Sandperches
Today I was, asked about an unusual, bottom dwelling fish traded as a 'lizard blenny'. In fact the fish in question, is known properly as a, sandperch, or Parapercis sp. These, are not a staple import of the marine aquarium trade, so it's unsurprising they are misunderstood to be blennies, and mistraded as such. Another trade name for sandperches, are the sandhopper blennies, though they are emphatically not blennies.
Sandperches are fortunately hardy carnivores, harmless to corals and tridacnid clams, but unfortunately prone to eating their fish and shrimp tankmates. This is in marked contrast to the benthic blennies, that are predominantly algivorous or detrivorous.
Sandperch lack a swim bladder, and as such rest on the substrate. In the wild, they inhabit areas of sand or rubble. This demersal nature is the habit that confuses aquarists, into misidentifying them as blennies. You should consider these ambush predators, more as you would a hawkfish.
The matured size of these fishes unfortunately varies by species, yet the species is unlikely to be identified, at the point of retail. One species I have identified in the trade, P. schauinslandii, the red spotted sandperch, grows to 18 centimeters, or a little beyond 7 inches. However other Parapercis from tropical waters, potentially grow to 'nearly a foot' or short of 30 centimeters. A fish this size may be characterful, but a danger to very small tankmates. They can be fed on defrosted, meaty fare of the sort usually intended, for crustacean- and fish-eating fishes.
I'm actually fond of the sandperch clade, and do not wish to disuade other aquarists from keeping the characterful genus. Other than to caution that they are mis-sold as blennies, even though their dietary habits are dissimilar, and some popular reef tank staples will not be safe when there is a big sandperch lurking around.