Fig. 1–3

Diagnosis. Metallic blue-green body will readily distinguish the species from all known species from Southeast Asia and the Neotropical regions.

Description. Male holotype: Length, 9.25 mm. Width, 2.75 mm. Body subcylindrical, elongate, tapering towards the elytral apex; integumental coloration metallic blue-green with surficial reflection of blue and violet on elytra when viewed from the top and oblique angles, with little orange and yellow at lateral angle when viewing the pronotum; venter metallic dark blue-green; antennae black; femur black with surficial reflection of metallic violet; tibiae black; tarsi dark brown with tarsomere V infuscate reddish; head, pronotum and elytra clothed with sparse, very short, yellow recumbent setae (Fig. 1).

Head: Sparsely punctate, subspherical; frons convex, with median carina and circular fovea above base of epistomal part of epicranium; surface shiny; apical margin of epistomal part of epicranium feebly trilobed, about 2 times wider than base; mandibles stout, bidentate, densely punctate.

Antennae: Flabellate from antennomeres IV–X, attaining the hind angles of the pronotum; antennomere III short, as long as II; ramus arising from base of antennomere IV; rami arising from apex of antennomeres V–X; antennomere XI elongate.

Pronotum: Surface shiny, with widely spaced granules; as long as wide, with moderate, sharp, slightly divergent hind angles; lateral sides sinuate above hind angles, widest near middle, arcuate towards apex; disc convex, with deep median groove and pair of circular gibbosities and horizontal impressions near center; base sinuate.

Scutellum: Shiny, short, sub-triangular, apically depressed and distally rounded.

Elytra: Strongly striate; interstices elevated, keeled, rugose.

Legs: First tarsomere as long as the combined lengths of the remaining four on mesothoracic and metathoracic tarsi; tibiae rounded in cross section; metathoracic tarsomeres I–III simple; metathoracic tarsomeres IV excavate-emarginate; metathoracic tarsomere V elongate with simple claws.

Venter (Fig. 2): Closely punctate, with short, sparse recumbent yellow setae; hypomeron simple, without antennal grooves; metathoracic episternum partially concealed under elytral epipleura; metathoracic coxal plates laterally wider than medially.

Male aedeagus (Fig. 3): Basal piece short, rounded, caudally bifid; remaining aedeagus slightly elongate, basally narrowed, widest near base of lateral lobes; median lobe short, narrowly bilobed; lateral lobes wide, short with lateral tooth.

Variation. Two adult male and three female paratypes are known. Lengths of two male specimens are 7.0–8.0 mm, both shorter than the holotype. Lengths of three female specimens ranged 7.5–10.3 mm. One female is longer than the holotype. One female specimen has a stronger golden coppery hue laterally. There are no variations in the exoskeletal structures among these paratypes in relation to the holotype.

Type material. Holotype, male, with label data: “ PHILIPPINES, N. Luzon, Abra, December 2002 ” / “ HOLOTYPE:, Calyptocerus, iridis, Otto, det. R.L. Otto, 2014” (♂ handwritten behind species name on label) [red printed label]. Holotype transferred from GERP to BMNH.

Paratypes. 5, each with label data: 1, “ PHILIPPINES, N. Luzon, Abra, December 2002 ” (WIRC); 1, “ PHILIPPINES, North Luzon, Bergnet, November 2013, Ismael Lumawig” (GERP); 1, “ Philippines, Luzon, Ifugao, Banaue, IV-2014, native collector leg.” (JMC); 1, “ Philippines, Luzon, Mountain province, Mt. Polis, IV-2014, local collector leg.” (JMC); 1, “ Philippines, Luzon, Ifugao, Banaue, VIII-2014, local collector leg.” (JMC). Each paraptype labeled: “ PARATYPE:, Calyptocerus, iridis, Otto, det. R.L. Otto, 2014” (either ♂ or ♀ handwritten behind species name on label) [yellow printed label]. Paratypes in GERP, JMC, and WIRC.

Distribution. The species is known from four localities in the northern areas of Luzon in the Philippines.

Biology. A number of specimens were collected in the upper montane cloud forests of Luzon. Developmental stages remain unknown.

Etymology. The specific epithet is derived from a Latin term “ iridis ” for rainbow; in reference to the remarkable metallic colorations associated with the species.

Remarks. Metallic coloration is quite rare for members of the family. Metallic coloration for the most part is normally confined as surficial reflections over a dark base color (i.e. some Fornax Laporte, Namolius lacordairei Bonvouloir, Plesiofornax nigrinus Fisher, species of Procladidus Fleutiaux, and some Semnodema Bonvouloir) or confined in dense setae on pronotal and elytral surfaces (i.e. some species of Galbites Fleutiaux and Lamprotrichus Bonvouloir). Calyptocerus iridis, along with the South American C. violaceus Chassain are true representations of metallic Eucnemidae, where integuments exhibit metallic coloration either throughout or confined to the elytra as in the case in the latter.