The blenniids of the genus Scartichthys represent key herbivore species of central and south American Pacific coastal reefs. Yet Scartichthys spp. remain difficult to identify in the field, especially across the c.a 6000 km where three of the four currently accepted species are known to occur in sympatry. The main diagnostic characters from traditional taxonomy that have been used to revise this genus are indeed elusive. At the same time, species can display multiple colour patterns in the field, depending on the ontogenetic stage, habitat association, and/or reproductive behaviour. Overall, molecular characterization is warranted to help address these issues. Here, we used a combination of colouration, morphological and molecular data for the first time, including specimens representative of the four currently valid species and seven described colour patterns. Our integrative approach revealed that only three of the four species should be considered as valid; Scartichthys gigas (Steindachner, 1876), S. variolatus (Valenciennes, 1836) and S. viridis (Valenciennes, 1836); while S. crapulatus Williams 1990 should be synonymized with S. viridis. In the same way, our analyses show that one of the colour patterns attributed so far to S. gigas is characteristic of the juvenile stages of S. viridis. Our time-calibrated phylogeny shows that this genus is relatively young, with an estimated time of divergence between Scartichthys gigas and S. viridis of around 1.71 Ma. In comparison, the Desventuradas and Juan Fernandez Islands endemic S. variolatus diverged about 1.95 Ma. Our results help to clarify the taxonomy of the Scartichthys genus.

The blenniids of the genus Scartichthys are one of the most common fishes of Central and South American Pacific coastal reefs. This being said, Scartichthys spp. remain difficult to identify in the field, and identification is particularly challenging across the c. 6000 km where three of the four currently accepted species are known to occur in sympatry. A reason for this is that the main taxonomic characters from traditional taxonomy are indeed elusive. In addition, at the same time, species can display multiple colour patterns in the field, depending on their ontogenetic stage, habitat association and reproductive behaviour. Overall, molecular characterization is warranted to help address these issues. In this study, the authors have used a novel approach to revise the genus by combining colouration, morphological and molecular data of representative specimens of the four currently valid species and seven described colour patterns. From this, the authors show that only three of the four species should be considered as valid; Scartichthys gigas (Steindachner, 1876), Scartichthys variolatus (Valenciennes, 1836) and Scartichthys viridis (Valenciennes, 1836), whereas Scartichthys crapulatus (Williams, 1990) should be synonymized with S. viridis. In the same way, the analyses in this study show that one of the colour patterns attributed so far only to S. gigas is characteristic of the juvenile stages of S. viridis. The time‐calibrated phylogeny of this study shows that this genus is relatively young and that the estimated time of divergence between S. gigas and S. viridis is c. 1.71 Ma. In comparison, the Desventuradas and Juan Fernandez Islands endemic S. variolatus diverged c. 1.95 Ma. The results of this study help to clarify the taxonomy of Scartichthys.

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