Polychaete worms, members of Class Polychaeta in Phylum Annelida, are extremely common in the ocean -- and they are extremely diverse; with over 30,000 known species, and thousands more waiting to be scientifically described. The phylum includes the common earthworm, and the leeches. All are segmented animals with body organs tending to be repeated within the segments.

The worm shown lives under rocks in low-oxygen environments. It feeds by transporting food particles alonng the tentacles to its mouth, and the tentacles are also used in respiration. This animal is really a close relative Larva #3, but not the exact adult that results when larva #3 settles