Smallest species of seahorse
Satomi's pygmy sea horse Hippocampus satomiae
13.8 millimetre(s)
Indonesia ()

The world's smallest species of sea horse is Satomi's pygmy sea horse Hippocampus satomiae, which as an adult has an average length of only 13.8 mm (smaller than an average human fingernail), and a height of approximately 11.5 mm. Formally described as a new species in 2008, it is found in the seas around Indonesia's Derawan Island, off Kalimantan (Indonesian Borneo), and it is named after Satomi Onishi, the dive guide who collected its species' type specimens.

The previous record holder is Denise's pygmy sea horse H. denise, an adult of which is typically just 16 mm (0.63 in) long. In the past they have been mistaken for the offspring of another of the 54 currently known species of sea horses. This species was discovered in 2003 in the delicate corals of the Flores Sea, off the coast of Indonesia, by a marine biologist working for Project Seahorse. It lives among the deeper corals and is a master of camouflage.