Rhynchotermes armatus, a new mandibulate nasute termite (Isoptera, Termitidae, Syntermitinae) from Colombia

Abstract Rhynchotermes armatussp. nov. is described from soldiers and workers collected in the Magdalena River Valley of Colombia. Both castes of this new termite are superficially similar to R. perarmatus (Snyder) but the former are smaller, head capsules yellowish instead of reddish, and among additional characters, the soldier has narrower mandibles and marginal teeth.


Introduction
The genus Rhynchotermes Holmgren constitutes a peculiar group of neotropical termites ranging from Belize to Argentina. They feed openly on surface litter during crepuscular or nocturnal forays. They nest underground or in shallow epigeal nests. Soldiers are either monomorphic or weakly dimorphic and workers are monomorphic. A thorough revision of Rhynchotermes by Constantini and Cancello (2016) included seven species: R. amazonensis Constantini & Cancello, R. bulbinasus Scheffrahn, R. diphyes Mathews, R. matraga Constantini & Cancello, R. nasutissimus (Silvestri), R. perarmatus (Snyder), and R. piauy Cancello. I herein describe an eight species, R. armatus sp. nov., from Colombia.

Material and methods
Live specimens were preserved in 85% ethanol. External and internal worker morphology was depicted using two different methods. In the first method, soldiers and workers were suspended in Purell Instant Hand Sanitizer in a plastic Petri dish. This allowed for transparent posturing and support during photography using a Leica M205C stereomicroscope controlled by Leica Application Suite version 4.0 montage software. The worker enteric valve armature (EVA) was prepared for photography by removing the entire worker P2 section in ethanol. Food particles were expelled from the P2 tube by pressure manipulation. The tube was quickly submerged in a droplet of PVA medium (BioQuip Products Inc.) which eased muscle detachment by further manipulation. The remaining EVA cuticle was longitudinally cut, splayed open, and mounted on a microscope slide using the PVA medium. The EVA was photographed with a Leica CTR 5500 compound microscope with bright field optics using the same montage software.  Fig. 1), one other soldier, 30 workers, and three larvae; CO880, eight soldiers and six workers; CO881, 17 soldiers and two workers (Fig. 3). All material is housed at the University of Florida Termite Collection in Davie, Florida, USA.

Rhynchotermes armatus
Description. The revised description of the genus Rhynchotermes by Constantini and Cancello (2016) includes all characters found in R. armatus.
Imago. Unknown. Soldier (Figs 1, 3; Table 1). Monomorphic. Head capsule, nasus, and mandible bases straw yellow; apical and marginal teeth yellow-brown. Head capsule dome shaped in lateral view. Nasus projecting well beyond mandibles; nearly cylindrical, tapering to rather large circular opening. Nasus hollow, thickness of outer wall even. Pilosity of head capsule limited to two faint setae near level of antennal fossae and one or two even shorter and fainter setae on vertex. Nasus without setae; curved slightly downward. Mandibles curved ~150-180° with greatest curvature beyond marginal teeth. Mandibles narrowing beyond marginal teeth. Apical teeth exceptionally narrow and sharp; marginal teeth extremely thin and angled ~60° toward labrum. Antennae very long, about twice the length of the nasus; 14 articles, 2<3>4=5. Pronotum slightly lighter than head; asymmetrically bilobed in dorsal view, posterior lobe larger; in lateral  view, margin of anterior lobe continuous with vertex, posterior lobe forming hump. Fore coxae with thorn-like process, slight downward curvature. Worker ( Fig. 2; Table 2). Monomorphic. Head capsule concolorous with soldier. Head capsule with eight-to-ten long, evenly spaced setae; postclypeus strongly inflated. In lateral view, posterior lobe of pronotum much longer and angled ca. 130° from plane of posterior lobe. Antennae with 14 articles. Forecoxa with elevated rise on anterior margin. Enteric valve weakly armed consisting of three rectangular cushions, each with 30-40 very small triangulate spines; cushions separated by wider cuticular lining interspersed with even smaller spines.
Comparison. Constantini and Cancello (2016) divided Rhynchotermes soldiers into two morphogroups: those with mandibles larger than the head (R. perarmatus and R. bulbinasus) and those with mandibles shorter than the head (all remaining species). Rhynchotermes armatus falls into the former group and is closest R. perarmatus, each  having a tubular nasus and large mandibles. Snyder (1925a) reported a soldier head length of 2.5-2.6 mm for R. perarmatus and 3.0-3.2 mm for its junior synonym, R. major (Snyder 1925b) from Panama and Costa Rica, respectively. These measurements are from 1.14 to 1.85 times larger than R. armatus. In addition to the head length, the R. armatus soldier is smaller in all measurements, has a yellowish head pigmentation versus reddish, and has narrower (thinner) mandibles, including the marginal teeth (Fig. 3A). The nasus of R. armatus has a greater curvature and the third antennal article is proportionately shorter (Fig. 3B). The workers of both species are concolorous with their respective soldiers. The R. armatus worker has a small and faint fontanelle ( Fig. 2A) compared to the proportionately larger and more contrasting fontanelle and cranial suture of R. perarmatus (Fig. 3C). The R. armatus worker EVA has fewer spines on the three cushions and the inter-cushion areas than R. perarmatus. Also the R. perarmatus EVA has longitudinal folds covered with fine fringes anterior to the cushions (Fig. 3D) which are lacking in R. armatus. The next closest species, R. bulbinasus, differs from the other two in having a median inflation of the nasus. The apical teeth of R. armatus are extremely sharp (point ca. 1.5 µm wide, Fig. 1D inset), probably only comparable with those of Silvestritermes gnomus (Constantino) (https://www.termitediversity.org/sandsi-sinocapri?lightbox=dataItem-jy00jfyy).
Etymology. The species name is a truncated derivative of its closest congener, R. perarmatus. Although Snyder (1925a) did not provide an etymology for R. perarmatus, he gave an apt analogy for the gestalt of all Rhynchotermes soldiers: "It is a thoroughly armed species and runs about audaciously with its nasus or beak elevated at an angle of 45°, reminding one of an antiaircraft gun".

Key addition
A new couplet (3) for the Rhynchotermes key by Constantini and Cancello (2016) is offered below to accommodate R. armatus: 1 Mandibles larger than head, clearly visible from dorsal view when closed; apical region of each mandible extending well beyond the opposite mandible when closed ( fig. 6B) (Snyder 1949). All remaining Rhynchotermes species have an Amazonian or austral distribution (Constantini and Cancello 2016). The Magdalena River Valley lies between the central and eastern ranges of the Colombian Andes and is host to various endemic faunas including birds (Cracraft 1985), fishes (Anderson and Maldonado-Ocampo 2011), frogs (Ospina-Sarria et al. 2015), lizards (Velasco and Hurtado-Gómez 2014), and insects (Huertas et al. 2009;Padilla-Gil 2015). Rhynchotermes armatus is apparently another endemic species from the Magdalena River Valley. It is plausible that R. armatus and R. bulbinasus evolved * Couplet 4 replaces 3 in original key so a digit is added to all ensuing couplets.
from an ancestor of R. perarmatus following the gradual land bridge closure joining Central and South America during the Miocene (Woodburne 2010). This timeframe coincides with the orogenic rise of the Eastern Cordillera of Colombia (Gregory-Wodzicki 2000) which may have led to the vicariant divergence and allopatric speciation across elevational gradients leading to one or both Colombian species. This scenario was reported for Rheobates frogs of the same region (Muñoz Ortiz et al. 2015). Additional undescribed termites known only from this valley include a new genus of Apicotermitinae, a new species of Rugitermes, and a new Obtusitermes (Scheffrahn and Pinzón, unpublished). No doubt further exploration will yield more new taxa.