I'm not Thomas, bur here is an answer for ya.
How come my BTA doesn’t have ‘bubble tentacles’?
The short answer is that no one knows. There have been lots of theories about why BTAshave bulbs or lack them, but no one has been able to prove one theory or the other. Thefactors that do not appear to have any impact include: presence or absence of clownfish,frequency of feeding, or brightness or quality of lighting. To confuse matters further,there have been instances of some BTAs that have had tentacles with bubbles and
tentacles without bubbles at the same time. The presence or absence of bubble tips does not appear to affect (or indicate) anemone health.