Body transparent, strongly elongate (height ~7% of SL) and compressed; mouth oblique, reaches under eye; eyes large and bulging; numerous cartilaginous and dermal bones (e.g the operculum) that are not fully developed; dorsal fin with long base, at rear of body, 19-22 unbranched fin rays; 11-13 anal fin rays, origin of fin ~under center of dorsal fin ; 11-18 pectoral rays; no pelvic fins; vertebrae 38-40, a long, rod-like structure at the end of the vertebral column; 13 main rays in bluntly triangular tail fin; no scales.
Reaches 4.8 cm (in the TEP)
Lives pelagically (near the bottom during the day, up in the water column at night) in shallow reef waters, including lagoons
Depth range 0-130m
In the TEP this species is known from the Revillagigedos (Clarion) and Cocos Islands.
Note: According to Randall (2007) S. praematura may be restricted to the Hawaiian Islands, the origin of the holotype, because these fishes have very short life cycles and many more new undescribed species have been recently identified using genetic techniques. Although Williams and Williams (2006) identified Cocos specimens as S. praematura, we refer to the TEP population as S. "cf praematura".