glass anemones and aptasia are 2 completly different things.
aptasia are tall brownish red colored Palm tree lookin things.
Glass nems are, clear, small pest anemones that short and stocky, like yours.
Both, however, are considered pests, and can violently sting and harm other corals.
i have dozens of those punks in my lil tank, and i nuke them every chance i get.
they ALMOST look like a dendro, but not quite
and if you notice, they have no def, calcified tube structure, no color, are much smaller, and are just a clear gooy critter.
plus they're much too small.
SOOOOOO yea, those are glass anemones. Just a common pest hitchhiker.