observing the length of the buccal tentacles and especially the tentacular membranes, the specimen in the photo reminds me of a pectinariidae, an adult specimen, is already beyond the larval stage
Based on the photograph you provided, it appears that the organism in question is a larva of a polychaete, which is a type of segmented worm. Polychaetes are members of the phylum Annelida, which also includes earthworms and leeches.
Polychaetes are a diverse group of worms that can be found in a variety of marine and freshwater habitats. They are characterized by their segmented bodies, which are composed of a series of repeating units called parapodia. Each segment bears a pair of parapodia, which are used for locomotion and sometimes also for respiration and sensory functions.
There are many different families of polychaetes, and it is not possible to determine which family this larva belongs to based on the photograph alone. In order to identify the larva to the family level, it would be necessary to examine additional characteristics such as the number and arrangement of parapodia, the presence or absence of tentacles or other specialized structures, and the overall shape and size of the larva. A trained specialist in polychaete taxonomy would be able to provide a more accurate identification based on these and other morphological features.