Solitary zooids: up to 180 mm long (Helicosalpa virgula). Two dorsal longitudinal muscles linking MI to MVI. Ventral longitudinal muscles between MI and MV, interrupted at MIII. Light organs continuous from MI to MVI.
Aggregate zooids: up to 35 mm long (Helicosalpa virgula 1). Total number of muscular fibers in the mid-dorsal line (MI-MIV): 27-51. Testis oblong, posterior to the gut, protruding into the test projection.