The mouth or anus are the two groups named after them.
This difference shows the fate of a structure called the blastopore, which becomes the mouth in the embryo and the anus in the embryo.
The mode of formation of the coelom and the early cell division of the embryo are differences between deuterostomes and Protostomes.
Eucoelomates can be divided into two groups based on their early development.
The way in which the coelom is formed and the origin of the mouth opening are two of the differences.
The kingdom of animals is divided into two groups, those with a backbone and those without.
Most of the animal species we are familiar with are invertebrates.
There are millions of species of animals in thevertebrates, which we can just begin to talk about here.
The sponges and the cnidarians are the simplest of animals.
Sponges appear to be an early stage of multicellularity in the animal clade.
They lack true tissues in which specialized cells are organized into functional groups.
The ancestors of animals might have been colonial, flagellated protists.
The simplest animal group that displays true tissues is the cnidarians, which have only two tissue layers.
The majority of sponges are marine.
The sponge's body structure is designed to move water through the body so it can eliminate waste, absorb dissolved oxygen, and filter out food.
The simplest animals are found in the Sponges.
The body wall has many pores.
Food particles are trapped in mucus produced by the sieve-like collar of the choanocytes.
The basic body plan of the sponge is shown.
sponges have persisted on Earth for more than half a billion years, despite their lack of complexity.
sponges depend on their choanocytes for their energy intake because of the lack of a true digestive system.
Food particles must be smaller than individual cells in this type of digestion.
Sponges reproduce both sexually and asexually.
Gemmules can grow into a new sponge in hostile environments.
Eggs may be produced first, followed by sperm later.
Eggs are retained within the spongocoel, whereas sperm are ejected through the osculum.
The sperm is carried by water currents.
The free-swimming larvae are released through the osculum.
sponges only exhibit mobility during this time.
As adults, sponges are attached to a fixed surface.
The video shows the feeding of sponges.
Almost all of the cnidarians are marine species.
Diversity of animals can cause toxins to be used in prey.
Nematocysts may have coiled threads.
The projection on the outer wall of the cell is sensitive to touch.
Animals from the Cnidaria have stinging cells.
There are nematocysts that hold a coiled thread and barb.
The thread, barb, and toxin are fired from the organelle when hairlike projections on the cell surface are touched.
As adults, polyps have a single opening to the digestive system, facing up with tentacles surrounding it.
The mouth and tentacles are hanging from the bell-shaped body.
The life cycle of other cnidarians alternates between the polyp and medusa forms.
The medusa and the polyp are the two distinct body plans of cnidarians.
All cnidarians have two tissue layers.
There are two tissue layers for all cnidarians.
The OpenStax book is free and can be found at http://cnx.org/content/col11487/1.9 differentiated cell types in each tissue layer.
The organs and organ systems are not present in this picture.
Nerve cells are scattered across the body in a network.
The function of the nerve cells is to carry signals.
Nerve cords are formed by cells in the nerve net.
A mouth and an anus are served by the only opening in the stomach.
There are four classes of Anthozoa, Scyphozoa, Cubozoa, and Hydrozoa in the Cnidaria.
There is no medusa stage within the life cycle of cnidarians that exhibit a sessile polyp body plan.
Some examples include sea anemones, sea pens, and corals.
Sea anemones can grow up to 10 cm in diameter and are usually brightly colored.
These animals are attached to something.
Class Anthozoa has sea anemones.
Scyphozoans are motile and exclusive to the marine with about 200 species.
The medusa is the most important stage in the life cycle.
The scyphozoans include the jellies.
Use this from the New England Aquarium to identify the life cycle stages of jellies.
The species can achieve sizes of 15 to 25 cm.
The Cubozoans are similar to the Jellyfish.
The arrangement of the tentacles is different between the two classes.
Cubozoans have muscular pads called pedalia at the corners of the square bell canopy.
In some cases, the bicyle may extend into the pedalia.
Cubozoans can be found in a polyp form.
The medusoid forms may be formed by the bud of the polyps.
You can learn more about the toxins of the box jellyfish in this video.
Most of the species in Hydrozoa are marine.
Most species in this class have both medusa and polyp forms.
colonies are composed of branches of specialized polyps Other species are solitary medusae.
An example from class Cubozoa is a box Jelly.
The class Hydrozoa has the (b) hydra.
The animal's embryo is sandwiched between the ectoderm and the endoderm.
The right and left sides of these phyla are mirror images of each other, and they are bilaterally symmetrical.
The evolution of a concentration of nervous tissues and sensory organs in the head of the organisms is associated with bilateralism.
The flatworms are acoelomate organisms.
The arthropods, one of the most successful groups on the planet, are coelomate organisms with hard appendages.
The arthropods and the nematodes are related to one another.
The ecdysozoan phyla need to be periodically shed and replaced for them to increase in size.
The relationships among flatworms are being revised and the description here will follow the traditional groupings.
Important parasites of humans are included in most flatworms.
Flatworms have three germ layers that cover tissues, internal tissues, and the lining of the digestive system.
A layer of circular muscle is covered by a layer of fused cells in the epidermal tissue.
The support cells and secretory cells are in the skin.
The flatworms' bodies are made of acoelomates, so they don't have any spaces between the outer surface and the inner digestive tract.
Flatworms are scavengers, whereas parasites feed from their hosts.
Some species have an anal opening.
The gut can be a simple sac or highly branched.
Digestion is caused by cells lining the tract and taking in materials from the same cells.
The cestodes don't have a digestive system because of their lifestyle and environment, which allows them to absorb vitamins and minerals directly across their body wall.
Flatworms have an excretory system with a network of tubules throughout the body that open to the environment and nearby flame cells.
The system regulates dissolved salts and excretion of nitrogenous waste.
The nervous system consists of a pair of nerve cords running the length of the body with connections between them and a large ganglion or concentration of nerve cells at the anterior end of the worm.
A planarian is a flatworm that has an incomplete digestion, an excretory system with a network of tubules throughout the body, and a nervous system with a concentration of nerves and photosensory and chemosensory cells.
Since there is no respiratory system, the exchange of gas and food is dependent on the junctions between cells.
This limits the thickness of the body in these organisms, which makes them "flat" worms.
The majority of flatworm species are monoecious, with both sets of sex organs.
Asexual reproduction is common in some groups in which an entire organisms can be regenerated.
Turbellarians include mainly free-living marine species, although some species live in freshwater or moist environments.
The planarians found in freshwater ponds are examples.
The underside of turbellarians is ciliated, which helps them move.
Turbellarians are capable of regenerating their body from a small fragment.
The monogeneans are external parasites of fish with life cycles consisting of a free-swimming larva that attach to a fish to begin transformation to the adult form.
They only have one host during their life.
The worms can produce enzymes that can be used to digest the host tissues.
It is normal for monogeneans to mate between individuals and not to self-fertilize.
Humans are parasites of mollusks and other groups.
The life cycles of trematodes involve a primary host in which sexual reproduction occurs and one or more secondary hosts in which asexual reproduction occurs.
The primary host is usually a mollusk.
200 million people in the tropics are affected by the disease, which leads to organ damage and chronic symptoms.
When a human enters the water, a larva is released from the primary snail host and can locate and penetrate the skin.
The parasites feed on red blood cells before they reproduce.
Many of the eggs are released in feces and find their way into a waterway where they are able to control the primary snail host.
The tapeworms are internal parasites.
The tapeworm's body is fixed using a sucker on the anterior end of the body.
The remaining body of the tapeworm is made up of a long series of units called proglottids, each of which may contain an excretory system with flame cells, but will contain reproductive structures, both male and female.
Tapeworms don't have a digestive system, so they absorb the nutrition from the food they eat.
When new proglottids form, they are pushed to the end of the tapeworm, at which point they are "mature" and all structures except fertilized eggs have died.
The proglottid is released from the host's feces.
An intermediate host eats fertilized eggs.
The worms take up residence in the muscle tissue of the intermediate host.
The cycle is completed when the primary host eats the muscle tissue.
Humans can acquire tapeworm parasites from eating pork, beef, and fish.
The slender tubes are similar to each other.
The nematode body is encased in a cuticle, a flexible but tough skeleton, which protects and supports it.
The animal must be continually shed and replaced as it increases in size because of the protection provided by the exoskeleton.
A nematode's mouth has three or six lips and teeth in the form of cuticular extensions.
A sharp stylet that protrudes from the mouth can be used to stab prey.
The rectum and anal opening can be found at the end of the mouth.
The excretory system is not specialized in nematodes.
Nitrogenous waste are removed.
The regulation of water and salt is achieved by specialized glands that remove unwanted cations.
There are four nerve cords that run along the length of the body.
The nerve cords are fused in a ring around the pharynx to form a brain of the worm.
Beneath the skin lies a layer of longitudinal muscles that allow only side-to-side undulation of the body.
Nematode can be seen moving about and feeding onbacteria in this video.
Each of the enormous number of species belonging to this phylum is described by the name "arthropoda."
The main characteristics of all the animals in this phylum are functional segmentation of the body and the presence of jointed appendages.
In terms of the number of species, arthropod is the largest group in the animal world.
The prostostomic development of arthropods is true coelomate.
The arthropods in this fossil are extinct.
A unique feature of arthropods is the presence of a segmented body with different sets of segments giving rise to functional segments.
A head, thorax, and abdomen can be formed by fused segments.
A two-chambered heart regulates the open circulatory system, in which blood bathes the internal organs rather than circulating in vessels.
The book lungs of arachnids have internal stacks of alternating air pockets and hemocoel tissue shaped like a book.
The book lungs of arachnids are made up of alternating air pockets and hemocoel tissue shaped like a stack of books.
The book gills of crustaceans are similar to book lungs but are external so that gas exchange can occur with the surrounding water.
There are animals that have been successful in colonizing habitats.
Trilobitomorpha is one of the subphyla that includes Myriapoda, centipedes, and relatives.
The Trilobites are a group of arthropods that were extinct until the end of the Permian period.
The fossils have identified 17,000 species.
The name suggests that the Hexapoda have six legs.
The thorax has wings and three pairs of legs.
The insects we encounter on a daily basis are examples of Hexapoda.
The insects have a developed digestive system, a respiratory system, a circulatory system, and a nervous system.
There are arthropods with legs that can vary in number from 10 to 750.
The most common examples are centipedes and millipedes.
There are about 47,000 crustaceans described.
Blood is pumped into the hemocoel by the heart of a crustacean.
Some crustaceans, like barnacles, may be hermaphroditic.
Some crustaceans have serial hermaphroditism, in which the gonad can switch from producing sperm to ova.
Early stages of development are seen in many crustaceans.
Detritivores and filter feeders are common in crustaceans.
An example of a crustacean is the crayfish.
There is a carapace around the heart in the thorax area.
There are an estimated 103,000 described species.
A distinct "head" is not always visible when the body of Cheicerates is divided into two parts.
In spiders, they inject venom into their prey in order to get them to eat.
A tube-like heart that pumps blood into the large hemocoel bathes the internal organs in blood.
Terrestrial species use either the book lungs or the tracheae for gaseous exchange, whereas aquatic species use gill respiration.
The "number of living species in Australia and the World" was last modified on August 26, 2010.
The "number of living species in Australia and the World" was last modified on August 26, 2010.