Hypselodoris cantabrica has following characteristics :
- the dorsum is blue bordered in yellow with a median yellow line and some yellow spots
- each side of the foot is blue with numerous yellow spots
- the rhinophores are blue with a posterior longitudinal yellow line
- the gills are blue with 2 triangular yellow lines on the external side of each gill and one yellow line on the internal side of each gill
This species is absent from the Mediterranean.

In Mediterranean and Atlantic Ocean there are 6 similar blue dorids species. Here is a comparative table of characteristics and a comparative draw of the rhinophores and gills.

H. cantabrica could be distinguished from Hypselodoris fontandraui by :
- its flanks : in H. cantabrica they consist in numerous yellow spots, while in H. fontandraui they consist in a pattern of irregular white lines
- its rhinophores : in H. cantabrica they have a yellow line, while in H. fontandraui they are uniform blue

H. cantabrica could be distinguished from Hypselodoris tricolor by :
- its flanks : in H. cantabrica they consist in numerous yellow spots, while in H. tricolor they have only a whitish yellow line
- its rhinophores : in H. cantabrica they have a yellow line, while in H. tricolor they are uniform blue
- its gills : in H. cantabrica they have 2 triangular yellow lines on each gill, while in H. tricolor they have only one yellowish line on each gill

H. cantabrica could be distinguished from Hypselodoris villafranca by :
- its flanks : in H. cantabrica they consist in numerous yellow spots, while in H. villafranca they consist in a pattern of irregular yellow and white lines
- its gills : in H. cantabrica they have 2 triangular yellow lines on each gill, while in H. villafranca they have only one white line on each gill

H. cantabrica could be distinguished from Hypselodoris orsinii by :
- its flanks : in H. cantabrica they consist in numerous yellow spots, while in H. orsinii they have only a white line
- its rhinophores : in H. cantabrica they have a yellow line, while in H. orsinii they are uniform blue
- its gills : in H. cantabrica they have 2 triangular yellow lines on each gill, while in H. orsinii they are uniform blue

H. cantabrica could be distinguished from the northern variant of Hypselodoris bilineata by :
- its dorsum : in H. cantabrica it has yellow spots in addition to a median yellow line, while in H. bilineata it has one or several lines only
- its flanks : in H. cantabrica they consist in numerous yellow spots, while in H. bilineata they consist in a pattern of irregular yellow lines

European Atlantic