The mantle of Egea inermis is shaped like a spindle, is approximately three times the length of the long and thin fins, and is made up of thin walls. Furthermore, the funnel is quite large and the species includes both a funnel organ and a developed valve. The head in contrast is small in size and includes two big eyes protruding toward the anterior. Both the head and the mantle are connected by a short neck, which therefore constricts the head. Moreover, the arms are short yet strong and include two rows of relatively large suckers. Overall, the best indications that an organism of this species is maturing into an adult are the fins increasing in length, the head and mantle experiencing changes, and the sexual organs developing.

Egea inermis is bioluminescent.