Scorpions were collected during daytime and night time (without UV light detection), by turning rocks and logs, and under leaf litter.

The material is deposited in the following collections: American Museum of Natural History, New York (AMNH), with tissue samples stored in the Ambrose Monell Cryocollection (AMCC); Natural History Museum, London (BMNH), Colección Nacional de Arácnidos, Instituto de Biología, Universidad Nacional Autónoma de México, Mexico City (CNAN); Colección Entomologíca, Escuela Agrícola Panamericana “El Zamorano” (EPAZ), Hope Entomological Collection, Oxford University of Natural History (OUMNH), Museo de Historia Natural, Universidad Nacional Autónoma de Honduras (UNAH).

Geographical coordinates of collection localities were recorded in the field with (on Útila) a Garmin eTrex Venture or (on Cayos) an eTrex HCx GPS device. Distribution maps were generated in ArcView Ver. 3.2 (ESRI), using the locality coordinates, a base map from the ArcView Ver. 3.2 Database, and a digital elevation model from the CGIAR Consortium for Spatial Information [12].

Observations were made using Nikon SMZ-800 and SMZ-1500 stereomicroscopes. Measurements, given in millimeters, were obtained with an ocular micrometer calibrated at 10 ×. Hemispermatophores were dissected following Vachon [13], and cleared with pancreatin. Digital images were taken under visible and UV light with a Nikon SMZ-800 with Nikon Coolpix S10 VR camera attachment. The focal planes of image stacks were fused with CombineZM [14] and composite images edited with Adobe Photoshop CS5.

The scorpion higher classification follows Prendini and Wheeler [15]. The nomenclature and mensuration follows Stahnke [16], except for hemispermatophore [17], trichobothria [18], carination of the metasoma [19] and pedipalps [20], carapace surfaces [21], and basitarsal spiniform setae counts [1–3,22].

Family DIPLOCENTRIDAE Karsch, 1880

Genus Diplocentrus Peters, 1861

Diplocentrus insularis n. sp.

Figs. 1–8, Tables 1–4

Type material.HONDURAS: ISLAS DE LA BAHÍA: Municipio de Roatán: Holotype ♂ (CNAN-T0918) Cayo Menor, Cayos Cochinos 15.9572°N 86.4998°W, 8.viii.2012, K. Sgastume; 3 ♂, 1 ♀, 2 juv. paratypes (CNAN-T0919), 3 ♂, 1 ♀, 2 juv. paratypes (AMNH), 2 ♂ paratypes (OUMNH), 1 ♂ paratype (BMNH), 2 ♂ paratypes (UNAH), 1 ♂ paratype (EPAZ), same locality, 2-8.viii.2012, K. Sagastume.

Additional material. HONDURAS: ISLAS DE LA BAHÍA: Municipio de Roatán: 1 ♂, 1 ♀, 1 juv. (OUMNH), 1 ♂ (BMNH), 1 ♂, 1 ♀. (UNAH), 2 ♂, 1 ♀ (CNAN), 2 ♂ (AMNH), same locality as paratypes, 9–13.viii.2012, S. Longhorn and K. Sagastume. Municipio de Útila: 1 ♂ subad., 1 ♀ paratypes, 1 juv. (CNAN), 1 ♀ (AMNH), 1 ♀ (OUMNH), 2 ♀ (UNAH) New Airport forest patch, Útila 16.2034°N 86.8833°W, 14-27.vii.2012, K. Sagastume.

Etymology. The specific epithet refers to the fact that this species appears to be an island endemic. It is neutral in gender.

Diagnosis. The following character combination is diagnostic for D. insularis, n. sp. Total length (adult), 50–54 mm. Base coloration (adult), brown to reddish brown. Carapace anteromedian notch moderately deep, U-shaped (Fig. 3). Pedipalp femur, width greater than height, dorsal surface flat (Fig. 5A). Pedipalp patella, dorsal median carina weakly developed, smooth (♂, Fig. 5B); dorsal retrolateral carina weakly to moderately developed, smooth; retrolateral median carina obsolete (♂; ♀); ventral median carina weakly to moderately developed, smooth (Fig. 5D). Pedipalp chela manus, dorsal intercarinal surface moderately reticulated (♂, ♀ Fig. 6); digital carina strongly developed, smooth (♂), or weakly to moderately developed, smooth (♀); dorsal secondary carina weakly to moderately developed, smooth to crenulated (♂) or weakly developed to obsolete, smooth (♀). Legs I–IV telotarsi, counts of spiniform macrosetae in pro- and retroventral rows, 4/4:4/4–5:5/5:5/5; basitarsi spiniform macrosetae pattern: leg I pst, rst, pm, rm, Rm; leg II pt, rt, pst, rst, pm, rm, Rm; legs III–IV pt, rt, vt, vst, vm. Pectinal tooth count, 11–13 (♂) mode = 12 or 10 mode = 10 (♀).

D. insularis n. sp. resembles D. lourencoi Stockwell, 1988 and D. coddingtoni Stockwell, 1988 in similar adult size and body coloration, and D. maya Francke, 1977 in similar telotarsi spiniform macrosetae count. It can be distinguished by the following. The telotarsi spiniform macrosetae counts on legs I–II are lower in D. insularis n. sp. (4/4:4/5) than in D. lourencoi and in D. coddingtoni (4/5: 5/5). The pedipalp chela manus (♂) is rounded in D. insularis, but slender in D. maya, D. lourencoi and D. coddingtoni. The pedipalp patella dorsal retrolateral carina is weakly to moderately developed, smooth in D. insularis, but moderately developed, slightly granular in D. maya and in D. lourencoi, or obsolete D. coddingtoni. The Rm spiniform macrosetae on basitarsi of leg I is present in D. insularis, but absent in D. coddingtoni, D. maya and D. lourencoi.

Description. Based on holotype ♂ and paratype ♀ (Fig. 2A) with differences in paratype ♀ (Figs. 2B) noted. Measurements in Table 1.

Coloration. Carapace medium to light brown, with weak fuscosity throughout, uniform around median eyes and variegated elsewhere; coxosternal region pale orange to pale brown. Pedipalps brown to orange–brown, carinae darker. Mesosoma medium brown (♂) to orange–brown (♀), ventral surface pale brown, tergites light to medium brown, with moderately dense variegated fusco-piceous pattern; sternites medium brown to pale brown. Metasoma reddish brown to pale brown. Telson orange brownish or reddish brown, uniformly fuscous. Legs orange–brown, uniformly infuscate.

Carapace. Anterior margin moderate to sparsely setose, anteromedian notch strongly deep, V-shaped (Fig. 3). Frontal lobes and interocular surface weakly granular to smooth; other surfaces shagreened. Three pairs of subequal lateral ocelli.

Pedipalps. Orthobothriotaxic, Type C. Femur width greater than height (Fig. 5A); dorsal intercarinal surface flat to slightly convex, shagreened to sparsely granular; retrolateral intercarinal surface smooth; ventral intercarinal surface flat, slightly shagreened to minutely granular; prolateral intercarinal surface coarsely and minutely granular, with moderate-size dark granules; dorsal prolateral carina moderately developed, granular; dorsal retrolateral carina moderately developed, fading distally, densely granular proximally and smooth distally; ventral retrolateral carina obsolete; ventral prolateral carina moderately developed, granular proximally, becoming obsolete distally. Patella (Figs. 5B–D), dorsal, retrolateral and ventral intercarinal surfaces finely reticulated (♂) to smooth (♀); prolateral intercarinal surface weakly, sparsely granular distally; proximal tubercle moderately developed, bifurcate; dorsal prolateral carina weakly developed to obsolete, slightly granular; dorsal median carina weakly to moderately developed, smooth; dorsal retrolateral carina, weakly to moderately developed smooth (♂) or weakly to obsolete, smooth (♀); retrolateral median carina obsolete (♂, ♀); ventral retrolateral carina weakly developed, smooth; ventral median carina weakly to moderately developed, slightly granular (♂) to weakly developed to obsolete, smooth (♀); ventral prolateral carina weakly to moderately developed, granular, comprising small granules and fading posteriorly. Chela manus, slender, height subequal to width (♂) or rounded, height greater than width (♀), densely (♂) or sparsely (♀) setose; dorsal intercarinal surface strongly reticulated (♂; Fig. 6A; ♀; Fig. 6B); retrolateral intercarinal surface reticulated, prolateral surface with shallow longitudinal depression where chela rests against patella; dorsal marginal carina moderately developed, strongly granular; digital carina strongly developed, smooth (♂) or weakly to moderately developed, smooth (♀); dorsal secondary and retrolateral secondary carinae weakly to moderately developed, smooth to crenulated (♂) or weakly developed to obsolete, smooth (♀); ventral retrolateral carina weakly developed, smooth distally (♂) or weakly developed to obsolete, smooth (♀), becoming obsolete proximally; ventral median carina strongly developed, crenulated proximally, becoming obsolete distally, directed towards midpoint of movable finger articulation; ventral prolateral carina moderately developed, crenulated; prolateral dorsal carina weakly developed, slightly granular; prolateral median and prolateral ventral carinae weakly developed, slightly granular. Chela fixed finger gently curved; length longer (♂) or equal (♀) to femur length and patella length; dorsal surface smooth and densely setose proximally, retrolateral surface flat; prolateral surface shallowly concave.

Legs. Legs I–IV femora and tibiae, prolateral surfaces shagreened; telotarsi, counts of spiniform macrosetae in pro- and retroventral rows (dextral/sinistral), 4/4 4/4: 4/5 4/5: 5/5 5/5: 5/5 5/5 (holotype) (variation shown in Table 2); basitarsi spiniform macrosetae pattern: (holotype) leg I pst, rst, pm, rm, Rm; leg II pt, rt, pst, rst, pm, rm, Rm; leg III pt, rt, vt, rst, vst, vm; leg IV pt, rt, vt, vst, vm (variation shown in Table 3).

Pectines: Tooth count: 12–12 (♂; Fig. 4A); 11-12 (♀; Fig. 4B) (variation shown in Table 4).

Mesosoma. Tergites I–VI, pre-tergites smooth, post-tergites sparsely, minutely granular, VII minutely granular. Sternites smooth; VII, submedian and lateral carinae weakly developed, smooth to slightly crenulated anteriorly, obsolete posteriorly.

Metasoma. Metasomal segments I–V, dorsal and lateral intercarinal surfaces shagreened to slightly granular; ventral intercarinal surfaces smooth on segments I–III, shagreened on IV–V. Segments I–IV, dorsal lateral carinae weakly to moderately developed (♂) to weakly developed (♀), granular; lateral supramedian carinae moderately developed, granular on I–IV; lateral inframedian carinae weakly developed, granular on I–IV; ventral lateral carinae moderately developed, crenulatedd to smooth on I–III, moderately developed, slightly granular on IV; ventral submedian carinae moderately to strongly developed, crenulated to smooth on I–II, weakly developed, crenulated to granular on III–IV. Segment V length: pedipalp femur length ratio, 1.35 (♂), 1.33 (♀); dorsal lateral carina moderately developed, granular; lateral inframedian carina weakly developed to obsolete, slightly granular; ventral lateral carina strongly developed, granular to slightly serrated; ventral median carina strongly developed, granular to serrated, with large subspiniform granules; ventral transverse carina moderately developed, comprising three subspiniform granules; anal arch semicircular; anal subterminal carina strongly developed, comprising ten subspiniform granules; anal terminal carina moderately developed, granular.

Telson. Telson width: length ratio, 0.42 (♂), or 0.57 (♀). Vesicle, lateral surfaces smooth; ventral surface granular anteriorly, shagreened posteriorly. Subaculear tubercle stout, subconical. Aculeus length 1.3.

Hemispermatophore. Lamelliform, weakly sclerotized (Fig. 7); total length 6.5 mm; distal lamella length 3.4 mm; capsular region, width, 1.2 mm; median lobe narrow, margin entire.

Distribution. D. insularis is only known from the type locality of Cayos Cochinos (specifically Cayo Menor) in north Honduras, and from a nearby island locality of Útila (Fig. 1). Comparable searches were also conducted on the largest island of Roatán, but did not yield any diplocentrids, which may not be present. Cayo Grande was not searched, however given the close proximity and ecological similarity to Cayo Menor, we consider D. insularis to be likely present, although one may note that recently introduced mammals, including feral dogs and cats, appear to have caused some disruption to its ecosystem [23,24] Given the inferred narrow insular geographic range of this new species, we consider it an important priority for conservation assessment (e.g., IUCN red listing), especially on Útila where populations are likely declining as increasing human development is continuing to destroy suitable habitat (Fig. 8).

Ecology. Specimens were collected under rocks and logs, also found under leaf litter at high elevations of the ridge in the island of Cayo Menor, and in the remaining forest patches close to the airport area in the island of Útila, on the eastern side. The main vegetation was evergreen oak forest. Forest floor was covered with high amounts of leaf litter mainly from Quercus and Simarouba trees, and dead wood was frequently encountered, both under which the majority our specimens were collected (Fig. 8). The habitat and habitus of D. insularis n. sp., are consistent with the humicolous ecomorphotype [25].

Biogeography. Útila, Roatán, and other smaller islands form the emergent crest of the continental Bonacca ridge along the Motagua/Swan Islands Fault Zone between the North American and Caribbean plates. Útila is partly formed by basalts from a Quaternary volcano, whilst Roatán and adjacent islands are largely composed of older metamorphic rocks comparable to those in Guatemala, with most recent folding around the Late Eocene, with exhumation and Tela Basin subsidence in the Miocene [26,27]. Cayos Cochinos consists of granite intrusions within metamorphic rocks. Together, the islands appear to be geologically allied to the Sierra de Omoa and/or Cordillera Nombre de Dios mountain ranges on the continental mainland, part of the Middle American Mountain Complex [24,28], with the Islas de la Bahía (Útila, Roatán, etc.) and Cayos Cochinos as topographical high points [24]. The Cayos Cochinos and Útila are situated on the continental shelf, surrounded by shallow 30–55-m-deep waters, and hence connected to mainland during the Pleistocene in the Wisconsin glacial period (ca. 13,000–18,000 years ago) [29]. As the ice sheets melted, rising sea levels would have led Cayos Cochinos and Útila to be increasingly isolated from mainland. We hypothesize that some elements of terrestrial fauna such as diplocentrids could have reached Útila and/or Cayos Cochinos by land connections around this glacial maximum, although uncertainty remains about whether their faunas (such as D. insularis) should then be more closely connected to those of the Sierra de Omoa (i.e. the lineage for D. lourencoi), or to those at the western end (around Tela) of the Cordillera Nombre de Dios (such as D. coddingtoni). If the latter route is more plausible, we might expect closest phylogenetic affinities of D. insularis to D. coddingtoni, and more distinct from others now separated by the Sula valley (i.e. D. lourencoi). In contrast, Roatán and Guanaja are oceanic islands, situated outside the continental shelf and surrounded by deeper waters (up to 275 m in depth) [29]. The drop in sea level of around 120–140 m during the Pleistocene would not have resulted in Roatán and Guanaja, being joined to the mainland, nor to each other, during this period [28,29]. Consequently these older islands therefore appear to have experienced prolonged isolation, and if diplocentrids are later found, we infer they could not have reached those islands via land-bridges.

Given that Cayos Cochinos are now separated from both the mainland and Útila by a relatively shallow sea, other hypothetical modes of marine transport for terrestrial components remain possible, particularly via rafting. For much of the year, easterly trade winds dominate the north coast of Honduras, and eastern surface currents exit from the Gulf of Honduras, with strong flow past Útila towards Cayos Cochinos [30]. This for example might have facilitated later colonization of terrestrial fauna (such as diplocentrids) on Cayos Cochinos from Útila (or other westerly terrestrial sources), particularly through rafting. However, disruption of typical environment occurs relatively frequently in the region though hurricanes, and a counter-clockwise current can also affect the Bay islands early in the year, when plumes of sediment can reach the Cayos Cochinos archipelago from coastal rivers [30]. Consequently, more recent independent colonization of Cayos cochinos by diplocentrids (etc.) appears especially plausible, either rafting from the mainland during environmentally disruptive events (like hurricane damage) or, as we suggest, more likely from Útila via dominant marine currents.