As a reminder, here's a photo I shared from the research paper that first described Polydora alloporis:
From Light, W.J. 1970. Polydora alloporis, new species, a commensal spionid (Annelida, Polychaeta) from a hydrocoral off Central California. Proceedings of the California Academy of Sciences 37: 459-472.
And here's your first view of a worm living in Stylantheca papillosa:
This worm is thought to live exclusively in hydrocorals. [Note the earlier paper discovered the worm in a different species of hydrocoral, Stylaster (formerly Allopora) californica.]
You can see the "double-barreled" tube that the worm lives in. A pair of tentaculate palps emerges from one opening, and the disc-shaped pygidium (or tail end) is sometimes visible in the other opening (see below):
The tentaculate palps are the most visible feature. They're very active and are used to explore the surroundings and to capture food. There is a prominent groove that runs down the middle of each palp. When a food particle is captured — either from the water or the surrounding surface — the particle is moved down the food groove towards the mouth by cilia. You can see particles in the food grooves below (white arrows):
Here's an explanatory diagram (below). Note that the food groove is deeper in the middle of the palp and shallower near the base of the palp.
Modified from Dauer, D.M., C.A. Maybury, and R.M. Ewing. 1981. Feeding behavior and general ecology of several spionid polychaetes from the Chesapeake Bay. J. Exp. Mar. Biol. Ecol. 54: 21-38.
As particles get closer to the base, they "ride up" into the shallower section of the groove and accelerate towards the mouth. You can see this for yourself in the video below.
Watch for the following: (1) exploring palps, (2) food particles moving along the food grooves (from ~18-28 seconds and ~29-32 seconds), and (3) the posterior end appearing near the surface of the tube.
We have lots of questions about the relationship between the worm and the hydrocoral. Does the worm steal food particles from the hydrocoral (from the surface or even from within the hydrocoral pores)? Does the feeding activity of the worm help keep the hydrocoral free of debris? How do the larval worms find the hydrocorals? Do the juvenile worms take over an established hydrocoral pore?