Hydrochasma Hendel

Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2013, A revision of the shore-fly genus Hydrochasma Hendel (Diptera, Ephydridae), ZooKeys 363, pp. 1-161 : 7-8

Genus Hydrochasma Hendel

Hydrochasma Hendel, 1936: 101. Type species: Hydrochasma zernyi Hendel, 1936 (= Discocerina faciale Williston, 1896), monotypy. Cresson 1938: 25-28 [review, discussion]; 1942: 113 [review of Nearctic species]; 1946: 141-142, 150 [review of Neotropical species]. Wirth 1965: 738-739 [Nearctic catalog]; 1968: 8 [Neotropical catalog]. Mathis and Zatwarnicki 1995: 182-183 [world catalog].

Diagnosis.

Small to moderately small shore flies, body length 1.50-3.10 mm; generally densely microtomentose, dull species. Head (Figs 18-20, 36-38, 49-51, 62-64, 124-126, 154-156, 172-174): Frons lacking anterior, proclinate, fronto-orbital seta. Face distinctly prominent at level of dorsal facial seta; antennal grooves generally sharply defined ventrally; face lacking secondary series of setae; facial setae 3, sometimes with a smaller 4th seta ventrally, setae generally decreasing in size from dorsum to venter, aligned vertically in a single series, dorsal setae not arising from shiny papilla, lacking an dorsoclinate seta at ventrolateral extremity; parafacial moderately wide to wide, expanded posteroventrally, bearing setulae; gena generally high, although variable. Eye generally oval with slight anteromedial expansion, moderately conspicuously microsetulose, bearing distinct interfacetal setulae. Maxillary palpus yellow apically. Thorax: Single presutural and postsutural supra-alar setae well developed; acrostichal setae present; notopleuron bearing several setulae in addition to 2 larger setae; anterior notopleural seta inserted conspicuously closer to posterior notopleural seta than to postpronotal seta. Wings transparent, shiny; costa bearing 4-6 long, dorsal setae between humeral and subcostal breaks. Hindtibia lacking or bearing a preapical, ventral, spur-like seta. Abdomen: Tergites variable, unicolorous or bicolorous, often with lighter colored areas laterally, sometimes as lateral wedges (Figs 12, 70-71, 142-143, 184-185). Male tergite 4 only slightly longer than tergite 3. Male terminalia: Epandrium generally elongate, dorsal portion above cerci weakly developed or usually not connected, with a dorsal gap; mid and posterior surface mostly covered with setae; cercus separate or fused ventrolaterally or ventrally with epandrium, in posterior view broadly lunate; gonite symmetrical, separate from hypandrium, bar-like, situated between base of aedeagus and posterior margin of hypandrium, lacking seta; aedeagus symmetrical, mostly tubular, sometimes very elongate, in ventral view elongate, often cigar-like, in lateral view slightly sinuous with rounded or expanded apex, rarely with dorsal projection; hypandrium in ventral view U- or V-shaped, sometimes narrow, with rounded or variously incised anterior margin, in lateral view almost flat or slightly arched; aedeagal apodeme separate from aedeagus, in lateral view elongate with variable ventral projection, usually small; ejaculatory apodeme absent.

Distribution.

Specimens of Hydrochasma have thus far been found only in the New World, occurring where temperate and tropical climates prevail.

Natural history.

Adults of Hydrochasma occur on bare, often exposed mud and sand, and many species abound in estuarine habitats, especially those along maritime coasts. Specimens are also common in inland alkaline and saline habitats. The immature stages are unknown.

Discussion.

Hydrochasma is usually readily recognized. For a few of the included species, however, determining generic assignment can be difficult because external characters are not always wholly concordant with interpretations of structures of the male terminalia (see species excluded near the end of this paper, p. 150).

Key to species groups of Hydrochasma Hendel