aquarium caudal dorsal eyes fin fish gill Gills head mouth nature ocean pectoral sea spiny swim swimming water algal-forager amblyrhynchus-cristatus black color colored colors colour coloured colours crest-of-spines forage forager graceful-swimmer heat-absorption Iguana large lethargic lethargy lizard long-sharp-claws marine-iguana marine-reptile reptile reptilian salt salty spikes spiky spiky-dorsal-fin subtidal-algae-forager sun-absorption Sunbather armor armored armorment armour armoured armourment Australian-freshwater-crocodile backstraps bony-ridges crocodile crocodylus-johnsoni danger dorsal-surface exotic fauna fresh-water-crocodile freshie hide Johnstone's-crocodile leather leathery omnivorous opportunistic opportunistic-predator osteoderms patterns powerful predator ridges rough rugged scales scutes semi-submerged skin tail tail-scutes territorial texture textured textures basking bony ridges crocodilian crocodylus-johnstoni dangerous hornback Johnston's-crocodile