Am I correct in assuming that this animal was found on a beach in Hawaii?
To my knowledge, there are no species of of the genus Lysiosquilloides in Hawaii. There are three species of the superfamily Lysiosquilloidea found in Hawaiil. These include:
Lysiosquillina maculata
Acanthosquilla multifasciata
Heterosquilloides insignis
All are burrowers in sand and should not be in a shell. Moreover, H. insignis is found deeper than 200m.
L. maculata settle out at nearly and inch long, so that doesn't sound right.
Acanthosquilla settles out smaller and has some strong yellow markings. It also lives relatively shallow, so it is possible that it could be found on a beach.
Roy