Spawn ribbon 2.6 mm wide in left image, May 2021 . Right specimen 15 mm long. May 2011. Both from Pacific Ocean in California, USA. © J. Goddard.

Features 1 to 4 are as on A. gibbosa.
1: two forward-pointing, not strongly-curved, linear processes at base of each rhinophore.
2: several erect linear processes by each side of the gills.
3: no linear processes on the anterior edge of the head.
4: orange pigment on distal part of appendages.
Distinguishing features of A. pacifica are an orange dorsal line from between the rhinophores to the tip of the tail interrupted by the gills, and an orange dorso-lateral line from each rhinophore to under the linear processes by the gills and a short distance beyond the posterior process.
Pacific specimens like these had BOLD COI sequences differing more than 10% from that of a specimen with typical Ancula gibbosa markings from Maine on the Atlantic .