Could be, but are they not coloured in Yellow, red, green or orange? Also from the first pick it seems as if there are several dark spots which to me looks like "craters", which is the appearance of cynachyra, although covered in algae. (It could be my eyes playing tricks on me, long day) Algae usually dont coat the surface of tethya. But give it a little squeeze, cynachyra is very stiff. Tethya is firm but softer. Also, Tethya has a smooth surface or it can also be bumpy but it does not have the little "craters". Either way they are both filter feeders.