THE CARPET SHARKS include the largish nurse sharks, the long-tailed and ridge-backed zebra shark (named for the stripes of the juvenile; the adults have spots and are one of several unrelated sharks that share the common name “leopard shark”), the broad, flat, ambush predator wobbegongs, the slightly smaller “blind sharks” (so named for their habit of closing their eyes when removed from water – they are far from blind) and the slightly more slender, longer-tailed bamboo sharks.
The grey carpet shark is a relatively common bamboo shark in parts of Australia. Despite living in that country Malcolm dived for years before seeing one, because their range was a little north of where he normally dived.
The grey carpet shark might just hold the record for the shark with the biggest number of common-name aliases, including brown-spotted catshark, spotted catshark and brown-banded bamboo shark.
A bull shark – this one is a crested horn shark.
All the carpet sharks live a similar low-energy, bottom-dwelling lifestyle around shallow coral and rocky reef areas, like the cooler-water dogfishes taking advantage of the upper food-web of large bottom-dwelling invertebrates and medium-sized fish.
One carpet shark species – the whale shark – has lifted up from the seafloor to find another niche. The same sucking mouth parts that nurse sharks and other carpet sharks use for slurping fish and invertebrates have expanded in the whale shark.
With expanded gills and a free-swimming lifestyle it has become adapted to sucking plankton, allowing this one carpet shark to become the biggest shark of all and live a rather different life to its cousins.
The 20 species of flattened angel sharks might at a glance look a bit like the wobbegongs, but they are their own group and not closely related.
They can seem somewhat ray-like, lying hidden half-buried in the sand with their dorsal- and tail-fins flattened to the seafloor but, unlike rays, which forage downwards, the angel sharks are like the wobbegongs in waiting for prey to swim over the top of them.
The nine species of heavy-headed bullhead sharks are not so far removed from the “typical” shark lifestyle and body shape, and may even represent something close to the original shark body plan. They are much older than other surviving sharks, pre-dating the Jurassic dinosaurs.
Their fin spines are reminiscent of the dogfishes, and their slightly pig-like snouts are not unlike those of some carpet sharks, though the ridges or crests above their eyes that give this group their common name are distinctive.
All of these groups of sharks – by far the majority of the group – have short gill-slits, which give a strong clue about their low-energy lifestyles.
They simply don’t have enough muscle or an active enough metabolism to need the huge gill-slits of a mako or a great white, or even of a reef shark.
Most of the oxygenation of their gills is achieved by pumping of the spiracle, the rounded gill-like structure that looks like an “ear”.
This allows them to keep their oxygen supply going while saving energy, spending much of their time resting on the seafloor.
The bodies of most sharks are somewhat flat-bottomed, broader than they are tall and suited to spending time resting on the seabed.
Many of us have a vague idea that sharks are ancient (modern sharks arose somewhere near the start of dinosaur times), and perhaps somewhat “primitive”. This is because they have
a physically simple, generally non-ossified skeleton.
Recent thinking, however, is that this skeleton, rather than being primitive, is an elegant exercise in energy-saving.