Deepsea polychaete (Paradiopatra willemoesii)

Is that a structure that the worm resides in or the worm itself? There also seems to be a crustacean or sea spider on the Schizopathid coral.

@splendens - It is a tube, in which the polychaete lives. There is a series of photos on this link from the Aquarium website which shows the worm itself.
イバライソメの棲管（せいかん）

Yes that is a little crab. The deepsea tanks often had random unsigned extra animals in them.