Unknown Polychaete B is similar in size and general outline; however, it lacks the long delicate chaetae of Archinome. In larger specimens a distinct jaw apparatus is visible through the body wall.
These larvae are very distinctive and unlikely to be confused with anything else. They are thick-bodied, tapering slightly toward the ends. Their chaetae are long, delicate and flexible and they often become tangled with debris or other animals in the sample. There are usually three pigmented areas visible on the head, as shown above at left.