Page 17 - Fish and Amphibians (Britannica Illustrated Science Library)

12 GENERAL CHARACTERISTICS FISH AND AMPHIBIANS 13

Bony Fish OCEAN SUNFISH The Swim Bladder
Mola mola
The largest osteichthian An appendage of the intestines that regulates flotation by filling with and
fish, it can grow to be emptying itself of gas. The gas enters through a gland that extracts the
gas from a net of capillaries, called the rete mirabile, and it leaves the
11 feet (3.3 m) long and
he group of fish that have evolved and diversified most in the can weigh 4,000 bladder through a valve that causes it to dissolve back into the blood.
last few million years are the osteichthyes, fish with spines pounds (1,900 kg).
EMPTY FULL
T and jawbones. In general, their skeletons are relatively When the fish empties its By reducing its
small but firm, being made mostly of bone. Flexible fins enable swim bladder, it sinks. density, the fish rises.
them to control their movements with precision. The various Rete Dorsal
species of osteichthyes have adapted to a wide variety of Mirabile Aorta
environments and even to extreme conditions.
FIRST
DORSAL FIN
SECOND
DORSAL FIN
Solid Structure
Gas SWIM
The skeleton of a bony fish is divided into the cranium,
Gland BLADDER
spinal column, and fins. The opercula, which cover their
gills, are also made of bone. The cranium holds the brain VERTEBRA
and supports the jawbone and gill arches. The vertebrae
of the spine are jointed; they provide support to Neural spine
the body and join the ribs at the abdomen.
Neural arch
VERTEBRAL
UPPER LACRIMAL
COLUMN
JAW BONE Centrum
The main nerves
and blood vessels
run above and
Hemal arch
below the bony (chevron)
center of the spine.
Hemal spine
CRANIUM
CAUDAL FIN
VERTEBRAE

LOWER RIB
PECTORAL
JAW
FIN
PERCH EYE OPERCULAR CLAVICLE INTERHEMAL SPINY RAYS
Perca fluviatilis SOCKET BONES (VENTRAL) SPINES OF ANAL FIN
protect support the spiny rays of
The skeleton, along with the
the gills. PELVIC the anal fin. CAUDAL FIN
bony structure of the fins
FIN propels the fish
through the water.
Actinopterygii PERCH SCALES CYCLOID Sarcopterygii
Perca fluviatilis They overlap Another name for the Choanichthyes,
The main characteristic of
and are
actinopterygian fish is their bony CTENOID a subclass of bony fish. Their fins, like
covered with
skeleton, with bony spines in their mucus. the fins of whales, are joined to the body
fins. They have a cartilaginous skull by means of fleshy lobes. In lungfish,
(partly calcified) and only one these lobed fins look like filaments.
pair of gill openings
covered by an COELACANTH
operculum. Latimeria chalumnae
GANOID
THERE ARE
OVER DETAIL OF
480 FLESHY FIN

FAMILIES