GOBIIDAE Mahidolia mystacina, 2.9 cm SL (photo by Koichi Shibukawa) Mahidolia mystacina (Valenciennes, 1837) Flagfin Prawn Goby D VI+I, 10; A I, 9; P1 17-18; LR 35-37; PDS 0. Body relatively short, compressed. Head compressed; jaws large, extending posteriorly to or beyond a vertical through posterior margin of eye; gill opening extending anteriorly beyond a vertical through preopercular margin. Pelvic fins united medially; frenum present. Scales ctenoid, excepting anterior part of body and breast with cycloid; head and pectoral-fin base naked. Sensory canals and pores present on head; distinct transverse sensory-papillae rows on cheek; a pair of short longitudinal sensory-papillae rows just behind chin. Color: body gray brown, with 4-7 oblique dusky bars; first dorsal fin with alternative dull-yellow and dusky semi-circular bands and/or black blotches. Size: 4.0 cm SL. Distribution: Indo-West Pacific. Remarks: found in bays and tidal estuaries with sandy-mud or soft muddy bottom.