This species reaches a maximal length of 80 mm (Bonnevie, 1920). Body cylindrical, similar to that of P. coronata, but less narrow and streamlined. Visceral nucleus shape highly variable; length ranges from two to four times width; the length to width ratio showing a general pattern of decrease with increased body length. Eye shape a function of body size; changes from narrowly triangular in small individuals (length about twice retinal width) to broadly triangular in large specimens (length about one and 1/2 times retinal width).
Recently, Seapy (2000) showed that Pterotrachea minuta Bonnevie, 1920 is not a valid species, and that it should be regarded henceforth as a junior synonym of P. hippocampus.