TRIPTERYGIIDAE Helcogramma lacuna, 2.8 cm SL (photo by Ukkrit Satapoomin) Helcogramma lacuna Williams and Howe, 2003 D III + XIV + I, 10 or 11; A I, 20; P1 16-17 (usually 17); P2 I, 2; LLp 21-27; MP 7-8 + 3-7 + 7. Body slender, covered with ctenoid scales. Orbital cirri present, usually minute. Head, nape, belly, and pectoral and 1st dorsal fin bases naked. Color: in male, head and body reddish; 1st dorsal fin, and basal and distal portions of 2nd and 3rd dorsal find reddish; anal fin black, reddish near base; pectoral fin reddish with 3 narrow pale bars; pelvic fin white; in females, head mottled with brown, white and iridescent yellow color; body with alternate brown and white bars; 1st dorsal fin with yellowish membrane between 1st and 2nd spines; anal fin translucent with dusky distal margin; pelvic fin white. Size: attaining to 3.5 cm. Distribution: known only from the Similan Islands and off Phuket, the Andaman Sea.