The Skunk Anemonefishes are a morphologically and ecologically distinctive group within Amphiprion, having been allocated their own subgeneric classification under the name Phalerebus. This certainly highlights how recognizable these fishes are, but molecular studies indicate this group is highly derived within the genus and probably does not warrant such a distinction. But exactly where they fit in Amphiprion evolution is still decidedly unclear, with studies differing wildly depending on the genes analyzed. The closest relative is undoubtedly A. sandaracinos, which diverged sympatrically by specializing in a distinct host anemone, Stichodactyla carpet anemones.
From a morphological standpoint, the perideraion group are smaller and more elongated than most other Amphiprion. The head is scaled from between the eyes to the dorsal fin in all members, including in A. chagosensis, a species which has not previously been recognized as a member of this lineage. There are 17 pectoral fin rays (18+ in other groups) and the dorsal fin has a completely smooth outline. And, of course, many of these species possess a unique dorsal white stripe not found anywhere else in the genus.
Ecologically, these fishes are almost entirely associated with the Magnificent Sea Anemone (Heteractis magnifica) and appear to be the most competitive species for this desirable resource, able to outcompete specialists (e.g. A. ocellaris) and generalists (A. clarkii). There has been seemingly little research into the specifics of how this competition works on a reef, particularly with regards to how two distinct groups have been able to specialize in a single host species. While A. ocellaris/A. percula do also regularly make use of Stichodactyla carpet anemones, it’s likely that there are environmental factors that dictate where these fishes occur. In general, skunk anemonefishes are more associated with deeper reefs, while the Actinicola clownfishes frequent shallow lagoons and reef flats.
Lastly, there is a strong indication that the unique species of the Chagos-Laccadive Ridge have speciated, in part, via the introgression of genes from the neighboring bicinctus group. This is evident in that these two species (A. nigripes, A. chagosensis) are the only members of their group lacking a dorsal stripe and having dark ventral fins. Genetic data also hints at this, as these two species have grouped alongside the bicinctus group in multiple studies. A plausible explanation for this could be that A. omanensis, which has notably dark ventral fins, has on occasion spread eastward beyond its current range, intermingling with the skunk anemonefishes of the Central Indian Ocean. Why it should interbreed with these fishes and not the others in this region (A. sebae, A. clarkii) is difficult to fathom. Apparently, the Amphiprion heart wants what it wants. More study is needed to elucidate the complex evolutionary history of these fishes.
Amphiprionology 