Reliquantha eocena, ROHÁýEK, 2014

ROHÁýEK, JindĜich, 2014, Reliquantha eocena sp. nov., first tertiary representative of an extant genus of Anthomyzidae (Diptera), Acta Entomologica Musei Nationalis Pragae 54 (2), pp. 773-784 : 776-782

Reliquantha eocena sp. nov.

( Figs 1–4 , 6–12 )

Type material. HOLOTYPE: J, labelled: ‘1734-1, Baltic amber (purchased from Dr. Andrey Krylov, Kaliningrad, Russia)’ and ‘ HOLOTYPUS J, Reliquantha eocena sp.n., J. Roháþek det. 2014’ (red label), embedded in polyester resin, size 18.3 × 15.8 × 7.5 mm ( Fig. 1 ), deposited in the collection of C. and H. W. Hoffeins, Hamburg, Germany. Syninclusions: 1 Cicadina adult, 1 Collembola cf. Hypogastruridae , 2 Acarina larvae, several stellate hairs of different shapes.

Etymology. The species is named eocena referring to the age of its Baltic amber deposit.

Description. Male. Total body length 2.3 mm; general colour blackish brown; legs largely brownish; thorax and abdominal sclerites probably more or less shining ( Fig. 4 ).

Head ( Figs 3 , 6 ) somewhat higher than long (not precisely measurable), dorsally slightly broader than thorax; dorsal part of occiput distinctly concave. Head largely blackish brown and mostly shining including occiput. Frons moderately broad, slightly tapering anteriorly, entirely brown to blackish brown (anteriorly slightly paler). Orbit brown, indistinctly separate from rest of frons. Frontal triangle delimited by a narrow marginal line, relatively long but narrow, reaching to anterior third of frons, concolourous with other parts of frons. Ocellar triangle distinctly elevated and ocelli large. Frontal lunule not visible in the specimen. Face (praefrons), parafacialia, gena and postgena completely milky coated and hence undescribed. Cephalic chaetotaxy: pvt small, short and slightly convergent; vti distinctly shorter than vte (longest cephalic seta), oc and posterior ors; 3 relatively short ors, the hindmost ors longest (about as long as oc), the middle distinctly shorter, the foremost small (about half of middle ors); there is 1 orbital microsetula in front of the foremost ors (visible on left side only!) but no microsetulae medially; postocular setulae (only 5–6 in dorsal part observable) in a single row, none of them enlarged; postgena with 2 (1 slightly longer) longer ventral setae; vi relatively short (about as long as middle ors) and also subvibrissa distinct (although only half length of vi); peristomals not visible due to milky coating. Eye large, covering most of head in pro¿le, with longest diameter subvertical to slightly oblique and only about 1.15–1.20 times as long as shortest diameter. Gena low; its height less than 0.1 times as long as shortest eye diameter (not precisely measurable). Palpus not visible. Mouthparts brownish, ¿nely setulose. Antenna slightly geniculate, with pedicel brown and distinctly darker than 1st flagellomere, the latter orange-ochreous, strongly laterally compressed and densely, very shortly pale pubescent. Arista ochreous to brown, only 1.6 times as long as antenna, with small and paler basal segment and darker brown terminal section being very shortly ciliate.

Thorax slightly narrower than head, uniformly blackish brown, including pleurae ( Fig. 3 ). Mesonotum obviously rather shining but with some microtomentum developed (visible only in parts covered by ¿ne air layer). Thoracic chaetotaxy: 1 relatively short hu (distinctly shorter and weaker than posterior npl), 2 npl (anterior distinctly longer), 1 relatively short sa (distinctly shorter than pa), 1 relatively long pa (as long as anterior dc), 1 distinct but relatively short prs (only as long as sa); 2 long dc (both postsutural), anterior about half length of posterior, the latter very long and strong; 7–8 dc microsetae in front of anterior dc; ac microsetae small, not very dense, in 4 regular rows, reaching posteriorly to level of posterior dc; 2 sc, apical strong and slightly longer than posterior dc (hence longest of thoracic setae), laterobasal much shorter and weaker, shorter than scutellum length; 1 minute hair-like upcurved ppl; 2 relatively long stpl (posterior distinctly longer and more robust) and 1 microseta (poorly visible) in front of them; only 2 short curved setae on ventral corner of sternopleuron. Scutellum rounded triangular and somewhat convex dorsally; postscutellum well developed, blackish brown.

Legs dark (as in Lacrimyza species , cf. Fig. 5 ), entirely brown (including all coxae, trochanters and tarsi); femora and tibiae somewhat darker brown although lighter than thorax. Femora relatively slender (in contrast to those of Lacrimyza species ). f 1 without ctenidial spine ( Fig. 8 ), with only usual rows of ¿ne and relatively sparse posterodorsal and posteroventral setae; f 2 simply setulose; f 3 ( Fig. 7 ) in distal half with posteroventral row of about 10 short, more or less thickened and erect setae, two most distal of which are small to minute. t 1 and t 3 uniformly short-setulose; t 2 with 1 short ventroapical seta and 2 (or 3?) smaller adjacent setulae. Tarsi simple, slender; fore and hind basitarsi with 2 slightly longer proximoventral setulae; claws relatively long.

Wing ( Fig. 10 ) not very long and moderately wide, hyaline, but with membrane and veins distinctly brownish tinged. C with thicker (but not longer and thus rather indistinct) sparse setulae among usual ¿ne hairs on Cs 2 and (partly) Cs 3. Sc fused with R 1 apically to form a distinct preapical kink ( Fig. 9 ). R 2+3 somewhat sinuous, subparallel to C and apically slightly upcurved to C, ending distinctly farther from wing apex than does M. R 4+5 slightly bent (recurved), and distally somewhat convergent to M. Discal (dm) cell moderately long and narrow, slightly widened distally behind r-m; anterior cross-vein (r-m) situated slightly in front of the middle of discal cell. CuA 1 not reaching wing margin, A 1 ending far from it. Terminal section of CuA 1 about 1.1–1.2 times as long as posterior cross-vein (dm-cu). Alula small and relatively narrow. Wing measurements: length 2.10 mm, width 0.79 mm, Cs 3: Cs 4 = 1.91, r-m\dm-cu: dm-cu = 2.39. Haltere with brownish knob; stem probably paler.

Abdomen with blackish brown and probably rather shining sclerites. All preabdominal terga obviously sparsely and shortly setose (poorly visible). T1 dorsally distinctly separate, laterally only shortly fused with T2. T2–T5 large but not very broad and reaching far laterally (pleural membrane large, Fig. 11 ). Preabdominal sterna brown and moderately to distinctly broad. S1 paler brown than S3–S5, probably short. S2 not visible due to air bubble. S3–S5 almost subequal in length but becoming strongly wider posteriorly. S3 slightly transverse, S4 markedly wider than long. S5 largest, more than twice as broad as long, strongly transverse and trapezoidal (posteriorly wider). S3–S5 simply shortly setulose ( Fig. 11 ).

Postabdomen ( Figs 11, 12 ) with sclerites heavily sclerotized and dark-pigmented. T6 not visible. S6, S7 and S8 partly fused but their borders distinct. S6 the shortest, strongly asymmetrical, tapered to band-like on left and right side ( Fig. 12 ); S7 longer, slightly asymmetrical, situated on left lateral side of postabdomen, blackish brown. Both S6 and S7 without setae. S8 longest, dark and heavily sclerotized, slightly asymmetrical (longer on left side) and situated dorsally, with sparse setae in posterodorsal half.

Genitalia. Epandrium ( Figs 11, 12 ) not very large, globose, de¿nitely wider than high ( Fig. 12 ), shining blackish brown, with single pair of enlarged setae, otherwise rather sparsely shorter setose (but probably only some of setae visible). Anal ¿ssure greatly reduced, unusually low (as in R. variipes and in fossil Lacrimyza species ); cercus well developed, relatively large (about half length of gonostylus) and dark pigmented, laterally somewhat flattened, ¿nely setose ( Fig. 11 ). Gonostylus ( Figs 11, 12 ) brown as cercus, relatively simple, shorter than epandrial height, slender and elongate, wider proximally and gradually tapered apically, with apex blunt and inclinate. Outer convex side of gonostylus micropubescent and bearing only very small setulae at posterior margin. Setae on inner concave side of gonostylus not observable. Basal part of hypandrium ( Fig. 11 ) too poorly visible to be described in any detail.

Female. Unknown.

Discussion. Apart from its only extant congener, R. variipes , this new fossil species externally most resembles the two species of another Eocene (Baltic amber) genus Lacrimyza . However, R. eocena sp. nov. cannot be included in the latter group because it lacks most of the synapomorphies on which Lacrimyza was based, viz. the oc arising close to each other and peculiarly erect; ac microsetae in two medial rows situated close to each other; stpl setae arising close to each other; male f 3 thickened; male cercus reduced. However, Reliquantha (both species) also differs distinctly from Lacrimyza species in the construction of the antenna where Lacrimyza has the 1st flagellomere directed strongly ventrally (cf. on Figs 4, 5 ).

The af¿liation of R. eocena sp. nov. with the genus Reliquantha is largely based on shared plesiomorphic characters (cephalic and thoracic chaetotaxies, formation of the male gonostylus and cercus), mostly because the majority of apomorphic features of Reliquantha are of internal structures of the male and female genitalia (cf. ROHÁýEK 2013b) which cannot be studied in fossils as a rule. Despite this fact, there are a few apomorphies indicating that R. eocena sp. nov. is most closely related to R. variipes , e.g. the completely bare male S6 and S7.

The new fossil Reliquantha differs from its extant congener R. variipes distinctly in a number of colour and structural characters, viz. the frons completely dark (also anteriorly), the antennal pedicel brown, the legs (including femora and tibiae) brown, not variegated, the male f 3 with spine-like setae in posteroventral row shorter and more numerous ( Fig. 7 ), the wing shorter with the R 2+3 shorter, the CuA 1 not reaching the wing margin and the alula narrower (see Fig. 10 ), the gonostylus very slender with the apex inclinate and the male cercus dark-pigmented ( Figs 11, 12 ). Reliquantha eocena sp. nov. can be distinguished from all other fossil species of the subfamily Anthomyzinae with the key below.

Notes on the habitat and distribution. The extant R. variipes (although known from only two specimens from Great Britain: Wales, England) is associated with woodland habitat, and the label data of the female paratype indicate the species may be associated with (tree) fungi, see ROHÁýEK (2013b). This habitat association could also be true for the fossil R. eocena sp. nov. because the holotype was caught in the tree resin of the Eocene “amber forest” ( TSCHIRNHAUS & HOFFEINS 2009, WEITSCHAT & WICHARD 2010). The composition of syninclusions found together with the holotype (particularly the presence of Collembola and Acarina specimens, see above under Type material) indicate that this amber was possibly formed close to the forest floor. The Middle Eocene Baltic amber forest is characterized as warm (subtropical) montane rainforest dominated by oak and pine ( WEITSCHAT & WICHARD 2010) in which also beeches ( Fagus ), maples ( Aceraceae ), elms ( Ulmaceae ) and a number of other trees occurred ( LARSSON 1978). Thus, it seems that there could be some tree components shared with those growing in recent woodland where R. variipes was found in Great Britain ( ROHÁýEK 2013b).

The holotype of R. eocena sp. nov. originates from Samland Penninsula (Kaliningrad vicinity), Russia. However, it is known that the Eocene amber is never found in primary deposits in the original forest floor but has been re-deposited through lateral transport by streams ( LARSSON 1978) and, more importantly, by glaciers during the Pleistocene. The present range of Baltic amber deposits extends from Fennoscandia eastwards to Russia, westwards to the Netherlands and the English coast and southwards to Germany (Bitterfeld deposit) and Ukraine (Rovno deposit) – these borders agree well with the distribution of glacial till ( WEITSCHAT & WICHARD 2010). The original Baltic amber forest in the Middle Eocene covered a vast territory probably ranging from Fennoscandia to Ukraine or more southeasterly ( WEITSCHAT & WICHARD 2010) but its exact distribution remains unknown as a result of these massive re-depositions of amber. However, it is presumed that in the Eocene most areas of Europe (wherever there was suf¿cient humidity) were covered by forests ( LARSSON 1978) so that the woodland fauna could spread throughout the continent. Considering these facts, it is not impossible that R. variipes could really represent a relic of the Tertiary woodland fauna of Anthomyzidae as ROHÁýEK (2013b) suggested.

Figures

Figs 1–3. Reliquantha eocena sp. nov., male holotype. 1 – Baltic amber sample 1734-1 with the holotype (circled) in situ (length of sample 18.3 mm); 2 – male holotype, the milky-coated right side; 3 – male holotype, left side of head and thorax. Length of holotype 2.30 mm. Photo by J. Roháþek.

Figs 4–5. Baltic amber fossil Anthomyzidae. 4 – Reliquantha eocena sp. nov., male holotype, left laterally (body length 2.30 mm). 5 – Lacrimyza lacrimosa Roháþek, 2013, male holotype, left laterally (body length 2.22 mm) (adopted from ROHÁýEK 2013a: Fig. 13A). Photo by J. Roháþek.

Figs 6–12. Reliquantha eocena sp. nov., male holotype. 6 – head dorsolaterally; 7 – right hind femur, posteriorly; 8 – left fore femur, posteriorly; 9 – venation in basal part of wing (different view than in Fig. 10); 10 – left wing; 11 – abdomen laterally (left side); 12 – postabdomen with genitalia, ventrocaudally. Reconstructed parts in dashed lines. All scales = 0.3 mm. For abbreviations see text (p. 774).