o.c.d. - most polychaetes have the same general body structure. Distinctions come from the appendages and type of setae (= bristles). The books usually list 10 or less of the bigger worms. There's perhaps 10,000 described species of polychaetes and a unknown - but high - number of undescribed ones. The same is true for shrimp, crabs, and all the other inverts. The incredible biodiversity is part of what makes marine biology so much fun.
