ID worm

Question
QUESTION: I have owned my established tank for 3 weeks now and the guy who owned it before me had it for 2 years.  Saying that, I found a worm under the sand the other night that neither of us had seen before.  The coloring, shape, and texture was similar to a night crawler but had a more flat head with two reddish stripes on the side.  It's mouth appeared to be circular shape.  I was wondering if you had any idea what it is...or if you can point me in the right direction?  Is it harmful, are there potentially more, etc?  I have searched the Internet but have not found anything that looks like it.
Also, my blue tang still appears to be thin, I can see ribs on both sides.  It is around 7 inches long so I was wondering if she is old or if there is something else I should do for her?
Thanks

ANSWER: Hi Heather,
Does it have cilia(little hairs)? If not it sounds like a sipunculid(this is the family of the peanut worm) of some kind. There are numerous forms and variations. You might try just plugging Sipunculid into your search engine and see if you see him in any images. If not, maybe you can get me a photo, that would be great too.
At 7 inches and 3 years I wouldnt think she is old. How is the Tangs diet? Does it eat well and eagerly? Do you offer seaweed and veggie matter as part of the diet? Does it have redness, swelling or discoloration too? If not, a good trick to get your Tang back on track to health is to pick up seaweed or a macroalgae at the fish store with a vitamin supplement. Soak the seaweed/algae in a little water with the vitamins and some garlic(some of the vitamin supplements have the garlic in them). This is almost guaranteed to get him eating again. And make sure you always have some seaweed in the system, or a macro algae, for them to nibble on through out the day.
If you could get back to me if you have any more info as far as my questions, we can get you a more definitive answer. But with what I have to go on it sounds like a diet issue. Let me know, Always glad to help when I can.

---------- FOLLOW-UP ----------

QUESTION: She eats fine.  Actually she might eat more but I have been too scared to feed her too much as I am already feeding her quite a bit. No redness or swelling but her color is not as blue as the tangs I am used to.  I did get flakes with seaweed in them but I will try your suggestion.  Makes sense for her to have something available all day.
As for the worm, I looked at some pics of the peanut worm but it didn't have a larger diameter body it just had more flattening around the head area.  I will keep trying and might be able to catch it again...one of these days!
If I do I will send you the pic.
Thanks again.

Answer
Hi Heather,
Sorry I couldnt be more specific on the worm. Do send me a photo if you get one, I'll be glad to help.
If she eats fine, and eagerly, and her coloring is just not as bright.... I'm 99% sure its simple nutrition problems. Try the fresh seaweed, macro algae, or freeze dried seaweed(last choice in my opinion)in the tank. Also get her a vitamin supplement and do the pre-feeding soak with her foods as well, that will get her weight and nutrition back in line. Garlic is a great nutritional supplement as well, stimulates growth, immune system and eating. So you can still add the garlic to the soak as well.
Thanks, keep me updated... Im always glad to help!