Hypselodoris fontandraui has following characteristics :
- the dorsum is blue bordered in yellow with a median white line and some white spots. The central line extends beyond the rhinophores and ends by a 'T'
- each side of the foot is blue with a pattern of irregular white lines
- the rhinophores are uniform blue
- the gills are either uniform blue or they have 2 triangular yellowish lines on the external side of each gill and one yellowish line on the internal side of each gill

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. fontandraui could be distinguished from Hypselodoris tricolor by :
- its flanks : in H. fontandraui they consist in a pattern of irregular white lines, while in H. tricolor they have only a whitish yellow line
- its gills : in H. fontandraui they are either uniform blue or they have 2 triangular yellowish lines on each gill, while in H. tricolor they have only one yellowish line on each gill

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

H. fontandraui could be distinguished from Hypselodoris villafranca by :
- its rhinophores : in H. fontandraui they are uniform blue, while in H. villafranca they have a white line
- its gills : in H. fontandraui they are either uniform blue or they have 2 triangular yellowish lines on each gill, while in H. villafranca they have only one white line on each gill

H. fontandraui could be distinguished from Hypselodoris orsinii by :
- its dorsum : in H. fontandraui it has a median white line and some white spots, while in H. orsinii it has only a thin white line
- its flanks : in H. fontandraui they consist in a pattern of irregular white lines, while in H. orsinii they have only a whitish line

H. fontandraui could be distinguished from the northern variant of Hypselodoris bilineata by :
- its rhinophores : in H. fontandraui they are uniform blue, while in H. bilineata they have a yellow line

Mediterranean