These fishes belong in the "Order Perciformes" and "Suborder Percoidei" as members of the "Family Microdesmidae" (Dartfishes & Wormfishes) consisting of 2 subfamilies, 10 genera, and 73 species.Often thought of as "Gobies" however, they are members of the Dartfish Family Microdesmidae. These fish are zooplankton feeders, and generally hover in open water, yet near the safety of an area where they can quickly retreat if threatened. They like the security of wedging themselves into tight places for a restful night's sleep. Unfortunately, nighttime predators such as crabs may make them an evening snack.
These paragraph are taken from http://www.saltcorner.com/sections/zoo/dartfishes.htm