Platycephalus longispinnus.
According to different authors of books, "grows to 34cm", "grows to 38cm."
The biggest I have pulled up is 32cm, though most are around the 20 to 25cm mark.
No legal size for them, have caught them at 20cm with fat roe so obviously breed from a small size. I have eaten a few of the larger ones, and the fillets are rather tasty.
This species is very common at times, grabbing large baits meant for the bigger blue spot and tiger flatties. The fillets of the spikies are a great bait for other flatties in the deeper water, the fillets are tough and can hook several fish before needing replacing.
The spikes on the side of the head are very long, hence the nickname 'Spikey,' and I have suffered a number of puncture wounds to the fingers. The dorsal fins have a mild poison that affects my fingers when spiked, with a mild pain lasting half and hour or so.
In reality, Spikey flatties are a pain in the arse to remove from the hook.