You are engulfed by some zoantharia. It thinks you are tasty food.

However, over time, it has found that allowing algae to live for a little while inside it makes them even better, as they can continue photosynthesising and making sugars inside it. In fact, it have already evolved to provide the chemicals you needs as food to extends your life inside it, and supersize its meal.

This adaptation has now reached the point where it can contain multiple photosynthesising algae and they can live on inside you indefinitely.

It has entered a symbiotic relationship, and will come to rely on its guest, providing food and protection, for the price of a few sugars.

You are a symbiotic polyp.

As you are soft and small, and now sweet, you are quite vulnerable to anything bigger and hungry that happens to be near you. An adaptation to create some kind of armour might be useful right about now, although it comes at a cost.