Extensive research has not been conducted on them due to being indirectly observed, with some species known only from their larvae.

Their myomeres (muscle segments) are V-shaped instead of W-shaped as in all other fishes, and their lateral lines have no pores, instead being modified to groups of elevated tubules.

The jaws are quite large, lined with small teeth, and several types are notable for being able to consume fish larger than themselves.

However, these larvae also have a number of unusual characteristics, such as remarkably deep bodies in the Cyematidae, long lower jaws in the Eurypharyngidae, and unique pigmented swellings at the ends of the gut in Saccopharyngidae and Eurypharyngidae.

[2][3] The three established families of the suborder Saccopharyngoidei (Eupharyngidae, Monognathidae, Saccopharyngidae) all exhibit sexual dimorphism.