Okay he is all mantle. He doesn't gape but frankly there isn't much tissue on either side of the openings. Most clams I see have alot of space around the openings but not mine. My mh are about 7 months old and I am replacing them with xm10000k very soon. I wonder if it is doing this because of the crappy coralife bulbs? It has good color and responds well to movement. You can see in the second pic that there isn't much tissue for it to open it's shell anyway, is that normal. The shell is about 4 inches long and the mantle 7-8.