This is from Sven & Fossa's "The Modern Coral Reef Aquarium volume 2":
In
Pterogorgia citrina (Yellow Sea Whip), the polyps grow individually along the edges of the branches. This distinguishes it from
P. guadalupensis (Grooved-Blade Sea Whip) and
P. anceps (Angular Sea Whip), where the polyps grow from a lengthways depression along the edge of the branches. In contrast to the other two species,
P. citrina grows in rather small colonies and is the most common of the three, not only on the reef, but also in aquaria. The cross-section of the branches of
P. guadalupensis is rather flat, and the wide and flat branches taper towards their tips. In
P. anceps, the cross-section of the branches has the shape of an "X" or a "Y." In
P. citrina the branches also taper towards their tips, but they are often twisted as well so that they look like a spiral."
No idea about "Ptetogorgia," but "Pterogorgia" is pronounced tare oh GORE jee uh.
-R