Coenia Robineau-Desvoidy, 1830

Mathis, Wayne N. & Sepúlveda, Luciane Marinoni and Tatiana A., 2025, Phylogeny and taxonomy of the shore-fly tribe Ephydrini with comments on related tribes in Ephydrinae (Diptera: Ephydridae), Zoologia (e 24044) 42, pp. 1-42 : 15-17

Coenia Robineau-Desvoidy, 1830

Figs 24–26

Coenia Robineau-Desvoidy 1830: 800 (feminine; type species: Coenia caricicola Robineau-Desvoidy 1830 (= Ephydra palustris Fallén 1823 ), monotypy). – Mathis 1975: 82–84 [revision of Nearctic species]. – Mathis and Zatwarnicki 1995: 237–238 [world catalog]. – Krivosheina 2001: 1367–1371 [review of Palearctic species].

Caenia , error for Coenia . – Walker 1853: 259 [unjustified emendation]. – Loew 1860: 38 [European Ephydridae ]. – Becker 1896: 207 [Palearctic fauna]; 1905: 214 [Palearctic catalog].

Diagnosis. Coenia is distinguished from other genera of Ephydrini by the following combination of characters: Moderately small shore flies, body length 2.20–2.80 mm.

Head: Frons much wider than high, only moderately to sparsely microtomentose, especially subshiny mesofrons; no cruciate interfrontal setae; two well developed fronto-orbital setae; paravertical setae weakly developed, not subequal to vertical setae. Arista bearing long rays dorsally on basal 3/4, length of longest rays subequal to height of basal flagellomere. Face with lateral margins and oral margin bearing long setae, otherwise setulose, although medial area with setae shorter than marginal setae. Gena short, about half height of basal flagellomere; genal seta well developed.

Thorax: Mesonotum generally dark colored, blackish brown; scutellum triangular, posterior angle rounded; no well-developed prescutellar acrostichal pair of setae; 4 (1+3) well-developed dorsocentral setae; postpronotal seta(e) either weak, at most 1/4 length of posterior notopleural seta, or lacking; 1 presutural supra-alar seta; 1 supra-alar seta; 1 postalar seta; prosternum bare; 2 scutellar setae; 2 notopleural setae; 1 large anepisternal seta; 1 well developed katepisternal seta. Costal vein ratio 0.21–0.22; M 1 vein ratio 0.66–0.69. Hindcoxa bare posteriorly; pulvilli well developed; tarsal claws short and distinctly curved.

Abdomen: Male with five visible tergites dorsally, sternite 5 longer than wide, triangular. Male terminalia: Surstylar bases adjacent, separated by a narrow groove, or fused, apically separated as surstylar arms, arms pointed or digitiform, sometimes irregularly; gonite moderately well developed, elongate, regularly to irregularly tapered to acute apex; aedeagus elongate, moderately thin to very thin, shallowly to conspicuously curved, tapered from base to apex, apex acutely pointed; phallapodeme short to elongate, shallowly to conspicuously curved, thin to moderately thick medially, if thick tapered toward apices, distinct keel not evident. Female abdomen: Female ventral receptacle with small operculum, helmet-like, extended process three times longer than opercular height, C-shaped with short dorsal extension into operculum.

Third-instar larva (based on Foote 1990): Small, body length 7.60 mm; elongate, nearly cylindrical, legless but with creeping welts; integument bearing slightly pigmented scales of similar shape, scales not forming patterns on dorsal surface; with circles of pigmented scales on thoracic segments, abdominal segments fully covered in scales; two types of sensilla:rayed and rosette-like (peg-like); pseudocephalon bilobed; antennae two-segmented; oral papillae comb-like;mouth brushes a long, fluffy comb at distal end; tips of oral hooks highly dentate; anterior spiracles with 4–6 finger-like projections; retractable respiratory tube branched at middle with two fleshy protrusions; anal opening smooth, transversely elongated.

Natural history: Krivosheina (2001: 1367) wrote that larvae feed on detritus and that adults are found at sites with stagnant water during the summer. Foote (1990) suggested that there can be as many as 9–12 generations during the summer season.

Distribution. The composite distribution for species of Coenia is Holarctic with six of seven species occurring in the Palearctic Region. Most species have relatively small distributions geographically with five species ( C. caucasica Krivosheina , C.deserta Krivosheina , C. elbergi Dahl , C. palustris (Fallén) , C. vulgata Krivosheina ) being found thus far only in the Palearctic Region, and one species ( C. alpina Mathis ) being exclusive to the Nearctic Region. Only C.curvicauda (Meigen) is more widespread, having a Holarctic distribution. Most species occur at higher latitudes with only C. palustris ranging southward to the Azores and Canary Islands in the Old World.

Remarks. The most recent revisions are Mathis (1975) for the Nearctic species and Krivosheina (2001) for the Palearctic species. Like some other genera of Ephydrini , specimens of Coenia are not commonly collected and are thus poorly represented in collections.

Figures

Figures 24–30.Coenia and Dimecoenia.Coenia palustris,(24) head anterior; (25) head lateral; (26) thorax dorsal. Dimecoenia spinosa, (27) head anterior; (28) head lateral; (29) thorax dorsal; (30) hind leg anterior.