Chaetonerius stichodactylus, Sepúlveda & Echeverry & Souza, 2020

Sepúlveda, Tatiana A., Echeverry, Angela & Souza, Diego De S., 2020, New species of Chaetonerius Hendel (Diptera: Neriidae) and key for identification of the Neriidae of Tanzania, Zootaxa 4755 (1), pp. 190-194 : 191-192

Chaetonerius stichodactylus sp. n.

( Figures 1 A–G)

Type locality: East Usambara , Amaní, Tanga Region, Tanzania .

Type material. Chaetonerius stichodactylus sp. n., holotype m# (dissected, with two legs attached to the pin): (1) TANZANIA, East Usambara , Amaní, 1000m, 30.i.1977 (2) Zool. Mus., Copenhagen, H. Enghoff., O. Lomholdt, O. Martin leg. [ ZMUC #490 ] ( Fig. 1 A–G) . Paratypes: 1 f#, same data as holotype [ DZUP #487 ]; 2 f#, same data as holotype, except − 27.i.1977 − [ ZMUC #1223 , # 1228 ] .

Diagnosis. Arista brown pubescent. Frontal vitta mostly blackish-brown, except for the yellow area from anterior margin, narrowing posteriorly; fronto-orbital plate yellow; anterior fronto-orbital seta thin and slightly shorter than half of mid fronto-orbital seta, equally separated from anterior margin of frons and mid fronto-orbital seta; posterior fronto-orbital seta lateroclinate, inner vertical seta inclinate; occiput dorsally yellow, contrasting with the dark brown median sclerite and the dorsal half occiput paler brown to yellow; dorsal scutum with yellow stripe, divided by median wide brown stripe narrowing near scutoscutellar suture; fore femur entirely brown, mid and hind femora with yellow ring on distal third; epandrium narrowing from both ends towards the middle; cercus rectangular, with apical width only slightly larger than base and apically truncate; cercus shorter than surstylus; cercus with ventral setae short and thick, densely positioned towards distal margin, and dorsal setae long, thin and scattered.

Male (holotype). Body length 6.1 mm. Wing length 5.0 mm, width 1.6 mm. Head. First flagellomere ovate. Inner process of pedicel digitiform. Underdeveloped antennal base present (sensu Sepúlveda & de Carvalho 2019); frontogenal suture faint anteriorly below the parafacial. Posterior fronto-orbital seta conspicuously long, reaching the size of postocellar seta. Four variegated postocular setae, not aligned with occipital setae; four occipital setae in one side and two on the other; postgena yellow with dense white pruinescence and yellow postgenal setae. Thorax. Four well-developed dorsocentral setae: one presutural, as long as posterior fronto-orbital and three postsuturals increasing in size posteriorly, being the pre-scutellar straight and same-sized as apical scutellar seta; katatergite yellow. Scutelum trapezoid with rounded margins; apical scutellar seta curved; discal scutellar seta long, measuring two thirds the size of apical scutellar seta. Legs. Fore coxa yellow with one spine-like anterolateral seta; mid and hind coxa brown. Fore femur brown with anteroventral row of short spine-like setae; mid femur with one diffuse yellow ring on distal third; hind femur with one well-defined ring on distal third. Fore tibia with spine-like seta posteriorly. Abdomen. Epandrium almost twice longer than syntergosternite 8; wide with medial and membranous contraction on distal half dorsally. Distiphallus dorsally sclerotized and ventrally membranous; ventral margin rough, covered with numerous membranous projections ( Fig. 1G ); apex trifurcate in two short membranous spikes and one larger median and partially sclerotized spike.

Female variation. Body length 6.5−7.0 mm. Wing length 5.4−6.0 mm, width 1.7−1.9 mm. First flagellomere and head slightly longer. Occiput pale brown dorsally and median stripe pale yellow. Postocular and occipital setae variable in number and size; postgena without dense pruinescence. Fore femur with one anteroventral spine-like seta on distal third; fore tibia without spine-like setae posteriorly. Oviscape yellow with brown tip.

Etymology. The species name C. stichodactylus is allusive to the shape of its cercus, which bears ventral cylindrical setae densely placed near the distal margin ( Fig. 1G ), resembling an anemone’s ‘carpet of Mertens’, Stichodactyla mertensii Brandt, 1835 (Cnidaria) .

Distribution. Tanzania.

Remarks. The cercus of C. stichodactylus is shorter than the surstylus and bears ventral cylindrical setae never described before in any species of Neriidae ( Fig. 1G ). Other peculiar character useful in the recognition of both male and female specimens of C. stichodactylus is the orientation of the head setae, with posterior fronto-orbital seta proclinate and inner vertical seta inclinate ( Figs 1 A–C), also described for the first time in Neriidae .

Two more species of Chaetonerius are known from Tanzania: C. apicalis and C. perstriatus . The former species belong to the apicalis -group proposed by Aczél (1954) and can be easily differentiated from C. perstriatus by its coarse male genitalia, characteristic of the species in this group. On the other hand, C. perstriatus presents simpler epandrium and surstylus, along with a larger cercus ( Barraclough 1993b).

It is possible that the genitalic structure of Chaetonerius species play an important role in species diversification within this genus, but this hypothesis has not been tested by phylogenetic approaches. The great morphological affinity between the new species, C. stichodactylus and C. perstriatus is also reflected in the shape of the epandrium and surstylus. However, despite those similarities, males of both species can be easily differentiated based on other characters of the genitalia. In contrast, the females can only be differentiated based on the head setae. In addition to the genitalia, the type of the arista and the color of the occiput, fore coxa and femora also hint on a close affinity between C. stichodactylus and C. perstriatus .

Figures

FIGURE 1. Chaetonerius stichodactylus sp. n., holotype male: A, head frontal; B, head lateroventral; C, head laterodorsal; D, habitus lateral; E, habitus dorsal; F, wing; G, genitalia ventral. Abbreviations: a f-orb s, anterior fronto-orbital seta; ar, arista; cerc, cercus; distph, distiphallus; epand, epandrium; hypd, hypandrium; i vt s, inner vertical seta; m f-orb s, mid fronto-orbital seta; o vt s, outer vertical seta; p f-orb s, posterior fronto-orbital seta; poc s, postocellar seta; sur, surstylus.