Discocerinini Cresson

Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2013, A revision of the shore-fly genus Hydrochasma Hendel (Diptera, Ephydridae), ZooKeys 363, pp. 1-161 : 4-5

Tribe Discocerinini Cresson

Discocerinini (as Discocerini ) Cresson 1925: 228. Type genus: Discocerina Macquart 1835. Mathis and Zuyin 1989: 435 [description, key to Asian genera]. Mathis and Zatwarnicki 1995: 163-186 [world catalog]. Zatwarnicki and Mathis 2001: 5-51 [revised classification].

Diagnosis.

A tribe of the subfamily Gymnomyzinae that is distinguished by the following combination of characters: Small to medium-sized shore flies, body length 1.15-3.50 mm; usually invested with considerable microtomentum, especially frons and mesonotum.

Head: Frontal vitta (or ocellar triangle) mostly bare of setulae, not conspicuously setulose; pseudopostocellar setae well developed, length greater than distance between either posterior ocellus and anterior ocellus, generally with proclinate orientation and slightly divergent; ocellar seta inserted anterior to lateral alignment of anterior ocellus, sometimes only slightly so; reclinate fronto-orbital seta inserted in front of proclinate fronto-orbital (if 2 proclinate fronto-orbital setae present, reclinate seta inserted in front of the larger proclinate seta); proclinate fronto-orbital seta subequal to length of reclinate seta. Pedicel bearing a large seta anterodorsally; arista with 5-7 dorsally branching rays evenly along aristal length. Compound eye bearing numerous, interfacetal microsetulae. Face generally smooth, not conspicuously pitted or rugose, in lateral view shallowly carinate between antennal bases and/or very shallowly conically produced, convex. Gena generally short (secondarily high in some species), bearing setulae (including midportion) and 1 large seta, its posterior (postgenal) margin rounded, not sharp. Oral opening and clypeus narrow; mouthparts generally dark colored; clypeus generally microtomentose, similar to microtomentum of face.

Thorax: Mesonotum generally microtomentose, usually densely so; supra-alar seta usually evident although sometimes reduced; acrostichal setulae arranged in about 8 irregular rows; prescutellar acrostichal setae approximate and inserted behind level of posteromost dorsocentral setae; scutellum usually moderately densely setulose, bearing more than 20 setulae, these evenly scattered; both anterior and posterior notopleural setae inserted at about the same level from notopleural/anepisternal suture; anepisternum with 2 equal setae along posterior margin. Wing with vein R2+3 long, extended nearly to level of apex of vein R4+5. Foreleg normally developed, not raptorial with greatly enlarged femur.

Abdomen: Five tergites visible, usually not covered with microtomentum. Male terminalia: Structures symmetrical; cerci paired, hemispherical, setose, bearing sides of rectum, sometimes fused with posteroventral margin of epandrium; epandrium U-shaped, encircling cerci, anterior margin rounded, in lateral view with setae mainly on dorsum and along anteroventral margin; presurstylus lacking or fused indistinguishably with epandrium; posterolateral arms of epandrium attached with ventral apex of gonites, middle of posterior margin a base for phallapodeme; phallapodeme situated under aedeagus, associated with hypandrium and with ventral part of base of aedeagus, ventral margin with lobate appendix providing attachment for genital muscles that move aedeagus, sometimes fused with base of aedeagus; gonites paired, connecting sides of base of aedeagus and laterodorsal margin of epandrium, bearing 1 or some setulae; subepandrial plate reduced; aedeagus tubular, tapered anteriorly; ejaculatory apodeme usually lacking, if present as a spatula-shaped structure against background of ductus ejaculatorius.

Discussion.

Starting with Cresson (1925), who first described Discocerinini , and including all students of the family until Mathis and Zuyin (1989), the diagnoses, descriptions, and catalogs of this tribe included some taxa that are not closely related phylogenetically, rendering the tribe polyphyletic. Mathis and Zuyin (1989) recharacterized Discocerinini using synapomorphies and resulting in a monophyletic tribe into which Mathis and Zatwarnicki (1995) included eight genera and 143 species in their world catalog. Zatwarnicki and Mathis (2001) then added two additional genera, Galaterina and Orasiopa , and altered the status of some subgenera in their phylogenetic study of the tribe. Finally, Mathis and Zatwarnicki (2012a) recently described Facitrichophora .

Phylogenetic relationships.

On a world basis, Zatwarnicki and Mathis (2001) proposed a phylogenetic hypothesis for the higher-level lineages within the tribe Discocerinini , dividing the included genera into three sublineages or groups: the Gymnoclasiopa , Diclasiopa , and Discocerina groups. Hydrochasma is included in the Discocerina group and is distinguished from other New World genera in the key and generic diagnosis that follow (characters being discussed are synapomorphies unless otherwise specified). Other genera in addition to Hydrochasma that are included in the Discocerina sublineage are: Discocerina Macquart, Facitrichophora Mathis & Zatwarnicki, Galaterina Zatwarnicki & Mathis, Lamproclasiopa Hendel, Orasiopa Zatwarnicki & Mathis, and Polytrichophora Cresson. Hydrochasma , along with other genera of the Discocerina sublineage, form a monophyletic lineage within the Discocerinini that is corroborated by two synapomorphies. The first is the setulose notopleuron. In other genera of the subfamily Gymnomyzinae , including other genera in the tribe Discocerinini , the notopleuron is bare except for larger anterior and posterior setae that are inserted near the ventral margin. In taxa of the Discocerina group, however, the notopleuron bears a few additional setulae that are usually inserted slightly dorsad and toward the anterior portion of the notopleuron, usually around or just dorsad of the anterior notopleural seta. The second synapomorphy confirming the monophyly of the Discocerina group is the shape of the gonite, which is narrowly bar-like, often nearly parallel sided. In other genera of Discocerinini outside of the Discocerina group, the gonite is elongate, variously swollen medially, and tapered toward one or both apices. Within the Discocerina group, an elongated male terminalia (hypopygium), at least 2.5 × longer than wide (the plesiomorphic condition is hypopygium of moderate length), occurs almost exclusively in four genera: Facitrichophora , Galaterina , Hydrochasma , and Polytrichophora . The genera Facitrichophora , Hydrochasma and Polytrichophora are characterized by a deeply incised posterior margin of hypandrium (the plesiomorphic condition is for the hypandrium to have a slightly to moderately concave posterior margin). Within the Discocerina group, Hydrochasma is distinguished by the following synapomorphies: (1) three facial setae (by convergence, some species in related genera also have three setae); (2) parafacial setulose (a species group within Discocerina also has a setulose parafacial, apparently by convergence); (3) gena high (the buccata species group within Discocerina also has a high gena); (4) cerci usually fused ventrally or ventrolaterally with epandrium (the cerci are similarly fused in many species of Facitrichophora and Polytrichophora ); (5) epandrium with dorsal portion or arch above the cerci weakened, thin, or absent; (6) posterior margin of hypandrium deeply incised.