The Kingdom Animalia is in the domain
Eukarya and in the supergroup Unikonta.
They are in the group Opisthkonta with fungi.
Both groups have different unicellular
organisms that they are their common
ancestor. That fact indicates the groups
became multicellular organisms independent
of one another.
Characteristics of the Animal Kingdom
1. Animals are multicellular, heterotrophic,
ingestive and eukaryotic.
2. The cells lack cell walls and are held
together by structural proteins which are
mostly collagen. They have intracellular
junctions such as tight junctions,
desmosomes and gap junctions.
3. Animal cells have nervous and muscle
tissues found only in this kingdom.
4. Most animals have a diploid life cycle with a
sperm fertilizing an egg. The zygote
undergoes cleavage forming a blastula
(hollow ball of cells). The blastula undergoes
mass movement of cells to form a gastrula
giving rise to three layers of tissue, endoderm,
mesoderm and ectoderm. Often there is a
larval stage to the animal which is sexually
immature. It often will undergo metamorphisis
to become an adult.
5. All animals contain both
the overall body plan of
group of cells) and
homeotic gene) encoding
the genes regulated by the
these genes with an
homeotic genes (any of the genes that control
animal by controlling the developmental fate of a
homeobox (a 180-nucleotide sequence with a
the part of the protein that binds to the DNA of
protein. There is an increase in the number of
increase in the complexity of the animal.
The protists most
closely related to animals
are the
choanoflagellates. It is
flagellated with a collar to collect food. It will form colonies.
Other interesting points about animals
Embryonic development
-Deuterostomes versus protostomes. During development many
animals first form a hollow ball of cells or blastula. Afterward that
there is a mass movement of the cells called gastrulation. This
process results in three layers of tissue being established.
Ectoderm-becomes skin and nervous tissue
Mesoderm-notochord, lining of coelom, kidneys, muscles and bone
and circulatory system
Endoderm-interior lining of organs and liver, pancreas, lungs and
lining of digestive tract.
During this process of gastrulation, the first opening to the gut or
archenteron forms. In deuterostomes, this opening becomes the
anus but in protostomes it becomes the mouth.
Body plans-Asymmetrical-These animals lack orientation like the sponges.
-Radial symmetry-The body plan is around an axis and any
plane going through the axis will produce opposite halves.
-Bilaterial symmetry The body forms a body in a longitudinal
plant that divides the body into two equal but opposite halves.
animals do not have a body
jelly fish
-True coelom-The body
derived from the mesoderm.
-Pseudocoelom-The body
mesoderm on the outer part
the inside. Round worms
Body cavities (coeloms)
-Acoelomate-These
cavity like a flat worm or
cavity is lined with tissue
cavity is lined with
and with endoderm on
have pseudocoeloms.
Clade Parazoa or
sponges-Most closely
related to colonial
choanoflagellates. These
protists and animals have
a common ancestor.
Phylum Porifera
1. Sessile with no
specialized tissue i.e.
nerves or muscle.
2. Size 1 cm-2 m. Mostly
marine species with few
freshwater. The body of a sponge has a cavity called a spongocoel. The body is perforated with
pores. Water flows into the pores and into the spongocoel and then out a larger opening called
the osculum. There are two layers of cells with a gelatinous layer in between called the
mesophyll. The outside of the body is lined with epidermal cells.
3. The pores are lined with cells (porocytes). The inside layer is lined with cells (choanocytes like
choanoflagellates). The flagella of choanocytes beat creating a water current. The choanocyte
cell has a collar with a flagella. It also secretes mucus to filter and catch food. There are also
amoebocytes which take food from the choanocytes and deliver it to the epidermal cells.
4. Sponges are hermaphrodites. Gametes come from amoebocytes and choanocytes. Eggs
reside in the mesohyl and sperm from neighboring sponges fertilize them.
Clade Eumetozoa-Animals with true
tissues.
Clade Radiata-Animals with radial
symmetry (top and bottom with no head or
rear end). Radiata has two tissue layers
ectoderm and endoderm and no
mesoderm resulting in diploblastic
embryos (no mesoderm).
Phylum Cnidaria-Jellyfish and hydra-The
basic body plan is a sac with a
gastrovascular cavity (GVC). The single
opening functions as both the mouth
and the anus. Two variations of this
body plan-the polyp and medusa. The
polyp is a cylinder form that is sessile
and adheres to the bottom of the
water. The medusa is a "flattenedversion of the polyp upside-down". It
moves in the water by drifting and
contracting its bell shaped body.
Some species exists as polyps and
others as medusas and others will
have both forms in their life cycles.
Both forms have two layers of tissue
with a gelatinous layer of material in
between called the mesoglea.
Surrounding the mouth of these animals is a ring of tentacles. These tentacles have stinging
cells called cnidocyte cells. These cells have poisonous, little dart like structures called
nematocysts. No muscles but cell will bundles of contractile fibers. There is also nerve net that
can detect stimuli causing the organism to react. The gastrovascular cavity has specialized cells
that release digestive enzymes to aid in digestion.
Class Hydrozoa-(Portuguese man-of-war, hydras, some corals). Mostly marine. Both medusa
and polyp forms present. Polyp form usually colonial.
Class Scyphozoa-(jellies, sea nettles). All marine. Polyp form greatly reduced. Medusa form up
to 2 m in diameter.
Class Cubozoa-(box jellies, and sea wasp) All marine. Polyp form greatly reduced. Medusa
forms a box like shape with complex eyes and potent venom.
Class Anthozoa-(sea anemones, most corals, and sea fans). Medusa stage completely absent
sessile, many colonial.
Phylum Ctenophora-Superficially looks like cnidarian medusas. These are the comb-jellies.
Small and spherical or ovoid. 8 rows of comblike plates fused cilia.
Clade Bilateria- These animals have bilateral symmetry. Gives animals dorsal and ventral side
as well as an anterior (head) and posterior (tail) end. Cephalization occurred or movement of
sensory organs to the anterior end. The anterior end is first to encounter danger, food and other
important stimuli.
This clade divides up three smaller clades, Deuterostomia, Lophotrochozoa, Ecdysozoa
The first clade are the deuterostomes. The deuterostomes are characterized by their embryonic
development and formation of a deuterostome.
The second clade are the lophotrochozoans either has a lophophore (a crown of ciliated tentacles
function in feeding) or the development of a trochophore larva. The third clade is Ecdysozoa.
These are animals that form an exoskeleton or thick cuticle. As the animals
grow they molt or shed their outer covering (ecdysis).
Clade Lophotrochozoa
Phylum Platyhelminthes: Flatworms
a. Have gastrovascular cavity with pharynx
as mouth on ventral side
b. Acoelomates
c. Nervous system is a pair of ventral nerve
cords. Can have eye spots on anterior end
that responds to light. In the anterior region
one can find a ganglion.
d. Nitrogenous wastes removed by the
Four Classes found in this phylum
Class Tubellaria- Mostly free-living, most
marine, few
terrestrial, predators, scavengers; body surface
ciliated.
Class Monogenea- Marine and freshwater parasites on external surfaces of fish.
Class Trematoda- Flukes are parasites of vertebrates. Complicated life history with intermediate
host.
Class Cestoda-Tapeworms with scolex. No head or digestive system. Complicated life history.
Phylum Rotifera-Rotifers have pseudocoelomates, jaws, crowns of cilia and a complete digestive
tract. Complete digestive tract allows for individual organs and processing of food differently for
maximum extraction of nutrients. While many rotifers are smaller than single-celled protista, they
are much more complicated than even flat worms. Some reproduction in some species is
parthenogenesis.
Phylum Ectoprocta- called moss animals because they resemble moss. Most species are marine
and are small and form colonies. Most of the colony is enclosed in a hard skeleton with the
lophophores that extend through the pores when feeding.
Phylum Brachiopods-Look like clams but stand up vertically. Called lampshells. Attach to bottom
by a stalk. The shells are opened slightly to allow water to flow through lophophores.
Phylum Nemertea-Ribbon worms seem to be acoelomate but contain a fluid filled proboscis sac
which is derived from a true coelom. A proboscis is a long retractable hollow tube at the anterior
end. Used to probe environment, capture
Phylum Mollusca-Soft-bodied animals with shells.
This phylum includes snails, slugs oysters,
clams octopuses and squid. Most are marine
with some fresh-water and terrestrial species.
They have three main parts:
-Muscular foot for locomotion
-Visceral mass that contains most of the internal
organs.
-A mantle, which is a heavy fold of tissue that
surrounds the visceral
mass and secretes the
shell. Many will contain a
radula or rasping tongue
to scrap food from
surfaces. Some species
are monoecious while
others are dioecious.
Gonads are located in the visceral mass. It is possible that mollusks evolved before annelids
because they lack segmentation or from an annelid like ancestor as they both have trochophore
larva. Most have open circulatory systems with a heart. Structures for gas exchange. Ventral
nerve chords with sensory organs.
Class Polyplacophora-This class includes chitons. They have an oval shape with eight dorsal
plates. The cling to rocks with foot a suction cup. They have a radula to gather food.
Class Gastropoda-Snails and slugs. Largest class, mostly marine. Torsion
occurs during development-Uneven growth in visceral mass causes the mass to rotate 180
degrees putting the anus above the head. Body protected by a conical shell. (absent in slugs and
nudibrances). Aquatic species have gills but terrestrial species use the mantel for gas exchange.
Class Bivalvia-contains clams, oysters mussels and scallops. These have a shell divided into two
parts. Held together by two adductor muscles. When open, the foot may be extended for motility
or anchorage. Siphons are used to move water over the gills. Most are filter feeders. Head is
absent and so is radula.
Class Cephalopods-Squids, octopuses, and nautiluses. Agile carnivores. Use a beak to crush
prey. Mantel covers visceral mass. The shell is either reduced, internal/or absent. Squid swim
backwards by drawing water into the mantle and firing the water in a stream through the
excurrent siphon. Directions can be changed by positioning the siphon differently. A giant squid
may reach 17 m longs and weigh 2 tons.
Phylum Annelida-Presence of a true coelom and segmentation are two big advances in this
phylum.
True coelom allows for
-development of complex organ systems
-protect internal structures
-permits internal organs to function separately
from the body wall muscles
-serve as a hydroskeleton
The body of annelids are divided up into many
sections separated by a septa. With the
exception of certain parts most of the sections
are identical to one another. Digestion-complete digestive tract pharynx>esophagus->crop->gizzard->intestine
Closed circulatory system with hemoglobin is
present
-Main dorsal and ventral vessels connected by
longitudinal vessels
-Five pair of hearts and many vessels in the skin
permit gas exchange. Marine annelids have gills
for each body section.
-Excretory system-For each section there is a
pair of metanephridia to remove waste from the
coelomic fluid. They have an external opening to
the outside.
-Reproduction-Hermaphrodites with cross-fertilization. Two earthworms will exchange sperm and
store it temporarily. The clitellum secretes a smooth mucous cocoon, which slides long the worm
picking up its eggs and stored sperm for fertilization. The cocoon slips of the worm and the
embryos develop inside the cocoon.
-Movement involves coordinating longitudinal and circular muscles in each segment with the fluid
filled coelom functioning as a hydrostatic skeleton. Similar to peristaltic waves.
Class Oligochaeta-Earthworms and some aquatic species. Important for breaking down and
fertilizing soil. Important in farming.
Class Polychaeta-Mostly marine species. Some are plankton, some crawl on ocean floor, others
live in tubes. Each segment has a parapodia which are highly vascularize for gas exchange and
motion.
Class Hirudinea-Majority are freshwater with some terrestrial
Many are carnivorous and others are external parasites feeding on blood. -Blade like jaw splits
the skin or drills a hole into the skin.The third clade in the bilaterial clade is Ecdysozoa. which
secretes and molts of an outer covering (ecdysis).
Phylum Nematoda-Round worms. These are nonsegmented pseudocoelomates. A tough cuticle
or exoskeleton covers the body which the worm will periodically shed. Molecular genetics puts its
relationship closer to the arthropods than the annelids.
-Complete digestive tract.
-No circulatory system, fluid in the pseudocoelom is used to deliver food. Many are parasites
and pest of animals and many attack the roots of plants. Pin worms and hook worms are
nematodes. Trichinella spiralis causes trichinosis in humans. Caused by eating undercooked
pork with juvenile worms encysted in the muscle tissue. These develop into adults that burrow
into the human intestinal wall and invades other organs.
Phylum Arthropoda –Most successful animal phyla. Greatest variety of species and more in
terms of numbers than any other animal phyla. Arthropods are covered by a cuticle or an
exoskeleton constructed of layers of protein and chitin.
This can be thin and flexible for the joints and thick and hard for other parts.
-Provide protection and points of attachment for muscles to move appendages.
-Impermeable to water
-It must be shed to the animal to grow and a new one secreted.
Circulation-Open circulatory system with hemolymph
present. Dorsal blood vessel with one way
valves and pores (ostia). The blood enters
the vessel and hearts pull the blood forward.
The blood moves through the hemocoel are
sinuses which are different from the true
coulomb. The true coelom is reduced in
adult arthropods.
-Gas exchange-is varied because the
arthropods are found in many different
environments. Include gills in aquatic
species, tracheal systems in insects and
book lungs in spiders.
Digestive tract is complete with specialized organs. i.e. Grasshopper
-Specialized appendages for mouth
-Foregut and midgut has gastric ceca to secrete digestive enzymes
-Malpighian tubules between midgut and hindgut act like kidneys to reclaim salts and water and
to put nitrogenous wastes into the hindgut
Nervous system is extremely well developed with two ventral nerve cords and extensive
cephalization with many sensory structures clustered at the anterior end. Sense organs include
eyes, olfactory receptors and tactile receptors.
Nervous system is extremely well developed with two ventral nerve cords and extensive
cephalization with many sensory structures clustered at the anterior end. Sense organs include
eyes, olfactory receptors and tactile receptors.
Main LinesTrilobites-Extinct class but important. Extensive segmented but little appendage specialization.
Evolutionary trend in arthropods is to fuse segments and have fewer segments and specialization
of appendages to form antennae, wings, mouth parts and so forth. specialize appendages.
Subphylum Cheliceriformes-have a feeding appendage called a chelicerae. Has a
cephalorthorax and posterior abdomen. Some specialization with appendages.Ex. Horseshoe
crab, arachnids like spiders, scorpions, ticks and mites.
Subphylum Myriapoda-Worm-like arthropods are segments with number of walking legs.
Millipedes have two pair of legs/segment and are nonpoisonous detritus eaters. Centipedes have
one pair of walking legs per segment and are poisonous carnivores.
Subphylum Hexapoda-Body with head, thorax and abdomen. 3 pairs of legs and modified mouth
parts Ex insects and springtails
Subphylum Crustacea-Body with 2-3 parts. Antennae present and chewing mouthparts. 3 or
more pairs of legs. Ex crabs, lobsters and shrimp.
Origins of segmentationTraditional classification suggests that arthropods evolved from annelids based on the superficial
similarities between annelids and centipedes/millipedes but molecular evidence shows this not to
be the case. Segmentation is found in all three major clades of the bilaterial cladeLophotrochozoa-annelids
Ecdysozoa-arthropods
Deuterostomia-chordates
However, in each of these clades there are also phyla that are not segmented.
Segmentation occurs during the development of the embryo. During the course of development
part of the embryo are sectioned off or blocked-out into regions where certain body parts will
develop.
For example each bilateral animal has a particular linear arrangement of anatomical features
along its anterior (head) to posterior axis. Eyes for example are located at the anterior end of the
animal.
Differential expression of various regulatory gene that code for transcription factors play a key
role in the blocking-out of anterior---->posterior anatomy in the developing embryo. The gene of
the Hox complex determine what organs will develop in each segment. For example, differential
expression of various Hox genes along the embryo of lobster cause antennae to develop on
certain segment and walking legs to develop on other segments. But even in non- segmented
animals, such as flatworms, Hox genes determine where certain organs, such as eyes, develop
along the animal's length. In fact, sponges have at least one Hox gene and cnidarian such as
jellies have several. In a cnidarian, for example, expression of a Hox gene determines where
tentacles will develop in the embryo. It can be concluded that the original Hox gene originated
prior to bilateral symmetry. The mechanism for the development of segmented bodies in certain
animal phyla is a variation on a basic regulatory scheme that dates back to the first animals. An
increase in the number of Hox genes through gene duplication and mutations, along with
adaptation of Hox gene function for development of segmented bodies, made it possible for a
great diversity.
Clade Deuterostomia1. Coelom from archenteron surrounded by mesodermal tissue.
2. Formation of the mouth at the opposite that of the anus which developed from blastopore.
Clade Deuterostomia- contains Phylum Echinodermata and Phylum Chordata
Phylum Echinodermata- Echinoderms with a water vascular system and secondary radial
anatomy. Sessile or slow moving animals.
The appendages are in multiples of five
that radiate out from a central disc and
there is a thin skin over hard calcareous
plates.
-Water vascular system. This contains
networks of hydraulic canals branching
into extensive called tube feet that
function in locomotion, feeding and gas
exchange.
There are about 7000 species of
echinoderms. The six recognized classes
are:
1. Class Asteroidea -includes the sea
stars which have five or more arms
extending from a central disc. They have
tube feet on the undersurface of the arms with suction cups at the end of each tube foot. They
are predators that attach tube feet to the prey and the arms of the wrap around the prey
2. Class Ophiuroidea contains the brittle stars which differ from sea stars with smaller central
discs and longer more flexible arms that have no suckers on their tube feet
3. Class Echinoidea contains sea urchins and sand dollars. Sea urchins are spherical while sand
dollars are flattened. These echinoideans lack arms but have five rows of tube feet and muscles.
that pivot their spines for locomotion. They have a complex jaw like structure used for feeding on
seaweeds and other food
4. Class Crinoidea contains the sea lilies which are sessile, living attached to substratum by
stalks. A few are motile and use their arms for a crawling form of locomotion. The arms circle the
mouth and are used in feeding.
5. Class Holothuroidea contains sea cucumbers which have little resemblance to other
echinoderms as they lack spines and the hard endoskeleton is reduced. Their body is elongated.
These species do possess five rows of tube feet, a part of the unique water vascular system and
some tube feet around the mouth have developed into feeding tentacles.
6. Class Concentricycloidea contains the sea daisies which are small (less than 1 cm), disc
shaped marine animals. They live in deep water and do not possess arms. The tube feet are
located around disc margin with water vascular system consisting of two concentric ring canals.