Litoleptis araeostylus Greenwalt, 2019

Dale E. Greenwalt, Daniel J. Bickel, Peter H. Kerr, Gregory R. Curler, Brian V. Brown, Herman de Jong, Scott J. Fitzgerald, Torsten Dikow, Michal Tkoč, Christian Kehlmaier & Dalton De Souza Amorim, 2019, Diptera of the middle Eocene Kishenehn Formation. I. Documenting of diversity at the family level, Paleontologia Electronica 22 (2), No. 50, pp. 1-56 : 26-28

Litoleptis araeostylus Greenwalt , sp. nov.

Figure 23 zoobank.org/ A3D6DD5B-109E-4C06-84AD-110E46CF4C54 Etymology. The specific epithet is a combination of the Latin term araios (thin, narrow) and stylus and refers to the thin seta at the end of the flagellum.

Holotype. USNM 624657 , deposited in the Department of Paleobiology , National Museum of Natural History (NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Type horizon. Middle Eocene Coal Creek Member, Kishenehn Formation.

Type locality. Dakin site, Middle Fork of the Flathead River (Pinnacle, Montana, USA).

Differential diagnosis. This species of Litoleptis araeostylus is distinguished by its small size, cerci widely separated, tergum 9 short, partially retracted within T8, tergum 10 absent, majority or entire length of the length of flagellum tapered, ending in a relatively long seta.

long,

Description

Female (Figure 23.1) 2.0 mm in length, not including cerci; head and notum black, abdomen reddish brown.

Head. Unfortunately, it is difficult to determine if the visible basal-most portion of the antenna is the pedicel or the basal bulbous portion of F1. Observable antennal length 0.257 mm; if pedicel not visible (this portion of the antenna lacks setae), basal portion of F1 bulbous, 48 μm long x 60 μm long, with thin tapering style 157 μm long and 18 μm wide at its base; needle-like seta approximately 40 μm in length at its terminus.

Thorax. Wing, 1.72 mm long and 0.65 mm maximum width (Figure 23.2-3). Halter, 0.3 mm in length, knob, 134 μm wide and 180 μm long, stem 65 μm wide. Legs without tibial spurs.

Abdomen and genitalia. Abdomen, 1.18 mm in length and 0.65 mm wide at maximum width; lengths and widths of T7, T8 and T9, 0.46 x 0.13, 0.34 x 0.16 and 0.22 x 0.36 mm, respectively. Basal half of T9 appears to be withdrawn into T8 (Figure 23.1 inset). Spermatheca not preserved/ sclerotized. Cercus 2-segmented, lengths and widths of C1 and C2 60 x 46 μm and 50 x 40 μm, respectively.

Allotype. Male unknown.

Syncompressions. Thysanoptera (3), Chaoboridae (8), dipteran pupae (3), Diptera (1), Corixidae (1), Bibionidae (1), Hymenoptera (1), Aphididae (1), Hemiptera (1).

Remarks

The family Rhagionidae consists of 47 genera and 756 described species. There are 89 species of fossil Rhagionidae mostly in extinct Mesozoic genera. Of the fossil species, 57 date to the Mesozoic and 27 to the Eocene, with 21 of the latter in Baltic amber. The oldest known Rhagionidae s.l., Gallia alsatica Krzemiński and Krzemińska, 2003 , is from the early Triassic. Solórzano Kraemer and Nel (2009) reviewed the fossil record of Rhagionidae . Litoleptis Chillcott, 1963 is a small genus with nine described extant members ( Imada and Kato, 2016). The EDNA (EDNA, 2017) and Bishop Museum fossil insect databases ( Evenhuis, 2017) list Litoleptis in the family Spaniidae Stuckenberg, 2001 , a taxon proposed by Stuckenberg, but rejected by Kerr (2010). The subfamily Spaniinae Nagatomi, 1982 , is unique within the Rhagionidae in the absence of a discal cell, tergite 9 short and withdrawn into T8, tibia, without spurs amongst other characters.

The only described fossil of Litoleptis , L. fossilis Arillo et al., 2009 , from Lower Albian San Just amber ( Spain) ( Arillo et al., 2009), is not closely related to either L. araeostylus or the extant members of the genus, in that the costa does not extend around the wing margin but terminates at R 5, the tibia of the middle leg (the only preserved leg) has a spur as well as marked differences in the female genitalia (e.g., cerci not widely separated). It also differs from all other species of the genus in that the stem of R and M are both longer than their forks, with R 4 curving anteriorly, parallel to the terminal portion of R 2+3.

The six extant species of Litoleptis from Japan have been divided into two groups, one of which contains only L. japonica Imada and Kato, 2016 . This species is differentiated from the others by a number of characters, including the presence of a long stout seta at the tip of the flagellomere, a character shared by L. araeostylus . Litoleptis japonica is differentiated from L. araeostylus by its larger size, 3.4 mm wing length vs. 1.7) and wing longer than body. Litoleptis araeostylus differs from L. chilensis Hennig, 1972 , in that the latter has the fork of R 4+5 distal of the fork of M 1+2, CuA reaching the wing margin and wing 3.0 mm long ( Hennig, 1972). Litoleptis orientalis is larger than L. araeostylus (2.7 mm wing length vs. 1.7 mm), and the fork of R 4+5 is distal to the fork of M 1+2. Litoleptis alaskensis Chillcott, 1963 , also has the fork of R 4+5 significantly distal to the fork of M 1+2; it also lacks the needle-like seta at the terminus of the flagellum ( Chillcott, 1963).

Litoleptis is distributed worldwide, albeit sparsely, with extant specimens described from Alaska, Japan and the Philippines. It is of particular interest to note that, while a number of rhagionids are hematophagous, the larvae of Litoleptis are obligate miners of liverwort thalli ( Imada and Kato, 2016), with species restricted to a single genus of host. Of those species whose host is known, only L. japonica feeds on a species in the liverwort family Conocephalaceae Grolle, 1972 . There are 13 fossil species of the genus Rhagio Fabricus, 1775 ( Evenhuis, 2017) ; the holotype of one of these, Rhagio fossitus (USNM 112626), is housed at the NMNH and is refigured here ( Figure 24 ). Although the posterior margin of the wing is not preserved, the separation between the distal termini of CuP and CuA suggests the presence of an open anal cell, a characteristic that distinguishes Rhagio from all other genera in the family Rhagionidae . The specimen is left as is without additional comment.

Figures

FIGURE 23. Litoleptis araeostylus sp. nov., USNM 624657. 1, Habitus. Upper inset: Arrows denote the thin termini of the arista. Lower inset: genitalia, arrow denotes boundary between segments of the cercus; 2, Left wing, arrow points to the halter; 3, Line drawing of left wing. Scale bars equal 1.0 mm (1), 0.10 mm (insets), 0.50 mm (2).

FIGURE 24. Rhagio fossitus Melander, 1949. USNM 112626. 1, Habitus; 2, Right wing; 3, Line drawing of right wing. Scale bars equal 5.0 mm (1) and 1.0 mm (2).