Specimens of Halophila decipiens Ostenfeld were collected at Sesoko Is
land and Nakagusuku Bay at Okinawa Island, the Ryukyu Islands, souther
n Japan. H. decipiens grows sparsely on coral sand at depths of 15-18
m. This is the first record of the occurrence of H. decipiens in Japan
ese waters and is the most northerly locality of this species in the P
acific Ocean. The morphological and anatomical characters as well as t
he ecological preference of the Okinawan H. decipiens are discussed an
d illustrated.