Page 325 - (DK) Ocean - The Definitive Visual Guide

CARTILAGINOUS FISH CLASSIFICATION 323

Reproduction Sharks and rays are classified together in one class (the Elasmobranchii),
while chimaeras, which include ratfish and rabbitfish, are placed in
In all cartilaginous fishes, the eggs are fertilized inside their own class (Holocephali). Sharks comprise nine orders and rays
the female’s body. Adult males have organs on the belly four orders. Chimaeras have one order, the Chimaeriformes.
called claspers—rodlike appendages derived from the
pelvic fins. During mating, one or both claspers are CHIMAERAS spiracles. They have large pectoral and
inserted into the female’s cloaca (the shared opening of Order Chimaeriformes pelvic fins, two small dorsal fins, but no
the digestive and reproductive tracts) to introduce the anal fin. Reproduction is yolk sac viviparity.
About 49 species
sperm. In sharks, mating can be a rough affair, although Chimaeras have a long, flabby body without
there may be some courtship. scales, a large head with sensory canals, BULLHEAD AND HORN SHARKS
Order Heterodontiformes
Chimaeras, as well as some sharks and rays, lay plate-like teeth, and one gill opening. The
first of two dorsal fins is erectile with a
eggs—that is, they are oviparous. The eggs are CATSHARK EGGS venomous spine. Reproduction is oviparous. 9 species
Small, bottom-living sharks, these species
protected by individual leathery egg capsules, often These egg capsules have pointed front teeth and molar-like
contain catshark
known as mermaid’s purses. The young then hatch back teeth, a blunt, sloping head, nostrils
embryos, which will FRILL AND COW SHARKS
out several months later. In contrast, most sharks and hatch after about Order Hexanchiformes connected to the mouth by a groove,
rays are viviparous: they give birth to live young after a year. The tendrils paddlelike pectoral fins, an anal fin, and
two spined dorsal fins. They are oviparous.
a long period of gestation. In some species, the eggs anchor the capsules 6 species
These sharks have a long, thin body, six or
to seaweeds.
simply remain inside the mother until they hatch, seven pairs of gill slits, small spiracles, and
sustained by yolk prior to birth (aplacental yolk sac a single dorsal fin near the tail. Frill sharks CARPETSHARKS
Order Orectolobiformes
viviparity). In about 10 percent of sharks, the young develop attached have three-pointed teeth; cow sharks’ teeth
are saw-like. Reproduction is yolk sac
to a placenta-like structure and are directly nourished by the female’s viviparity. 42 species
These mainly bottom-living sharks include
body (placental viviparity). In wobbegongs and nurse sharks. They have a
all cases, the young are born SLEEPER AND DOGFISH broad, flattened head, barbels, and nostrils
fully formed, and they are able SHARKS joined to the mouth by a deep groove. They
to hunt and feed. Immediately Order Squaliformes have an anal fin and two spineless dorsal
fins. Reproductive strategies vary.
after birth, the female swims
130 species
away and the young are left Six families form this large, varied order:
MACKEREL SHARKS
to fend for themselves. bramble, dogfish, rough, lantern, sleeper, Order Lamniformes
gulper, and kitefin sharks. All have spiracles,
five gill slits, and two dorsal fins, but no
LEMON SHARK BIRTH 15 species
Lemon sharks move to shallow, sheltered anal fin. They have yolk sac viviparity. These large sharks, which include the
bays or lagoons to give birth. The young white, basking, and megamouth sharks,
emerge tail first and swim away. The BRAMBLE SHARKS have a cylindrical body, conical head, two
mothers then leave the nursery grounds. Order Echinorhiniformes dorsal fins, an anal fin, and a long upper tail
lobe. Many can maintain a high body
temperature. They have yolk sac viviparity.
2 species
Large, slow-moving deepwater sharks with
thorn-like skin denticles. They have yolk
GROUND SHARKS
sac viviparity. Order Carcharhiniformes
At least 291 species
SAWSHARKS Body shapes vary in this the largest and
HAMMERHEAD SHARK Order Pristiophoriformes
most diverse shark group. All species have
The broad head of this shark provides
two spineless dorsal fins and an anal fin.
space for extra electrical sense organs on 8 species
Small, slender sharks, these species Reproductive strategies vary.
the snout and gives a wide field of view,
have a flattened head and saw-like
making it a formidable hunter.
snout with barbels. They have two
RAYS AND SKATES
spineless dorsal fins, no anal fin, and have Orders Rajiformes, Myliobatiformes,
yolk sac viviparity.
Pristiformes, Torpediniformes
718 species
ANGELSHARKS These are mostly bottom-living fish with
Order Squatiniformes
a flat, disk-shaped body, winglike pectoral
fins joined to the head, and a long, thin tail.
About 20 species
These flattened, raylike sharks have a Reproduction is mostly viviparous with
rounded head with gill slits on the side, and many live young, but some are oviparous.
Hunting Senses
Cartilaginous fishes have acute senses that help them to find prey, even if it is distant
or buried in sediment. Predatory sharks smell or taste tiny amounts of blood as water
passes over highly sensitive membranes in their nostrils, while catsharks also use smell
to recognize each other. All cartilaginous fish have a system of pores called ampullae
of Lorenzini that allows them to detect weak electrical signals given off by other
animals. Most also have a lateral-line system, similar to
that of bony fishes, which detects water movements.
Cartilaginous fishes have eyes similar to those of
mammals, and most have acute vision. They have no
eyelids, but some sharks have a transparent “nictitating
membrane,” which protects their eyes
when they are attacking prey. OCEAN LIFE
AMPULLAE OF LORENZINI BARBELS
The black spots on a shark’s snout are Active at night, nurse sharks can
tiny electrical sense organs that help find buried prey by touch and smell,
it find prey even in complete darkness. using their sensory barbels.