Setacera Cresson, 1930

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 : 30-32

Setacera Cresson, 1930

Figs 82–86

Setacera Cresson 1930: 116 (feminine; type species: Ephydra pacifica Cresson , by original designation). – Sturtevant and Wheeler 1954: 201–204 [key to North American species]. – Wirth 1965: 754–755 [catalog of North American species]; 1968: 24 [catalog of South American species]. – Mathis 1982b: 1–57 [revision, global]. – Zack 1983b: 10–25 [biology and immature stages S. needhami ]. – Mathis and Zatwarnicki 1995: 252–254 [world catalog]. – Krivosheina and Ozerov 2020: 1190–1200 [review of Russian species].

Diagnosis. Setacera is distinguished from other genera of Ephydrini by the following characters: Moderately small to large shore flies, body length 2.46–5.85 mm.

Head: Mesofrons shiny, with metallic luster; cruciate, interfrontal setae lacking or weakly developed; lateroclinate, fronto-orbital setae 2 pairs; fronto-orbits shiny with metallic luster concolorous with mesofrons; basal flagellomere with prominent seta on lateral surface below aristal insertion; arista with subpectinate branching along dorsal surface from between onehalf to 2/3 of aristal length; dorsum of interfoveal facial ridge sloping very gradually; ridge projecting markedly forward in many species attaining broad apex from which arched face extends ventrally at nearly a right angle, face receding to oral margin in other species; antennal groove distinct but not deeply impressed; postocular setae normally developed, not conspicuous; larger facial setae declinate.

Thorax: Dorsocentral setae 5 (1+4); presutural supra-alar seta 1, generally subequal to posterior notopleural setae in species from Western Hemisphere. Costal vein ratio 0.28–0.30; M 1 vein ratio 0.84–0.90. Tarsal claws shallowly curved, nearly straight, comparatively long; pulvilli lacking or greatly reduced.

Abdomen: Structures of male terminalia symmetrical but unusually complicated by addition of several secondary processes and prongs; epandrium elongate; well-developed surstyli generally fused medially, projecting from ventral margin of epandrium. Female terminalia: Female ventral receptacle with operculum as high as wide, broadly rounded dorsally; extended process more or less J-shaped.

Natural History: The immature stages of Setacera and Ephydra closely resemble each other, and Johannsen (1935) considered them to be the most highly specialized of the family. Like larvae of Ephydra , those of Setacera are characterized by long, terminal respiratory tubes and by eight pairs of short, conical, abdominal prolegs, of which the last pair is the largest, with claws opposable to those of the other prolegs. Johannsen (1935) published a figure of the cephalopharyngeal skeleton of S. needhami , a species described inadvertently from the immature stages ( Cresson 1935), and Foote (1982) described and illustrated the immature stages of S. atrovirens .

Unlike Ephydra , specimens of Setacera occur primarily in freshwater habitats, although Johannsen (1935) reared a specimen of S. atrovirens from a puparium collected in a brine pool near Ithaca, New York. Where members of Setacera do occur, even within what appears to be their preferred habitat, specimens are not collected frequently, and collection of a good series usually requires diligent persistence.

Most species seem to prefer lentic aquatic systems, especially where a layer of floating algae has accumulated on the water’s surface. This is the typical habitat of most species of Ephydrini , and their crochetbearing prolegs are apparently an adaptation to this habitat, allowing movement through and attachment to the algae.

Distribution. Among the genera of Ephydrini , Setacera is by far the most widely occurring, genus with species being found in all major faunal realms. The Neotropics, however, have a depauperate fauna.

Remarks. Some members of Setacera exhibit sexually dimorphic features that are probably secondary. Males of these species bear prominent hair-tufts of varying lengths at tibial apices and often on the coxae. The extent and length of tufts, or their absence, are excellent species-level characters.

Some species now included in Setacera were previously placed in the genus Ephydra Fallén , and some recent authors still prefer the precedent of Setacera as an included subgenus of Ephydra ( Giordani Soika 1956b, Dahl 1959). Setacera is indeed closely related to Ephydra , as evidenced by the similarity of adults and immatures of both genera. Setacera , however, can be consistently distinguished in both sexes from all other genera of Ephydrini and its monophyly corroborated by the following synapomorphies: (1) Basal flagellomere seta: Aside from the arista, there are usually no other large structures emanating from the basal flagellomere. Specimens of Setacera , however, have a large seta inserted just below the aristal insertion on the lateral surface. (2) Vertico-orbits: Within the tribe Ephydrini , the vertico-orbits are generally either shiny or densely microtomentose and grayish, appearing dull. This area, in specimens of Setacera , is uniquely invested with a dense patch of microtomentum that appears velvety. Velvety areas occur elsewhere in a few species of the tribe (parafrons in Cirrula gigantea Cresson ; frons and orbits in Ephydra auripes Aldrich ) but not in the specific area as described for Setacera . (3) Genal seta: This seta is usually very prominent, arising below the eye. Although this seta is still larger than surrounding ones in specimens of Setacera , its comparative size is smaller, and for convenience, we have compared it with the length of the arista. (4) Cruciate interfrontal setae: Although some species of the tribe Ephydrini do not have these setae, most genera have at least a few species in which they occur. Consequently, our interpretation of the general groundplan of the tribe is for their presence, and their absence in Setacera is apparently unique, i.e. a synapomorphy. (5) Prescutellar acrostichal setae: As with the preceding characters, these setae are generally present in Ephydrini . We know of no specimens of Setacera , however, where they are present, and we interpret this apparent loss to be synapomorphic.

Mathis (1982b) recognized five monophyletic species groups that are relatively finely divided (for example, the aurata and trina groups could be combined) and are characterized as follows.

The aldrichi Group is the sister group of the pacifica group, and it is characterized and its monophyly established by: (1) Configuration of aedeagus: As before, the aedeagus is typically broadly rounded apically and almost as wide as long. Males of the aldrichi Group have a somewhat pointed aedeagus that we interpret to be apomorphic. (2) Configuration of epandrium: Males of the aldrichi Group have an anteroventral, digitiform process, apparently a unique condition, and one that we interpret to be apomorphic.

The aurata Group ( S. aurata (Stenhammar)) is the sister group of the trina Group, as evidenced by the distance between the cerci and setae on sternite 9. This distance is generally not greater than the height of the cerci. In females of this species group, the setae on sternite 9 re inserted farther ventrad, making the distance between them and the cerci conspicuously loner than the cercal height. Length of female sternite 8. The length is three to four times its width, not the more generalized five or more times. Length of female tergite 8. Tergite 8 in females is very long and partially accounts for the ventral position of sternite 9. This longer dimension of tergite 8 is a synapomorphy for this lineage. The aurata Group is distinguished from the trina Group by the shape of the epandrium. Although it is not uncommon for the epandrium to have appendages of various shapes, this is the only lineage to have a bluntly rounded, parallel-sided, posterolateral process arising from each side.

The breviventris Group ( S. breviventris (Loew) , S. multicolor (Soika) , S. viridis Miyagi) occurs in the Old World and is characterized and its monophyly established by the following synapomorphy: Development of the presutural supra-alar seta weak. In most Ephydrini , this seta is well developed, usually as long as the presutural seta. In species of this group, however, this seta is weak and is considerably smaller than the presutural seta.

The micans Group ( S. atrovirens (Loew) , S. micans (Haliday)) . This species group has a Holarctic distribution. The group is characterized and it monophyly established by the following synapomorphies: (1) Configuration of aedeagus. The aedeagus among most ephydrines is nearly as wide as long, and its apex is broadly rounded. In males of the micans Group the aedeagus is three to four times longer than wide, and its apex is acutely pointed. (2) Shape of female ventral receptacle. Usually, the operculum is nearly as high as the extended process, sometimes more so, and its width is subequal to its height. In females of the micans Group, the operculum is relatively small, both its width and height, especially compared to the size of the extended process.

The monophyly of the pacifica Group ( S. durani Cresson , S. jamesi Mathis , S. needhami Johannsen , S. pacifica (Cresson) , S. pilicornis (Coquillett) , S. trichoselis Mathis ) is established by: (1) Configuration of vertico-orbits: In Setacera this band is more or less broad and usually has a subanterior swelling. But in members of the pacifica Group this band is very narrow and is sometimes difficult to detect. The narrowed aspect of this character is interpreted to be a synapomorphy. (2) Configuration of female ventral receptacle: For most ephydrines, the operculum is typically wider than high. For females of the pacifica Group, however, the height is subequal to its width, an apomorphic character.

The trina Group ( S. freidbergi Mathis , S. meneghinii Canzoneri , S. trina Collin ). See our comments under the aurata Group for character evidence that these two group a closely related. The monophyly of the trina Group is established by the shape of the male gonite, which is unique for this group. A second character is the shape of the epandrium, which is similar in the species of this group, having the ventrolateral angles explanate and slightly recurved.

Figures

Figures 67–86. Paracoenia, Paraephydra and Setacera. Paracoenia wirthi, (67) head anterior; (68) head lateral; (69) thorax dorsal; (70) epandrium and surstyli posterior; (71) epandrium and surstyli lateral; (72) male 5th tergite lateral; (73) male 5th sternite ventral; (74) female ventral receptacle lateral. Paraephydra freitasi, (75) head anterolateral; (76) thorax dorsal; (77) epandrium and cerci posterior; (78) internal structures of male terminalia lateral; (79) surstylus lateral; (80) gonite lateral; (81) female ventral receptacle lateral. Setacera trichoscelis, (82) head anterolateral; (83) thorax dorsal; (84) internal structures of male terminalia lateral; (85) male terminalia lateral; (86) fused surstyli posterior.