The colour of Mastigias papua is greenish-brown, attributed to the presence of algae, specifically Zooxanthellae. The exumbrella displays very fine granulations, and the gelatinous substance is firm. There are deep furrows between the eight velar lappets in each octant. Numerous small, club-shaped vesicles are found between the mouth openings. The rhopalar canals are slender and typically feature anastomoses.