Hylomyrma plumosa

This species occurs in wet forests at elevations between 50 and 300 m. Seventeen specimens were collected in the leaf-litter, which suggests that this species nests in fallen logs, rotten wood, between leaves, or inside natural cavities of the superficial soil layers. (Ulyssea & Brandao, 2021)

Identification
Pierce et al. (2017) - At least some of dorsal setae branched, usually trifid. Though the plumose setae and short gastral striation of Hylomyrma plumosa are distinctive, the species is otherwise extremely similar to Hylomyrma dentiloba and Hylomyrma versuta.

Ulyssea & Brandao (2021) - Mesosoma and petiole covered with thin striae (microsculpture) superimposed on irregular and thick striae (macrosculpture), interspaces between thinner striae indistinguishable; conspicuous and trifid setae.

Hylomyrma plumosa is identified based on the conspicuous and trifid setae (Fig. 80K). This species resembles Hylomyrma versuta, described by Kempf (1973) as “long hairs, pointed at tip, gently curved on petiole and postpetiole”. However, the types of H. versuta and additional examined material comprise specimens with unbranched and branched setae. The branched setae of H. versuta, mostly present on the petiole, postpetiole, and gaster, are composed of a variable number of short branches with similar size (Fig. 80F). These branched setae are not conspicuous as in Hylomyrma longiscapa, H. plumosa, and Hylomyrma transversa, being better observed in SEM images. Hylomyrma plumosa and H. versuta are locally sympatric (Figs. 85, 88), having been collected in the same sample (ALAS #03/WF/02/) near La Virgen (300 m), and in different samples (H. plumosa #AMI-1-W-006-01, and H. versuta #AMI-1-W-006-05) from the La Selva Biological Station (50 m); both locations in Heredia Province, Costa Rica. The two species have very similar body sculpture. The difference between them is very subtle: the propodeum is laterally covered by thin striae (microsculpture) with indistinguishable interspaces superimposed on irregular and thick striae (macrosculpture) in Hylomyrma plumosa, whereas H. versuta presents thin striae (microsculpture) with indistinguishable interspaces between irregular and thick striae (macrosculpture). Initially, we understood that H. plumosa and H. versuta belonged to a continuum of variation due to their body sculpture similarity, variable setae, and co-occurrence. But molecular data show H. plumosa as sister to the H. cf. dentiloba sp.2 (the true H. dentiloba)–H. versuta clade (Pierce et al. 2017). In this scenario, we have decided to maintain all three species as valid until additional evidence is gathered. Further investigative approaches using UCEs should include representatives of all the variation found in these taxa (or nominal species).

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica.

Nomenclature

 * . Hylomyrma plumosa Pierce, M.P., Branstetter, et al. 2017: 140, figs. 3, 5, 7 (w.) COSTA RICA.
 * Type-material: holotype worker, 13 paratype workers.
 * Type-locality: holotype Costa Rica: Limón, Hitoy-Cerere, 9.66480, -83.02346±10 m., 250 m., 10.vi.2015, Wa-E-02-2-38 (project ADMAC); paratypes with same data.
 * Type-depositories: CASC (holotype); MCZC, JTLC, UCDC, UCRS, USNM (paratypes).
 * Status as species: Ulysséa & Brandão, 2021: 89 (redescription).
 * Distribution: Costa Rica, Ecuador, Panama.

Type Material

 * Holotype worker: Costa Rica, Limón, Hitoy-Cerere, 9.66480 - 83.02346 ± 10 m, 250 m a.s.l., 10 June 2015 (collection code: ADMAC#Wa-E-02-2-38), unique specimen identifier CASENT0638700].
 * Paratype workers (n = 13): Same data as holotype, CASENT0638687; , CASENT0638688; , CASENT0638693; , CASENT0638697; , CASENT0638720, CASENT0638701, CASENT0638703, CASENT0638725, CASENT0638698, CASENT0638700, CASENT0638722, CASENT0638724, CASENT0638735.

Worker
(holotype worker): EL 0.211, EW 0.13, GSL 0.089, HFL 0.735, HL 0.799, HW 0.784, ML 1.042, OMD 0.109, PpL 0.253, PpW 0.3, PronW 0.573, SL 0.591, SPL 0.228, CI 98, GSI 9, OI 27, PpWI 119, SI 75, SPI 29. Measurements (range, n = 15): EL 0.202 - 0.235, EW 0.109 - 0.138, GSL 0.089 - 0.12, HFL 0.709 - 0.801, HL 0.793 - 0.871, HW 0.759 - 0.842, ML 0.991 - 1.137, OMD 0.095 - 0.12, PpL 0.227 - 0.285, PpW 0.293 - 0.331, PronW 0.55 - 0.618, SL 0.544 - 0.622, SPL 0.212 - 0.253, CI 93 - 99, GSI 8 - 11, OI 26 - 28, PpWI 114 - 133, SI 70 - 77, SPI 27 - 31.

Head subquadrate, occipital margin very slightly convex, occipital corners rounded. Clypeus bidentate, area between denticles mostly straight. Frontal lobes convex, ending anteriorly in a rounded angle, projecting over antennal insertions. Rugae on head running longitudinally and parallel, not intersecting; rugae interrupted occasionally by short gaps. Interrugal spaces microstriate, subopaque. Eye large, ending anteriorly in elongate tapering lobe. Scape tapered toward insertions and covered by abundant suberect non-branched hairs.

In profile view mesosoma convex, profile uninterrupted. Sides and dorsum of mesosoma reticulate rugose, interrugal spaces microstriate, subopaque. Propodeal spines relatively short, projecting posteriorly.

Peduncle of petiole present but not well developed. Sides and dorsum of petiole rugulose. Postpetiole subquadrate, covered on dorsum by longitudinal striae. Gaster mostly smooth and shining, striations on dorsum of tergum 1 short, but longer than Hylomyrma montana.

Body color reddish to reddish-brown, legs somewhat lighter, gaster darker brown. Dorsum of head, mesosoma, and gaster abundantly setose, at least some setae branched, bifid or more often trifid.

Etymology
This species is named for the distinctive branched hairs that distinguish it from all other Hylomyrma.

References based on Global Ant Biodiversity Informatics

 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.