An Idea Taketh Shape...

 There's no way I'll be able to work with limbs as thin as the one on my model so I had an idea to etch some thin lines into the acrylic and then fill them with UV ink. Then when I shine a black light on it these thin tendrils will appear. This sort of reminds me of bioluminescence. I'm also going to test glow-in-the-dark paint. That way you won't need a black light to see the effect. But I don't think there are any glow-in-the-dark paints that are invisible in the light. I got this blue one to do some tests with.