Acartophthalmites tertiaria Hennig, 1965; Baltic amber (mid Eocene).

The new species is named in honour of Willi Hennig (1913–1976), the founder of phylogenetic systematics and an outstanding dipterist who discovered the genus Acartophthalmites as well as many other fossil acalyptrates in Baltic amber.

Holotype ♂, MCZ-PALE-19475. The amber piece preserving the holotype is encased in an Epoxy resin prism of 18 × 18 × 5 mm. The Epoxy prism is mounted on a glass slide with labels “Mus. Comp. Zool. 19475, No. 6545a [the latter number scratched] Haren Coll., Baltic amber”, “Fam. Acartophthalmidae. Acartophthalmites electrica Hennig, ♂”, and “HOLOTYPUS ♂, Acartophthalmites willii sp. n., R. Pérez-de la Fuente, C. Hoffeins & J. Roháček det.” (red label). Deposited in the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA.

Baltic Sea coast, probably the Samland Peninsula (Weitschat and Wichard 2010). Ypresian to Priabonian, Eocene, 56−33.9 Ma (Weitschat and Wichard 2010).

Slightly smaller than both A. tertiaria and A. clusioides. Arista relatively shortly ciliate; vi relatively well-developed; two dc setae; prescutellar ac setae well developed; anterior pa very long (together with apical sc the longest thoracic seta); male f₂ not longer than f₃, not particularly tapered distally and ventrally with a single short row of six thicker setae; t₂ with a long row of erect posterior setae (six or seven longer and thicker) and with three short dorsal setae (including a preapical one); wing relatively elongated and with darkening along anterior margin (in cells r₂₊₃ and r₄₊₅); R₁ with a few setulae subapically; M reaching the wing margin; R₄₊₅ slightly bent; dm cell elongated; apical part of CuA₁ short, not longer than dm-cu; A₁ relatively long, almost reaching wing margin; alula large and broad; dorsal pregenital sclerite T6+S8(?) of male short.

Male (female unknown). Total body length nearly 3.2 mm (Fig. 1); general colour probably bicoloured, dark brown to light brown and ochreous; legs light brown to ochreous.

Figures 1–2. 

Habitus photographs of Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475 in Baltic amber (mid Eocene). 1 Ventrolateral habitus 2 Dorsolateral habitus. Scale bar 1 mm (both photographs at the same scale).

Head (Figs 3–4, 15). Higher than long, 0.78 mm high, 0.66 mm long, 0.91 mm wide, dorsally somewhat wider than thorax; dorsal part of occiput concave. Head distinctly bicoloured; frons mostly light brown; occiput darkest (dark brown); face, gena and postgena ochreous. Frons moderately narrow (probably slightly wider than eye in dorsal view), slightly tapering anteriorly, largely light brown, with foremost part ochreous and only ocellar triangle dark brown. Frons rugose in texture. Orbit colouration apparently not distinct from that of frons. Frontal triangle not visible. Ocellar triangle somewhat tubercle-like, protruding among ocelli. Frontal lunule not obvious, probably small. Face (praefrons) dark ochreous, parafacialia and gena ochreous. Postgena and adjacent part of occiput large, expanded, ochreous. Cephalic chaetotaxy (Fig. 15): pvt relatively strong (longer and thicker than oc), divergent and inserted rather closely; vti very strong (longest cephalic seta), almost twice as long as vte; oc relatively weak, inserted between ocelli and directed forward; three reclinate ors becoming shorter anteriorly, the hindmost ors longest and strongest (nearly as long as vte); no microsetulae on frons medially or in front of ors; postocular setulae in a single long row surrounding posterior eye margin, none of them enlarged but there are numerous additional and erect setulae scattered on adjacent lateral parts of occiput and postgena; postgena with two or three (one distinctly longer) posteroventral setae in addition; foramen not visible; vi distinct and relatively well developed (Figs 4, 15), about twice as long as foremost peristomal setulae, curved medially; subvibrissa not developed; peristomal setulae small and sparse (four observed). Eye large, bare, strongly convex and covering most of head in profile, subovoid, its longest diameter 1.35 times as long as shortest diameter. Gena very low, its height 0.05 times as long as shortest eye diameter. Palpus ochreous, small, with ventropreapical seta the longest and a few setulae subdorsoapically. Mouthparts ochreous; labella large and fleshy, setulation not apparent. Antenna porrect and relatively small (Figs 3–4, 15), scape and pedicel light brown; pedicel externo-laterally without anterior process in the middle but with somewhat excavated anterior margin, with one stronger erect seta dorsally and two finer setae ventrally in addition to series of marginal and submarginal setulae; first flagellomere strongly laterally compressed, in profile subcircular with posterior side at least not evidently excavated, probably slightly so. Arista dorsobasal, 2.5 times as long as antenna, with elongated and whitish basal segment and darker ochreous terminal section being distinctly but relatively shortly ciliate (Figs 3, 15).

Figures 3–6. 

Photomicrographs of Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475 in Baltic amber (mid Eocene). 3 Head in frontolateral view 4 Head in lateral view 5 Partial thorax in lateral view 6 Right foreleg. Scale bars 250 µm.

Thorax (Figs 5, 16). Slightly narrower than head, bicoloured, largely brown to ochreous, with some parts dark brown. Scutum ochreous, with a longitudinal medial light brown band wider proximally and distally, and two brown spots at the posterior half of the scutum which enclose the sa, pa and the two dc setae (see Fig. 16). Humeral (postpronotal) callus brown and markedly protruding; notopleural area ochreous; scutellum and subscutellum light brown; pleural part of thorax distinctly bicoloured: dorsal part of mesopleuron (anepisternum) and pteropleuron (anepimeron) dark brown; ventral part of mesopleuron and pteropleuron ochreous; metapleuron (katatergite) dark brown; metanotum (anatergite) ochreous; propleuron, sternopleuron (katepisternum), hypopleuron (meron) ochreous. Scutellum subtriangular with rounded apex, slightly convex dorsally; subscutellum well developed. Thoracic chaetotaxy (Figs 5, 16): one strong and long hu (plus a number of microsetae on humeral callus), two npl (anterior npl slightly longer than posterior npl), one long and robust sa (but much shorter than anterior pa), two pa (anterior pa very long and strong, the longest thoracic seta; posterior pa thinner and less than half the length of the anterior pa); no prs; two dc (both postsutural), anterior dc situated slightly behind level of sa, short (about half length of posterior dc), posterior dc robust but clearly shorter than apical sc or anterior pa; enlarged prescutellar ac present immediately after the level of posterior dc, subequal in length and thickness to posterior pa; scutum otherwise covered by uniform and relatively dense microsetae (around 15 dc microsetae in row in front of anterior dc); ac microsetae arranged in about eight rows in front of suture but less posteriorly, and only four rows reaching the level of posterior dc); two sc, apical sc strong and very long but shorter than anterior pa, laterobasal dc relatively robust, as long as three-fourths of the apical sc; one long ppl; mesopleuron with one distinct mspl in posterodorsal corner and numerous microsetae on most of its surface (except for anterodorsal part); sternopleuron with one long stpl and a number of scattered microsetae (anterior part of sclerite covered by a bubble); prosternum not visible.

Legs (Figs 6, 10–12, 18–21). Originally probably all light brown to ochreous, relatively long and slender. Fore, mid and hind legs differing in length of their segments (but not as strikingly as in A. clusioides). Femur, tibia and basitarsus of mid leg 1.5−1.7 times as long as those of foreleg, mid tibia only slightly longer than hind tibia (other leg segments between mid and hind legs subequal in length); cx₃ with an acute distoventral setose process directed caudally (Fig. 10) (a similar process also is present in A. clusioides); f₁ with a short row of four or five longer posteroventral to ventral setae in distal third and with about four posterodorsal setae forming a row in the middle of third of femur; f₂ elongated, slightly thicker than f₃ but subequal in length to the latter, not particularly tapered distally, finely densely setulose but ventrally with a single short distal row of six thicker setae; brush of ventral upright hair-like setulae in proximal half of f₂ lacking; f₃ without specific setae, uniformly densely finely setulose; t₁ also uniformly finely setulose but with a few distal slightly thicker setae; t₂ with distinctive chaetotaxy formed, besides usual short setosity, by a row of sparse erect posterior setae (six or seven longer and thicker, Fig. 20–21) starting in proximal two-fifths, three short dorsal setae (one in distal third, one at the level of distalmost posterior seta, and one preapical) and one longer and thicker ventroapical seta plus an anteroapical whirl of two or three shorter thicker setae near the latter (Fig. 19) and four smaller, short but thicker setulae also posteroapically (Fig. 20); t₃ without dorsopreapical nor ventroapical seta, but with four longer and thicker anteroapical setae (Fig. 21), otherwise uniformly finely setulose. Tarsi simple, slender; forebasitarsus with four or five longer, thicker setae ventrobasally, setae increasing in length distally; mid and hind basitarsi long and with thicker laterally directed setulae (more apparent in mid basitarsus); claws relatively small.

Figures 7–10. 

Photomicrographs of Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475 in Baltic amber (mid Eocene). 7 Left wing (slightly narrower than in reality due to the photographic angle, see Fig. 17 for an accurate wing shape) 8 Detail of the A₁ vein from the left wing 9 Detail of the A₁ vein from right wing 10 Sternum and basal leg segments in frontal view, showing the distoventral processes in Cx₃ (arrows). Scale bars 250 µm.

Wing (Figs 7–9, 17). Elongated and narrow; veins light brown; membrane apparently darkened in the anterior third of wing, darkening more restricted to roughly the anterior half of the spaces between C and R₂₊₃, and R₂₊₃ and R₄₊₅ (Fig. 17). C strikingly attenuated beyond R₄₊₅ but this slender nebulous part reaching to M; C finely setulose but basally with a pair of longer setae and Cs₂ (sector between apices of R₁ and R₂₊₃) with thicker (but not longer) sparse spine-like setulae in addition. No costal break. Sc fine, distally ending into C, not fused with R₁. R₁ short, robust and bearing four setulae subapically, preapical kink present at the level of Sc end. R₂₊₃ long, very slightly sinuate, apically somewhat upcurved to C, ending distinctly farther from wing apex than M. R₄₊₅ shallowly but distinctly bent posteriorly, distally subparallel with M, ending close to wing apex. Distal part of M very slightly bent and reaching wing margin (it appears as not reaching the wing margin in left wing due to preservation, but this character is well visible in the right wing). Discal (dm) cell relatively elongated; anterior cross-vein (r-m) situated in about the middle of discal cell. Distal part of CuA₁ subequal in length to dm-cu cross-vein and reaching wing margin; A₁ elongated, almost reaching the wing margin. Cells bm and cup closed. Anal lobe moderately developed. Alula well developed, large and broad. Wing measurements: length 2.2 mm, width 0.85 mm, Cs₃ : Cs₄ = 2.05, r-m\dm-cu : dm-cu = 3.24. Haltere ochreous.

Abdomen (Fig. 1). Piriform in dorsal view, widest at distal end of T2. All preabdominal terga rather sparsely but distinctly setose, with longest setae (some upright) at posterior and lateral margins. T1–T3 dorsally ochreous, darker laterally, T4 and T5 dark brown. T1−T2 separation not conspicuous. T1–T5 relatively narrow, only slightly bent laterally (pleural membrane rather well developed). Preabdominal sterna ochreous, sparsely and shortly setose (only S2−S3 visible, very narrow). Postabdomen (Figs 13–14, 22) with sclerites well developed, asymmetry of postabdominal sterna not clearly assessable. T6 not present as separate sclerite, either reduced (absent) or completely fused with S8 to form with it a large but not long synsclerite T6+S8(?) being dark brown, densely shortly setose. S6 and S7 not clearly discernible, but probably asymmetrical and largely situated left laterally.

Figures 11–14. 

Photomicrographs of Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475 in Baltic amber (mid Eocene). 11 Right mid- (left) and hind tibiae’s distal half and tarsi (right) in anterior (i.e., lateral, external) view 12 Right mid- (right) and hind tibiae’s distal half and tarsi (left) in posterior (i.e., lateral, internal) view 13 Apex of abdomen in dorsal view 14 Apex of abdomen in ventral view. Scale bars 250 µm.

Genitalia. Epandrium short, width not assessable, shortly uniformly setose. Cerci barely visible and gonostyli not visible as the sample is currently prepared (but originally depicted by Hennig 1969: fig. 20; see Fig. 22). Based on his description and illustration gonostylus is simple, slender, seemingly bare and slightly bent posteriorly and cercus is elongated, shorter than gonostylus, setose, and with longer setae apically (Fig. 22). However, as the anteroventral parts of external genitalia were not visible (also to Hennig), we cannot exclude the possibility that he observed and illustrated only the posterior lobe of the left (bilobed) gonostylus. In any case, this lobe is distinctly different from that of A. clusioides, where it distinctly bends anteriorly (cf. Roháček 2016: fig. 17).

Figures 15–16. 

Camera lucida drawings of Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475 in Baltic amber (mid Eocene). 15 Head in frontolateral view with the cephalic chaetotaxy tagged; note the inset of the distal half of the left arista 16 Head and thorax in posterolateral view, with the thoracic chaetotaxy tagged. Scale bars 250 µm.

Figures 17–20. 

Camera lucida drawings of Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475 in Baltic amber (mid Eocene). 17 Wing with venation tagged; the asterisk marks a depressed area of the wing 18 Distal quarter of the right hind tibia in anterior (lateral, external) view 19 Distal quarter of right mid tibia in anterior (i.e., lateral, external) view 20 Distal half of the right mid tibia in posterior (i.e., lateral, internal) view. Scale bars 250 µm (18–20 at the same scale).

Figures 21–22. 

Reproductions of the original illustrations depicted by Hennig (1969, figs 20, 21) on Acartophthalmites willii sp. n., holotype ♂ MCZ-PALE-19475. 21 Setation of mid and hind tibiae and tarsi in anterior view (scale bar 0.5 mm) 22 Apex of abdomen in lateral view (scale bar 0.3 mm).