Page 20 - Fish and Amphibians (Britannica Illustrated Science Library)

16 GENERAL CHARACTERISTICS FISH AND AMPHIBIANS 17

Anatomy SIMPLE EYE BRAIN SPINAL CORD DORSAL DORSAL MUSCULATURE THE SURFACE AREA OF THE GILLS
around the spinal 10
Each eye focuses to one side;
is concentrated
receives information
FIN
AORTA
IS 10 TIMES THE SURFACE AREA
there is no binocular vision. and coordinates all OF THE REST OF THE FISH.
the fish's actions column and the tail.
Retina
ost fish have the same internal organs as amphibians, Suspensory and functions.
ligament LATERAL LINE CAUDAL FIN
reptiles, birds, and mammals. The skeleton acts as a Lens Optic has sensitive is divided into
nerve
M support, and the brain receives information through Iris receptors that symmetrical
are connected lobes.
the eyes and the lateral line to coordinate the motions of the to the brain.
muscles in propelling the fish through the water. Fish breathe
with gills, they have a digestive system designed to
transform food into nutrients, and they have a heart that
pumps blood through a network of blood vessels.

Cyclostomata THE CURRENT BROWN
Its digestive tract is little more than 45 NUMBER OF SPECIES MOUTH GILLS TROUT
a straight tube extending from its OF CYCLOSTOMATA Structures Salmo fario
round, jawless mouth to the anus. with multiple HEART STOMACH SWIM BLADDER ANUS ANAL
Because of their simplicity, folds that receives all
A gland fills it with gas An opening for the FIN
many species of lampreys provide oxygen the blood and
LIVER INTESTINE and empties it to regulate expulsion of feces, urine,
are parasites. They live EYE to the blood pumps it toward
CAUDAL swimming altitude. and reproductive fluid
off the blood of other the gills.
fish and have thin FIN BREATHING
pharyngeal SACS
sacs instead ANUS Osteichthyes REGULATION OF SALINITY
of gills. FRESHWATER FISH Salt SALTWATER FISH Water Water outlet
HEART Typically, their organs are absorption
compressed in the lower front Freshwater fish run These fish intake
quarter of the body. The rest of the risk of losing salt constantly absorb
FIRST to their environment. salt water to
LIVER their internal structure consists
DORSAL
mainly of the muscles that the They drink only a replenish the water
FIN
fish uses to swim. Some bony small quantity of in their bodies, but
TOOTHED fish, such as carp, have no water, and they Water intake Elimination of they must eliminate
MOUTH stomach but rather a tightly obtain additional salt water in urine excess salt from the Excretion of salts Excretion of salts
coiled intestine. from their food. marine environment. through the gills through urine
LAMPREY
Lampetra sp. INTESTINE
SUPPORT FOR NOTOCHORD INTESTINE SPERM SEMINAL MUSCLE
PHARYNGEAL SACS CONDUITS VESICLE SEGMENTS
TESTICLES
DORSAL RECTAL SECOND UPPER
AORTA GLAND DORSAL FIN CAUDAL LOBE
VERTEBRAE
STOMACH
BRAIN
RIGHT
KIDNEY
GONAD

620
Chondrichthyes
A shark has the same organic KNOWN SPECIES OF
structures as a bony fish, except for CHONDRICHTHYES
NASAL PIT
the swim bladder. A shark also has a
corkscrew-like structure called a spiral LOWER
valve at the end of its intestine to SHARK GILL PECTORAL SPIRAL ANAL CAUDAL
increase the surface area for
Carcharodon sp. MOUTH SLITS HEART LIVER STOMACH FIN VALVE CLOACA KIDNEY FIN LOBE
absorption of nutrients.