Foods and Feeding 147
Cookiecutter sharks that feed by gouging round plugs of flesh from larger
tunas, whales, dolphins, swordfish, Megamouth Sharks, and swimmers.
(See “What kind of teeth do sharks have?” in chapter 2 and “Are sharks
dangerous to people or pets?” in chapter 9.) Cookiecutters are among the
few bioluminescent sharks, having light-emitting photophores (light cells)
along their bellies. It is thought that their photophores help them blend
into the background of dim lights produced by other small organisms in an
otherwise black ocean. When larger predators swim down to feed on small
fishes and invertebrates, the Cookiecutters, who have camouflaged them-
selves among these small animals, lunge out and remove a plug of flesh.
It has even been suggested that the Cookiecutter’s lighting could lure its
“prey” to within striking distance.
Suction Feeders. Most sharks, skates, and rays (but not chimaeras)
suction food into their mouths. For some, it is the primary means of cap-
turing prey, especially among the heterodontiform horn sharks, orectolo-
biform carpet sharks, and Nurse Sharks, and a number of batoid skates.
Sharks generate suction (negative) pressures by rapid “buccopharyngeal
expansion”—pushing down on floor of their mouth and throat, thereby ex-
panding the mouth cavity. Unlike bony fishes, sharks cannot produce much
suction by shooting their mouth out, although doing so does bring a shark,
or at least its mouth, closer to a food item. Phil Motta and his associates
found that in Nurse Sharks, the negative pressures generated during suc-
tion can be as high as one atmosphere (14.7 pounds per square inch), “the
greatest subambient pressures reported for an aquatic-feeding vertebrate”
A Japanese Angel Shark (Squatina
japonica) lies on the bottom, with its
mouth partially open. Angel sharks
frequently bury most of their bodies
in the sand, making them more dif-
ficult to detect. They can erupt from
the sand quickly, whereupon they
literally suction prey out of the water
column, helped by a large mouth
and long, spiky teeth that prevent
the prey’s escape. Photo by Ryo Sato,
Wikimedia Commons, http://en.wikipedia.org/
wiki/File:Squatina_japonica 2 .jpg