Atelopus harlequin Coloma, Plewnia, Böning, Boistel, Ellwein, Lötters, Paluh, Roca-Rey Ross and Venegas, 2025

Atelopus harlequin Coloma, Plewnia, Böning, Boistel, Ellwein, Lötters, Paluh, Roca-Rey Ross and Venegas sp. nov.

Species account authors: Luis A. Coloma, Amadeus Plewnia, Philipp Böning, Renaud Boistel, Denise J. Ellwein, Stefan Lötters, Daniel J. Paluh, Bernardo Roca-Rey Ross, Pablo Venegas

LSID: urn:lsid:zoobank.org:act:429FD89A-7986-42DF-AA71-5689EAFA8CDB

Figs. 18–20 View FIGURE 18 View FIGURE 19 View FIGURE 20

Atelopus View in CoL “harlequin ”.— Coloma 1997: 39 (conditional name).

Atelopus spumarius View in CoL non-Cope.— Asquith & Altig 1987: 32; Lötters et al. 2002a: 169; Lötters et al. 2003: 170; Lötters et al. 2005: 345; Rueda-Almonacid et al. 2005: 126 (by implication).

Atelopus spumarius spumarius View in CoL .— Cocroft et al. 1990: 638, Lötters 1996: 47 (by implication).

A. sp. cf. spumarius View in CoL “harlequin ”.— Lötters et al. 2023: Supplementary Table 1.

Holotype. PERU: Loreto: km 74 on road from Iquitos to Nauta along a tributary of the Río Itaya (4°17’08”S, 73°31’45”W, ca. 100 m asl), MUBI 2448 ( Fig. 18 View FIGURE 18 ), adult male, leg. 28 August 2008 by Stefan Lötters and Philine Werner. GoogleMaps

Paratypes. PERU: Loreto: Pucacuro (3°26’57”S, 75°25’42”W, 150 m asl), FHGO 0177 , 7584 , 7760 , adult males, FHGO 7587 , adult female, leg. Jorge Valencia. GoogleMaps

Referred material. ECUADOR: Pastaza: Lorocachi , QCAZ 8898 View Materials , 8899 View Materials (cleared and stained) , 8900, 9447– 9450, 9522, 9544, males, leg. 21–25 February 1996 by Omar Torres Carvajal, María Cecilia Terán and Xavier Cisneros; PERU: Loreto: Andoas , CORBIDI 4883 View Materials ; Loreto: Platanoyacu, Trompeteros , MUBI 7822 .

Definition. Atelopus harlequin sp. nov. is placed in the genus Atelopus based on its mt and nc markers nested within Atelopus (and with the 16S rRNA fragment showing uncorrected p-distance <5% to the genus type species A. flavescens Duméril and Bibron ), and on having presacrals I and II fused. The species is dinstinguished from all other species by the combination of the following characters: (1)A small-sized species with mean SVL of adult males 20.6 ± 0.51, N = 4 and adult female 25.7; (2) slender body ( SW / SVL = 0.250 ± 0.003 in 4 males, 0.272 in female) with (3) long legs ( TIBL / SVL = 0.479 ± 0.024 in 4 males, 0.490 in female) and (4) acuminate snout, protruding beyond apex of lower jaw; (5) tympanic membrane absent, tympanic annulus not visible, columella present, ostia pharyngea present; (6) phalangeal formula of hand 1-2-3-3; webbing absent on hand; (7) first finger short ( THBL / HAND = 0.432 ± 0.021 in 4 males, 0.400 in female), in adult males with keratinized brownish nuptial pad; (8) phalangeal formula of foot 2-2-3-4-3, webbing formula of toes I 0–0 to 1 II 1 / 2 to 1–1 to 2 III 1 to 2–3 IV 3–1 V; (9) skin smooth, dorsally and laterally covered with dense, poorly distinct minute spiculae; ventrally smooth to slightly areolate, cloaca and adjacent thighs areolate; (10) vertebral column conspicuous, neural processes absent; (11) in life: dorsum dark brown with numerous dense yellowish gold irregular circles or lines, in some specimens forming a continuous foam-like reticulation pattern on dorsum; on head, dark brown blotch running from one to another eyelid, centrally connected to a line running to tip of snout forming a irregular T-shaped mark in some specimens; dorsal pattern fused with dorsolateral yellowish golden reticulation forming a band with numerous dark brown irregular spots (smaller than EYDM); laterally a dark brown band from tip of snout almost to groin, sometimes posteriorly interrupted by few yellowish golden lines; limbs and dorsal surfaces of hand and foot with yellowish golden foam-like reticulation with dark brown spots (smaller or larger than EYDM), thumb and sometimes tips of fingers and toes dorsally orange to bright red; in both sexes, throat, chest and venter white to cream, in some specimens with few scattered small brown dots (smaller than EYDM); soles, palms and a triangular blotch below cloaca and adjacent ventral surfaces of thighs bright red; iris black with a broad golden ring surrounding horizontally oriented pupil; (12) in preservative: above brown with cream pattern, below whitish; bright red life markings faded to yellowish white; (13) pulsed call 680 ± 30 ms at frequency range 3,450 –4,050 Hz GoogleMaps .

Diagnosis. Atelopus harlequin sp. nov. ( Figs. 18–20 View FIGURE 18 View FIGURE 19 View FIGURE 20 ) can be readily distinguished from all other Atelopus (as far known) by molecular genetics, with an uncorrected p-distance of the 16S rRNA fragment of 2.37% to its closest known described relative, A. colomai (Appendices 8, 9). It can be morphologically distinguished from all congeners by the combination of minute size, dorsal and lateral skin covered with dense, poorly distinct minute spiculae, ventral skin smooth to slightly areolate, presence of a columella and dorsal pattern.

Atelopus harlequin sp. nov. ( Figs. 18–20 View FIGURE 18 View FIGURE 19 View FIGURE 20 ) is similar to its congeners of the flavescens-spumarius clade, to A. andinus Rivero , A. loettersi De la Riva, Castroviejo-Fisher, Chaparro, Boistel and Padial , A. reticulatus Lötters, Haas, Schick and Böhme and the A. tricolor Boulenger complex (including the junior synonyms A. rugulosus Noble and A. willimani Donoso-Barros ) from the eastern Andean versant of Peru and Bolivia, and to A. minutulus Ruíz-Carranza, Hernández-Camacho and Ardila-Robayo from the eastern Andean versant of Colombia. It differs from A. manauensis Jorge, Ferrão and Lima in dorsal pattern in life (dark brown, with numerous dense yellowish gold irregular circles or lines, fused with dorsolateral yellowish golden reticulation vs. few irregular circles, lines and blotches, not broadly fused with the foam-like reticulated dorsolateral band). It differs from the nominal A. barbotini Lescure , A. flavescens Duméril and Bibron (including its junior synonym A. vermiculatus McDiarmid ), A. franciscus Lescure and the A. hoogmoedi Lescure complex (including the available name A. hoogmoedi nassaui Ouboter and Jairam ) in pattern and coloration in life (dorsally dark brown with numerous dense yellowish gold irregular circles or lines, sometimes forming a continuous foam-like reticulation pattern on dorsum; dorsolateral yellowish golden reticulation forming a band with numerous dark brown irregular spots; below white to cream, sometimes with few scattered small brown dots with a triangular red blotch below cloaca and adjacent ventral surfaces of thighs vs. dorsally black with red to pink markings, ventrally reddish pink in A. barbotini ; dorsally unicolored reddish, brownish or yellow or brown and with olive, brownish reddish and copper-like vermiculation, ventrally reddish pink in males, pink in females in A. flavescens ; dorsally olive to blackish brown, ventrally reddish in A. franciscus ; dorsally dark brown or black with yellow, pink, bluish, white, greenish or orange irregular spots and reticulated dorsolateral bands or solid bars, ventrally yellow, pink, bluish, white, greenish or orange, in some specimens with dark spots or blotches in the A. hoogmoedi complex). All these forms, except some populations of the A. hoogmoedi complex, lack red palmar and plantar surfaces in life (present in A. harlequin sp. nov.). Further, with 680 ± 30 ms A. harlequin sp. nov. has a shorter call than A. barbotini (1,490 ± 140 ms), A. flavescens (1,530 ± 220 ms), A. franciscus (1,490 ±150 ms), the A. hoogmoedi complex from French Guiana (1,190 ± 10 ms), in the A. hoogmoedi complex from Amapá, Brazil (1,160 ± 390 ms) and the A. hoogmoedi complex from Pará, Brazil (1,060 –1,240 ms) ( Lescure 1981; Cocroft et al. 1990; Costa-Campos & Carvalho 2018). In addition, with its small SVL (20.6 ± 0.51 in adult males, N = 4), the new species is readily distinguished from the larger A. barbotini (26.5 ± 0.9, N = 10 from the type locality) and the A. hoogmoedi complex (25.4 ± 1.4, N = 8, from the type locality). Atelopus harlequin sp. nov. can be distinguished from A. spumarius Cope sensu stricto, A. colomai Plewnia, Terán-Valdez, Culebras, Boistel, Paluh, Quezada Riera, Heine, Reyes-Puig, Salazar-Valenzuela, Guayasamin and Lötters and A. histrionicus sp. nov. by call duration (680 ± 30 ms vs. 922 ± 24 ms in A. spumarius sensu stricto; 2,049 ± 220 ms in A. colomai ; 807 ± 80 ms in A. histrionicus sp. nov.; Asquith & Altig 1987). Further, the new taxon differs from these species in dorsal pattern (reticulation pattern not densely developed on the dorsum and not broadly fused with dorsolateral bands in A. spumarius sensu stricto, A. colomai and A. histrionicus sp. nov.), female ventral pattern (absence in the new species vs. presence of dots) and male SVL (20.6 ± 0.51, N = 4, vs. 22.2 and 23.4, N = 2, in A. spumarius sensu stricto; 23.2 ± 1.46, N = 6, in A. colomai ; 25.0 ± 0.67, N = 7, in A. histrionicus sp. nov.). The new species can be distinguished from A. pulcher Boulenger by shorter calls (680 ± 30 ms vs. 1,200 ± 100 ms; Lötters et al. 2002a). Atelopus harlequin sp. nov. further differs from A. pulcher by smaller male SVL (20.6 ± 0.51, N = 4, vs. 27.27 ± 1.07, N = 13; Lötters et al. 2002a) and male coloration in life (dorsally dark brown with numerous dense yellowish gold irregular circles or lines, sometimes forming a continuous foam-like reticulation pattern on dorsum; dorsolateral yellowish golden reticulation forming a band with numerous dark brown irregular spots vs. dark brown dorsum with green spots, circles and blotches and a green broad dorsolateral band, rarely interrupted by small dark brown dots; in females, bright red venter with dark brown spots and a dark brown line on chest in some specimens). The new species differs from A. seminiferus Cope in smaller SVL (single female 25.7 vs 40.0), the absence of lateral warts (present in A. seminiferus ) and dorsal coloration (dorsally dark brown with numerous dense yellowish gold irregular circles or lines, sometimes forming a continuous foam-like reticulation pattern on dorsum; dorsolateral yellowish golden reticulation forming a band with numerous dark brown irregular spots vs. dark brown without pattern in A. seminiferus ). From A. andinus , A. loettersi , A. reticulatus and the A. tricolor complex, A. harlequin sp. nov. can be distinguished by the presence of a columella (vs. absence; Lötters et al. 2011; Authors’ unpubl. data). From A. loettersi , it can be distinguished by female ventral coloration and pattern in life (below white to cream, sometimes with few scattered small brown dots with a triangular red blotch below cloaca and adjacent ventral surfaces of thighs vs. mostly red, in some specimens with irregular brown blotches; De la Riva et al. 2011). Further, it can be distinguished from A. andinus , A. reticulatus and the A. tricolor complex by the absence of warts (presence), by presence of dorsal reticulation (absence), except A. reticulatus (which shows dark reticulation on a yellow dorsum) and by smaller male SVL (20.6 ± 0.51, N = 4 vs. 26.4 and 27.5, N = 2, in A. andinus ; 24.7, N = 1, in A. reticulatus ; 20.8 ± 0.86, N = 17, in the A. tricolor complex). Based on its small size, A. harlequin sp. nov. resembles A. minutulus from which it can be distinguished by the absence of spiculae on the flanks (vs. present in A. minutulus ) and by coloration and pattern in life (dorsally dark brown with numerous dense yellowish gold irregular circles or lines, sometimes forming a continuous foam-like reticulation pattern on dorsum; dorsolateral yellowish golden reticulation forming a band with numerous dark brown irregular spots vs. numerous green blotches on a brown dorsum and flanks).

Description of holotype. Adult male. Body slender (SW/SVL = 0.245), head about as long as wide (HLSQ/ HDWD = 1.081), snout protruding beyond apex of lower jaw, acuminate in dorsal view; nostrils directed laterally, slightly protuberant, situated above apex of lower jaw at one fourth distance from tip of snout to eye; canthus rostralis distinct, slightly concave in dorsal view between eye and nostril; loreal region concave; lips not flared; top of snout depressed; head slightly concave in lateral view; interorbital region and occiput flat; eyelid flared; tympanic membrane absent, tympanic annulus not visible; supratympanic crest poorly developed; choanae medium-sized, rounded, widely separated; ostia pharyngea present; tongue three times as long as wide, broadest anteriorly, free for half its length posteriorly; vocal slits present; limbs long and slender (TIBL/SVL = 0.481); webbing absent on hand; fingers and toes lack lateral fringes; palmar tubercle rounded, almost indistinct; supernumerary palmar and plantar tubercles indistinct; thenar and subarticular tubercles indistinct; tips of digits rounded, except on third finger possessing acuminate tip; phalangeal formula of hand 1-2-3-3; first finger short (THBL/HAND = 0.432), dorsally bearing keratinized nuptial pad; inner metatarsal tubercle almost indistinct; outer metatarsal tubercle rounded, poorly developed; relative length of toes I<II<III<V<IV; phalangeal formula of foot 2-2-3-4-3, webbing formula of toes I 0–0 II 1 / 2 –1 III 11 / 2 –3 IV 3–1 V; tarsal fold absent; foot roughly two thirds of tibia; skin smooth on entire body, dorsally and laterally covered with dense, poorly distinct minute spiculae; skin weakly areolate on ventral surfaces of cloaca and adjacent thighs, venter and throat; cloacal opening in an inconspicuous tube, directed posteriorly; vertebral column visible through the skin, neural processes absent.

In life, dorsum dark brown with dense irregular golden yellow circles and foam like reticulation; dark brown marks (larger than EYDM) and bordered by smaller ones (smaller than EYDM); on head, dark brown blotch running from one to another eyelid, centrally connected to a bar running from tip of snout to posterior corner of head; golden yellow becoming pale toward flanks; dorsolaterally pale-yellow foam-like reticulation, forming a band from above eye to groin with diffuse borders; upper lips and ventrolateral region pale yellow with small brown spots (smaller than or equal to diameter of finger III); laterally a dark brown band from tip of snout to groin; throat and venter whitish cream; limbs dorsally dark brown, covered in golden yellow reticulation, ventrally lower arm and lower leg white with brown blotches, upper arm white, thigh white, towards cloaca bright red; thumb and tips of fingers and toes dorsally orange to red; palms, plants and a triangular blotch on ventral surface of cloaca and adjacent areas of thighs bright red; iris black with a broad yellowish-golden ring around pupil.

In preservative, above brown with cream pattern, below whitish; bright red markings (in life) yellowish white.

Measurements: SVL 20.8, TIBL 10.0, FOOT 6.5, HLSQ 6.7, IOD 2.4, HDWD 6.2, EYDM 2.3, EYNO 1.7, ITNA 2.0, FAL 6.3, HAND 4.4, THBL 1.9, SW 5.1.

Variation. For meristic variation of characters see Table 5. The paratypes ( Fig. 19 View FIGURE 19 ) correspond to the holotype description. Variation exists in the extent of a brown mark on the head which varies from several discontinuous large blotches to a band from eye to eye to a T-shaped mark from tip of snout to a line between the eyes. Sometimes, the lateral band is interrupted or replaced by separated brown spots, particularly posteriorly.

Sexual dimorphism is apparent in A. harlequin sp. nov. with the female being larger and lacking vocal slits and nuptial pads. Further, eggs are visible through the ventral skin in the female.

Skull osteology. General osteological features of the holotype (MUBI 2448) are depicted in Figures 5–6 View FIGURE 5 View FIGURE 6 and Appendix 4. The skull of A. harlequin sp. nov. (MUBI 2448, MorphoSource media 000618606) is triangular in dorsal view. The skull length is 6.6, the skull width is 5.6, and the skull height is 4.2. The skull roof is moderately rugose. In anterior view, the septomaxilla is U-shaped with medial and lateral rami that extend posteriorly towards the vomer. The lateral ramus is much broader than the medial ramus and bears a nasal process. The ossified sphenethmoid is smooth and underlies the posterior and medial margins of nasals, as well as the anterior and anterolateral margins of the frontoparietals. The posterior limit of the sphenethmoid is about one-third the length of the margin of the orbit. The prootics are slightly rugose and are fused to posterolateral edge of the frontoparietals. The exoccipitals encircle the foramen magnum and are fused to the frontoparietals dorsally, the prootics laterally, and the parasphenoid anteroventrally. The otic capsule is well-ossified. Columellae are present and medially bifurcated. The pars media of the columella is slender and slightly bowed, and the pars interna is broad. The operculum in the fenestra ovalis is not mineralized and therefore not visible in the microCT dataset. The nasals are triangular and bear an acuminate maxillary process that extends ventrolaterally toward the maxilla and nearly contacts the pars facialis of the maxilla. The nasals are widely separated medially. The frontoparietals are coarsely rectangular and the orbital edges are straight. Medial articulation is incomplete with the anterior half of the bones lacking articulation and the posterior half being completely fused with no suture line visible. A supraorbital flange is absent. Occipital groves, which are canals for the carotid artery, are present and nearly entirely open (not roofed with bone), except for the anterior tip. Posteriorly, the frontoparietals are fused to the prootics and exoccipitals. The vomers are small, edentate, medially separated, crescent-shaped, and triradiate with an anterior ramus, prechoanal ramus, and postchoanal ramus. The anterior ramus is directed anterolaterally, rounded at the anterior tip, and is larger than the other rami (nearly reaching the junction of the maxilla and premaxilla). The pre- and postchoanal rami are short, of nearly equal length, pointed, and form the anteromedial margin of the choana. The prechoanal ramus is directed towards the maxilla, and the postchoanal ramus is directed parallel to the midline. The postchoanal ramus of the right vomer is fused to the overlying sphenethmoid, while the two elements nearly contact on the left. The neopalatine is elongate and triangular. It underlies, and is partially fused to, the sphenethmoid and extends towards the maxilla, making contact with the preorbital process. The neopalatine is narrow and pointed at its medial tip, widens as it approaches the maxilla, and is cylindrical and rounded at its anterior border. The parasphenoid has an inverted T-shape and the cultriform process slightly underlies the sphenethmoid. The cultriform process extends beyond the midpoint of the orbit. The terminal end of the cultriform process is irregular and biradiated in shape. The parasphenoid alae are directed posterolateral to the cultriform process and are fused to the overlying otic capsule. The posterior margin of the parasphenoid and a medial posterior process are difficult to discern. The maxillary arcade is complete and edentate. The paired premaxillae each possess a dorsal alary process that is directed anterolaterally. The lower half of the alary process is slightly wider than the upper half. The pars palatina is biradiate with medial and lateral processes. The lateral process is more than twice as long as the medial process. The medial process is well developed and triangular. A concave border is present where the lateral and medial processes of the pars palatina come together. The posterior tip of the pars dentalis is pointed and articulates with the maxilla. The external surface of the maxillae is rugose. The pars palatina, which extend along the lingual margin of the maxilla, is narrow, and the posterior half of this shelf articulates with the anterior ramus of the pterygoid. The pars fascialis of the maxilla is directed medially and is a jagged, irregular shape; its anterior margin is biradiate; its dorsomedial margin contacts the neopalatine and sphenethmoid and nearly contacts the maxillary process of the nasal. The anterior end of the maxilla is truncate and slightly overlaps the premaxilla. The posterior end of the maxilla is pointed and contacts the quadratojugal. The quadratojugal is a small, slender, L-shaped bone that underlies the ventral arm of the squamosal and contacts the posterior process of the maxilla at is anterior margin. The paired squamosals possess an otic ramus posterodorsally, a zygomatic ramus anterodorsally, and a ventral ramus. The otic ramus is expanded dorsally and has a broad articulation with the crista parotica of the otic capsule, leaving only the posterior end of the prootic free. The zygomatic ramus is small and triangular. The angle between the dorsal surface of the squamosal and the anterior margin of the ventral ramus is nearly perpendicular. The ventral ramus is flat and blade-like. A squamosal keel is present, extending along the outer surface from the zygomatic ramus to the upper half of the ventral arm. The pterygoid is triradiate, bearing anterior, medial, and posterior rami. The anterior ramus articulates with the pars palatina of the maxilla. The medial and posterior rami are of equal length. The medial ramus nearly contacts the prootic. The posterior ramus is flat and blade-like. The palatoquadrate is cartilaginous and therefore not visible in the microCT dataset. The lower jaw is composed of three ossified elements and Meckel’s cartilage, which is not visible in the microCT dataset. The mentomeckelian is the most anterior element that forms a cartilaginous symphysis at the midline of the jaws. Posterodorsally, the mentomeckelian is fused to the dentary. The dentary is slender, thin, and edentate; this element overlays the anterior half of the angulosplenial. The angulosplenial is the largest mandible element and forms the lingual surface of the lower jaws. The lower jaw length is 5.5, nearly the same length as the skull from the occipital condyle to the premaxilla.

Atelopus harlequin sp. nov. differs from the other species (re)described in this paper by having the medial side of the posterodorsal process of the squamosal being attached along its entire length to the prootic (vs. the distal end of the process remaining free; Fig. 6 View FIGURE 6 ), the frontoparietals being dorsally more convex, and the separation of the occipital condyles being greater; Fig. 6 View FIGURE 6 ).

Further, the new species can be distinguished from the neotype of A. spumarius sensu stricto by the squamosal laterally extending beyond the posterolateral limit of the maxilla and the jugularis process of the quadratojugal thus contacting the posterior process of the maxilla anteriorly (vs. the posterior end of the maxilla being free, laterally protruding beyond the lateral limit of the squamosal), the pars glenoidalis of the quadratojugal being triangular with an enlarged but narrow pars jugularis (vs. pars glenoidalis thickened, pars jugularis short) and a less straight orbital margin of the maxilla. However, variation in these characters exists between the two populations of A. spumarius sensu stricto, which might be attributed to imaging conditions or natural variation. Atelopus harlequin sp. nov. differs from A. colomai by its slightly rugose skull roof (vs. smooth), in having the frontoparietals fused only over two posterior thirds of their total length (vs. completely fused), the squamosal laterally extending beyond the posterolateral limit of the maxilla, and the jugularis process of the quadratojugal contacting the posterior process of the maxilla anteriorly (vs. maxilla protruding beyond the lateral limit of the squamosal, posteriorly, contacting the jugularis process of the quadratojugal) and the pars glenoidalis of the quadratojugal being triangular with an enlarged but narrow pars jugularis (vs. pars glenoidalis subrectangular, pars jugularis elongated). Atelopus harlequin sp. nov. is distinguished from A. histrionicus sp. nov. by a less rugose skull roof. On the lateral margins corresponding to the maxilla, a slight curvature is visible on the posterior third in A. harlequin sp. nov. (vs. lateral margins straight), its posteroventral incisure of the sphenethmoid is less deep, the parasphenoid is more developed, and the dorsal end of the dorsal process of the premaxilla (= pars facialis) remains at the same level (vs. protrudes anteriorly beyond the anterior limit of the nasals). For details see Figures 5–6 View FIGURE 5 View FIGURE 6 and Appendix 4.

However, the discriminatory power of osteological features needs to be seen with caution as intraspecific variation, sexual dimorphism and taxonomic value remain poorly understood for the species discussed.

Vocalization. Asquith & Altig (1987) described pulsed calls under the name A. spumarius from a population close to Nauta ( Peru, Loreto) which we assign to A. harlequin sp. nov. due to its proximity to its type locality and on a color photo of the recorded specimen provided to us by the authors. Their description is based on five calls (recorded in a collection bag at 26° C) with an average call duration of 680 ± 30 ms (670–710 ms). Intervals between calls are described as 2,200 ± 300 ms (5,400 –8,000 ms), where, however, either mean ± SD or range is given in error. Frequency at the beginning of the call is 3,578 ± 98 Hz (3,450 –3,690 Hz) and at the end of the call 3,900 ± 100 Hz (3,770 –4,050 Hz). Each call consists of 23.4 ± 2.4 pulses (20–27), at a pulse rate of 23.4 ± 2.2 (27.5–30.6) at the beginning of the call and 61.3 ± 7.9 (52.2–71.4) at its end. For details see Asquith & Altig (1987).

In addition, vocalizations were recorded by BR-RR from an uncollected male during handling on 1 February 2020, ca. 01:00 pm, close to the type locality on the Iquitos-Nauta road, with an iPhone 6s. Distance to recorder was 0.05 m, the ambient temperature is unknown. A 16,462 ms recording was available for analysis ( CJ ec.cj.aud.18; Fonozoo Sound Code 14650). It consists of 12 pure tone short calls and 9 pulsed short calls ( Fig. 21 View FIGURE 21 ). Pure tone short calls have duration of 16 ± 4 ms (12–25 ms) and a dominant frequency of 3,270 ± 244 Hz (2,724 –3,553 Hz). Frequency shows harmonics and is modulated with a decrease towards the end. Pulsed short calls have call duration of 44 ± 8 ms (26–55 ms) and a dominant frequency of 3,495 ± 77 Hz (3,388 –3,612 Hz). Amplitude peaks with the first pulse and descends over the course of the call. Frequency shows harmonics and is modulated in the last pulse with a decrease towards the end. Pulsed short calls ( Fig. 22 View FIGURE 22 ) consist of 3 ± 1 (2–5) pulses that show a length of 8 ± 7 ms (2–24 ms) each. The last pulse is the longest in all pulsed short calls GoogleMaps .

Tadpole. The tadpole of A. harlequin sp. nov. is unknown.

Distribution. In Peru, A. harlequin sp. nov. is known from various localities between the Río Napo (to its right) and the Río Marañon (to its left) and west of the Amazon River at ca. 100–150 m asl ( Fig. 2 View FIGURE 2 ). As far known, the geographic range is delimited by the latter two rivers, while the distributional limits to the North remain difficult to assess. In Ecuador, this species is known only from Lorocachi in Pastaza Province, situated in the upper Amazon basin at ca. 220 m asl, in the Río Pastaza drainage. It is unknown if the area between Lorocachi and the N and W banks of the Marañon and Amazon Rivers is continuously colonized as the area remains poorly studied and here A. harlequin sp. nov. is known only from two localities in between (Pucacuro and Andoas).

Natural history. The species inhabits terra firme lowland rain forest and can be found in close proximity to small streams ( Fig. 23 View FIGURE 23 ). The holotype was collected during the day in disturbed forest in the leaf litter. We observed this diurnal species in proximity to slow-moving streams with sandy substrate that were approximately 1–3 m wide and 30 cm deep. During the day, adult males are mostly found actively walking on the forest floor, close to the stream.

Conservation status. We suggest listing A. harlequin sp. nov. as Data Deficient as its population status and its distributional range remain little understood. The species’ EOO is 38,420 km ² and AOO is 40 km ². While most parts of the species’ geographic range are covered in undisturbed primary forest with few human settlements, the populations on the easternmost edge of the species range along the road from Iquitos to Nauta (including its type locality) are highly threatened by habitat loss through large-scale deforestation, agriculture and the construction of roads. Three populations along the Iquitos-Nauta road of the species persisted into the 2010s, but could not be confirmed in 2022 with almost no suitable habitat remaining. In a population a few kilometers further westwards, the species remained abundant despite ongoing deforestation in close proximity to the stream ( Fig. 24 View FIGURE 24 ). Most other populations have not been visited in years hampering a thorough assessment of the species’ conservation status.

Presence and potential impact of Bd remain unknown.

Atelopus harlequin sp. nov. is further likely to be threatened by climate change in the near future, which might both impact the species habitat as well as interfer and exacerbate existing threats such as disease ( Lötters et al. 2023). The species from the western Amazon are among the harlequin frogs likely to be most affected by climate change ( Lötters et al. 2023).

Etymology. The specific name is a noun in apposition (nominative case, singular) and refers to the widely used common name “harlequin ” for frogs of the genus Atelopus that possess striking color patterns and occasionally make awkwarded moves.