ECOLOGICAL STUDY OF DEAD CORAL-BORING BIVALVIA FAUNA OF OKINAWA, SOUTHERN JAPAN A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF THE RYUKYUS IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN BIOLOGY FEBRUARY 1993 -BY FABIO MORETZSOHN ADVISER: MAKOTO TSUCHIYA