It does have segmented legs, I posted a second picture (not as sharp), but you can't really make them out without seeing the enlarged image: http://bugguide.net/images/raw/3HE/HFH/3HEHFH7HBHIHVHMHAHSLCH7HOHZL5ZMLYH8LAZ4L1ZNHBZ8LPZXHVHHLCH8HCH5HZR2HBHZLAHZL2ZGH.jpg.

The silk sand tubes were not attached to the plant. When I lifted a plant limb out of the sand, the tubes would dangle like little streamers.

The habits and habitat match those of Areniscythris brachypteris, whose known hosts include plants in Asteraceae, Boraginaceae, Fabaceae, and Lamiaceae. The larva at least superficially matches the drawing in the original description, including the markings.

The adults are finally out :o)

I couldn't find any accessible papers showing larval morphology of that species, but there was one from a related Polish species: http://www.entomologicafennica.org/Volume14/EF_14_4/2Baran.pdf and the larvae illustrated looks similar in gross morphology and the sand tubes depicted are identical to those this larvae was found in.

This morning I sent a scan of the paper that described Areniscythris brachypteris to the email address listed on your profile. If you didn't receive it, email me to be sure I have the right address, and I'll try again. Or maybe check your spam folder first.

Thanks so much for the paper, it did get routed to spam. The habitat, location, and morphology all seem to match perfectly with this larva. I'll keep an eye out for adults. Finding adults might be challenging as much of the foredune habitat is closed to protect breeding snowy plovers come March but it also means that the moths are protected from off-road vehicles.