The Arc-finned Clade
This well-defined grouping has a number of features setting it apart from other Mirolabrichthys. Most readily observable to an aquarist is the smooth edge to the dorsal fin. This is due to the interspinal membranes of the fin extending to the tips of the dorsal fin spines, whereas in most other Pseudanthias these membranes deflect downwards posteriorly, giving the fin a more jagged look. Note that this feature develops most fully in large specimens. Another critical difference is the unusually high number of scales along the lateral line, ranging from 53-64 in number, whereas most Pseudanthias have a count in the low to mid 40’s. And, lastly, the pectoral fin ray count (19-21) is higher than the vast majority of its congeners, which typically have 17 or 18 rays. These unusual morphological features are possessed by several species classified in Pseudanthias sensu stricto (e.g. P. cooperi & P. thompsoni), and it appears likely that this branch of Mirolabrichthys is derived from them. Pseudanthias bicolor
P. bicolor was described in 1979 by Randall for specimens collected in Hawaii. Soon, more specimens would reveal this species to have a biogeography that spans all the way to Mauritius and the Maldives in the Indian Ocean. This is by far the largest range in the subgenus, and molecular study is warranted to determine if there may be three cryptic species here: Indian Ocean, Pacific Ocean and Hawaiian. The only possible regional variation I’m aware of is the larger sized attained by Hawaiian specimens, 13cm versus approximately 9cm elsewhere.A common and inexpensive aquarium import, the Bicolor Anthias can be identified by its two-toned body (orange & white), as well as the elongated 2nd and 3rd dorsal fin spines (related species in this group have the 3rd spine much longer than the 2nd). Less obvious is that the 2nd anal spine is longer than the third, while the reverse is true in related taxa; the anal fin of bicolor also has a purplish margin lacking in other species. The nuptial coloration of bicolor is unlike any other, with the cheek stripe elongating posteriorly, the pelvic, pectoral and anal fins turning red, and the dorsal fin depressed along the middle to accentuate the elongate anterior spines.
Spawning P. bicolor in Japan. Credit: Itaru Takaku
I’ve always found this species to be more delicate than most, with freshly-imported specimens often dying without obvious cause, but, interestingly, there are records from Japan of this species in 59℉ water!… More:
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