A), 0.1 mm (B,C), and 0.2 mm (D).