1. of, pertaining to, or resembling twilight; dim; indistinct.
2. Zoology. appearing or active in the twilight, as certain bats and insects.
I'm sure I've learned this word before. To me, it sounds like a word describing the exoskeleton of some creature of the deep rather than something associated with twilight, that mysterious, brooding, and romantic time of night. (note: I'm talking about twilight, not Twilight with a capital T :P).