[1] The subspecies are considered to vary in size depending on the temperature of the waters in which they develop, which could be an indication of them being synonymous species.

[2] With exception for the benthic species Spadella, arrow worms are all adapted for planktonic existence.

Most of the time they drift passively, but they can dart forward in swift spurts, using their caudal fin and longitudinal muscles.

Horizontal fins bordering the trunk serve largely as stabilizers, and are used in flotation rather than in active swimming.

Parasagitta elegans and the three subspecies occur in Arctic and subarctic waters.