Roa excelsa. The pinnacle of butterflyfish perfection.
Nestled within the family Chaetodontidae is a complex of butterflyfish with a particular proclivity for deep reefs in the mesophotic twilight zone. They share a pattern of alternating broad brown and white bands, and possess a distinctive ocellus on the posterior soft dorsal fin. In stark contrast to most other shallow water representatives, this retiring and reclusive group receives little attention, owing to their penchant for the dreary depths. Specimens are most often seen as bycatch from commercial trawler fisheries, where they are regarded as trash species of no commercial value. With careful elucidation, however, the intriguing beauty of this group becomes evidently apparent, and in the recent decade, has garnered much attention from butterfly “a-fish-cionados”. These banded beauties are members of the genus Roa, and in this article, we explore the intricacies that besiege this group. Roa suffers from a rather giddying state of taxonomic limbo. R. modesta was the first of its kind known from the subtropical waters of Japan. However, Temminck & Schlegel first described the species in 1844 as Chaetodon modesta. Almost a century later in 1921, Jordan described a similar looking species from Hawaii. He noticed several key differences in morphology from the standard Chaetodon, and subsequently described the Hawaiian specimen as Roa excelsa. Chaetodon modesta was later moved to the new genus Roa, and in 1939, Roa jayakari was described, bringing the total species count to three. Most authors have considered Jordan’s genus Roa to be nothing more than a subgenus of Chaetodon, with various literatures switching back and forth between the two. However, in 1989, Blum reinstated Roa back to generic status based on an unpublished cladistic analysis in his PhD thesis. Ferry-Graham et al. (2001) concurred with Blum’s data analysis, and came to a consensus that Roa was a monophyletic group comprising of three species distinct from Chaetodon. This elevation of Roa to genus level was agreed upon by Pyle (2001) and Kuiter (2002) as well. In this article, we follow the agreed upon classification of Roa at genus level. The Roa butterflies are most frequently found at depths exceeding 100m, and because of this, are very poorly known by divers and taxonomists. Currently, four species are scientifically recognized, with a handful of other undescribed members distributed throughout the Indo-Pacific. It is also interesting to note that although hybridization in this genus has not been documented, it should not be discounted.… More:
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