Hydrochasma patens Cresson

Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2013, A revision of the shore-fly genus Hydrochasma Hendel (Diptera, Ephydridae), ZooKeys 363, pp. 1-161 : 19-21

5. Hydrochasma patens Cresson Figs 26-30

Hydrochasma patens Cresson, 1938: 27 [Uruguay. Montevideo; HT ♂, BMNH]; 1946: 141 [review]. Wirth 1968: 8 [Neotropical catalog]. Mathis and Zatwarnicki 1995: 183 [world catalog].

Diagnosis.

This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.85-2.60 mm. Head: Subglobose, very broad ventrally, oral opening comparatively large. Pedicel mostly black; medial surface of basal flagellomere extensively yellow, lateral surface with some blackish coloration. Parafacial silvery white, concolorous with face; gena-to-eye ratio 0.32-0.35. Thorax: Mesonotum generally gray but with faint bluish or slightly greenish metallic coloration, especially on posterior portion, including scutellum, not on notopleuron or lateral margins of scutellum; pleural area gray. Wing with costal vein ratio 0.50-0.62; M vein ratio 0.49-0.51. Femora and tibiae gray, tarsi yellow; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface but with a posteroventral row of 5-7 short, spine-like setae; hindtibia bearing a long, spur-like seta ventroapically. Abdomen: Tergites generally dull gray, becoming brownish gray medially; lacking wedge-shaped, gray to silvery gray areas; tergite 5 gray. Male terminalia (Figs 26-29): Combined structures generally moderately elongate, in posterior view height slightly less than 3 × width, generally sparsely setulose, especially dorsally; epandrium with dorsal arch above cerci relatively well developed, thin, completely connected, in posterior view (Fig. 26) as an inverted U on dorsal third to half, ventral portion with lateral margins shallowly concave medially, cruciate subapically, deeply bifurcate medially, medial bifurcation almost as wide as ventral process of epandrium at same level, extended epandrial process tapered, apex rounded; cerci moderately long, height nearly twice width, widely semi-hemispherical (Fig. 26), not attached lateroventrally with epandrium; aedeagus in lateral view (Fig. 29) elongate, about 5 × longer than wide, tubular, shallowly curved, slightly tapered toward apex with apical portion moderately pointed and with a subapical, rounded projection, in ventral view (Fig. 28) mostly tapered from base to pointed apex; phallapodeme in lateral view (Fig. 29) narrowly triangular with extended keel skewed and pointed on portion toward attachment with hypandrium, in ventral view (Fig. 28) an elongate, robust T with crossbar very short; gonite in lateral view (Fig. 29) narrow, elongate, bar-like, very shallowly curved and spatulate, in ventral view (Fig. 28) shallowly curved; hypandrium in lateral view (Fig. 29) elongate, moderately shallow, tapered at both apices and with lateral, posteriorly directed process evident, in ventral view (Fig. 28) with posterior half spindle shaped, becoming wider with long extended lateral processes just before posterior margin, posterior margin deeply emarginated, emargination V-shaped, anterior portion as an arrowhead with posteriorly directed narrow, elongate, lateral extensions and with lateral and anterior margins shallowly arched, forming a V-shaped anterior margin.

Type material.

The holotype male of Hydrochasma patens is labeled "Holo- type [round label with red margin]/9100/Uruguay: Montevideo, 21-22. i. 1927 [21-22 Jan 1927]. F. & M. Edwards. B. M. 1927-63/TYPE Hydrochasma PATENS E. T. Cresson, Jr. [carmine; Hydrochasma PATENS handwritten]". The holotype is double mounted (minuten in a plastic rectangle), is generally in good condition (lacking left foretarsus), and is deposited in the BMNH.

Type locality.

Uruguay. Montevideo: Montevideo (34°53.3'S, 56°11'W).

Other specimens examined.

Neotropical. CHILE. Osorno: Lago Puyehue (SE shore; 40°45'S, 72°25.2'W), 10 Feb 1978, W. N. Mathis (3♂, 10♀; USNM). Talca: Rio Lircay (11 km N Talca; 35°23'S, 71°39'W; 85 m), 23 Jan1978, W. N. Mathis (22♂, 31♀; USNM).

Distribution

(Fig. 30). Neotropical: Uruguay, Chile (Osorno, Talca).

Remarks.

The identity of this species has been confused, resulting in misidentifications in collections that we have examined. Structures of the male terminalia of this species are distinctive, however, and distinguish it from congeners, especially the elongated and slender general conformation of these structures, which can only be mistaken with those of Hydrochasma viridum . Both of these species have elongated, very slender, ventrolateral epandrial processes that are very similar. The hypandrium, especially in ventral view, however, has more elongated, posterolaterally directed processes in Hydrochasma patens . Additionally, the dorsum of the head and the mesonotum are mostly gray with only faint bluish or greenish coloration.