Hydrochasma octogonum, 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 : 60-61

19. Hydrochasma octogonum sp. n. Figs 106-110

Hydrochasma incisum of authors, nec Coquillett (misidentification). Cresson 1942: 113 [generic combination; list Florida]. Mathis and Zatwarnicki 1995: 182-183 [in part; world catalog].

Diagnosis.

This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.25-1.80 mm. Head: Antenna mostly yellowish, at most with dorsal surface of pedicel and basal flagellomere dark; face, parafacial, and gena almost unicolorous, yellowish tan to tan, not contrasted; gena-to-eye ratio 0.23-0.25. Thorax: Wing with costal vein ratio 0.79-0.81; M vein ratio 0.0.49-0.53; apex of wing acutely pointed, faintly infuscate at apex. Forecoxa mostly gray to whitish gray to yellowish toward apex; forefemur lacking a comb-like row of stout setulae along anteroventral surface; tibiae mostly gray. Abdomen: Tergites 3-4 with distinct, lateral, silvery-gray wedges, wedge on tergite 3 frequently very shallow, little evident, wedge on tergite 4 frequently narrow; tergite 5 of male mostly gray, with posterior margin darkened. Male terminalia (Figs 106-109): Combined structures generally elongate, in posterior view height about twice width, sparsely setulose; epandrium with dorsal arch above cerci attenuated, not connected, in posterior view (Fig. 106) with dorsal half forming a diamond with a U-shaped cercal cavity dorsally, ventral portion with each lateral half robustly developed, parallel sided then apical nearly half tapered to ventral apex, apex pointed, narrowly incised medially along entire length from cercal cavity to apex, in lateral view (Fig. 107) very shallow L-shaped, obtuse angle, ventral 1/3 tapered to narrowly rounded apex; cerci moderately short, height more than twice width, widely semi-hemispherical (Fig. 106), pointed dorsally, not attached lateroventrally or ventrally with epandrium; aedeagus in lateral view (Fig. 109) very elongate, almost 6 × longer than width, tubular, shallowly curved, apex rounded and with a subapical rectangular extension, in ventral view (Fig. 108) mostly tapered from base apical, rounded expansion; phallapodeme in lateral view (Fig. 109) narrowly elongate with extended keel small, short and barely extended, skewed, irregularly rectangular on portion toward attachment with hypandrium, in ventral view (Fig. 108) an elongate, moderately narrow Y with arms of Y very short; gonite in lateral view (Fig. 109) narrow, elongate, bar-like, very shallowly and obtusely angulate, in ventral view (Fig. 108) shallowly angulate; hypandrium in lateral view (Fig. 109) moderately elongate, very shallow, tapered to curved point anteriorly, in ventral view (Fig. 108) moderately broadly developed, posterior emargination robustly U-shaped, anterior margin bilobed with medial narrow, short incision.

Type material.

The holotype male of Hydrochasma octogonum is labeled "ECUADOR. Pich-incha[,] Manabi[,] August 1955/Collr.Levi-Castillo/USNM ENT 00118298 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma octogonum Mathis & Zatwarnicki, USNM [red]." The holotype is double mounted (glued to a paper triangle)), is in excellent condition, and is deposited in the USNM. Eight paratypes (6♂, 2♀; USNM) bear the same label data as the holotype. Other paratypes are as follows: ECUADOR. Guayas: Río Bobo (01°53.8'S, 79°42'W), Aug 1955, R. Levi-Castillo (3♂, 1♀; USNM).

Type locality.

Ecuador. Manabí: Pichincha (01°01'S, 79°49'W).

Other specimens examined.

Neotropical. ECUADOR. Manabí: La Palma (0°45.7'S, 80°30.7'W), Aug 1955, R. Levi-Castillo (1♂; USNM).

Distribution

(Fig. 110). Neotropical: Ecuador (Guayas, Manabí).

Etymology.

The species epithet, octogonum, is of Latin derivation and means eight sided, referring to the eight-sided polygon of the epandrium in posterior view.

Remarks.

Externally, this species is very similar to Hydrochasma incisum and has often been misidentified as that species in collections. Structures of the male terminalia are quite different, however, and readily distinguish between these two species. In addition, the apex of the wing in Hydrochasma octogonum is acutely angulate, and the vertex of the angle, the apex, is faintly to conspicuously infuscate. In specimens of Hydrochasma incisum , the apex is narrowly rounded and hyaline, typical of most congeners.