8 Sharks: The Animal Answer Guide
and skates or rays are flat from top to bottom—too many exceptions occur
to make that a reliable distinction.
Telling selachian sharks apart from batoid skates and rays is relatively
easy (with some exceptions noted below), but telling skates (rajiforms) apart
from rays (myliobatiforms) can be more challenging. In general, skates lay
eggs that have a horny shell (often called a “mermaid’s purse”), whereas
rays give birth to live young. Both skates and rays have long, skinny tails
that are separate from the body (in selachians the tail is thick and continu-
ous with the body), but in skates the tail is thicker and has two small dorsal
fins and a caudal (tail) fin at its end. In rays the tail is long and whiplike and
has barbs (stings) on the top near the base. Stingray barbs develop embry-
onically from scales, so ultimately they are another kind of teeth.
And then we have elasmobranchs that appear intermediate between
groups: the selachian wobbegongs, angel sharks, and saw sharks; and the
batoid sawfishes and guitarfishes. Wobbegongs (Orectolobidae), also called
carpet sharks because of their shape, color, and bottom-living habits, are
true sharks (selachians). They are highly flattened top-to-bottom (dorso-
ventrally depressed). But the gills are on the sides, the pectorals are at-
tached behind the head, and the teeth are fanglike, all good “shark” char-
acteristics. Saw sharks (Pristiophoriformes) and especially angel sharks
(Squatiniformes) are also dorsoventrally flattened. Angel sharks are even
referred to as “raylike” in technical books, and their scientific name actu-
ally comes from the Latin word for skate. But again, an angel shark is a
true shark because its large pectoral fins are not fused to its head, the tail
is thick and continuous with the body, the teeth are long and pointy, and it
bears live young, unlike any skate. Confusing the issue a little is the loca-
tion of the gills, which are below the pectorals, but we will have to ignore
that deviation.
Saw sharks (Pristiophoriformes), as their name implies, are also true
selachians. However, they have the look of batoid sawfishes (Pristiformes),
not of rays or skates. In biological terms, they have converged during evo-
lution on the body plan of a sawfish, having a long snout armed with teeth
on the outside, which they apparently use to slash prey. In saw sharks, gill
openings are on top (the shark condition), whereas in sawfishes they are
under the pectoral fins, a batoid trait. Saw sharks never get over 150 cm (5
ft) long and are usually much smaller. Sawfishes are huge, up to 7 m (23 ft)
long. Saw sharks live in relatively deep water, some at temperate latitudes,
whereas sawfishes are shallow dwellers in tropical and subtropical areas and
even live in fresh water.
The last, slightly confusing group contains the rajform guitarfishes, an
intermediate between sharks and rays that are even referred to in some
taxonomic publications as “sharkrays.” Sharklike features include the tail
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