Christelenka multiplex Rohacek, 2023

Rohacek, Jindrich, Hammel, Joerg U. & Baranov, Viktor, 2023, Christelenkidae, a new extinct family based on a new taxon from Eocene Baltic amber (Diptera: Acalyptratae), with X-ray synchrotron microtomography imaging of its structures, Arthropod Systematics & amp; Phylogeny 81, pp. 475-498 : 475

3.3. Christelenka multiplex Rohacek sp. nov.

Figs 1-2 , 3, 4 , 5-7 , , 11, 12 , 13, 14 , 15, 16 , 17 , 18, 19 , 20-23 , 24, 25 , 26, 27 , 28-30 , 31-35

Description.

Male. Total body length 3.1 mm; general colour brown to dark brown, with some parts of head and abdomen lighter coloured (see below); thorax and abdominal terga probably subshiny to partly shiny (Figs 1 - 4 ). - Head: (Figs 5 - 10 ) about 1.3 times as high as long, dorsally very slightly wider than thorax. Dorsal part of occiput distinctly concave (Fig. 7 ). Head distinctly bicolourous, dorsally and posteriorly largely dark brown, anteriorly and ventrally orange ochreous to whitish yellow. Frons (Figs 6 , 9 ) moderately broad, hardly tapered anteriorly, largely bare, dark brown behind apex of ocellar triangle and ors, reddish brown to orange ochreous in middle part and yellow to whitish yellow on crescent-shaped anterior margin surrounding bases of antennae. Orbital plate hardly delimited, slightly visible only at base of ors, dark brown behind latter, reddish brown to orange ochreous anteriorly, up to level of ptilinal fissure. Frontal triangle not developed. Ocellar triangle blackish brown, small, somewhat elongate, slightly protruded among ocelli. Ocelli small (Fig. 9 ). Lunule absent (or concealed within dorsal medial part of face). Face (praefrons) slightly concave, yellow to yellowish white. Parafacialia and gena yellowish white, obviously whitish microtomentose; gena narrowly yellow-margined ventrally. Postgena darker yellow to ochreous, adjacent part of occiput brown, becoming darker dorsally (Fig. 5 ). Cephalic chaetotaxy (Figs 8 - 10 ): pvt relatively small, with apices crossed; vti long and strong (longest cephalic seta); vte shorter and weaker, about two-thirds length of vte; oc divergent, more upright than proclinate, relatively thin and short (shorter than ors), situated within ocellar triangle; only 1 (relatively robust) ors situated near level of anterior ocellus; no setae or setulae in large anterior part of frons; postocular setulae (13 or 14) in single long row behind posterior margin of eye, none of them enlarged but 1-2 most dorsal somewhat inclinate (see Figs 9 , 10 ); a few additional setulae on adjacent lateral parts of occiput above postgena; postgena with 1 distinct posteroventral seta (Fig. 8 ); vi distinct though not very long, curved medially (Figs 8 , 9 ); subvibrissa not developed; peristomal setulae fine, short and sparse (5 visible, Fig. 8 ); no genal seta. Eye relatively large, bare, strongly convex (Figs 5 , 6 ), suboval, with straighter posteroventral margin; longest diameter slightly oblique, about 1.3 times as long as shortest diameter. Gena low but distinct; height about 0.17 times as long as shortest eye diameter (Fig. 8 ). Palpus poorly visible in light microscope (where seemingly short and robust, Fig. 8 ) but actually slender, somewhat twisted in microtomographs (Figs 11 , 12 ), probably yellow, with a few fine black setulae (Fig. 8 ). Subcranial (oral) cavity relatively large (Figs 11 , 12 ). Mouthparts yellow to pale yellow; clypeus short, narrow and projecting little from oral cavity (Fig. 11 ), labellum fleshy, finely pale setulose (Figs 8 , 11 , 12 ). Antenna (Figs 5 , 6 , 8 , 9 ) strongly decumbent, geniculate between pedicel and 1st flagellomere, somewhat exclinate, relatively small. Scape and pedicel reddish brown, markedly darker than 1st flagellomere; pedicel with simple margin dorsally and laterally, with 1 longer but fine dorsal seta in addition to series of very small marginal setulae; 1st flagellomere somewhat longer than scape and pedicel combined, yellow, elongate suboval, distinctly compressed laterally, very finely pubescent (Figs 8 , 9 ). Arista dorsobasal, inserted at posterior margin of 1st flagellomere, only about 1.8 times as long as antenna, completely brown, with two basal segments (aristomeres) elongate (not thickened); terminal section very shortly ciliate (pubescent), with longest cilia preapically (Figs 9 , 15 ). - Thorax: very slightly narrower than head (Fig. 2 ), pale brown to blackish brown, darker and subshiny to shiny dorsally, paler laterally (Fig. 3 ). Mesonotum distinctly convex, somewhat hump-like anterodorsally (cf. Figs 1 , 3 , 13 , 14 , 17 ), blackish brown in anterior half and also laterally (outside of dc lines) up to scutellum, light brown medially (between dc lines) in posterior half (see Fig. 2 ). Humeral (postpronotal) callus and notopleural area light brown and more (postpronotum) or less protruding; scutellum light brown (concolourous with posterior half of mesonotum), narrowly darkened only basolaterally, with suture between scutum and scutellum distinctly dark brown-margined (Fig. 3 ). Pleural part of thorax also somewhat variegated (Fig. 3 ): mesopleuron (anepisternum) light brown, with darkened area along dorsal margin; sternopleuron (katepisternum) also light brown, with darkened posterodorsal corner; propleuron (proepimeron + proepisternum) and most of posterodorsal part of pleuron including metanotum (anatergite) and subscutellum dark brown. Mesopleuron with slightly elevated ridge at posterior margin; dorsal membranous part of pleural suture separating it from pteropleuron (anepimeron) enlarged. Scutellum large, broad, rounded subtrapezoidal, distinctly convex dorsally (cf. Figs 13 , 15 , 17 ); subscutellum also distinctly protruding as shown in microtomograph image (see Fig. 17 ). Metasternal area obviously lacking setae. Thoracic chaetotaxy (Figs 15 , 16 ): 1 moderate hu (about as long as posterior npl) plus 6-8 microsetae on humeral callus); 2 npl (anterior relatively strong, distinctly longer than posterior); 1 distinct prs (as long as anterior npl); 1 long sa (slightly longer than anterior npl); 1 short and weak pa (smaller than hu); only 1 postsutural dc, very long and strong (almost as long as laterobasal sc), situated far behind level of sa; scutum otherwise covered by uniform, somewhat irregularly scattered microsetae; ac microsetae also unordered, in about 6-8 incomplete rows in front of suture, with only 4 ac microsetae posteriorly, between dc macrosetae (Fig. 16 ); 2 sc, apical strong and crossed, markedly shorter than laterobasal sc; latter longest and strongest thoracic seta (Fig. 16 ); no ppl observed; no mesopleural (anepisternal) seta or setula; sternopleuron (Fig. 15 ) with only 1 upcurved (posterior) stpl, about as long as anterior npl and a few, hardly visible, microsetae (1 dorsally, 3 or 4 on ventral corner of sclerite); prosternum obviously bare. - Wing: (Figs 2 , 18 , 19 ) rather elongate, with apex somewhat pointed at insertion of R4+5, not rounded; veins pale brown, membrane brownish-tinged, most darkened in cell r2+3 (between R2+3 and C). C reaching apex of M but last segment (Cs4) attenuated; C with uniform, very dense, dark setulae (except for longer seta basally, and somewhat enlarged setulae on Cs1, see Figs 18 , 19 ) ending in middle of Cs3 (see Fig. 18 ). Two costal breaks, smaller humeral and larger subcostal. Sc proximally distinct, distally attenuated and gradually fused with R1, without forming a preapical kink on the latter. Humeral crossvein not visible. R1 short, robust and bare, slightly bent to C. R2+3 long, slightly curved, subparallel with C, apically straightened, ending in C distinctly farther from wing apex than vein M. R4+5 also shallowly but distinctly curved, distally subparallel with M, ending in C at wing apex. Distal part of M almost straight or indistinctly bent forward, distally attenuated, reaching (left wing, Fig. 19 ) or not reaching (right wing, Fig. 18 ) wing margin. Discal (dm) cell elongate, distally widened, with side veins slightly curved; upper distal corner obtuse-angled, lower distal corner acute-angled; anterior crossvein (r-m) situated slightly beyond basal fourth of cell dm. Distal part of CuA1 slightly (about 1.2 times) longer than dm-cu crossvein and reaching wing margin; A1 short, distally attenuated, ending far from wing margin. Cells bm and cup closed. Anal lobe distinct. Alula (not visible) probably small and narrow. Wing measurements: length 2.68 mm, width 0.99 mm, Cs3: Cs4 = 1.69, r-m\dm-cu: dm-cu = 3.63. Haltere (Figs 13 , 15 ) relatively large, with dirty yellow stem and whitish yellow knob. - Legs: largely pale brown to brown, femora darkest, coxae, tibiae and tarsi paler, cx1 lightest. All legs relatively slender and long. Fore leg shortest but cx1 (Figs 3 , 13 , 15 ) distinctly elongate, only slightly shorter than f1, with 1 long seta in the middle of ventral margin. f1 with distinct dorsal seta at anterior two-fifths (Figs 20 , 21 ) and row of 4 long posteroventral setae on distal half, with last (preapical) distinctly longer; anteroventrally with row (ctenidium-like) of 8 small, very short blunt spines (Fig. 21 ) extending from midpoint of f1 to distal fifth; f2 (Fig. 22 ) longer than f1, lacking distinct dorsal seta, with row of anterior (not posterior) setae becoming longer towards apex, with last (longest) seta at about distal sixth; f3 with 1 longer anteroventral seta at distal third and 1 shorter dorsal seta at distal fourth (Fig. 23 ). Probably all tibiae with dorsal preapical seta, although not verified on t1 (apex of tibia not visible in either fore leg); t2 (Fig. 22 ) with 1 distinct but relatively short dorsal preapical seta, 1 slightly shorter ventroapical seta and 2 small anterior setulae on apex; t3 (Fig. 23 ) with 1 dorsal preapical seta longer and more distant from apex of tibia than that on t2, with 1 or 2 small curved ventroapical setulae. Hind basitarsus (Fig. 23 ) with ventrobasal setulae somewhat enlarged; claws well developed. Other parts of femora, tibiae and tarsi uniformly shortly setulose. - Abdomen: (Figs 24 - 28 ) slender, elongate, unusually bicolourous, having anterior half pale and posterior half dark (see Figs 1 , 3 , 4 ). Preabdominal terga modified: T1 short (slightly shorter than T2), darker, narrower and distinctly separated from T2; T2-T4 short (see also Fig. 17 ), transverse, subequal in length, all unusually pale, translucent, silvery grey to whitish yellow and shiny and each sparsely but distinctly setose, with longest setae at posterior margins (Fig. 28 ); T5 enlarged, extremely elongate (Figs 24 - 28 ), longer than T1-T4 combined and also broad, expanded lateroventrally, brownish black, heavily sclerotized and sparsely finely setose. Preabdominal sterna pale-pigmented (cf. Fig. 3 ); S1-S4 short, combined length subequal to T1-T4 (cf. Figs 17 , 25 , 28 ); S1 and S2 ochreous brown, S3 and S4 dirty yellow; S1 (shortest) and S2 (longer than S1) with sparse and short setulae, S3 and S4 (both longer and wider than S2) with a few fine but longer setae (Fig. 28 ). Margins of S5 not recognizable, only some setae discernible in light microscope (Fig. 28 ); in microtomographs (Figs 25 , 31 , 32 ) S5 very elongate (though somewhat shorter than T5), narrow and probably pale-pigmented. Spiracles not visible in (reduced) pleural membrane nor at margins of terga. - Postabdomen: (Figs 24 - 27 , 29 , 30 , 32-35 ) more or less symmetrical, with dorsal sclerites dark-pigmented. T6 seemingly absent (cf. Figs 29 , 30 ) but recognized in microtomographs (Figs 27 , 31 , 32 ), forming short transversely band-like (probably bare) sclerite largely hidden under large T5, visible as narrow strip on right side of postabdomen (Fig. 32 ). S6 visible only in microtomographs (Figs 25 , 31-35 ), of moderate length, trapezoidal, broader posteriorly where wider than long (Fig. 35 ). Slightly asymmetrical brown saddle-shaped sclerite dorsally (shorter on left side but reaching more ventrally, cf. Fig. 25 and Fig. 27 ) considered to be fusion of S7+S8; sclerite bears 1 strong dorsolateral seta on each side of posterior margin (Figs 3 , 29 , 30 ) and 1 or 2 short setae. - Genitalia: Epandrium (Figs 25 , 27 , 29 , 30 ) simple, arch-shaped, open ventrally (Fig. 35 ), only slightly asymmetrical, with longer left side and a few small setae; anal fissure not clearly visible in light microscope but surely large (cf. Figs 34 , 35 ). Cerci also large, symmetrical, free and projecting below anal fissure posterior to gonostyli (cf. Fig. 30 ); each cercus yellow, subconical with apex rounded, with (mainly posterior) fine, pale setae distinctly longer than setulae on gonostylus. Another medial sclerite situated between cerci (only visible in microtomograph image, Figs 34 , 35 ) probably homologous to medandrium (= bacilliform sclerite, S10). Gonostyli (Figs 27 , 30 , 32 ) separate, yellow, elongate, somewhat asymmetrical. Left gonostylus (Figs 25 , 30 ) more robust than right, elongate, wider proximally, gradually tapered distally; blunt apex slightly widened and bent posteriorly; right gonostylus (Figs 27 , 29 ) of equal length to left, but slender (including apex) and distinctly curved; left gonostylus externally with a few small setae at anterior margin of proximal half and several fine pale-pigmented setulae on posterior margin of distal half (those on right gonostylus not seen). Internal genitalia: some indistinctly discernible sclerotized structures visible in front of external genitalia in light microscope (Figs 29 , 30 ). More dorsal sclerite considered hypandrium, clearly frame-shaped in ventral view as shown in microtomograph images (Figs 34 , 35 ). Paired and apparently symmetrical postgonites below hypandrium (Figs 27 , 30 , 32 ) - simple sclerites, situated dorsolaterally to distiphallus of aedeagus; each postgonite projecting anteriorly, acutely pointed and bare except for 2 preapical microsetulae (Fig. 30 ). Distiphallus (situated most ventrally) short, basally narrow, broad and dilated distally (see Fig. 35 ), of rather simple structure (appears more sclerotized dorsally and ventrally, see Fig. 30 ). Pair of slender tooth-like acutely pointed projections of uncertain homology (visible in microtomograph image of terminalia in ventral view, see “??” in Fig. 35 ) in front of apex of distiphallus appears derived from distal end of dorsal sclerite of distiphallus. - Female. Unknown.

Etymology.

The name " Christelenka multiplex " (Lat. adjective = various, manifold) refers to the unusual mixture of external characters of the new species precluding its association with any of the currently recognized families of Diptera Acalyptratae .

Comparative remarks.

As remarked above, Christelenka multiplex sp. nov. at first glance looks like an opomyzoid fly, in external appearance most resembling some species of Opomyzidae , Anthomyzidae , Stenomicridae or Aulacigastridae (cf. images in Marshall 2012). However, it differs from any member of these families by a combination of its most diagnostic characters (see above under Christelenkidae ) and can be immediately recognized by the bare forefrons, absence of the frontal triangle and lunule, a single posteriorly positioned ors, the extremely dorsobasal arista, the wing pointed at apex of R4+5, a strong seta on fore coxa, peculiar chaetotaxy of the fore (with dorsal seta and an anteroventral row of small spines) and hind (with a dorsal and a longer anteroventral seta) femur (see Figs 20 , 21 , 23 ), enlarged laterobasal and crossed apical sc setae, the enlarged and extremely elongate male T5 and S5 and the strong pair of setae on the dorsal pregenital synsclerite S7+S8.

Biology.

The species was plausibly a member of the ancient dipterous community in the "Baltic amber forest". This Eocene tropical to warm-temperate humid forest ( Weitschat and Wichard 2010; Sadowski et al. 2020) covered most of northern Europe (from Fennoscandia to Ukraine) and evolved thanks to the very warm and humid climate during the Early Eocene Climatic Optimum (see Słodkowska et al. 2013), for more detail see Introduction. The presence of stellate trichomes of Quercus spp. in the amber sample (see Figs 3 , 4 ) indicate occurrence of this fly in a warm-temperate type of forest (as characterized by Sadowski et al. 2020).

Type locality and horizon.

Russia: Kaliningrad region, Yantarny mine. Mid-late Eocene, 48-34 Ma (cf. Seyfullah et al. 2018; Kasiński et al. 2020).

Type material.

Holotype ♂ (inventory number Dip-00820), labelled: 'Faszination Bernstein, Christel Hoffeins, Hans Werner Hoffeins’ (framed on obverse), '1818-3, Diptera : Acalyptratae , cf. Anthomyzidae ' (handwitten by Ch. Hoffeins), 'Baltic amber, Russia: Kaliningrad region, Yantarny‘, 'obtained in early 2017 from Marius Veta, owner of the amber company “Ambertreasure4u”, Lithuania’ and 'HOLOTYPUS ♂, Christelenka multiplex sp.n., J. Roháček det. 2020' (red label). The specimen is embedded in polyester resin, size of preparatum 10.4 × 6.6 × 5.9 mm, size of cut amber 7.5 × 4.5 × 3 mm (Fig. 1 ), deposited in SDEI. Syninclusions: only a few stellate hairs of various shapes.

Figures

Figure 17. Christelenka multiplex sp. nov., male holotype, anterior part of body: sagittal section right laterally. Scale bar: 0.5 mm. For abbreviations see 2.2.4. Morphological terminology. Microtomograph image by V. Baranov.

Figures 1, 2. Christelenka multiplex sp. nov., male holotype. 1 specimen in the whole amber preparatum, left laterally, with blue background; 2 whole specimen dorsally, with blue background. Scale bars: 1.0 mm. Photos by J. Rohacek.

Figures 3, 4. Christelenka multiplex sp. nov., male holotype. 3 whole specimen, left laterally; 4 ditto, right laterally. Scale bars: 1.0 mm. Photos by J. Rohacek.

Figures 5 - 7. Christelenka multiplex sp. nov., male holotype. 5 head left laterally; 6 ditto, frontally; 7 ditto, laterocaudally. Scale bar: 0.5 mm. Photos by J. Rohacek.

Figs 8 - 10. Christelenka multiplex sp. nov., male holotype, cephalic chaetotaxy. 8 head left laterally; 9 ditto, frontally; 10 ditto, laterocaudally. - Scale bar: 0.5 mm. For abbreviations see 2.2.4. Morphological terminology.

Figures 11, 12. Christelenka multiplex sp. nov., male holotype. 11 head frontoventrally, with some structures coloured; 12 ditto, without colours. Scale bar: 0.5 mm. For abbreviations see 2.2.4. Morphological terminology. Microtomograph image by V. Baranov.

Figures 13, 14. Christelenka multiplex sp. nov., male holotype. 13 whole specimen, left laterally; 14 ditto, right laterally. Scale bar: 1.0 mm. Microtomograph images by V. Baranov.

Figures 15, 16. Christelenka multiplex sp. nov., male holotype, thoracic chaetotaxy. 15 thorax, left laterally; 16 ditto, dorsally. Scale bar: 0.5 mm. For abbreviations see 2.2.4. Morphological terminology.

Figures 18, 19. Christelenka multiplex sp. nov., male holotype, wings. 18 right wing, dorsally; 19 left wing, dorsally. Scale bar: 1.0 mm. For abbreviations see 2.2.4. Morphological terminology.

Figures 20 - 23. Christelenka multiplex sp. nov., male holotype, legs. 20 left fore femur, dorsally; 21 right fore femur, anteriorly; 22 right mid femur and tibia, anteriorly; 23 left hind femur, tibia and tarsus, anteriorly. Scale bar: 0.3 mm. For abbreviations see 2.2.4. Morphological terminology.

Figures 24, 25. Christelenka multiplex sp. nov., male holotype. 24 abdomen, left laterally; 25 ditto, with some structures coloured. Scale bar: 0.5 mm. For abbreviations see 2.2.4. Morphological terminology. Microtomograph image by V. Baranov.

Figures 26, 27. Christelenka multiplex sp. nov., male holotype. 26 posterior half of abdomen, right laterally; 27 ditto, with some structures coloured. Scale bar: 0.2 mm. For abbreviations see 2.2.4. Morphological terminology. Microtomograph image by V. Baranov.

Figures 28 - 30. Christelenka multiplex sp. nov., male holotype, abdominal structures. 28 abdomen, left laterally; 29 postabdomen with terminalia, right laterally; 30 ditto, left laterally. Scale bars: 28 - 0.5 mm; others - 0.2 mm. For abbreviations see 2.2.4. Morphological terminology.

Figures 31 - 35. Christelenka multiplex sp. nov., male holotype, abdominal structures. 31 abdomen (without 1 st segment), sagittal section right laterally, with some structures coloured; 32 posterior end of abdomen, right ventrolaterally, with structures coloured; 33 ditto, without colours; 34 posterior end of abdomen, ventrally; 35 ditto, enlarged and coloured. Scale bars: 0.2 mm. For abbreviations see 2.2.4. Morphological terminology. Microtomograph images by V. Baranov.