IUCN threat status:

Critically Endangered (CR)

Comprehensive Description

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Diagnosis: Isthmohyla calypsa can be distinguished from all other congeners by the following character combination: highly tuberculate and spiny dorsal surfaces of head, body and limbs; coloration in life bright metallic green with brown blotches; dorsal thigh surfaces free of transverse bars; lack of conspicuous markings on anterior and posterior thighs; lack of tarsal fold; chin and throat bright white with a few dark brown spots near the margins; short, truncated snout; male prepollex with numerous small black spines; paired vocal slits in males; call usually a single ascending note (sometimes two notes) (Lips 1996); male size 26-36 mm SVL and female size 31-41 mm SVL (Savage 2002).

Description: Isthmohyla calypsa is a moderately small, bright, metallic green treefrog with dark, olive green to brown blotches as markings. Adult male SVL is 26 to 36 mm while adult female SVL is 31 to 41 mm. Conspicuous tubercular spines cover the upper surfaces, and females are much spinier than the males. The venter is strongly granular. The head is wider than long, with a short, truncated snout. Eyes are large. The tympanum is distinct and has a diameter about 4/5 the diameter of the eye. Vomerine teeth are present in a transverse series, with the anteriormost located between the subcircular, widely spaced choanae. Vocal slits are paired, small, and round, and adult males have fully distensible single external subgular vocal sacs. Fingers are short and thick, with medium-sized finger discs; the width of the disc on Finger III is slightly smaller than the diameter of the tympanum. Under Finger IV, the distal subarticular tubercle is usually bifid. No palmar tubercle is present. Fingers are weakly webbed, with vestigial webbing between Fingers I and II. The prepollical pad is somewhat enlarged. Male nuptial pad at base of thumb has numerous black spines. A series of warts extends along the outer margin of the forearm, and there is a series of spines along the outer margin of both the tarsus and the foot. Toes are strongly webbed. The inner metatarsal tubercle is low, flat, and shaped like an ellipse, while the outer metatarsal tubercle is small and subconical. An inner tarsal fold is present (Lips 1996; Savage 2002).

In life, the upper surfaces of Isthmohyla calypsa are shining metallic green with a few large dark olive green to brown blotches in males. Dark mottling is present in females. Lips are striped with green and dark brown bars. Groin is bright white with some black spots. Irregular transverse dark bars are present on dorsal surfaces of limbs. Anterior and posterior surfaces of the thigh are gray to white, with tiny black spots. The venter is dirty white with numerous black flecks and some large black blotches. Iris is cream-colored with irregular brown line around the margin. Palms and soles vary from gray-white to pale lemon yellow; in some individuals, numerous black dots are present on the palms. No other Costa Rican frog is covered by spines on the upper surfaces of head, body, and limbs (Lips 1996; Savage 2002).

Larvae are large, measuring 54 mm in total length at stage 37. Larval body is depressed. Mouth ventral, nostrils dorsal, eyes dorsolateral. Spiracle lateral and sinistral; vent tube is dextral. Tail is long, with low fins. Tail tip is rounded. Oral disc is small with tiny beaks and 2/3 rows of denticles; A2 with narrow gap above mouth. Beaks have medium-sized serrations. Two or three rows of small papillae border the mouth, and many additional papillae are present in ventrolateral folds. Series of large submarginal papillae present. Larval body is olive brown suffused with orange. Tail musculature is the same color as body, but with darker gray splotches at the midline and on anterior half of tail. Posterior portion of tail has large black spots, especially in larger tadpoles. Tail fin is translucent (Lips 1996; Savage 2002; Lips and Savage 1996).

Similar species: I. calypsa can be distinguished from I. lancasteri by skin texture (spiny in I. calypsa vs. smooth to bumpy in I. lancasteri), nuptial excrescences (black in I. calypsa vs. brown flattened pad in I. lancasteri), smaller average mass (1.8 g in I. calypsa vs. 2.2 g in I. lancasteri), and lack of transverse barring on dorsal and posterior thigh surfaces (vs. dorsal and posterior thigh surfaces with transverse bars in I. lancasteri). I. calypsa tadpoles can also be distinguished in appearance (more streamlined: relatively longer tail, smaller fins, relatively short, flattened, and thinner body; eyes are larger and more anterior and the snout is truncate) from those of I. lancasteri (more robust, rounded tadpole body; rounded snout; shorter tail). The call of H. calypsa lacks harmonics and males rarely overlap notes; in contrast, the call of H. lancasteri always has one and sometimes two harmonics, and males frequently overlap calls with neighbors (Lips 1996).

A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).

Isthmohyla calypsa was previously included in Isthmohyla lancasteri, but it has been distinguished from that species based on adult and larval morphology, oviposition site (leaves for I. calypsa vs. attached to submerged vegetation and debris in small pools of slow-flowing streams for I. lancasteri), egg and clutch characteristics (10-36 yellow eggs per clutch for I. calypsa, vs. 70-80 chocolate-brown eggs for I. lancasteri) and vocalizations (Lips 1996).

The specific epithet calypsa derives from the Greek nymph Calypso, who hid the hero Ulysses. It refers both to the frog's camouflage and to the species having been hidden within H. lancasteri (Lips 1996).


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