yes it\'s an original (when it\'s not an original, I mention the inventor). I invented the name \"kaulak\" 3 minutes before I posted it to the forum...
Anyways, Nerocon\'s intuition is going in the right direction, the shell really is turtle-like. On the other hand, the kaulak has some insect-like features. so in order to take off a bit of it\'s tutleness, I would advise on closing the shell on the back, as if the top and pottom part got \"soldered\" together by evolution.
In order to get it more spider like, you\'ll need to get the legs a bit longer, and bet differently, but I guess you knew that. (I think the second pair of legs is longer than the others, the back pair is shorter and the front one shortest. but if making them all the same size makes it easy for rendering speed, go for it.)
The mouth (I thought you could see it in the pic, my bad) is similar to a squid mouth (beak surrounded by a ring-like muscle), see
http://www.columbia.edu/~gp350/gabe/squidbeak.gifAs to the textures, beats me. never thought of colors here. (maybe in the direction of a crab. it lives on the beach after all...)