Hylomyrma plumosa Pierce, Branstetter & Longino, 2017

Figures 58, 80F, 80K, 85 (map)

Hylomyrma plumosa Pierce, Branstetter & Longino, 2017: 138 (W). Holotype: COSTA RICA: Limón: Res. Biol. Hitoy-Cerere, 9.66480 -83.02346 ± 10 m, 250 m [a.s.l.], 10 June 2015, [Project] ADMAC [collection code] #Wa-E-02-2-38, tropical rainforest, ex sifted leaf litter (1W) (CASENT0638700) [CASC] [examined by image]. Paratypes: same data as holotype (1W) (CASENT0638687) [MCZC] [not examined]; (1W) (CASENT0638688) [UCD] [not examined]; (1W) (CASENT0638693) [UCR] [not examined]; (1W) (CASENT0638697) [USNM] [not examined]; (1W) (CASENT0638703 MZSP67408) [MZSP] [examined]; (8W) (CASENT0638720, CASENT0638701, CASENT0638725, CASENT0638698, CASENT0638700, CASENT0638722, CASENT0638724, CASENT0638735) [JTLC] [not examined].

Worker (Fig. 58 A-C) Diagnosis. Mesosoma and petiole covered with thin striae (microsculpture) superimposed on irregular and thick striae (macrosculpture), interspaces between thinner striae indistinguishable; conspicuous and trifid setae.

QUEEN Unknown.

MALE Unknown.

Etymology. The specific epithet is a reference to the distinctive branched setae of this species.

Comments. Hylomyrma plumosa is identified based on the conspicuous and trifid setae (Fig. 80K). This species resembles H. 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 H. longiscapa, H. plumosa, and H. 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. Hylomyrma plumosa occurs in Costa Rica (Fig. 85).

Natural history. 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.

Additional material examined (4 workers): COSTA RICA: Heredia: 11km ESE La Virgem, 10.35, -84.05 + 2km, 300m, 10.iv.2004, ALAS #03/WF/02/all montane wet forest, ex sifted leaf litter (1W) [MZSP]; La Selva, E. O Wilson col., 19.iii.85 (1W) [MCZC]; La Selva Biological Station, 10.41639, -84.02 + 500m, 50m, 16.iii.2004, TEAM #AMI-1-W-006-01, mature wet forest, ex sifted leaf litter (2W) (MZSP67470, MZHY84) [MZSP] .