Protista: The Macroalgae or Seaweeds
of the photosynthetic organisms found in the ocean belong to a group
of organisms classified by biologists as Protistans. Protistans
include unicellular organisms such as formaniferans and diatoms—organisms
that may be found in the intertidal zone but that are too small
to be seen with the naked eye. The most familar types of Protistans
are the seaweeds, which are multi-cellular organisms that are more
complex than their unicellular counterparts in the Kingdom Protista.
is an unfortunate term, because these organisms are not weeds. Biologists
prefer the term macroalgae or macrophytes.
Macroalgae are eukaryotic, photosynthesizing multi-cellular organisms
that lack the specialized structures and reproductive mechanisms
characteristic of true plants. Macroalgae lack the true leaves,
stems, and roots of plants but have analagous parts: the thallus,
blades, pneumatocysts, stipe,
and holdfast. The thallus is the complete "body"
of the macroalgae and includes the blades, stipe, and pneumatocysts.
The blades are the leaf-like flattened portions of the thallus,
and the stipe is the stemp-like sstructure that provides support.
The pneumatocysts are gas-filled bladders present on some macroalgae
to help keep the blades near the sunlit surface. A structure that
looks like a root, the holdfast, attaches the thallus to the bottom.
are three types of macroalgae: green algae (Phylum
Chlorophyta), the brown algae
(Phylum Phaeophyta), and the red algae
(Phylum Rhodophyta). The macroalgae in these phyla are distinguished
by the different types of photosynthetic pigments found in their
on the links below to learn more about different types of macroalage
that are found in the intertidal of the Gulf of California. To go
back to the Gallery of Marine Life, click here.
take a practice quiz on the Macroalgae, click here.