Libanopelopia cretacica, Veltz & Azar & Nel, 2007

Veltz, Isabelle, Azar, Dany & Nel, André, 2007, New chironomid flies in Early Cretaceous Lebanese amber (Diptera: Chironomidae), African Invertebrates 48 (1), pp. 169-191 : 171-175

Libanopelopia cretacica sp. n.

Figs 1–3

Etymology: After the Cretaceous period.

Description: Head deformed, 0.4 mm long. Ocelli absent.Antenna 0.88 mm long, much longer than head, distinctly hairy; scape broad and short, rounded; pedicel very short; 14 flagellomeres, flagellomeres 1–13 covered with long setae (shortest 0.01 mm long, longest 0.48 mm long), flagellomere 13 very long (0.5 mm), flagellomere 14 evenly tapering from base to apical nipple, twice as long as broad at base. Eye bare, deformed but with an apically expanded dorso-medial extension, with 4 rows of ommatidia at minimum width. Clypeus 0.14 mm long, with few dorsal setae. Mouthparts lacking functional mandibles; all palpomeres with numerous setae, but the second with 2 distinctly longer setae. No postocular setae; 5 or 6 long frontal setae; inner vertical and outer vertical setae not visible.

Thorax 0.7 mm long, 0.33 mm wide, 0.5 mm high; postnotum bare, with a very distinct longitudinal median groove; scutellum bare but with 8 long setae on its posterior margin; scutal tubercle absent; 1 supraalar, 3 prealars, a series of 7 or 8 anterior acrostichals, a series of few aligned dorsocentrals; postanepisternal setae absent.

Wing macropterous, 1.44 mm long, 0.48 mm wide, hyaline, covered with macrotrichia. Costa ending just beyond insertion of last branch of radius, produced by 0.06 mm, shorter than cross-vein RM, ending slightly before M 1+2. Radius with 3 branches R 1, R 2+3, and R 4+5; R 2+3 well separated from R 1 and R 4+5, R 2+3 apically forked into R 2 and R 3; R 2 0.04 mm long, ending in R 1, R 3 0.1 mm long, ending in costa. Only M 1+2 and M 3+4 present; cross-vein MCu present; cross-vein RM 0.04 mm distal of MCu; cubital fork 0.02 mm proximal to cross-vein MCu. Anal vein An 2 absent. Halter 0.22 mm long.

Fore femur length 0.72 mm, tibia 0.82 mm, tarsus 1.06 mm; mid femur 0.71 mm, tibia 0.66 mm, tarsus 0.9 mm; hind femur 0.54 mm, tibia 0.70 mm, tarsus 0.96 mm. Tibial spur formula 1–2–2, all with lateral teeth, comb-like; those of hind legs not flattened – a state similar to extant Derotanypus (see Murray & Fittkau 1989, fig. 5.13D); 2 hindleg tibial spurs, 0.04 mm and 0.02 mm long respectively. Fourth tarsomeres of all legs cylindrical, not cordiform.Middle leg claw simple as in front and hind legs; not pectinate. Hind tibial comb disposed in 1 row.

Abdomen 1.6 mm long, 0.24 mm wide. Gonostylus nearly bare, strongly curved, short, 0.07 mm long, 0.03 mm wide, distinctly shorter than gonocoxite; gonocoxite 0.12 mm long, 0.06 mm wide, with numerous long setae. Anal point very smooth, broad and small (0.7 mm wide at base, 0.02 mm deep?). Inferior volsella not visible; if present, very small.

Holotype: ơ HAR 2. LEBANON: South Lebanon district [Mouhafazit Loubnan el-Janoubi]: Caza Jezzine, locality between villages Homsiyyeh, Aazour and Roum; Early Cretaceous, Neocomian sandstone (D. Azar coll.).

Note:This amber outcrop was discovered in July 1999 by one of the authors (D.A.), but biological inclusions were only found when the exact layer bearing amber was located in June 2004. The present chironomid fly is the first fossil insect to be described from this outcrop.

Discussion: According to the key to dipteran families ( McAlpine 1981), this fossil can be included within Chironomidae because of the combination of the following characters: anal vein An2 absent; radius with only three branches R 1, R 2+3, and R, costa ending just beyond insertion of last branch of radius; ocelli absent; antennae much longer than head, and distinctly hairy; wings narrow; only M 1+2 and M 3+4 present; mouthparts lacking functional mandibles; postnotum with a very distinct longitudinal groove.According to the Nearctic genera keys of Oliver (1981) and the key to Holarctic subfamilies of Oliver and Dillon (1989) and to Palaearctic subfamilies in Saether et al. (2000), this fossil belongs to the subfamily Tanypodinae because of the combination of the following characters: macropterous, wing extending posterior to first abdominal segment; crossvein MCu present; R 2+3 present, apically forked into R 2 and R 3; postnotum with longitudinal groove; wing covered with macrotrichia.

4+5

Saether (2000 a) proposed a phylogeny of the chironomid subfamilies. He considered the Tanypodinae as a part of the semifamily Tanypodoinae (= Tanypodinae + Usambaromyiinae + Podonominae + Aphroteniinae ), mainly characterised by the presence of a gonotergite in male adults formed by the fusion of tergite IX, laterosternite IX and sternite IX. Unfortunately, the laterosternite IX is not visible in our fossil.

Nevertheless, the specimen can be attributed to the clade ( Tanypodinae + Usambaromyiinae) because it shows the main synapomorphy, i.e. “tibial spurs with lateral teeth, comb-like” (Saether 2000 a). Affinities with the Usambaromyiinae (Andersen & Saether 1994) can be excluded because of the presence of vein MCu, tarsomere 4 elongate and not cordiform, and claw of middle legs simple, as in front and hind legs and not pectinate.

Ansorge (1999) proposed a fossil Liassic subfamily Aenneinae , also known from the late Triassic (Krzemiński & Jarzembowski 1999), based on the presence of a long basal part of Rs (plesiomorphy), not present in our fossil. Ansorge (1999) considered Aenneinae to be a possible sister group of a clade comprising other chironomid subfamilies; however, he appears to have ignored the Telmatogetoniinae and some other subfamilies.

Kalugina (1993) erected the Cretaceous fossil subfamily Ulaiinae , based on the genus Ulaia , with three species, U. communis (pupa and an adult wing),? U. magna (pupa), and U. kangilica (pupa). As it is impossible to rear a fossil pupa, the allocation of a pupa and an adult wing to the same species is problematic. The wing attributed to U. communis is of a tanypodine-type. It differs from our fossil in that its R 2 is longer than R 3. Thus affinities with this genus and subfamily can be excluded. Furthermore, the validity of this fossil subfamily remains debatable.

According to the key to Nearctic tanypodine tribes and genera of Oliver (1981) and to Fittkau (1962), Libanopelopia gen. n. falls in the Pentaneurini because of the following characters: fourth tarsomeres cylindrical, not cordiform; cubital fork proximal to crossvein MCu; costa produced beyond the radius by distance less than length of cross-vein RM; postanepisternal setae absent; postnotal setae absent; tibial spurs of hind legs not flattened. However, there are no recent Pentaneurini which bear the configuration of the R veins found in Libanopelopia . Apart from the short costal extension, the overall wing venation conforms to the tribe Macropelopiini , particularly in the shape of radial veins. The costal extension is quite variable and obviously less important than the overall wing venation. We thus consider the possibility of the genus belonging to the tribe Macropelopiini .

In the keys to Tanypodinae by Murray and Fittkau (1989) and Saether et al. (2000), Libanopelopia keys to couplet 32 and couplet 44 respectively, since vein MCu is placed beyond FCu, the costa is produced beyond the radius by a distance less than the length of RM and ending slightly before M 1+2, the gonostylus is short, volsellae appear to be absent, the gonostylus is not robust and has parallel sides, the claws are not spatulate, and the eyes are bare. Included in couplet 32 are the pentaneurine genera Zavrelimyia Fittkau, 1962 , Reomyia Roback, 1987 , Krenopelopia Fittkau, 1962 and Telmatopelopia Fittkau, 1962 ( Roback 1987) . However, unlike Libanopelopia , all these genera have a reduced R 2, and veins R 1 and R 2+3 are very closely parallel. In addition, Zavrelimyia has an indistinct R 3 which does not reach the costa. Reomyia has a scutal tubercle and a gonostylus which is not strongly curved. In Krenopelopia , the costa ends above or slightly beyond M 1+2 and the gonostylus is about three quarters the length of the gonostylus. Telmatopelopia has a gently curved gonostylus but otherwise, among the species included in couplet 32, it appears to be the genus most similar to Libanopelopia .

If the short costal extension is disregarded, Libanopelopia keys to the macropelopiine genus Derotanypus Roback, 1971 ( Murray & Fittkau 1989; Saether et al. 2000), since vein MCu is placed beyond FCu, the tibial spurs have lateral teeth, the postnotals are absent and tibial combs are present only on the hind legs. Libanopelopia differs from the genus Derotanypus Roback, 1971 in the presence of a shorter costal extension and an unequal length of the tibial spurs.

Figures

Figs 1–3. Libanopelopia cretacica gen. et sp. n., holotype HAR 2: (1) details of general habitus; (2) wing; (3) general habitus. Scale bars = 1 mm in Figs 1, 3 and 0.5 mm in Fig. 2.