3. Molluscs can be divided
into three categories:
Uni-valve molluscs have one shell—periwinkles, whelks
and limpets. These molluscs can be found on the
seashore.
periwinkles whelks limpets
4. molluscs
Bi-valve molluscs have two shells hinged at one end—
mussels, oysters and scallops.
mussels oysters scallops
5. Cephalopods
Cephalopods have no outer shell, just a single internal
one called a pen. Examples include squid and cuttlefish.
squid cuttlefish
6. Crustaceans
Crustaceans are mobile creatures with hard, segmented
shells and flexible joints. Examples include prawns,
shrimp, crab and lobster.
lobster
shrimp prawns crab
7. Finfish
Finfish are divided into whitefish and oil-rich fish.
oil-rich fish
whitefish
8. Whitefish
Whitefish are sometimes referred to as "lean fish"
because all the oils are contained in the liver, which is
removed during gutting
lean fish
9. Whitefish are further sub-
divided into:
Round Whitefish—Examples include cod, haddock,
hake and pollock.
hake
pollock
haddock
cod
10. Flat Whitefish
Flat Whitefish—Examples include plaice, lemon sole,
brill, turbot and black sole.
lemon sole turbot
black sole brill
plaice
11. Cartilaginous Fish
Cartilaginous Fish—Examples include ray, dogfish,
shark.
ray dogfish
shark
12. Oil-Rich fish
Oil-Rich fish are so called because the oils are
distributed throughout the flesh of the fish. Mackerel,
herring, salmon and trout are examples.
herring salmon
mackerel trout
13. Finfish, Demersal and
Pelagic fish
Finfish are occasionally classified in a different way—
according to where they swim in the sea.
Demersal fish are those which live on or near the seabed.
Round and flat whitefish fall into this category.
Pelagic fish swim in mid-waters or near the surface.
Examples are oil-rich fish such as mackerel, herring and
tuna.
