(by original designation): Elpidium bromeliarum F. Müller, 1880.

Other species allocated: Elpidium inaequivalve Danielopol, 1980; Elpidium laesslei (Tressler, 1956) Danielopol, 1980; Elpidium maricaoensis (Tressler, 1941) Danielopol, 1980; Elpidium pintoi Danielopol, 1980; Elpidium purperae Danielopol, 1980.

Medium sized to relatively large ostracods; carapace broad, generally bigger in width than in height; ventral margin flat; pale to dark brown smooth surface; in dorsal and ventral view males with greatest width at midlength, females with posterior part expanded into a brood pouch carrying eggs and greatest width displaced posteriorly; strongly interlocking selvages along ventral margin leaving an anteroventral gap between left and right valve margins; hinge a crenulated cardinal bar on the smaller valve forming rudimentary anterior and well developed posterior teeth; A1 with 5 functional articles, the first one bearing a sub-apical expansion with a tuft of tiny setules on the dorsal margin; in males, A2 with a serrated apical claw on the terminal segment (no such serration in females); terminal segment of A2 with a small lobe (hyaline formation) in both males and females; second and third endites of the maxillule bearing two spatulate claws each; copulatory process of hemipenis a hook-like structure placed ventrally on the muscular body, near the base of distal lobe.

Elpidium is closely related (Pinto et al. 2008) to the terrestrial genus Intrepidocythere Pinto et al., 2008. Nonetheless several differences can be recognized. The carapace of Intrepidocythere is smaller and considerably less broad in dorsal view compared to Elpidium species. Furthermore, the marginal zone and hinge structures are different, while Elpidium has a long bar on the smaller valve ending in a small anterior tooth and a crenulated posterior tooth, Intrepidocythere has a smooth medial ridge and a posterior socket in left valve with the complementary smooth medial groove and posterior tooth in right valve. The antennule has 2 medio-dorsal setae on the fourth segment in Elpidium, but only 1 in Intrepidocythere; the male antenna has 1 serrated claw on the terminal segment in Elpidium, but 2 in Intrepidocythere; and the female caudal ramus has three setae in Elpidium, but only two in Intrepidocythere.

Cusuco National Park, Honduras at an altitude of 1840 masl. Geographical coordinates: 15.5133N, 88.2417W. Water accumulated in bromeliad (Tillandsia guatemalensis) leaf axils. Material collected on 15 July 2006 by M. Jocqué.

Holotype: a dissected male, with valves dried and coated for scanning electron microscopy stored in a micropaleontological slide and soft parts mounted in a permanent slide with CMC-9AF mounting medium (MZUSP 29072). Allotype: a dissected ovigerous female, with valves stored dry in a micropaleontological slide and soft parts mounted in a permanent slide with CMC-9AF mounting medium (MZUSP 29073). Paratypes: two males (MZUSP 29074 and MZUSP 29075), dissected and stored like the allotype; an ovigerous female (MZUSP 29076) dissected and stored like the holotype; three males (MZUSP 29077, MZUSP 29078 and MZUSP 29079) and three females (MZUSP 29080, MZUSP 29081 (carapace broken) and MZUSP 29082), dried and coated for scanning electron microscopy stored in micropaleontological slides; 25 males and 8 females kept whole in a vial with 70% ethanol (MZUSP 29083).

The species is named after the Merendón mountains in Honduras, where the specimens described in the present work were collected.

Small sized Elpidium (c. 700 μm). In dorsal and ventral views carapace relatively elongated for the genus (length/width c. 1, 4). In right lateral view carapace elongated (length/height c. 2), with left valve overlapping right valve on all margins, but very strongly at the posterior end of the carapace, especially in females, where this overlap produces a conspicuous outgrowth of the outer lamella, apparently without substantial change to the inner marginal structures. Ventral margin flat, with a subtle ventro-lateral ridge on each valve, at the edge of the flat area. Distal lobe on hemipenis triangular, with a pointed tip and with a finger-like projection at the base of the internal margin next to the dorsal seta; copulatory process a stiff hook-like structure, thick at the first half of its length and then quickly narrowing to the orifice at the tip.

Carapace (Fig. 1G–I). Small sized (length = 657–685 μm), with brown surface and sparse setae; surface smooth except for a subtle ventro-lateral ridge on each valve; elliptically elongated in lateral view (length/height=1.96), with greatest height just behind the mid-length; left valve overlapping right valve on all margins, strongly interlocking in antero-ventral, ventral and postero-ventral margins; ventral area flat; dorsal margin arched; posterior and anterior margins rounded, both produced towards the ventral side; oval shaped in ventral and dorsal views, with maximum width behind mid-length; dorsal margin straight in dorsal view; ventral margin sinuous in ventral view with well-marked ridges.

Left valve (Fig. 1A–C). In internal view, anterior and posterior margins rounded, produced towards the ventral side; ventral margin nearly straight; dorsal margin arched; calcified inner lamella well developed anteriorly, with a short line of concrescence near the valve margin leaving a vestibule; vestibule less developed posteriorly, but present; prominent selvage running on all margins except in the middle of dorsal margin; a short flange is formed at the antero-ventral margin; central muscle scars consisting of 4 spots arranged in a vertical row relatively separated from each other and a round small frontal scar.

Right valve (Fig. 1D–F). In internal view, anterior and posterior margins rounded, produced towards the ventral side; ventral margin nearly straight; dorsal margin arched; calcified inner lamella well developed anteriorly, with a short line of concrescence near the valve margin leaving a vestibule; vestibule less developed posteriorly but present; prominent selvage running all around, forming the hinge structures on the dorsal margin; a continuous flange is present, being wide on the antero-ventral margin, very narrow at the mouth region and narrow on the ventral and postero-ventral margins; central muscle scars consisting of 4 spots relatively separated from each other arranged in a vertical row and a round small frontal scar.

Hinge (Fig. 1A–F). A long (c. 3/4 of the valve length) cardinal ridge is present on the right valve, forming at each end, respectively, a small anterior tooth and a large posterior tooth; the ridge is slightly crenulated, especially at the posterior end; RV with complimentary groove and sockets.

Pigmented naupliar eye present; carapace less pigmented at the eye region.

Antennula (Fig. 2A). 5 functional articles; first article relatively large, bearing on the dorsal margin a sub-apical expansion with a tuft of tiny setules; second article the longest with a ventro-proximal long and thick seta; third article small with a short dorso-apical seta; fourth article partially subdivided in two, medially (where the segment is subdivided) with two dorsal and one ventral setae, and apically with a long ventro-apical, two short and one long dorso-apical setae; fifth (terminal) article with two long setae, one short seta and a short aesthetasc (Ya).

Antenna (Fig. 2B). Protopodite 2-segmented, the first one very short and the second one long, wide and curved; endopodite 3-articulated; first segment relatively short, bearing a long ventro-apical seta; second segment very long and narrow, dorsally with two sub-apical setae, one three thirds as long as the other, ventro-medially with a short seta and an aesthetasc (Y), and apically with two setae, one large and one minute; last segment small, with three claws, the ventral one strongly serrated and the other two slender, a minute seta and a tiny lobe (hyaline formation); exopodite with a very small seta and a spinneret seta.

Mandible (Fig. 2D–E). Coxa with 7 strong teeth and 6 setae on inner edge and a seta on outer edge (near the articulation with the palp); palp 4-segmented (basis + 3-segmented endopodite); basis externally with respiratory plate (exopodite) consisting of 3 rays and one reflexed seta, and internally with two setae, one two thirds as long as the other; first endopodal segment with two apical internal setae, one less than half as long as the other; second endopodal segment with an internal apical seta and 4 external apical setae, one short, two long and one intermediate; terminal endopodal segment with 2 setae and one slender claw, all equally long.

Maxillula (Fig. 2F). Internally with three endites, first one with 2 setae, second and third ones each with 3 setae and two claws, the latter with a conspicuous spoon-shaped apex; palp not segmented, tapering, with 2 apical setae; respiratory plate well developed, carrying a reflexed seta (i.e. reversed towards the front) and 16 long rays.

First thoracopod (Fig. 3A). 4-segmented; first segment with a long medio-proximal dorsal seta, a medium-sized medio-ventral seta and two stout short ventro-apical setae; second segment quite long, with a strong ventro-apical seta; third segment devoid of setae; terminal segment with an apical claw that bears a minute seta at its base.

Second thoracopod (Fig. 3B). 4-segmented; first segment with a long medio-proximal dorsal seta, a medium-sized medio-ventral seta and a relatively short ventro-apical seta; second segment long, with a strong ventro-apical seta reaching tip of following segment; third segment devoid of setae; terminal segment with an apical claw bearing a minute seta at its base.

Third thoracopod (Fig. 3C). 4-segmented, quite slender; first segment with a medio-proximal dorsal seta, a medio-ventral seta and a ventro-apical seta; second segment quite long, with a slender ventro-apical seta; third segment devoid of setae; terminal segment with a very long and slim apical claw carrying a minute seta at its base.

Hemipenis (Fig. 3D). Consisting of a large rounded muscular body, an articulating distal lobe and a dorsal seta; distal lobe triangular, with a pointed tip and with a finger-like projection at the base of the internal margin, next to the dorsal seta; copulatory process a stiff hook-like structure, thick at the first half of its length and then quickly narrowing to the orifice at the tip; lower ramus (“crochet accessoire”) sinuous and with a rounded tip; caudal ramus a hirsute rounded lobe bearing a pair of setae.

Carapace (Fig. 4G–I). Small sized (length = 697–722 μm), with brown surface and sparse setae; surface smooth except for a subtle ventro-lateral ridge on each valve; elliptically elongated in lateral view (length/height=1.96), with greatest height just behind mid-length; left valve overlapping right valve on all margins, strongly interlocking in antero-ventral, ventral and postero-ventral margins; valve overlap very strong at the posterior end of the carapace, producing a conspicuous outgrowth of the outer lamella, apparently without substantial change to the inner marginal structures; ventral area flat; dorsal margin arched; posterior and anterior margins rounded, both margins produced towards the ventral side; valves oval shaped in ventral and dorsal views, with maximum width displaced towards the posterior end in comparison to the male, producing a brooding cavity; up to 10 eggs were observed in a brood (mean egg size = 4.87 ± 4.0 μm, N = 8); dorsal margin straight in dorsal view; ventral margin sinuous in ventral view with well-marked ridges.

Left valve (Fig. 4A–C). In internal view anterior margin rounded, produced towards the ventral side; posterior margin narrowly rounded, produced towards the ventral side, forming a bulge at the postero-ventral area; ventral margin nearly straight; dorsal margin arched; calcified inner lamella well developed anteriorly, with a short line of concrescence near the valve margin leaving a vestibule; vestibule less developed posteriorly, but present; prominent selvage running on all margins except in the middle of dorsal margin; a short flange is formed at the antero-ventral margin; at the postero-ventral region, with outer lamella expanded towards the posterior end; central muscle scars consisting of 4 spots arranged in a vertical row relatively separated from each other and a round small frontal scar.

Antenna (Fig. 2C). As in the male, except for the small terminal segment with three equally slender claws, a minute seta and a tiny lobe (hyaline formation).

Abdomen (Fig. 3E). Genital operculum rounded, internally connected by tubes to a trabecula; caudal rami two hirsute rounded lobes, each with two apical setae in juxtaposition, a medio-external seta and an inconspicuous external seta nearer the base of the caudal ramus; end of body rounded, with a dorsal seta inserted in a strongly chitinized structure.

Male. Holotype: length = 674 µm, height = 347 µm; Paratype MZUSP 29077: length = 685 µm, height = 349 µm; Paratype MZUSP 29078: length = 657 µm, width = 463 µm; Paratype MZUSP 29079: length = 677 µm, width = 461 µm. Female. Paratype MZUSP 29076, LV: length = 721 µm, height = 344 µm; Paratype MZUSP 29080: length = 715 µm, height = 355 µm; Paratype MZUSP 29081: length = 697 µm, width = 513 µm; Paratype MZUSP 29082: length = 722 µm, width = 518 µm.

The carapace of Elpidium merendonense sp. n. resembles that of Elpidium inaequivalve in being relatively elongated in dorsal view and having a wide valve overlap at the posterior end of the carapace. However, the valve asymmetry is more pronounced in Elpidium inaequivalve, while females of Elpidium merendonense sp. n. show a unique outgrowth at the posterior end of the left valve where it overlaps the right valve. Elpidium merendonense sp. n. and Elpidium laesslei both present a distal lobe on the hemipenis with similar shape, but the copulatory process and the lower ramus are smaller in the latter species. These two species can furthermore be distinguished by the shape of the carapace in dorsal view, which is broad and rounded in Elpidium laesslei and oval in Elpidium merendonense sp. n.

Elpidium merendonense was found only in water accumulated in leaf axils of bromeliads from 1, 400 to 2, 242m elevation in CNP. Only Tillandsia sp. were examined. In this altitudinal range, bromeliads occur all through the area in varying densities depending on microclimatic conditions. Specimens of this species were common in collections throughout the park, sometimes co-occupying bromeliads with a species of candonid ostracod and/or a species of Anomopoda (Ceriodaphnia laticaudata Müller, 1867). Ostracoda were more common in larger bromeliads.