Rheosmittia seni, Published, 2007

Published, First, 2007, Chironomid midges from early Eocene amber of France (Diptera: Chironomidae), Zootaxa 1404, pp. 1-66 : 39-40

Rheosmittia seni n. sp.

( Figs. 36, 37)

Etymology: This species is named for our colleague Dr. Sevket Sen, palaeontologist at the MNHN.

Diagnosis: Male antenna with 11 flagellomeres; antennal ratio 0.45; 2 vertical postocular setae; male antenna without strong subapical setae; scutum without median longitudinal groove; acrostichals absent; 6 dorsocentrals; 4 setae on scutellum; scutum with pronounced scutal tubercle but without microtrichial tuft; lateral spines on median and hind tibial spurs not diverging; costa strongly extended beyond R 4+5; squama bare; gonostylus simple; no pars ventralis between gonocoxite bases; inferior volsella without sharp hook; 2 long setae on anal point.

Description: Head 0.13 mm long, deformed; ocelli absent; antenna 0.42 mm long, much longer than head, distinctly hairy, with 11 flagellomeres covered with long setae (shortest 0.008 mm long, longest 0.23 mm long), pedicel broad and short, rounded, 11 th flagellomere 0.13 mm long; antennal ratio about 0.45; eye bare, without dorsomedial extension; mouthparts lacking functional mandibles; 5 palpomeres with setae; 2 vertical postoculars; frontal, inner and outer vertical setae absent. Thorax 0.4 mm long, 0.24 mm wide, 0.38 mm high; postnotum bare; surface of scutellum with 4 long setae; small scutal tubercle; acrostichals absent, 6 dorsocentral uniserial setae; scutum without median longitudinal groove; 2 prealar setae, no supraalar setae; epimeron II and preepisternum bare. Wing macropterous, 0.76 mm long, 0.24 mm wide, hyaline, membrane bare; anal vein An 2 absent; radius with 3 branches R 1, R 2+3 and R 4+5, R 2+3 not divided into R 2 and R 3; R 4+5 ending in costa before apex of wing, costa with numerous setae, strongly extended beyond R 4+5, produced by 0.05 mm; only M 1+2 and M 3+4 present; Cu 1 strongly curved; cross­vein MCu absent; anal lobe not developed; squama bare. Halter 0.1 mm long. Fore femur 0.28 mm long, tibia 0.27 mm long, tarsus 0.37 mm long; mid femur 0.3 mm long, tibia 0.26 mm long, tarsus 0.32 mm long; hind femur 0.29 mm long, tibia 0.28 mm long, tarsus 0.36 mm long; ta4 of all legs cylindrical, not cordiform; fore tibia with 1 long spur, mid tibia with 2 small spurs and hind tibia with 2 long spurs, hind tibial comb well developed; small pulvilli present. Abdomen 0.65 mm long; gonostylus simple, elongate, 0.03 mm long and 0.008 mm wide, hinged to gonocoxite and folded inward; gonocoxite 0.05 mm long, 0.03 mm wide at base, with long setae apically and on outer surface; anal point broad and conical, 0.01 mm long, 0.04 mm wide at base, with 2 strong setae on base; inferior volsella simple, without sharp hook.

Discussion: In the key to the Holarctic orthocladiine genera of Cranston et al. (1989), these Orthocladiinae fall in the genus Rheosmittia because of the following characters: wing well developed, without thick clavus; scutum without median longitudinal groove; eye not hairy; wing membrane bare; epimeron II, posterior mesanepisternum, and dorsal antepronotum bare; lateral spines on median and hind tibial spurs not diverging; anal point short without lateral lamellate setae; squama bare; antenna without strong subapical setae; gonostylus simple; tarsomere 4 cylindrical; no pars ventralis between gonocoxite bases; acrostichals absent; costa strongly extended beyond R 4+5; anal point without marginal setae; scutum with hump; terminal palp segment less than 7 times as long as wide; and scutum without microtrichial tuft. This last character separates Rheosmittia from the closely related Parakiefferiella Thienemann, 1936 ( Cranston & Saether 1986). Cranston et al. (1989) listed two Holarctic species, R. spinicornis ( Brundin, 1956) and R. languida ( Brundin, 1956) . A third Nearctic species R. arcuata Caldwell, 1996 , and a fourth, the Turkish R. hamulata Caspers & Reiss, 1989 , also were described ( Caspers & Reiss 1989, Caldwell 1996). Based on Cranston & Saether (1986) and Caldwell (1996), Rheosmittia seni n. sp. is close to R. spinicornis and R. arcuata because of its pronounced scutal tubercle, 11 flagellomeres, same wing venation, antennal ratio 0.45 and pilosity, presence of two vertical postocular setae, and shape of the gonocoxite. Rheosmittia seni differs from R. arcuata by its inferior volsella without a sharp hook, two rows of six dorsocentrals, four setae on the scutellum and apparently two long setae on the anal point, as opposed to four dorsocentrals, two setae on the scutellum, and four setae on the anal point, as in R. spinicornis . Seredszus (2003) described and figured a Baltic amber ‘ Rheosmittia spec. nov.’ with a sharp anal point and long gonostyli, unlike in the extant species and R. seni .

FIGURE 37. Rheosmittia seni n. sp., holotype PA 1652, drawing of male genitalia (scale bar = 0.1 mm). Material: Holotype PA 1652, paratypes PA 2964, PA 944 (2/2), PA 944 (1/2) and PA 132 (2/12), PA 944 (1/2) all males.