Acartophthalmites clusioides, Roháček, 2016

Roháček, Jindřich, 2016, The second species of Acartophthalmitesfrom Baltic amber (Eocene), with notes on the relationships of the genus (Diptera: Acalyptrata), Acta Entomologica Musei Nationalis Pragae 56 (1), pp. 409-422 : 411-419

Acartophthalmites clusioides sp. nov.

( Figs 1–19 )

Type material. HOLOTYPE J, labelled: ‘ Baltic amber, Russia: Kaliningrad region, Yantarny. Purchased from Jonas Damzen (8th ICD, Potsdam 10.-15.viii.2014)’ and ‘ HOLOTYPUS ♂, Acartophthalmites clusioides sp.n., J. Roháček det. 2015’ (red label), embedded in polyester resin, size 13.8 x 10.0 × 4.9 mm ( Fig. 1 ), deposited in SMOC. Syninclusions: only a few stellate hairs of various shapes.

Description: Male. Total body length 3.85 mm; general colour probably bicolourous, dark brown and yellow or ochreous; legs pale brown; thorax and abdominal sclerites probably subshining ( Figs 1, 2 ). Head ( Figs 5, 6 , 9 , 18 ) about as long as high (not precisely measurable), dorsally somewhat wider than thorax; dorsal part of occiput concave. Head distinctly bicolourous, occiput darkest (dark brown), frons, face, gena and postgena pale, ochreous to whitish yellow except for some small parts. Frons moderately narrow (as wide as eye in dorsal view), slightly tapering anteriorly, largely yellow to ochreous with only ocellar triangle dark brown and orbits pale brown. Orbit narrowly brownish but this darkening tapered anteriorly, narrow and faded at foremost ors. Frontal triangle ochreous-brown, rather short (less than half length of frons) and its anterior corner identical with that of ocellar triangle. Ocellar triangle somewhat tubercle-like, protruding among ocelli. Frontal lunule poorly visible in the specimen, probably small. Face (praefrons), parafacialia (both only partly visible) and gena yellowish white and apparently whitish microtomentose; gena with brownish line at ventral margin in addition. Postgena and adjacent part of occiput large, expanded, pale yellow behind eye to pale brown medially (near foramen). Cephalic chaetotaxy ( Figs 9 , 18 ): 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 strikingly (possibly unnaturally) erect in the holotype; 3 reclinate ors becoming shorter anteriorly, the hindmost ors longest and strongest (about 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 relatively long erect setulae (see Figs 6 , 18 ) scattered on adjacent lateral parts of occiput and postgena; postgena with 2 or 3 (1 distinctly longer) posteroventral setae in addition; occiput with a brush of small setulae above foramen; vi ( Fig. 19 ) distinct though relatively short, curved medially; subvibrissa not developed; peristomal setulae small and sparse (5 observed, Fig. 19 ). Eye large, bare, strongly convex and covering most of head in profile, subcircular (slightly concave along posteroventral margin); its longest diameter oblique and only about 1.1 times as long as shortest diameter. Gena very low; its height about 0.06 times as long as shortest eye diameter. Palpus not visible, only its ventropreapical seta discernible. Mouthparts ochreous to (posterodorsally) brownish; labella large, fleshy and finely setulose, setulae pale. Antenna porrect ( Figs 9 , 19 ) and relatively small, yellowish white or scape + pedicel somewhat darker; pedicel externally laterally without anterior process in the middle but with somewhat excavated anterior margin, with 1 stronger erect seta dorsally and 2 finer setae ventrally in addition to series of marginal and submarginal setulae; 1st flagellomere strongly laterally compressed, in profile subcircular with excavated posterior side ( Fig. 19 ). Arista dorsal subbasal, about 3 times as long as antenna, with elongate and whitish basal segment and darker ochreous terminal section being distinctly but relatively short ciliate ( Figs 9 , 18 ).

Thorax obviously slightly narrower than head ( Fig. 4 ), bicolourous, largely brown, with some parts paler, ochreous ( Fig. 1 ). Mesonotum originally probably entirely brown, possibly darker medially and posteriorly, with finely shagreened surface (this microstructure arranged transversely in anterior part of mesonotum). Humeral (postpronotal) callus brown and markedly protruding; notopleural area pale brown; scutellum and subscutellum dark brown, the former with surface densely grooved longitudinally; pleural part of thorax distinctly bicolourous: anterior part of mesopleuron (anepisternum) and almost entire sternopleuron (katepisternum) pale ochreous; propleuron, posterior part of mesopleuron, hypopleuron (meron) and metanotum (anatergite) pale brown; pteropleuron (anepimeron) and metapleuron (katatergite) dark brown. Scutellum subtriangular with rounded apex, slightly convex dorsally; subscutellum well developed. Thoracic chaetotaxy ( Figs 1, 2 , 10 ): 1 strong and long hu (plus a number of microsetae on humeral callus), 2 npl (anterior strong, twice as long as posterior; both setae broken on right side), 1 very long and robust sa (only slightly shorter than pa), 2 pa (anterior very long and strong, longer than posterior dc; posterior pa thinner and about half length of the anterior), no prs; 2 dc (both postsutural, also anterior situated behind level of sa), anterior short (slightly more than half length of posterior), posterior robust but shorter than apical sc or anterior pa; scutum otherwise covered by uniform and relatively dense microsetae (more than 15 dc microsetae in row in front of anterior dc; ac microsetae arranged in about 8 rows in front of suture but less posteriorly, and only 4 rows reaching slightly beyond level of posterior dc); 2 sc, apical strong and very long (with anterior pa the longest thoracic seta), also laterobasal relatively robust, as long as three-fourths of the apical sc; 1 long upcurved ppl plus 2 microsetae near its base; mesopleuron with 1 distinct mspl in posterodorsal corner and numerous microsetae on most of its surface (except for anterodorsal part); sternopleuron with 1 long stpl and a number of scattered microsetae (also those on ventral part relatively short) leaving only anterodorsal corner of sclerite bare; prosternum obviously bare.

Legs originally probably all brown or pale brown (the densely brown-spotted appearance of femora is probably an artefact caused by the process of fossilization), relatively long and slender. Fore, mid and hind legs strikingly differing in length of their segments (see below); it seems like the mid leg is markedly prolonged in this species while the fore and hind legs have their normal proportions. Femur, tibia and also tarsus (basitarsus in particular) of mid leg are almost twice as long as those of fore leg, and distinctly longer than those of hind leg (cf. Figs 11–13 ). f 1 ( Figs 6 , 9 ) with a short row of 4–5 longer posteroventral to ventral setae in distal third and with about 4 posterodorsal setae forming a row in the middle of third of femur; f 2 ( Figs 5 , 11 ) very elongate, tapered distally, finely densely setulose but its distal fourth ventrally with a double row of thicker, shorter, denser setae (those in posterior row longer) and its proximal half with a dense brush of ventral upright hair-like setulae; f 3 without specific setae, uniformly densely finely setulose. t 1 ( Fig. 12 ) also uniformly finely setulose but with a short dorsopreapical seta and a similar ventroapical one in addition; t 2 with distinctive chaetotaxy ( Figs 11, 14 ) formed, besides usual short setosity, by a row of sparse erect posterior setae (4–5 longer and thicker) in distal two-fifths, 2 short dorsal setae (1 preapical, 1 in distal third) and 1 longer and thicker ventroapical seta plus 2 shorter setae on apex; t 3 ( Fig. 13 ) without dorsopreapical seta, but with 1 longer ventroapical and 1 shorter anteroapical seta, otherwise uniformly finely setulose. Tarsi simple, slender; mid and hind basitarsi long and with thicker laterally directed setulae; claws relatively small.

Wing ( Figs 8 , 15 ) somewhat elongate (narrower than in A. tertiaria ); veins pale brown; membrane distinctly brownish darkened in anterodistal half, having an elongate lanceolate light spot in otherwise brownish cell r 2+3. C reaching only slightly beyond apex of R 4+5, finely setulose but basally with a pair of longer setae and Cs 2 (sector between apices of R 1 and R 2+3) with thicker (but not longer) sparse spine-like setulae in addition. No costal break. Sc fine, proximally attenuated, distally ending into C, not fused with R 1. R 1 short, robust and bare, having a distinct preapical kink ( Fig. 15 , pk) on the level of end of Sc. R 2+3 long, very slightly sinuate, apically somewhat upcurved to C, ending distinctly farther from wing apex than would M. R 4+5 shallowly but distinctly bent posteriorly, and distally subparallel with M. Distal part of M almost straight but not reaching (ending slightly in front of) wing margin. Discal (dm) cell relatively elongate; its upper distal corner somewhat acutely projecting; anterior cross-vein (r-m) situated in about the middle of discal cell. Distal part of CuA 1 shorter than dm-cu cross-vein and not reaching wing margin; A 1 short, ending far from it. Cells bm and cup closed. Anal lobe moderately developed. Alula obviously small and narrow. Wing measurements: length 3.53 mm, width 1.35 mm, Cs 3: Cs 4 = 2.00, r-m\dm-cu: dm-cu = 2.28. Haltere pale brown, knob somewhat darker.

Abdomen ( Figs 1, 2 ) relatively slender, elongate, largely brown to dark brown, with dorsal sclerites elongately shagreened. All preabdominal terga rather sparsely but distinctly setose, with longest setae (some upright) at posterior and lateral margins. T1 and T2 (at least dorsally) ochreous, T3–T5 dark brown. T1 probably separate (visible only laterally) from T2. T1–T5 relatively large and long, distinctly bent laterally (pleural membrane not large). Preabdominal sterna pale brown, sparsely and shortly setose (only S4 and S5 visible, Fig.17 ) and obviously becoming wider posteriorly; S4 distinctly transverse; S5 largest and very broad, strongly transverse.

Postabdomen ( Figs 7 , 16, 17 ) with sclerites well developed, dark-pigmented and asymmetrical. T6 not present as separate sclerite, either reduced (absent) or, more probably, completely fused with S8 to form with it a large, long synsclerite termed here T6 +S8(?) being particularly extended on right side ( Fig. 16 ). S6 elongately subtriangular, ventrally attenuated, situated on left side of postabdomen ( Fig. 17 ) and probably (not precisely visible) attached to T6 +S8(?) dorsally and, at least partly, also to S7 ; S7 probably also subtriangular but its shape is not precisely discernible in the holotype. S6 apparently bare but S7 with at least 1 setula (most of sclerite covered by white moulding so that its setosity cannot be recognized). T6 +S8 (?) rather densely shortly setose but setae are only visible on its right side ( Fig. 16 ) .

Genitalia. Epandrium ( Figs 16, 17 ) short and high, with posterior side oriented ventrally due to enlarged synsclerite T6+S8 (?), probably shortly uniformly setose (only a few setae visible on left side). Anal fissure cannot be seen in the holotype. Gonostyli ( Figs 16, 17 ) relatively small but clearly asymmetrical. Right gonostylus ( Fig. 16 ) strongly bilobed, with anterior lobe very narrow and pale-pigmented, distinctly pointed and with a pair of small setae on apex; posterior lobe digitiform, dark, heavily sclerotized and bare, apically rounded. Left gonostylus ( Fig. 17 ) with posterior lobe curved and distally dilated, markedly longer than that of right gonostylus, but its anterior lobe not observable or absent. Cerci probably also asymmetrical (cf. Figs 16, 17 ) and situated ventrally between posterior lobes of gonostyli and projecting below ventral epandrial margin; left cercus with apex in profile more rectangular, right cercus larger and with apex more rounded, both pale-pigmented and finely haired. Internal genitalia (aedeagal and/or hypandrial complex) not visible in the holotype.

Female. Unknown.

Etymology. The name of the new species is derived from its similarity to druid flies ( Clusiidae ), adjective.

Comparison with related species. Because the type series of the only known relative, A. tertiaria Hennig, 1965 , is apparently not conspecific, A. clusioides sp. nov. is below compared with the female holotype of A. tertiaria but also with the male associated under A. tertiaria subsequently by HENNIG (1969). The new species differs from A. tertiaria (female holotype) in a number of characters including the following: (1) anterior ors smaller ( Fig. 9 ); (2) vi short but distinctly larger than peristomal setulae ( Fig. 19 ); (3) arista short ciliate (as in female paratypes of A. tertiaria , cf. HENNIG 1965: Fig. 173); (4) 1st flagellomere excavated posteriorly (in lateral view, Fig. 19 ); (5) thorax markedly narrower ( Fig. 4 , cf. HENNIG 1965: Fig. 176); (6) only 2 dc, the anterior dc short and situated beyond level of sa; (7) no prescutellar ac; (8) wing more elongate ( Figs 8 , 15 ) and distinctly (mainly distally) brown darkened ( Fig. 8 ) with small pale spot in cell r 2+3; (9) R 1 without setulae(!) and (10) with a distinct preapical „kink“ at level of end of Sc ( Fig. 15 ); (11) M not reaching wing margin and (12) dm-cu longer than distal section of CuA 1 ( Fig. 15 ); (13) mid tibia with 2 short dorsal setae (including the preapical one) in addition to a long row of posterodorsal setae ( Figs 11, 14 ), but the latter obviously overlooked by HENNIG (1965: Fig. 180) in the A. tertiaria holotype; (14) mid femur ventrally with double row (antero- and posteroventral) of dense short curved setae in distal fourth ( Fig. 11 ) but this feature can be sexually dependent (see note below) and hence missing in the female. Moreover, the scutellum of A. clusioides sp. nov. has a distinctive, longitudinally grooved surface structure hitherto unknown in Acartophthalmites .

The male of Acartophthalmites affiliated by HENNIG (1969) with A. tertiaria seems to be more similar to A. clusioides sp. nov. and hence also differing from the A. tertiaria female holotype. It is therefore highly plausible that this male does not belong to true A. tertiaria . This specimen resembles A. clusioides sp. nov. in the elongate wing (cf. HENNIG 1969: Fig. 19 ), short distal section of CuA

1

and in mid tibial chaetotaxy (cf. HENNIG 1969: Fig. 21). On the other hand it cannot be conspecific with the above new species because it has a simple (lacking preapical kink) and setulose R 1, M reaches the wing margin, A 1 is very long, the dorsal pregenital sclerite (= T6+S8?) is short and the posterior lobe of the gonostylus is bent posteriorly (see HENNIG 1969: Fig. 20).

A number of morphological characters found in A. clusioides sp. nov. revealed that the genus Acartophthalmites is apparently much more morphologically diverse than formerly anticipated. Particularly, the absence of setulae on R 1 (considered to be a generic character by HENNIG 1965) is rather surprising, although this may be the result of simple reduction only occurring in this species. Another important finding is the fact that a peculiar posterodorsal row of setae along t 2 has proved to be present in both males and females (seen in the unidentified specimens in Coll. Hoffeins), and was probably overlooked by HENNIG (1965). These setae may possibly be a diagnostic character of the whole genus (but see below). Further, the presence of a (albeit short) dorsal preapical seta on t 2 indicates a relationship to Clusiidae (see below) as does the more elongate and distally darkened wings of the new Acartophthalmites species. The strikingly prolonged mid leg, also seen in the male of ‘ A. tertiaria ’ ( HENNIG 1969: Fig. 21), and the setosity of f 2 (possibly an adaptation for copulation), may also be male-associated sexual characters. The preapical kink (see Fig. 5 ) on R 1 is another unexpected feature regarding the fact that there is no subcostal break on C (as is normal for the genus).

Figures

Figs 1–2. Acartophthalmites clusioides sp. nov., male holotype. 1 – right side. 2 – left side. Length of holotype 3.85 mm. Photo by J. Roháček.

Figs 3–8. Acartophthalmites clusioides sp. nov., male holotype. 3 – Baltic amber sample embedded in polyester resin in situ (length of preparatum 13.8 mm); 4 – head and thorax dorsally; 5 – head and anterior part of thorax, left laterally; 6 – ditto, right, laterally; 7 – postabdomen, right, laterally (body length of holotype 3.85 mm); 8 – left wing (length 3.53 mm). Photo by J. Roháček.

Figs 9–15. Acartophthalmites clusioides sp. nov., male holotype. 9 – head and fore femur, left, sublaterally; 10 – thorax, left, laterally; 11 – left mid trochanter, femur, tibia and basitarsus, posteriorly; 12 – left fore tibia, posteriorly; 13 – left hind tibia, anteriorly; 14 – distal part of right mid tibia, posteriorly; 15 – left wing. Scales = 0.3 mm (Figs 9, 10), 0.5 mm (Figs 11–13, 15) and 0.2 mm (Fig. 14). For abbreviations see text (p. 411).

Figs 16–19. Acartophthalmites clusioides sp. nov., male holotype. 16 – apex of abdomen laterally, right side; 17 – the same, left side; 18 – head, dorsally; 19 – anteroventral part of head with antenna, right, laterally. Reconstructed parts in dashed lines. All scales = 0.2 mm. For abbreviations see text (p. 411).