Ambrysus scolius La Rivers

Sites, Robert W. & Reynoso-Velasco, Daniel, 2015, Review of the Ambrysus stali La Rivers species complex (Heteroptera: Nepomorpha: Naucoridae) with the description of a new species from Mesoamerica, Zootaxa 4018 (2), pp. 279-291 : 286-287

Ambrysus scolius La Rivers

( Figs. 1 , 5 )

Ambrysus scolius La Rivers 1970 : Great Basin Natur. 1–4.

Discussion. This species is known by only three females from the Guyana Shield countries of Guyana, Trinidad, and Venezuela. Males are not known. Although we have been unable to locate the holotype, the paratypes in the CAS ( Fig. 5 ) that we examined do not resemble the habitus figure of the holotype in the original description. La Rivers (1970) gave the sigmoid posterior margin of laterosternite VI (La Rivers' segment V) as the diagnostic feature of this species. We have examined the two paratypes housed at the CAS and considered this feature in both anterior/posterior and dorsal/ventral planes, but are uncertain how to interpret the sigmoid nature of the margin and how it differs interspecifically. In addition, the left laterosternite VI has a well-developed posteromedial spine directed posteroventrad, whereas the right laterosternite is developed differently in the two paratypes: In one specimen the posterior margin is more strongly developed medially and becomes deflexed ventrad at the corner, whereas the other specimen has the posteromedial corner tuberculate and deflexed ventrad.

La Rivers (1970) described A. scolius without knowledge of the related species he would describe in the next few years; thus, he did not know if the sigmoid posterior margin of laterosternite VI would be a unique feature. However, he made no mention of its condition in the original descriptions of A. bifidus and A. tricuspis . Because A. scolius and A. tricuspis have the same subgenital plate shape and our examination reveals nearly the same condition for the posterior margin of laterosternite VI, we are not able to satisfactorily distinguish between them.

We provisionally determined eight specimens including four females from northwestern Pará, Brazil as A. scolius . However, there is substantial variation in the condition of the female subgenital plate and laterosternite VI. Specifically, the subgenital plate posterior margin varies from straight to strongly convex, but is not bifurcated. The right laterosternite VI varies from a flat, unmodified posterior margin to bearing a short posteromedian spine. This suggests that considerable intraspecific variation in these features might also exist in other species in the complex. As such, species determinations can be equivocal for most of these species and series of specimens should be collected when possible to establish the limits of expression of these features. For these specimens from Brazil, geographic proximity suggests conspecificity with A. scolius rather than with A. tricuspis .

Type locality. VENEZUELA, Monagas, 42 km SE Maturin. Repository of holotype unknown; two female paratypes are housed at CAS.

Material examined. BRAZIL: Pará state, 378, Rio Mapuera, Igarapé do Aracu, 19 June 1986, Py-Daniel & Barbosa (2♂, 2♀, INPA; 2♂, 2♀, UMC). BRITISH GUIANA: Honey Camp Cr., Oct. 24 1937, S. Harris / A. scolius ♀ Paratype / Ira La Rivers Collection Bequeathed to the California Academy of Sciences (♀, CAS). TRINIDAD: B.W.I., Port of Spain, Nov. 5 1931, W. E. Broadway / A. scolius ♀ Paratype / Ira La Rivers Collection Bequeathed to the California Academy of Sciences (♀, CAS).

Published records. ( La Rivers 1970): VENEZUELA, Monagas state.

Figures

FIGURE 1. Distribution of species in the Ambrysus stali species complex.

FIGURE 5. Ambrysus scolius female paratype. (A) dorsal habitus, (B) terminal abdominal sterna showing subgenital plate with posterior and lateral margins outlined in black (terminal terga missing).