Megacentron eocenicus, Published, 2007

Published, First, 2007, Chironomid midges from early Eocene amber of France (Diptera: Chironomidae), Zootaxa 1404, pp. 1-66: 51-53

publication ID

1175­5334

persistent identifier

http://treatment.plazi.org/id/03CE87EB-4941-072D-FF36-FBADFC5BDDDB

treatment provided by

Felipe

scientific name

Megacentron eocenicus
status

n. sp.

Megacentron eocenicus   n. sp.

( Figs. 48 –50)

Etymology: This species is named after the Eocene age of the species.

Diagnosis (male characters): Wing hyaline; RM oblique to R 4+5; antenna with 14 flagellomeres; fore tibia bearing well developed scale with strong black spur, similar to those of mid and hind tibiae; anal point sharp; 3 pairs of volsellae; gonostylus distinctly longer than volsellae; body length relatively short, 4.5 mm long; antennal ratio about 2.55.

Description: Head 0.46 mm long; ocelli absent; antenna 1.25 mm long, much longer than head, distinctly hairy, with 14 flagellomeres covered with long setae (shortest 0.08 mm long, longest 0.57 mm long), antennal ratio 2.55 (> 0.35), pedicel broad and short, rounded, 14 th flagellomere 0.93 mm long; eye bare but deformed, with dorsomedial extension, with 4 rows of ommatidia at minimum width; mouthparts lacking functional mandibles; 5 palpomeres with numerous setae; numerous postocular setae, frontal an inner vertical and outer vertical setae absent. Thorax 1.12 mm long, 0.54 mm wide, 1.1 mm high; preepisternum bare. (The type specimen was partly destroyed during its preparation and the wing is no longer visible, but we examined it before preparation). Wing hyaline, with general pattern of chironomine type and with RM oblique to R 4+5. Halter 0.37 mm long. Fore femur 0.9 mm long, tibia 1.25 mm long, tarsus 2 mm long; mid femur 1.16 mm long, tibia 1.13 mm long; hind femur 0.9 mm long, tibia 1.05 mm long; fore tibia bearing well­developed scale with strong black spur, similar to those of mid and hind tibiae; hind tibial combs separate; mid and hind tibiae with 2 spurs, 1 on each comb. Abdomen 2.69 mm long; gonostylus with setae, 0.21 mm long, 0.05 mm wide; fused to gonocoxite 0.21 mm long, 0.08 mm wide, with setae; anal point conical and long, 0.16 mm long; inferior volsella elongate, 0.1 mm long, apically truncated, apically with numerous strong setae and 2 long setae (longest 0.23 mm long and shortest 0.07 mm long); median volsella present, 0.1 mm long, covered with numerous setae.

FIGURE 49. Megacentron eocenicus   n. sp., holotype PA 12709, photograph of male genitalia.

FIGURE 50. Megacentron eocenicus   n. sp., holotype PA 12709, drawing of male genitalia (scale bar = 0.2 mm).

Discussion: These fossils fall in the Chironominae   . In the key to Holarctic genera of Cranston et al. (1989), they fall near the genus Pseudochironomus Malloch, 1915   , because of the following characters: RM oblique to R 4+5; antenna with 14 flagellomeres; and fore tibia bearing a well­developed scale with a strong black spur, similar to those of the mid and hind tibiae. This last character is diagnostic for the Pseudochironomini Saether, 1977   , which is mainly present on the Austral continents (South America, Australia). Five other genera are currently listed in this tribe ( Andersen & Saether 1997). Affinities with the genera Riethia Kieffer, 1917   , Pseudochironomus Malloch, 1915   , and Manoa Fittkau, 1963   , can be excluded because they have no true anal point, unlike Megacentron eocenicus   ( Freeman 1961, Andersen & Saether 1997). Also, Riethia   has only two volsella ( Freeman 1961). Aedokritus Roback, 1958   , has spotted or banded wings ( Roback 1960; Saether 1977a, b; Trivinho­Strixino 1997). Comparison with Psilochironomus Sublette, 1966   , was not possible, but this genus seems to be poorly known, as Spies & Reiss (1996) consider its status dubious because the terminalia of the male type are missing. Megacentron eocenicus   corresponds in the main characters with the diagnosis of the last genus Megacentron Freeman, 1961   , especially in the presence of a long and narrow anal point ( Freeman 1961). Megacentron   is recorded from Australia ( M. erebeus (Skuse, 1889))   and Argentina ( M. cuneicalcar Edwards, 1931   ) ( Saether 1977b). Megacentron eocenicus   differs from M. erebeus   by its longer gonostylus, distinctly longer than the volsellae. Our fossil is similar to M. cuneicalcar   , but differs from it in body length (4.5 mm instead of 6 mm in M. cuneicalcar   ) and antennal ratio, which is about 2.55 in our fossil (1.7 in M. cuneicalcar   ) ( Edwards 1931). For these reasons, we recognize a new species for this fossil.

Material: Holotype PA 12709, paratype PA 692, both males.