Centrioncus angusticercus Feijen, 1983

Feijen, Hans R. & Feijen, Cobi, 2023, A revision of Centrioncus Speiser (Diptera, Diopsidae, Centrioncinae) with descriptions of new species from Angola, Burundi, and Kenya, ZooKeys 1144, pp. 1-93 : 1

Centrioncus angusticercus Feijen

Figs 31 , 32

Centrioncus angusticercus Feijen, 1983: 75.

Type material.

South Sudan, holotype, ♀, Nagichot, [4°16'37.99"N, 33°33'34.99"E, 1980 m], D.J. Lewis (NHMUK) (not examined, but notes and pencil drawings for Feijen (1983) were used).

Diagnosis

(after Feijen 1983). Centrioncus angusticercus can be recognised by its pruinose, mesally slightly depressed frons with two glossy spots; dark brown collar; blackish brown scutum; blackish brown scutellum with pale brown lateral sides and spines; pleura blackish brown except for brown propleuron and anterior anepisternum; apical seta/scutellar spine ratio:> 1.0; pale brown fore femur with distal third on inner side dark brown and small dark spot apically on outer side, with 36 tubercles; small round central wing spot (Fig. 31 ) around junction of crossvein r-m and vein M1 in tip of cell br and base of cell r4+5 slightly extending into cell bm+dm; tergites blackish brown, apical edges paler; female 7th spiracle just in tergite; anterior sclerite of female sternite 7 rectangular, w/l ratio: ~ 4.4; posterior sclerite of female sternite 7 consisting of well-sclerotised trapezoidal anterior plate and two weakly sclerotised posterolateral extensions (Fig. 32 ), anterior edge of anterior plate parallel to its posterior edge, short lateral sides straight, slightly broadening posteriorly, posterior side concave, weakly sclerotised posterolateral extensions irregularly shaped and posteriorly with 6-8 setulae; very elongate female cercus with l/w ratio: 5.4 (Table 8 ); pentagonal subanal plate; smooth round spermathecae with some tiny pustules and small dimple surrounded by ridge-like ring.

Supplementary description.

Wing. Small, rounded, elongate central wing spot (Fig. 31 ) around junction of crossvein r-m and vein M1, in posterior part of tip of cell br and posterior part of base of cell r4+5 to halfway to crossvein dm-m, slightly extending into cell bm+dm; very vague infuscation along vein M4 between cell cua and crossvein dm-m; vein CuA+CuP from vein CuP onward extending under an angle of 25° to wing margin in straight line; vein M4 continuing distally from crossvein dm-m in straight line to wing margin.

Female postabdomen. Anterior sclerite of sternite 7 rectangular, tapering posteriorly, lateral sides convex, w/l ratio: ~ 4.4 (Fig. 32 , Table 8 ); posterior sclerite of sternite 7 consisting of well-sclerotised trapezoidal anterior plate and two weakly sclerotised posterolateral extensions (Fig. 32 ); anterior edge of anterior plate parallel to posterior edge of anterior sclerite, short lateral sides straight, slightly expanded posteriorly, posterior edge concave; weakly sclerotised posterolateral extensions irregularly shaped and posteriorly with 3-4 pairs of setulae; very elongate female cercus with l/w ratio: 5.4 (Table 8 ).

Distribution and habitat.

In the Shillito archive (now in NHMUK), a letter was found written on 22 January 1950 by D.J. Lewis, the collector of the holotype, and addressed to J.F. Shillito. It provided information on the collecting locality of the single known specimen: "The Diopsid, Centrioncus prodiopsis Speiser, was taken at an altitude of about 1980 metres among vegetation near a small stream in a patch of forest. Nagichot is on the Didinga Hills, one of the many isolated ranges, and may be considered as part of the Eastern and Southern zoogeographical Province ..." The type locality is shown on the map for Eastern Africa (Fig. 29 ).

Remarks.

Feijen (1983) described the posterior sclerite of sternite 7 as "very roughly U-shaped with eight hairs, anterior edge parallel to posterior edge of sternum 7, anterior section well sclerotized, but arms of the U connecting to posterior hairs of sclerite weakly sclerotized." However, the view that this sclerite can be described as “U-shaped” is now rejected (compare Fig. 32 vs. Figs 43 , 62 , 82 , 119 , 133 , 148 ). Centrioncus angusticercus is now placed outside the group of Centrioncus with a U-shaped sclerite. Instead, it is considered as closer to the other Centrioncus without a U-shaped sclerite: C. aberrans and C. crassifemur sp. nov. Other similarities like l/w ratio of ♀ cercus and w/l ratio of ♀ anterior sternite 7 also support this group. For a confirmation of this relationship, the discovery of the male sex and study of the male genitalia of C. angusticercus and C. crassifemur sp. nov. and molecular analyses will be required.

Figures

Figure 29. Distribution map of the seven Eastern African Centrioncus species.

Figures 31, 32. Centrioncus angusticercus, ♀, holotype, Nagichot, South Sudan 31 wing, dorsal view 32 sternite 7, ventral view. Scale bars: 0.5 mm (31); 0.1 mm (32). Both drawings were processed based on original pencil drawings from Feijen (1983: figs 13, 27).

Figures 41 - 43. Centrioncus bururiensis sp. nov., Bururi Nat. Forest 41, 43 ♀, paratype 42 ♀, holotype 41 sternites 1 - 5, ventral view 42, 43 sternite 7, ventral view. Scale bars: 0.5 mm (41); 0.1 mm (42, 43).

Figures 61 - 67. Centrioncus bytebieri, ♀ 61 Ngangao Forest 62 - 67 Vuria Forest 61, 62 sternite 7, ventral view 63 subanal plate ventral view 64 spermathecae 65 sternites 8, 10, cerci, ventral view 66 egg 67 egg, detail. Scale bars: 0.2 mm (61, 62, 66); 0.1 mm (63 - 65, 67).

Figures 80 - 83. Centrioncus copelandi sp. nov., ♀, paratype, Kasigau Mtn 80 sternites 1 - 6, ventral view 81, 82 sternite 7, ventral view 83 terga 8, 10 and cerci, dorsal view. Scale bars: 0.2 mm

Figures 118 - 121. Centrioncus decoronotus, ♀, Ol Doinyo Orok 118 sternites 1 - 5, ventral view 119 sternite 7, ventral view 120 spermathecae 121 egg, detail of external structure (L = line, R = ridge). Scale bars: 0.2 mm (118, 119); 0.05 mm (120, 121).

Figures 132 - 135. Centrioncus jacobae, ♀, paratype, Mt Soche 132 sternites 1 - 6, ventral view 133 sternite 7, ventral view 134 abdomen, ventral view 135 abdomen, dorsal view. Scale bars: 0.5 mm (132, 134, 135); 0.2 mm (133).

Figures 146 - 149. Centrioncus prodiopsis, ♀, Oloitokitok 146 sternites 1 - 6, ventral view 147, 148 sternite 7, ventral view 149 tergite 7 and cerci, posterolateral view. Scale bars: 0.5 mm (146); 0.1 mm (147 - 149).