The rainforests of the Marojejy massif in northern Madagascar are a well-known hotspot
of amphibian species diversity and endemism. In the present paper, we re-describe
Rhombophryne serratopalpebrosa (Guibé 1975), a cophyline microhylid frog from high
altitude on this massif, based on a re-examination of its holotype, and describe Rhombophryne
vaventy sp. nov. using characters of external morphology and osteology, illustrated
by pdf-embedded comparative 3D models of their skeletons. Rhombophryne serratopalpebrosa
differs from R. vaventy sp. nov. by smaller size (28 mm snout-vent length vs. 52.9
mm), skin texture (granular vs. rough and tubercular skin respectively), supratympanic
fold shape (strong, long and straight reaching the eye vs. curved and not extending
anteriorly beyond the tympanum), relative tympanum diameter (78% vs. 41% of eye diameter),
shape of the postchoanal prevomerine palate, shape of the footplate of the columella,
length of prepollex, and by other subtle osteological features. Morphological comparisons
suggest that a specimen from Ambolokopatrika assigned to R. serratopalpebrosa in previous
genetic studies might belong to yet another undescribed species, closely related to
R. vaventy sp. nov., whereas DNA sequences of the topotypic R. serratopalpebrosa remain
unknown. We therefore emphasise the need for collecting additional material from high
altitudes of the Marojejy massif to understand the systematics, as well as the natural
history, of this poorly known species. For the new species described herein, we propose
a Red List threat status of Vulnerable, in line with other Marojejy endemics from
a similar altitude.