The false plum anemone (Pseudactina flagellifera) is one of the larger and most venomous anemones found in Cape waters. That said, it won’t hurt you unless you have an open wound that you somehow manage to get in contact with its tentacles! They can grow to prodigious sizes. Like all anemones, the prey is captured with the tentacles (which are sticky and cause paralysis in the molluscs and crustaceans that it feeds on) and stuffed into the central mouth cavity.
The anemone has spherules, which are small bead-shaped protrusions, at the base of its tentacles, as well as vesicles filled with toxins, which are used for defence. They contain nematocysts or stinging cells. These anemones can move about slowly, and will attack other, unrelated anemones with its vesicles. We often see Cape rock crabs sheltering next to large false plum anemones.
Their tentacles frequently have mauve tips, which I think are very pretty. They apparently do not readily retract their tentacles (according to Two Oceans), and I was surprised to see several at A Frame recently with their tentacles completely hidden.
Pseudactinia
Thank you Peter, blame it on my fat fingers 🙂