Mahidolia mystacina
Mahidolia mystacina, the flagfin prawn goby, flagfin shrimpgoby or smiling goby, is a species of goby native to the Indian Ocean and the Pacific Ocean from Delagoa Bay, Mozambique to the Society Islands and from southern Japan to Samoa and northern Australia. This species occurs in marine and brackish waters, being found in coastal bays, estuaries and reef bases where the bottom is silty or muddy at depths of from . This species is a commensal with a species of alpheid shrimp, using its burrow as its home. This species can reach a length of TL. This species can  also be found in the aquarium trade. It is currently the only known member of its genus. Its genus name "Mahidolia" is named in honour of Mahidol Adulyadej, Prince of Songkla who was the father of King Ananda Mahidol (Rama VIII) and King Bhumibol (Rama IX), as a supporter of fisheries in Siam (today's Thailand). It was first discovered at the mouth of the Chanthaburi River, Amphoe Laem Sing, Chanthaburi Province, Eastern Thailand by H. M. Smith.