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Systematics
Systematics is the science of categorizing organisms into like groups and
establishing their relationship relative to each other.
Seven major categories are used to classify organisms:
kingdom
phylum
class
order
family
genus
species
Systematics
In case of humans:
kingdom: Animalia
phylum: Chordata
class:
Mammalia
order: Primates
family:
genus:
Hominidae
Homo
species: sapiens
Note that Homo sapiens is italicized. Another acceptable notation would be to
underline the Genus and species… Also note that the first letter of the Genus is
capitalized, whereas the species is not.
Systematics – Domains and Kingdoms
Note that Taxonomies are constantly changing. Part of the reason is new information
(mostly based on molecular biology) being discovered about different groups.
Here for example, it is suggested that there should be three Domains, each of which
would then contain the various Kingdoms. Other suggested changes are occurring at
the other taxonomic levels of classification…
Systematics –Kingdoms
Relationships are not quite as
simple as suggested by this figure.
Ideally, each branch point is where a new form
(i.e. adaptation) has created two distinct forms
from a single common ancestor.
Kingdom Animalia
Animal features:
1. Multicellular
2. Heterotrophic
3. Lack cell walls
4. Motile (at least at some stage of life)
5. Typically can reproduce sexually
(although there is a lot of variation)
6. Most can rapidly respond to external stimuli
Kingdom Animalia – Phylum Porifera
Phylum Porifera – Sponges (9000-10,000 species)
General features:
Cellular level of organization with no tissues or organs
Adults are typically asymmetrical
Cells tend to be totipotent
Can reproduce sexually or asexually
Adults are sessile suspension-feeders; larval stages are motile
Skeletal elements, when present, composed of calcium carbonate,
silicon dioxide, and/or collagen fibers
An ancient group, probably originated from flagellated protist
ancestors
Kingdom Animalia – Phylum Porifera
Sponges are essentially made up of a loose aggregate of cells… You could even pass
a sponge through a mesh, and the individual cells would come back
together to reform the animal.
Kingdom Animalia – Poriferan Body Plan
Kingdom Animalia – Poriferan Body Plan
Choanocytes (collar cells) produce water flow through the sponge body.
Why is water flow such an important part of biology of sponges?
Feeding
Waste removal
Gas exchange
Reproduction
Kingdom Animalia – Poriferan Body Plan
Sponges depend on the water flow
for every aspect of their lives.
The only way they can get larger is
by creating complex series of water
canals throughout the body.
The different body forms are:
A. asconid
B. simple syconoid
C. complex syconoid
D. leuconoid
Kingdom Animalia – Poriferan Body Plan - Spicules
Sponges use spicules made up of
silicon dioxide and calcium carbonate
for both structural support as well as
for defense against potential predators.
Cells called sclerocytes are responsible
for producing the spicules.
The spicules can have many forms.
They vary from one species to the
next, and have different shapes, sizes,
forms, and make-ups.
In addition to the spicules, sponges
use layers of the protein collagen
for additional structural support.
this intercellular matrix is referred
to as the spongin.
Kingdom Animalia – Porifera
Sponge Classification:
1.
Class Calcarea Sponges with calcium carbonate spicules.
2. Class Demospongiae –
Sponges with siliceous spicules, spongin fibers, or
both. Approximately 90% of all poriferans, they
include boring sponges, bath sponges, and many
other forms…
3. Class Hexactinellida –
Deep water sponges with siliceous six-pointed
spicules and long siliceous fibers… includes the
Genus Euplectella, or the Venus’s flower basket.
Kingdom Animalia – Porifera
Sponges are often very
colorful. Why do you think
this is?
Kingdom Animalia – Cnidaria
corals, sea anemones, jelly fish, box jellies, hydra, sea fans
Phylum Cnidaria (~3000 species); general characteristics:
Have tissue level of organization, with two tissue layers (diploblastic)
Have radial symmetry
Have specialized stinging structures called cnidae
Have only one opening to the body cavity / digestive cavity
Have no head, no centralized nervous system (only a nerve net), no
discrete gas exchange, excretory, or circulatory systems
Exhibit alternation of asexual polypoid and sexual medusoid generations.
Kingdom Animalia – Cnidaria
General body forms
2 body forms: Polyp and Medusa
2 tissue layers (diploblastic), ectoderm
to the outside (blue), and endoderm
to the inside (yellow). The layer in
between is just a jelly-like material
called the mesoglea (it is not a true
tissue)
Only one opening to the
gastrovascular cavity acts as mouth
and anus
Kingdom Animalia – Cnidaria
General body forms
Cnidarians have radial symmetry:
Kingdom Animalia – Cnidaria
All cnidarians have specialized stinging or adhesive structures called cnidae
Discharge
acceleration is
at 40,000g!!!
When triggered, the the cnidocyte cells
discharge the cnidae. A specialized form
of cnidae called the nematocyst, has a
harpoon like structure that enters the
flesh of the potential predator or prey,
releasing neurotoxins.
Need both physical and chemical stimulation to induce release. Why do you think this is?
Kingdom Animalia – Cnidaria
No matter what the size or shape of the cnidarian, they all have cnidae, and they
are all made up of one or more of polyp or medusoid body forms
Kingdom Animalia – Cnidaria
In general, cnidarians
alternate between
sexual medusoid and
asexual polypoid forms
There are a lot of
exceptions though…
Kingdom Animalia – Cnidarian Classification
1. Class Hydrozoa – Both polyp and medusa present, with both marine and freshwater
forms represented. Includes hydra, siphonophora, and the
Portuguese man-of-war.
Kingdom Animalia – Cnidarian Classification
2. Class Anthozoa – Medusa absent, these are entirely marine cnidaria including corals,
sea anemones, sea fans, sea pens, and zoanthids.
Kingdom Animalia – Cnidarian Classification
3. Class Scyphozoa - Medusa dominant (although both body forms are present), these
are entirely marine cnidaria including the jelly fish.
Kingdom Animalia – Cnidarian Classification
4. Class Cubozoa – Meduasa cuboidal in shape, these marine cnidaria include the
box jellies.
Kingdom Animalia – Cnidarian Diversity
Hydra
Box jelly
Corals
Sea pen
Jelly fish
Zoanthids
Sea fan
Sea anemone
Kingdom Animalia – Symbiosis in Cnidaria
Many cnidarians live in symbiosis with unicellular algae… This symbiosis may
be the reason for their great success in otherwise nutrient poor waters of the tropics...
Kingdom Animalia – Platyhelminthes
Phylum Platyhelminthes – flat worms (~20,000 species); general characteristics:
Have tissue level of organization, with three tissue layers (triploblastic – with
endoderm, ectoderm, and mesoderm)
Have bilateral symmetry
Have only one opening to the body cavity / digestive cavity
Have cephalization (and at least at some stage of their lives, so will all the animals that
we’ll discuss from now on).
Are hermaphroditic, with complex reproductive systems
Can be free-living or parasitic
Have great regenerative abilities!!!