Platycephalus speculator was first formally described in 1872 by the German zoologist Carl Benjamin Klunzinger with its type locality given as Hobson's Bay in Victoria.

[2] The specific name speculator means "explorer" , "searcher" or "investigator", an allusion Klunzinger did not explain, but it may refer to the much larger eyes of this species in comparison to the bartail flathead (P.

There are between 3 and 5 large white-margined black spots or blotches on the distal part of the caudal fin, progressively shrinking dorsally.

The breeding season peaks in the summer and early autumn, in December to March.

[5] Platycephalus speculator is the commonest flathead sold in Western Australian fish markets.