Isocanace mauritiana Munari, 2021

Munari, Lorenzo, Kirk-Spriggs, Ashley H. & Mcgregor, Gillian K., 2021, The surf flies of the Mascarene Islands (Diptera: Canacidae: Canacinae), with the description of a new species, Zootaxa 4990 (3), pp. 563-570 : 566-568

Isocanace mauritiana Munari sp. nov.

Figs 3, 6 , 10

Etymology. The specific epithet mauritiana is a Latin toponymic adjective that highlights the type locality, the Mauritius Island.

Description. Male (primarily based on holotype).

Measurements: body length (excluding antenna) 1.85–2.05 mm; wing length 1.67–1.82 mm.

Head. With 3 large interfrontal setae (mostly broken or missing) along lateral margin of frontal vitta (= mesofrons of authors), appearing slightly inclinate and proclinate; frontal vitta brown, dull; mid portion of frontal vitta with 2–3 pairs of inconspicuous, sparse setulae; postocellar setae distinct, divergent, slightly proclinate, about 1 / 2 length of ocellar setae, the latter strongly divergent; fronto-orbital plate (= parafrons of authors) dull, changing from pale grey to whitish grey; 4 lateroclinate fronto-orbital setae; antennal arista ( Fig. 3 ) not plumose, branches short, as long as or very slightly longer than basal arista width; 3 anaclinate genal setae, anterior seta arising from peristomal margin, posterior pair just below mid portion of eye; both bulging face and gena appearing of changing hue, white microtomentose (in frontal view), grey microtomentose (in lateral view); minimum height of gena ca 0.6 × height of compound eye, measured perpendicular to mid-section.

Thorax. Both holotype and paratype setal vestiture of mesonotum highly depauperated, with many setae and setulae missing or misoriented. Dorsocentral setae 4 (1 + 3); acrostichal setulae in approximately 2–3 irregular rows anteriorly, reduced to 1–2 rows posteriorly, median 2 rows with larger setulae, numbering approximately 12–13 (calculated from both setulae and setal sockets), prescutellar acrostichal setae much longer than other acrostichal setulae; 1 supra-alar seta; lateral postalar seta very strong and long.

Scutellum. With 2 pairs of long, strong marginal setae; scutellar disc apparently bare, or at most with 2–3 microscopically perceptible sockets (possibly remnants of missing discal setulae; very scarcely visible in the holotype); mid portion of scutellar disc bare, glossy black (this character should be corroborated based on additional material); anterior notopleural seta black, shorter and finer than posterior seta; propleuron bare of setulae; 1 proepisternal seta; 1 proepimeral seta; anepisternum with 2 long, posteromarginal black setae and 1 anaclinate seta on dorsal margin; katepisternum with long, black seta at posterodorsal corner.

Wing. Membrane yellowish grey to pale grey; costal vein ratio = 0.20; M vein ratio = 0.37‒0.43; haltere white to pale yellowish.

Legs. Femora dark grey; tibiae distinctly paler, yellow (holotype) to brown or yellowish brown (paratype); tarsomeres yellow, except for 2 distal tarsomeres brown infuscated; fore femur without anteroventral ctenidium of spine-like setae; hind tibia without apical anteroventral seta.

Abdomen. Moderately sclerotized, entirely dark grey, sparsely setose; male terminalia with surstylus as illustrated in Fig. 6 (lateral view), long and slender, constricted proximally (neck-shaped), swollen in median portion, sickle-shaped apically; posterior margin without trace of heel-shaped swelling (the latter typical in Isocanace briani ); 3 long setae medially on posterior margin.

♀ Unknown.

Differential diagnosis. Similar and closely related to I. briani and I. freidbergi Mathis, 1999 , but distinguished from these by the following combination of characters: aristal branches ( Fig. 3 ) noticeably shorter than those of I. briani , some as long as or very slightly longer than basal aristal width; 4 fronto-orbital setae; frontal vitta with very inconspicuous, sparse setulae; disc of scutellum mostly bare, with large black, shiny macula, without evident discal setae or setulae; anepisternal and katepisternal setae black; male terminalia in lateral view ( Fig. 6 ) with gently sinuous, foot-like surstylus, lacking more or less produced posterior heel-shaped swelling and also lacking obvious anteromedial swelling; anteroapical part of surstylus slender, sickle-shaped.

Type material. MAURITIUS: holotype ♂ “ Sweeping intertidal / zone & coastal / vegetation [printed] // Mau- ritius: Pamplemousses / Le Goulet / 20°06′14″S, 57°31′02″E / 30.i.2018, 1– 3 m / Kirk-Spriggs & Muller [printed] // Entomology Dept. / National Museum / PO Box 266 / Bloemfontein 9300 / South Africa [printed; pale blue card] // BMSA (D) / 102449 [printed] // HOLOTYPUS ♂ / Isocanace mauritiana sp. nov. / L. Munari des. 2021 [printed white label with double red frame]” ( BMSA). Holotype micro-pinned and double-mounted in small block of Plast- azote. In fairly good condition (setal vestiture of frons and mesonotum strongly depauperated, with many setae and setulae missing). Abdomen removed and terminalia dissected and stored in genitalia vial in glycerine pinned beneath specimen . MAURITIUS: paratype ♂ “ Sweeping intertidal / zone & coastal / vegetation [printed] // MAU- RITIUS: Rivière du / Rempart / Grand Gaube / 20°01’00”S, 57°40’55”E / 31.i.2018, 1– 3 m / Kirk-Spriggs & Muller [printed] // Entomology Dept. / National Museum / PO Box 266 / Bloemfontein 9300 / South Africa [printed; pale blue card] // BMSA (D) / 101060 [printed] // PARATYPUS ♂ / Isocanace mauritiana sp. nov. / L. Munari des. 2021 [printed white label with double red frame]” ( LMC). Paratype micro-pinned and double-mounted in small block of Plastazote. In good condition, with abdomen in situ, exhibiting broadly exposed terminalia, especially surstyli .

Distribution. Mascarene Islands ( Mauritius).

Bionomics. Intertidal zone and coastal vegetation, specifics unknown.

Figures

FIGURES 2‒6. Antennae and male terminalia of surf flies. 2. Left antenna of Isocanace briani Mathis, lateral view (after Mathis 1982a, from a stereoscan micrograph). 3. Same, I. mauritiana sp. nov. (pubescence of postpedicel omitted); 4. Male left surstylus of I. briani, lateral view, exhibiting characteristic posterior “heel” (from type locality: Madagascar, Sambirano Lokobe Nossi-Be) (after Mathis 1982a). 5. Same, from Aldabra Is. (after Mathis 1982a). 6. Same, I. mauritiana sp. nov. Scale bars: 2‒3 = 0.2 mm; 4‒6 = 0.1 mm.

FIGURES 7‒11. Mapped coastal sampling stations of surf flies in the Mascarene islands and distributions of species. 7. Map of sampling stations on La Réunion (2015). 8. Same, Mauritius (2018). 9. Distribution of Nocticanace mahensis (Lamb) on La Réunion. 10. Same, Isocanace mauritiana Munari sp. nov. on Mauritius. 11. Same, Nocticanace mahensis (Lamb), Procanace pninae Mathis & Freidberg and Procanace sp. grisescens-group on Mauritius.