I'm fairly certain it's not a 8 line. P.octotaenia is generally a bigger flasher, and it has 8 distinct horizontal lines (sometimes only six are visible) running the entire length of the body .... it's name's sake.
Definitely Paracheilinus. I've been staring at juvie photos of P. filamentosus and P. octotaenia for about 15 minutes now and it looks like both. Shrug.
I would find it incredibly odd that a Red Sea 8 line would get sold as an unID'd wrasse though. And it looks like it doesn't have enough lines.
Um, just thought of something. P. octotaenia doesn't have the filaments that P. filamentosus has on the rear part of the dorsal fin. If you see it flash you can tell for certain.
I could be mistaken. I did have a "school" of P.filamentotous that I once bought as "Misc Wrasse." All of them did not have the "filament-like" rear dorsals when I bought them (about 1" in size) but they developed it after a year in captivity (about 1.5" in size).
The body shape definitely reminds me of P.octotaenia, but all the 8-lines I've seen had unmistakable body markings, even the juvies.