Eulimnadia ovisimilis Martin and Belk, 1989

(Figs. 4 G, H)

Material examined. Argentina: Formosa Province: Bermejo Department: Laguna Yema region, temporary pool at 24°15' S, 61°15' W, 160 m asl, collectors: J. Faivovich, J.C. Fernicola and A. López, I-2013, one ovigerous female from the pond and two females (one ovigerous) from the stomach contents of a Lepidobatrachus laevis Budgett, 1899 (Budgetts frog) larva of the same pond, IC-DBBE-UBA. Corrientes Province: San Roque Department: San Roque City, roadside pool near National Route 12 at Santa Lucía River, 28°34'28.34" S, 58°43'20.30" W, 55 m asl, collector: M.T. Jordá, 12-III-2000, two hermaphrodites (one ovigerous), IC-DBBE-UBA.

Selected characters of the observed specimens. Carapace yellowish, with 6 to 7 growth lines (plus margin). Number of segments: 20–21, number of telsonal spines: 21–25, number of setae of cercopods: 30–32, spine of cercopods small and subapical.

Female rostral variability. The specimens originally described by Martin & Belk (1989) from Paraguay, present bluntly rounded rostrum, whereas all five females from Argentina have pointed rostral tips, resembling the females of E. texana. However, the head shapes of both species differ in the longer distance from the dorsal organ to the ocular protuberance in E. ovisimilis. Female rostral variability (from rounded to pointed) has been experimentally induced in E. texana derived from a single clutch exposed to different predatory pressures (Rogers et al. 2012), or in E. magdalenensis by raising specimens at different temperatures (Roessler 1995).

Eggs. Cylindrical, bearing 12 or 14 longitudinal parallel ridges that separate narrow grooves running from rim to rim (Figs. 4 G, H), ends flat or slightly concave, with two parallel ridges (Fig. 4 H) or two crossed-linked ridges (Fig. 4 I); rims slightly flaring. Egg diameter somewhat wider at the ends (135–174 µm) than at midpoint (135–148 µm); length (120–130 µm); surface textured with minute pores.

Size. Putative hermaphrodite. Carapace length 8.3–10.0 mm, height 6.0– 7.2 mm, height/length 0.70–0.73 (n = 5), width 3.4 mm (n = 1).

Breeding system. Three out of the five females collected in Argentina, were ovigerous. However, since E. ovisimilis was originally described from a population comprising 12.5% males, we can assume that this species is androdioecious. No spermatophore-like structures were observed.

Ecology. The type locality is a “shallow region with submerged grass about one week after heavy rains that filled a formerly dry pond-marsh” (Martin & Belk 1989). The new localities for E. ovisimilis were a temporary pond and a roadside pool. The unexpected finding of two specimens in the stomach contents of a Budgetts frog larva suggests the frog is a passive dispersal agent for this clam shrimp and that this species is relevant in seasonally astatic aquatic habitat food webs in the Chacoan biogeographical province.

Distribution. Paraguay: Chaco Department, National Park Defensores del Chaco (type specimens described by Martin & Belk 1989) and Argentina: Formosa Province (434 km apart from the type locality) and; Corrientes Province (920 km apart from the type locality). All three sites are located within the Chacoan biogeographical province of the Chacoan subregion (Fig. 6).