Body colour variable: opaque white body to light brown with dark brown/red pigmentation spots on the dorsum and matte red body with dark spots on anterior segments. A white luminescent spot on the prostomium between two pairs of small black eyes. White luminescent spots on middle to posterior end forming the characteristic chain-like pattern for Platynereis. A distinct red dorsal midline from anterior to posterior. Two slender, tapering frontal antenna on prostomium. A pair of palps laterllay positioned with swollen bases and round distal ends. Four pairs of tentacular cirri. Dark brown jaws with 7 teeth. Paragnaths on pharynx arranged in distinct areas and consist of faint rods in tight lines or rows: : I & II = 0, III = 3 discontinuous rows in an oval patch, IV = 4 rows in a pyramid shape, V = 0, VI = 2 rows in an arc shape, VII-VIII = 4 groups of 1 row in an arc. Dorsal and ventral cirri present. Chaetae consist of: homogomph spinigers, heterogomph falcigers with terminal tendons and heterogomph spinigers.
Very common in the lower intertidal rocky zone under Ulva sp. Laurencia flexuosa and Jania verrucosa beds. Found in soft flexible tubes made out of mucous secretions, sand and detritus. In the Gansbaai Harbour specimens were found between thickets of sand cakes.
South Africa: Lamberts Bay in the Western Cape to Kidds Beach in the Eastern Cape. More abundant along the warmer parts of south and south-east coasts.
This species is known to be part of the Platynereis dumerilii species complex in South Africa and the Mediterranean. Genetic results indicate this species is indigenous to South Africa and alien in the Mediterranean. However, the identification of this species as P. massilensis is doubtful, and should therefore be referred to as Platynereis sp until the identification of the species in the Mediterranean has been clarified.