The Maroon Clownfishes of the biaculeatus group have traditionally been classified within their own genus, Premnas, owing to the distinctively spined operculum. However, genetic data has consistently argued against this, instead, placing them as a close relative to the ocellaris group of clownfishes. Together, these form the basalmost clade in Amphiprion, and, for this reason, the genus Premnas should be sunk into synonymy.
Both of these species groups share a similar pattern of three well-defined vertical stripes and a highly scalloped margin to the dorsal fin. Both groups are also rather unique for being restricted to the West Pacific and Eastern Indian Ocean, suggesting a strong impediment for dispersing beyond this region.
Careful study of these fishes across their distribution reveals some familiar patterns that hint strongly at the presence of cryptic species. The Eastern Indian Ocean form is most recognizable, but those from Melanesia are also quite distinctive. Seen side by side, it would be impossible to confuse the two, but the populations found between these extremes are a bit less obvious and are likely to differ more dramatically in their genetics than in appearance or morphology.
Ecologically, this fish is found exclusively in the Bubbletip Anemone (Entacmaea quadricolor). This host is also shared with the distantly related melanopus group, though it’s not clear what environmental differences allow these two to coexist. The two groups are seldom seen in close proximity. Fautin has suggested that there may be two species of Bubbletip Anemone: a smaller, colonial form and a larger, solitary form. If this is true, the melanopus group seems to have specialized in the former, while the biaculeatus group is associated with the latter. It is quite rare to find more than a single pair of the Maroon Clownfish in a given location, due to the isolated nature of their hosts, while the melanopus anemonefishes are often seen in vast assemblages with hundreds of anemones.
Amphiprionology 