15.2 Sponges and Cnidarians

• 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.