ZOOLOGY CHAPTER 9
ARCHITECTURAL PATTERN OF AN
ANIMAL
Zoologists today recognize 32
phyla of multicellular animals, each
phylum characterized by a
distinctive body plan and biological
properties that set it apart from all
other phyla.
All are survivors of perhaps 100
phyla that appeared 600 million
years ago during the Cambrian
explosion, the most important
evolutionary event in the
geological history of life.
The basic uniformity of biological
organization derives from the
common ancestry of animals and
from their cellular construction.
9.1 HIERARCHICAL ORGANIZATION
OF ANIMAL COMPLEXITY
The unicellular groups- are the
simplest eukaryotic organisms and
represent the protoplasmic grade of
organization. They are nonetheless
complete organisms that perform all
functions of life seen in more complex
animals.
The multicellular animals- evolved
greater structural complexity by
combining cells into larger units. An
animal cell is a specialized part of the
whole organism and, unlike a
unicellular organism, it is not capable
of independent existence.
The simplest metazoans show the
cellular grade of organization, in which
cells demonstrate division of labor but
are not strongly associated with
performing a specific collective
function.
In the more complex cell-tissue grade
of organization, cells are grouped
together and perform their common
functions as a highly coordinated unit
called a tissue.
Animals at or beyond the cell-tissue
grade of the organization are termed
eumetazoans.
In animals of the tissue-organ grade
organization, tissues are assembled
into still larger functional units called
organs.
The chief functional cells of an organ
are called parenchyma.
The supportive tissues are its stroma.
Most animals have an additional level
of complexity in which different organs
operate together as organ systems.
9.2 ANIMAL BODY PLANS
Animal Symmetry
Symmetry- refers to balanced
proportions, or correspondence in size
and shape of parts on opposite sides
of a median plane.
Spherical symmetry means that any
plane passing through the center
divides a body into equivalent, or
mirrored, halves. This type of
symmetry occurs among some
unicellular forms and is rare in
animals.
Radial symmetry applies to forms
that can be divided into similar halves
by more than two plane passing
through the longitudinal axis, as might
be achieved when slicing a pie. These
are tubular, vase, or bowl shapes
found in some sponges and in hydras,
jellyfish, sea urchins, and related
1
BS.BIO-YC || XAVIER ATENEO DE CAGAYAN
