Ambrysus bifidus La Rivers & Nieser

Ambrysus bifidus La Rivers & Nieser

(Figs. 1–2)

Ambrysus bifidus La Rivers & Nieser 1972: Biol. Soc. Nevada Occas. Pap. 4–8.

Ambrysus bifidus: Nieser 1975, Stud. Fauna Suriname Guyanas 56–57 (suppl. descript.).

Discussion. This species is known from Suriname and northern Brazil (La Rivers & Nieser 1972). Reported here is the first record from Guyana. This species was distinguished from A. scolius by a "slight bifurcation" of the apical median lobe of the female subgenital plate (Fig. 2 F) (La Rivers & Nieser 1972), and from A. tricuspis by the same bifurcation of the subgenital plate and also the male accessory genitalic process less massive or elongated laterally (Fig. 2 B) (La Rivers 1974). Nieser (1975) provided a supplemental description in his treatment of the water bugs of the Guyana region, in which he documented the variation in the shape of the accessory genitalic process of tergum VI. A. bifidus can be distinguished from the other species in this complex by the bifurcated median lobe of the female subgenital plate.

The habitat of the type series was given in the original description as "floating plant-debris upstream of a barrier of tree branches, etc., velocity of current 5 m /min." In Suriname, A. bifidus, A. stali, and A. usingeri La Rivers were considered to be common in small streams in savannah woodlands with dark water low in electrolytes (La Rivers & Nieser 1972). A. bifidus was collected with A. stali in Surinam mostly in barriers of branches and dead leaves or at the bases of trees standing in water where the current is strong.

Type locality. SURINAME, Zanderijsavanne. Holotype is housed at CAS.

Material examined. GUYANA: Pirara Ranch, 3º 22.1' N, 59º 40.5' W, Pirara River, 25 Apr 1995, colln #19, PJ Spangler & SA Perry (1♀, UMC). SURINAME: Zanderijsavanna Carolina Cr. / (reverse side of locality label) 1969 Aug 18, N. Nieser / Ambrysus bifidus L&N 1972 Paratype / Ira La Rivers Collection Bequeathed to the California Academy of Sciences (1♂, 1♀, CAS).

Published records. (La Rivers & Nieser 1972): BRAZIL, Amazonas, Pará; SURINAM, Zanderijsavanne. (Pereira & Melo 2007): BRAZIL, Amazonas, Waimiri-Atroari Biological Reserve.