Satomi's pygmy seahorse (Hippocampus satomiae) is one of the hardest species to find, let alone photograph. Not only is it the world's smallest seahorse, reaching a maximum total length of less than 1.4 cm but it is nocturnal and very active. I was shown a group of these tiny fish by my friend Yann Alfian whilst aboard the Paradise Dancer in Raja Ampat. I used a very small, dull focus light with a red filter to observe these diminutive seahorses to reduce any disturbance to them. They were more active than any other pygmy species I've observed.
They were scientifically described in 2008 and are known only from a few localities in Indonesia and northern Borneo. Their small size and nocturnal habits probably mean they are more widely distributed than this but have just evaded detection. Satomi's pygmy seahorses were originally found by Satomi Onishi (hence the scientific name!) off Derawan Island in Borneo. There is very little scientific information on Hippocampus satomiae but their classification like other seahorses places them in the Syngnathid subfamily Hippocampinae and as fishes they are within the phylum chordata. The habitat prefered by Satomi's pygmy seahorses is rich coral walls, I saw them under overhangs with diverse soft coral growth at a depth of 18 m.
Satomi's pygmy seahorse can be identified by their small size, a small black dot between the eye and the snout as well as orange filaments and markings on the back, tail and chin.
Follow this link to more facts about the diet, habitat and diversity of pygmy seahorses.