Page 236 - (DK) Ocean - The Definitive Visual Guide

234 CHROMISTS

Chromists GIANT CHROMISTS
The largest chromists are brown seaweeds
called kelps. Firmly attached to rocks, they
are seen flourishing in this clear, shallow
MOST CHROMISTS are microscopic
DOMAIN Eucarya water along the coast of South America.
in size, including many of the
PHYLA At least 11
important photosynthetic
SPECIES 31,200
plankton groups such as diatoms.
However, brown seaweeds, which can grow to a huge
size, are also chromists and unlike green seaweeds are not
considered to be true plants. Like true plants, chromists
make their own food by photosynthesis but they use
different pigments to capture the sun’s energy.

Anatomy

Brown seaweeds and the various kinds of microscopic
chromists all have very different shapes and structures.
Their shared characteristics are at the cellular level.
Chromists use an additional type of chlorophyll
(a pigment) for photosynthesis and, unlike true
plants, the food they manufacture is not stored as
starch. They also have other colored pigments,
which give brown seaweeds their color. Like green
and red seaweeds, brown seaweeds do not need roots
to absorb water and nutrients. Some have stiff stalks
(stipes) and gas-filled bladders (pneumatophores)
that hold up their leaflike fronds to the light. Some
microscopic chromists, such as diatoms, have a rigid BROWN SEAWEED
In place of roots, brown seaweeds
outer skeleton and float passively. Others, including
have a holdfast which acts as an
dinoflagellates, can propel themselves along using anchor. In this one, called Laminaria
whiplike threads called flagella. hyperborea, the holdfast is a small disk.
DIFFERENT SHAPES
There are thousands
of species of diatoms.
Each has a differently
shaped silica skeleton.

CHROMIST OR
PROTIST?
Scientists used to place all
single-celled eukaryotes including
microalgae, protozoans, and
chromists in one taxonomic
OCEAN LIFE DRIFTING to indicate any of these diverse
group, the Protista. Today the
term protist is used informally
unicellular organisms. But there is
PLANKTON
no final agreement as to whether
Radiolarians use their
all the organisms included as
delicate arms to trap
chromists in this book really
food particles and aid
belong together in this kingdom.
buoyancy as they float
in the plankton.