Setacera Cresson

Mathis, Wayne N. & Marinoni, Luciane, 2016, Revision of Ephydrini Zetterstedt (Diptera: Ephydridae) from the Americas south of the United States, Zootaxa 4116 (1), pp. 1-110 : 97-99

Genus Setacera Cresson

Setacera Cresson 1930: 116 [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].— Mathis and Zatwarnicki 1995: 252 –254 [world catalog].

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 one-half 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 of Western Hemisphere.

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; see Figs. of species for further detail. Female ventral receptacle with operculum as high as wide, broadly rounded dorsally; extended process more or less J-shaped.

Distribution. Among the genera of Ephydrini , Setacera is by far the most widely distributed, with species occurring in all major faunal realms. The neotropics, however, have a depauparate fauna, and the species considered herein are members of a single species group, known only from the Western Hemisphere. A single species, S. trichoscelis , is known from South America.

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) figured 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 , members 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 crochet-bearing prolegs are apparently an adaptation to this habitat, allowing movement through and attachment to the algae.

Discussion. Some members of Setacera have secondarily sexually dimorphic features. 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.

The 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 1956, 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 lack in Setacera is apparently unique. (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.

As only the pacifica group occurs in the Neotropics, the comments to follow will deal primarily with that taxon. Earlier, Mathis (1982b) presented his hypotheses on the arrangement of other lineages.

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 monophyly of the pacifica group 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 apomorphic. (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.