Classification of
Organisms
Classification of Organisms
► The
study of the kinds and diversity of
organisms and their evolutionary
relationships is called systematics or
taxonomy
 Taxonomy is the work involved in the original
description of a species.
 Systematics is the assigning of species into
evolutionary groups.
Father of Modern Classification
► The
modern classification system originated
with the work of Carolus Linnaeus
 he recognized the different species could be
grouped into broader categories based on
shared characteristics
 any grouping of animals that shares a particular
set of characteristics forms an assemblage
called a taxon
Modern taxonomists use 7 taxa:
► kingdom,
phylum, class, order, family, genus
and species
 as taxa increase organisms get more specific
Binomial Nomenclature:
► when
a species is talked about only the
genus and species names are used
 this is called the scientific name
 unique to each type of organism
► Required
by the International Code of
Zoological Nomenclature
Writing Scientific Names
► the
genus names is always capitalized
► both names are either italicized or
underlined
 leave a space in the underline between names
ex.
Homo sapien
Felis leo
Quercus rubra
Kingdoms of Life
► In
1969, Robert H. Whitaker classified
kingdoms based on cellular organization and
mode of nutrition
 this lead to the formation of the 5 kingdoms
5 Kingdoms of Classification:
Monera: comprised of bacteria and cyanobacteria
► distinguished by being single cell prokaryotes
Protista: comprised of Amoeba, Paramecium
etc….
► distinguished by being single celled eukaryotes
Plantae: multi-cellular photosynthetic
eukaryotes
► plants have cell walls and are non-motile
5 Kingdoms of Classification:
Fungi: multi-cellular heterotrophic eukaryotes
► fungi have cell walls and usually non-motile
► digest organic matter extra-cellularly (outside of
cell) and absorb the breakdown products
Animalia: multi-cellular heterotrophic eukaryotes
► animal cells lack a cell wall and usually motile
► feed by ingesting other organisms or parts of
other organisms
Monera
prokaryote
single-cell
Protista
eukaryote
multi-cell
Plantae
eukaryote
multi-cell
autotrophic
Fungi
eukaryote
multi-cell
heterotrophic,
external digestion
Animalia
eukaryote
multi-cell
heterotrophic,
internal digestion
DOMAINS???
► Many
taxonomists have pushed the idea
that the five kingdom system isn’t enough
 they feel that organisms share too much
similarities and need to be grouped otherwise
►
the push has led to the addition of 3
domains
3 Domains
1.
Archae: bacteria that live in extreme
conditions
2.
Eubacteria: “true bacteria”
3.
Eukarya: all eukaryotic organisms
Patterns of Organization
► Once
the kingdom of an organism has been
decided other aspects of the organism must
be looked at to determine it’s classification
► Symmetry:
describes how the parts of an
animal are arranged around a point or an
axis
Types of symmetry
► Asymmetry:
the absence of a central
point or axis around which body parts are
equally distributed
 characterizes most protists and many sponges
 not known to be an adaption or advantage to
anything
 organisms do not develop complex
communication, sensory, or locomotor
functions
Types of symmetry
► Radial
Symmetry: arrangement of body
parts such that any plane passing through
the central oral-aboral axis divides the animal
into mirror images
 oral-aboral axis: one point of reference is the
mouth (oral end) and a second point of
reference is the end opposite the mouth (aboral
end)
 often modified by the arrangement of some
structures in pairs , or in other combinations,
around the central oral-aboral axis
Types of symmetry
► Bilateral
Symmetry: the arrangement of
body parts such that a single plane, passing
between upper and lower surfaces and through
the longitudinal axis of an animal, divides the
animal into right and left mirror images.
 characteristic of active, crawling, or swimming
animals
 tend to move in one direction, so one end is generally
more complex
Cephalization: the development or formation of a
distinct head
► Planes
of symmetry are used to describe the
organisms based on the relationships of
body parts
► Not
all animals are easily described and can
be confusing if different people try to
explain them differently
► To
make it simpler some terms have been
universally adopted.
Terms of Directions:
► Aboral:
► Oral:
► Anterior:
► Posterior:
► Caudal:
► Cephalic:
► Distal:
the end opposite the mouth
the end containing the mouth
the head end; usually the end of
a bilateral animal that meets its
environment
the tail end
toward the tail
toward the head
away from the point of
attachment of a structure on the
body (the toes are distal to the knee)
Terms of Directions:
toward the point of attachment of a
structure on the body (the hip is proximal
to the knee)
► Dorsal:
the back of an animal; usually the upper
surface; synonymous with posterior for
animals that walk upright
► Ventral:
the belly of an animal; usually the lower
surface; synonymous with anterior for
animals that walk upright
► Inferior:
below a point of reference (the mouth is
inferior to the nose in humans)
► Superior:
above the point of reference (the neck is
superior to the chest)
► Lateral:
away from the plane that divides a bilateral
animal into mirror images
► Medial (median):
on or near the plane that divides a
bilateral animal into mirror images
►
Proximal:
Other Patterns of Organization
1.
Unicellular (Cytoplasmic) level: all
single celled organisms




characteristic body plan of the Protista
is not “simple”
must provide for locomotion, food acquisition,
digestion, water and ion regulation, sensory
perception, and reproduction all in a single cell
colonies can exist, but show little signs of
interdependence, cooperation, or coordination
of function
Other Patterns of Organization
Diploblastic Organization: simplest tissue-level
organization
2.
 tissue is derived from two embryonic layers
A. Ectoderm: gives rise to the epidermis, the outer
layer of the body wall
►
composed of epithelial and muscular cells
B. Endoderm: gives rise to the gastrodermis, the
tissue that lines the gut cavity
►


composed of digestive and muscular cells
between the epidermis and gastrodermis is the
mesoglea, a noncellular layer
cells in each layer are functionally interdependent
Other Patterns of Organization
3.
Triploblastic Organization: tissues are
derived from three embryological layers



like diploblastic, the ectoderm forms the
outer layer and the endoderm lines the gut
in between these two layers is the
mesoderm: which gives rise to supportive,
contractile, and blood cells
most organisms have organ-system level of
organization
Triploblastic Subgroups
►
Based on the presence of and what kind of
body cavity they have.
Body Cavity: a fluid-filled space in which the
internal organs can be suspended and
separated from the body wall
Why are Body Cavities
advantageous?
1.
2.
3.
4.
5.
6.
Provide more room for organ development.
Provide more surface area for diffusion of gases,
nutrients, and wastes into and out of organs
Provide and area for storage.
Often act as hydrostatic skeletons.
Provide a vehicle for eliminating wastes and
reproductive products from the body
Facilitate increased body size.
Triploblastic Subgroups:
A.
Triploblastic Acoelemate Pattern: the
mesoderm layer is a relatively solid mass
of cells between ectodermal and
endodermal layers


acoelemate means “without” a “cavity”
some of the mesodermal cells are
parenchyma: loosely organized cells not
specialized for a specific function
Triploblastic Subgroups:
B.
Triploblastic Pseudocoelemate Pattern:




pseudocoelom: a body cavity not entirely lined
by mesoderm
No muscular or connective tissues are
associated with the gut tract
No mesodermal sheet covers the inner surface
of the body wall
No membranes suspend organs in the body
cavity
Triploblastic Subgroups:
C.
Triploblastic Coelemate Pattern:



coelem: a body cavity completely surrounded
by mesoderm
peritoneum: thin mesodermal sheet that
lines the inner body wall .
serosa: thin mesodermal sheet that lines the
outside of visceral organs.
►
►
peritoneum and serosa are continuous and
suspend visceral organs in the body cavity.
mesentery: the suspending sheets of organisms.
Three major groups of the
Animal Kingdom:
Mesozoa: includes phylum Mesozoa, or the
mesozoans
B. Parazoa: includes phylum Porifera, or the
sponges
C. Eumetazoa: includes all other phyla
A.
Eumetazoa are further divided into two groups
based on body symmetry
►


Radiata: animals that have radial symmetry
Bilateria: animals that have bilateral symmetry
► Bilateria
animals are divided into two group
based on embryological characteristics
Comparative Embryology: studies based
on the observation that embryological
events may be similar because of shared
ancestry
Two Bilateria Groups:
A.
B.
Protostomes: include animals in the
phyla Platyhelminthes, Nematoda,
Mollusca, Annelida, Arthropoda, and others
Deuterstomes: include animals in the
phyla Echinodermatat, Hemichrodata,
Chordata, and others.