a: F. auriculata 17 mm. b: F. bostoniensis 9.8 mm.

a) Body slender, length about 8 X width. b) Body broad, length about 4 X width.

a) Propodial extensions(1) short and stout. b) Propodial tentacles (2) slender, curved and longer than on a.

a) Extended oral tentacle (3) (35%) less than 50% of extended body length.
b) Extended long oral tentacle (4) (56%) about 50% or more of extended body length.

a) Menai Strait, Wales. February 2011. b) Outer Hebrides, Scotland. April 2018. Leg. D. McKay & S. Taylor.