Hydrochasma distinctum, Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2013

Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2013, A revision of the shore-fly genus Hydrochasma Hendel (Diptera, Ephydridae), ZooKeys 363, pp. 1-161 : 37-38

12. Hydrochasma distinctum sp. n. Figs 72-76

Diagnosis.

This species is distinguished from congeners by the following combination of characters: Moderately small shore flies, body length 2.20 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.13. Thorax: Wing with costal vein ratio 0.82; M vein ratio 0.51. Forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray. Abdomen: Tergites 3 and 4 with wedge-shaped silvery-gray areas; otherwise, tergites dark brown to black. Male terminalia (Figs 72-75): Combined structures generally moderately compact and wide, in posterior view height 1.8 × width, generally moderately setulose dorsally, setulae sparse or lacking ventrally; epandrium lacking dorsal arch above cerci, in posterior view (Fig. 72) with basal 2/3 rectangular, lateral margins of basal portion shallowly sinuous, ventral epandrial process conspicuously narrowed, tapered, each process digitiform, bifurcate apically with inverted V-shaped gap between, in lateral view (Fig. 73) much higher than wide, posterior margin arched, anterior margin with a midlength, shallow but elongate concavity, apex obtusely rounded; each ventral epandrial process with 2-3 dentate structures subapically; aedeagus in lateral view (Fig. 75) basically elongate, slender, tubular, tapered toward apex but with a large, somewhat quadrate structure at midlength, in ventral view (Fig. 74) elongate, slender, tubular, with quadrate structure at midlength, quadrate structure with basal margin shallow emarginate, apical margin with wide, shallow projection, truncate apically; phallapodeme in lateral view (Fig. 75) elongate, narrow, shallowly sinuous, keel as irregular, apical knob, in ventral view (Fig. 74) elongate, narrow, T-shaped, truncate at each end, basal half gradually expanded; gonite in lateral view (Fig. 75) a very shallowly sinuous, rod-like process, about 3/4 length of phallapodeme, in ventral view (Fig. 74) shallowly sinuous, bluntly rounded at both apices; hypandrium in lateral view (Fig. 75) narrowly developed, generally narrowly ovate, anterior margin moderately narrowly rounded, gradually tapered toward posterior margin, in ventral view (Fig. 74) longer than wide, more sclerotized and darker laterally, posterior margin widely emarginate, anterior margin membranous.

Type material.

The holotype male of Hydrochasma distinctum is labeled "COSTA RICA. Prov. Limón. P[arque]. N[acional]. Barbilla, Sector Casas Negra, 1.5 Km NO[RTH] de la Estación, 300m, 13 JUL 2002, E. Rojas, Libre, L_N_ 219900_598400 #70494/INB0003513948 INBIOCRI COSTA RICA [plastic bar code label]/HOLOTYPE ♂ Hydrochasma distinctum Mathis & Zatwarnicki, USNM [red]." The holotype is double mounted (minuten in a block of plastic), is in good condition (some setae of the head are misoriented or missing; abdomen removed and dissected), and is deposited in INBio.

Type locality.

Costa Rica. Limón: Parque Nacional Barbilla, Sector Casas Negras, (10°0.8'N, 83°28.1'W; 300 m).

Distribution

(Fig. 76). Neotropical: Costa Rica ( Limón).

Etymology.

The species epithet, distinctum, is of Latin derivation and means separate or different, referring to the unique and distinct structures of the male terminalia.

Remarks.

Thus far, this species is known only by the holotype male. As implied by its species’ name, distinctum, this species is readily distinguished from congeners by the distinctive structures of the male terminalia, which are unique among congeners. The shape of the epandrium with a somewhat large and rectangular base and the short, tapered, ventral epandrial processes that bear tooth-like structures subapically are unique, as is the aedeagus that has a relatively large, quadrate structure at its midlength. Only Hydrochasma denticum , which also has subapical tooth-like structures on the ventral epandrial processes, is similar. The ventral epandrial processes of Hydrochasma denticum , however, are much longer than their base, the aedeagus does not have a quadrate structure at its midlength, and the hypandrium is V-shaped.