Related Clues:

• Navy commandos
• Brief afterthoughts
• Penguin hunters
• BTWs, in letters
• Ltr. writers' afterthoughts
• Elite Navy group that's fittingly camouflaged in the four longest answers in this puzzle
• Playful mammals
• Closes and stamps
• Impressive marine animals?
• Creatures from the deep lagoons outside
• Shuts up animals
• Great swimmers: they're impressive
• Remarks akin to 'btw'
• Fun-loving flappers
• Harp and harbour follower