Hydrochasma digitatum, 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 : 12-14

3. Hydrochasma digitatum sp. n. Figs 12-17

Diagnosis.

This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.40-1.90 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.15-0.17. Thorax: Wing with costal vein ratio 0.77-0.81; M vein ratio 0.47-0.49. Forecoxa whitish gray to gray; hindtibia with prominent ventroapical, shallowly curved, spur-like seta. Abdomen: Tergites broadly brown medially, becoming lighter gray laterally but unevenly, almost shallowly wedge-like, tergite 5 of male gray with a thin, medial brown stripe (Fig. 12). Male terminalia (Figs 13-16): Combined structures generally moderately elongate, in posterior view height over 2 × width, generally setulose on cerci, setulae sparse or minute ventrally; epandrium with dorsal arch above cerci not interrupted, narrowly connected, in posterior view (Fig. 13) with basal 1/2 somewhat rectangular with angles rounded, apical 1/2 narrowed, extended as separate, narrow, almost parallel sided processes with a deep and moderately wide gap between processes, lateral margins very shallowly arched, each process rounded apically, in lateral view (Fig. 14) generally shallowly arched with curvature relatively even, widest just ventrad of cercus, apical third abruptly narrowed, tapered, curved anteriorly subapically, apex narrowly rounded, bearing minute setulae; aedeagus in lateral view (Fig. 16) elongate, narrow, irregularly tubular, shallowly curved, gradually tapered on basal 3/4, thereafter widened to form a boxlike apex (angles rounded), in ventral view (Fig. 15) mostly parallel sided on basal 2/3, apical 1/3 more narrowed but still parallel sided, apex rounded; phallapodeme in lateral view (Fig. 16) oriented perpendicular to aedeagus, narrowly elongate, keel very evident as an extension on portion toward hypandrium, portion toward aedeagal base rod-like in ventral view (Fig. 15) as a short, rounded, isosceles triangle with a circular structure at base, foreshortened; gonite in lateral view (Fig. 16) rod-like, straight, narrow, in ventral view (Fig. 15) short due to foreshortening; hypandrium in lateral view (Fig. 16) elongate, comparatively wide, anterior margin narrowly rounded, posterior margin as 2 narrow, elongate processes, which form a deep gap between, posterior projection acutely pointed and shorter than anterior projection, in ventral view (Fig. 15) as an arrowhead that is deeply incised posterolaterally with a tapered, elongate, acutely pointed, posterolateral projection, base extended posteriorly, parallel sided along middle portion, thereafter flared posterolaterally as 2 symmetrical processes, forming a wide, V-shaped posterior margin.

Type material.

The holotype male of Hydrochasma digitatum is labeled "PERU. Madre de Dios: Manu, Diamante, 400 m, 12°25' [sic 19.9']S, 70°57[.5]'W, R[ ío]. AltoMadre de Dios, 7 Sep 1988, W.N.Mathis/USNM ENT 00285974 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma digitatum Mathis & Zatwarnicki, USNM [red]." The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Thirteen paratypes (3♂, 10♀; USNM) bear the same label data as the holotype.

Type locality.

Peru. Madre de Dios: Diamante ( Río Alto Madre de Dios; 12°19.9'S, 70°57.5'W; 400 m).

Other specimens examined.

Neotropical. PERU. Cuzco: Paucartambo, Atalaya ( Río Alto Madre de Dios; 12°53.3'S, 71°21.6'W; 600 m), 4 Sep 1988, W. N. Mathis (1♂; USNM). Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7'S, 71°23.3'W; 550 m), 5-6 Sep 1988, A. Freidberg, W. N. Mathis (2♂, 1♀; USNM).

Distribution

(Fig. 17). Neotropical: Peru (Cuzco, Madre de Dios).

Etymology.

The species epithet, digitatum, is of Latin derivation and refers to the finger-like ventral extensions of the epandrium.

Remarks.

This species, as implied by its name, is distinguished from congeners by the elongated, slender, very shallowly curved, digitiform, ventral epandrial processes. These digitiform processes are separated from each other in posterior view by a deep, narrowly U-shaped pocket or gap. In lateral view, these processes are tapered and slightly curved subapically.