More Costasiella cf. kuroshimae from Philippines

Thanks Erwin,
The algae is almost certainly a species of Avrainvillea, which Kathe Jensen says is the normal food plant of this genus. The biggest problem with identifying species of Costasiella is not so much difficulties with their anatomy, but difficulties with previous descriptions. It is just not possible to know how variable a species is when it is described from a single specimen, and that description gives a minimal amount of information on the colour, and a stylised black & white drawing. These photos, and your earlier ones, which I labelled Costasiella cf. kuroshimae, suggest that this species is quite variable in colour, sometimes having a reddish spot below the ceratal tip, and in some photos at least showing iridescent blue spots on the cerata. It also seems the upper half of the rhinophores are black, but can sometimes have a white tip. The head also has a broad brownish band from the rhinophores to the mouth and a second patch from the rhinophores back towards the pericardium.

I guess we may as well accept that the animal we are now identifying as Costasiella kuroshimae is correctly identified. I suspect there is no way of ever being sure. To prevent confusion it is probably best to amalgamate the Costasiella cf. kuroshimae messages and the Costasiella sp. 3 messages and call them all . It doesn't give the species a name, but the many photos we now have of it certainly give us a better idea of its colour variation than we have of most of the named species.
Best wishes,
Bill Rudman