10 Sharks: The Animal Answer Guide
section, which is thick and continuous with the head and trunk, and the tail
fin, which is large, as are the dorsal fins. But as with (other) skates and rays,
the body is flattened, the pectoral fins are expanded and attached from the
head back to midbody, and the gill openings are underneath.
How many kinds of sharks are there?
The most recent analysis of chondrichthyan diversity puts the num-
ber of sharks, skates, rays, and chimaeras at almost 1,300 species. Break-
ing this total down into its taxonomic parts, selachian sharks make up
roughly 40% of the total, batoid skates and rays make up 58%, and chimae-
ras around 2%. Ground or reef sharks (of the order Carcharhiniformes,
containing Blacktip Reef and Oceanic Whitetip sharks, Blue Shark, Tiger
Shark, Lemon Shark, and others) constitute more than half the shark spe-
cies. They are followed by the squaliform dogfishes (about 100 species);
32 orectolobiform carpet, nurse, and bamboo sharks; 15 lamniform mack-
erel sharks (makos, White, threshers, and Basking Shark); and 15 squatini-
form angel sharks. About 20 species are in smaller orders (heterodontiform
horn sharks, hexanchiform cow and frill sharks, echinorhiniform bramble
sharks, and pristiophoriform saw sharks). (Recall that the taxonomic name
for orders is shortened as an adjective or noun—e.g., order Lamniformes,
the lamniform sharks.)
Among the batoids are about 300 species of skates and guitarfishes (or-
der Rajiformes); 200 species of myliobatiform stingrays, butterfly rays, and
manta or eagle rays; 60 torpediniform electric rays; and fewer than 10 pris-
tiform sawfishes. Chimaeras (subclass Holocephali) include 46 species, all
in the order Chimaeriformes (see appendix A for details).
The total of 1,300 species is not a final number because researchers find
and describe a few new species almost every year. The number of discover-
ies surprises people unfamiliar with shark diversity: just in the first decade
of the twenty-first century, more than 180 new species of chondrichthyan
fishes were described. Most of these are deepwater elasmobranchs or ani-
mals from tropical regions that have not been as well studied as temperate
waters. Twenty previously unknown sharks and rays were discovered dur-
ing surveys of local fish markets in Indonesia, giving new meaning to the
idea of adventure in shopping. Some species are discovered when we look
in places we hadn’t sampled before or when we “sample” by different meth-
ods. For example, a new species of swell shark, Steven’s Swellshark (Cepha-
loscyllium stevensi), was described in 2011 on the basis of five individuals
caught in a trap set for chambered nautilus (a mollusk) off Papua, New
Guinea. The traps were set 250 to 275 m (820–900 ft) deep, well below the
depths that can be reached by divers using even advanced, mixed-gas scuba
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