The Invertebrates Phylum Porifera General Characteristics 9,000 species (100 live in fresh water the rest are marine). Sessile, and asymmetrical. Resembles a sac perforated with holes. Porifera (poh-RIF-ur-uh) means “pore bearers.” Water is drawn through the pores into a central cavity spongocoel, then flows out of the sponge through a larger opening called the osculum. This is how the sponge carries out feeding, respiration, circulation, and excretion. Suspension-feeders- collect food particles from the water passed through some kind of food-trapping equipment. Sponges have a simple skeleton. In harder sponges, the skeleton is made up of spicules, (spike-shaped structures), made up of calcium carbonate or glasslike silica. Softer sponges have an internal skeleton of spongin. (bath sponges) Lining the inside of the body are flagellated choanocytes (collar cells). The flagella create a water current, collars trap food particles and ingest them by phagocytosis. Amoebocytes take nutrients to other cells. Sponges can reproduce either sexually or asexually. Most sponges are hermaphroditic and produce both eggs and sperm by meiosis. The eggs are fertilized inside the body (internal fertilization). Sperm are released from one sponge and carried by water currents to another sponge. They form a zygote and later a larva which is motile and uses the water current to settle on the sea floor. This sponge is not genetically identical to its parents. Sponges can reproduce asexually by budding where part of the parent sponge breaks off, settles to the sea floor, and grows into a new sponge. This new sponge is genetically identical to its parent. Least complex of all animals, capable of extensive regeneration (replacement of lost parts). Lack organs, cell layers, no nerves or muscles. Individual cells can sense and react to changes in the environment. Sponges provide habitats for marine animals such as snails, sea stars, and shrimp. Sponges also form partnerships with photosynthetic bacteria, algae, and plantlike protists. (Mutualism both partners benefit). Cnidarians General Characteristics Cnidarians (ny-DAYR-ee-ans) are soft-bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths. They are the simplest animals to have body symmetry and specialized tissues. Members of phylum Cnidaria include hydras, jellyfish, sea anemones and coral animals. Some live as individuals, while others live in colonies in freshwater and oceans. Cnidarians get their name from cnidocytes, or stinging cells, that are located along their tentacles. Cnidarians use these for defense and to capture prey. Within each cnidocyte is a nematocyst. A nematocyst is a poison-filled, stinging structure that contains a tightly coiled dart. When a shrimp or small fish brushes up against the tentacles, thousands of nematocysts explode into the animal, releasing enough poison to paralyze or kill the prey. Form & Function Cnidarians are radially symmetrical. They have a central mouth surrounded by numerous tentacles that extend outward. Cnidarians have a life cycle that includes two different-looking stages: a polyp and a medusa. Polyp Medusa A polyp is a cylindrical body with arm-like tentacles. Polyps are sessile with their mouth pointing upward. A medusa has a motile, bell-shaped body with a mouth on the bottom. Cnidarians have a body wall that surrounds an internal space called a gastrovascular cavity. This is where digestion takes place. Nutrients are transported through the body by diffusion. Cnidarians respire and eliminate their waste by diffusion through their body walls. They are able to gather information from their environment using specialized sensory cells or a nerve net. They can detect stimuli such as light and touch. Reproductive Cycle Cnidarians move in different ways. Sea anemones have a hydrostatic skeleton (layer of circular and longitudinal muscles) while medusas move by jet propulsion. Jellyfish (Class Scyphozoa) means “cup animals.” Jellyfish live their lives primarily as medusas. The polyp form is limited to the larval stage, and no colonies form. Jellyfish reproduce sexually and may grow up to 4 meters in diameter with tentacles more than 30 meters long. Hydras (Class Hydrozoa) contains hydras and other related animals. The polyps of most hydrozoans grow in branching colonies. Within the colony, polyps are specialized to perform different functions. (ex. Portugese man of war). Hydras are different from other cnidarians in their class as they lack a medusa stage. Instead they live as single polyps and reproduce asexually or sexually. Sea Anemones and Corals (Class Anthozoa) These flower animals include the sea anemones and corals, animals that have only the polyp stage in their life cycle. Many species are colonial, or composed of many individual polyps. The Worms The Flatworms The phylum Platyhelminthes (plat-ih-hel-MIN-theez) consists of the flatworms. Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry and cephalization. Flatworms are known as acoelomates meaning without coelom. A coelom is a fluid filled body cavity that is lined with tissue. Flatworms are thin therefore materials can pass easily into and out of their body cells. They rely on diffusion for respiration, excretion, and circulation. Flatworms are free-living or parasitic. Free-living flatworms can be carnivores, or scavengers. They have a digestive cavity with a single opening or a mouth, through which food and wastes pass. Parasitic worms feed on blood, tissue fluids, or pieces of cells within the host’s body. Many parasitic worms obtain nutrients from foods that have already been digested by their host. As a result they have a very simple digestive system. Tapeworms have no digestive system. In free-living flatworms a head encloses several ganglia, or groups of nerve cells, that control the nervous system. Parasitic worms have a less complex nervous system. Free-living flatworms typically move by using cilia on their epidermal cells and through muscle cells. There are three main groups of flatworms; the turbellarians, flukes and tapeworms. Most turbellarians are free-living while the other flatworm species are parasites. Turbellarians The free-living flatworms belong to the class Turbellaria. Most live in marine or fresh water. Most species live in the sand or mud under stones and shells. Planarians are the most familiar flatworms. Flukes Members of the class Trematoda are known as flukes. Flukes are parasitic flatworms. Most flukes infect the internal organs of their host. (ex. The blood fluke Schistosoma mansoni needs two hosts a human and a snail and causes schistosomiasis). Tapeworms Members of the class Cestoda are called tapeworms. Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts. The head of an adult tapeworm contains a scolex with suckers or hooks allowing it to attach to the intestinal wall. Transmitted through intermediate hosts such as cows, fish which are improperly cooked and consumed by humans. The Roundworms The phylum Nematoda, are among the most numerous of all animals. A single rotting apple can contain as many as 90,000 roundworms. Roundworms are slender, unsegmented worms with tapering ends. They range in size from microscopic to a meter in length. Most species are free-living inhabiting soil, salt flats, sediment and water. Many others are parasitic and live in the hosts of almost every kind of plant and animal. Roundworms develop from three germ layers and have a pseudocoelom. It is a false coelom because the body cavity is lined partially with tissue. Unlike flatworms, roundworms have a digestive tract with two openings; a mouth and an anus. Roundworms reproduce sexually and most species have separate sexes. Their response and movement is similar to flatworms. They exchange gases and excrete waste through their body walls using diffusion. Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms. Humans get trichinosis by eating raw or incompletely cooked pork. Causes terrible pain in organs. Filarial worms lead to elephantiasis where the affected part of the body swells enormously. These threadlike worms affect the lymphatic vessels and are transmitted through biting insects. Ascaris lumbricoides is a serious parasite of humans and other vertebrates which causes malnutrition in more than one billion people worldwide. It is spread through eating unwashed vegetables and food. This is why puppies are wormed when they are young. Hookworms affect as many as one-quarter of the population. They live in the soil and use sharp tooth- like plates and hooks to burrow into the skin of an unprotected foot. They enter the bloodstream and suck the host’s blood causing weakness and poor growth. The Segmented Worms Phylum Annelida refers to the ring-like appearance of annelid’s body segments. Earthworms, seaworms and leeches are examples of annelids. Annelids are worms with segmented bodies. They have a true coelom that is lined with the tissue derived from mesoderm. Annelids range from filter feeders to predators. Annelids typically have a closed circulatory system, in which blood is contained within a network of blood vessels. Land-dwelling annelids breathe through their moist skin, while aquatic annelids breathe through their gills. Annelids produce two kinds of waste. Digestive waste passes out the anus. Nitrogenous waste passes out the nephridia. Most annelids have a well developed nervous system consisting of a brain and several nerve cords. Annelids move using two groups of body muscles; longitudinal and circular. Earthworms have bristles called setae to prevent slipping. Marine annelids have paddle-like appendages called parapodia on each segment for swimming and crawling. Most annelids reproduce sexually. Some use external fertilization and have separate sexes. Others are hermaphrodites. They rarely fertilize their own eggs however. Annelids are divided into three classes- oligochaetes, hirudinea, and polychaetes. The class Oligochaeta (AHL-ih-goh-keets) contains earthworms and their relatives. Most live in soil or fresh water, have streamlined bodies and relatively few setae. The class Hirudinea (hir-yoo-DIN-ee-uh) contains the leeches, most of which live in moist habitats in tropical countries. Leeches are external parasites that suck the blood and body fluids of their host. The class Polychaea (PAHL-ih-keets), contains sandworms, bloodworms and their relatives. Polychaetes are marine annelids, that have paired, paddle-like appendages tipped with setae. Phylum Mollusca Phylum Mollusca “soft bodies” Snails and slugs, oysters and clams, and octopuses and squids are all mollusks. 50,000 species mostly marine, some inhabit fresh water and snails / slugs live on land. Mollusks are soft-bodied animals, but most are protected by a hard shell made of calcium carbonate. Squids and octopuses have reduced shells that have been internalized All mollusks have a similar body plan with 3 main parts: a muscular foot, usually for movement, a visceral mass, containing most of the internal organs, and a mantle, a heavy fold of tissue that may secrete a shell. Class Gastropoda The largest of the molluscan classes (40,000 sp) Most gastropods are marine, but there are also many freshwater species and garden snails and slugs that have adapted to land. Protected by single, spiraled shells into which the animals can retreat when threatened. Shell is often conical, sometimes flattened Slugs and sea slugs have lost their shells during their evolution Many have distinct heads with eyes at the tips of tentacles. Gastropods inch along by a rippling motion of the elongated foot. Most gastropods graze on algae or plant material. Several other groups, however, are predators. Aquatic gastropods respire using gills, terrestrial gastropods have a lung. Among the few invertebrate groups to have successfully populated the land. Gastropod Pics Class Bivalvia Include clams, oysters, mussels and scallops. Bivalves have shells divided into two halves. Two parts of the shell are hinged at the mid- dorsal line and powerful adductor muscles draw the two halves tightly together to protect the soft-bodied animal. Bivalves contain gills that are used for feeding as well as gas exchange. Most are suspension feeders, they trap fine food particles in mucus that coats the gills. Water flows into the mantle cavity through the incurrent siphon, passes over the gills and then exits the mantle cavity through an excurrent siphon. No distinct head; lead rather sedentary lives Sessile mussels secrete strong threads that cling to rocks Clams pull themselves into the sand or mud using the muscular foot Scallops dig and skitter along the seafloor by flapping their shells Bilvalve Pics Class Cephalopoda “head foot” Unlike sluggish gastropods and the sedentary bivalves, cephalopods are built for speed, an adaptation that fits their carnivorous diet. Squids and octopuses use beaklike jaws to bite their prey; they then inject poison to immobilize the victim. The mouth is at the center of several long tentacles. The shell is usually either reduced and internal (squids) or missing altogether (octopuses). A squid darts, usually backward by drawing water in and then firing a jet stream of water through the excurrent siphon that points anteriorly. Steers by pointing in different directions. Octopuses live on the seafloor where they creep and scurry about in search of crabs and food. Only mollusks with a closed circulatory system. Have a well developed nervous system with a complex brain. Why? Ability to learn and behave in a complex manner is more critical to fast moving predators. Cephalopod Pics Phylum Arthropoda General Characteristics Arthropoda means “jointed feet.” Nearly one million arthropod species have been described, mostly insects. Most successful phylum of animals, in all habitats. Their success is related to their segmentation, hard exoskeleton, and jointed appendages. All arthropods have the same basic body plan or some variation of it. The body is made up of three segments: the head, thorax, and abdomen. The body of an arthropod is completely covered by a cuticle, an exoskeleton made up of protein and chitin. Exoskeleton can be modified into thick hard armor or paper thin and flexible. One Problem. In order to grow an arthropod must shed its old exoskeleton and secrete a larger one. This process is called molting and it takes a lot of energy and leaves the animal temporarily vulnerable to its environment. The first arthropods appeared in the sea 600 million years ago. Since arthropods have moved to all habitats. They have evolved specialized appendages for feeding, movement and other functions. Arthropods tune into their environment with well developed sensory organs including eyes (simple and compound), olfactory receptors for smell, and antennae for touch and smell. Cephalization is extensive. Arthropods have an open circulatory system where fluid called hemolymph is pumped by the heart through short arteries and then into spaces surrounding organs and tissues. Terrestrial arthropods have a tracheal system which consist of open tubes that connect to the outside by spiracles (pores in the cuticle). Classification Arthropods are classified based on the number and structure of their body segments and appendages- particularly their mouthparts. Arthropods are divided into four subphyla 1. Trilobitomorpha- trilobites (extinct). 2. Chelicerata- spiders, mites & ticks, scorpions. 3. Uniramia- insects, centipedes, millipedes. 4. Crustacea- crabs, lobsters, shrimps, barnacles, crayfish etc. Trilobites Cheliceriformes Uniramia Crustacea Review Questions 1. What is the term for an organism which can produce both sperm and eggs? 2. Why are sponges classified as part of the animal kingdom? 3. Why is it helpful for an organism to be able to reproduce both sexually and asexually? 4. How does a jellyfish obtain food? 5. How has the digestive system of planaria been improved over that of the jellyfish? 6. How does an animal in the phylum Platyhelminthes obtain oxygen? Why is this sufficient for these organisms? 7. A tapeworm is a parasite that lives in the intestines of its host. What system would you expect to be missing from the tapeworm that would be found in other flatworms? By not having this system, the tapeworm has created extra space in its body. How do you think the worm has used this space? 8. How have the digestive systems of the roundworm and segmented worm been improved compared to that of flatworms? 9. What is meant by segmentation? How is segmentation an evolutionary advantage? 10. Some organisms have a circulatory system with blood but the blood has no hemoglobin. What is the function of the blood in these organisms? Why is it an advantage to have hemoglobin in the blood? 11. How is the annelid coelom different from the body cavity of the roundworm. 12. Why is a simple circulatory system important for the earthworm? 13. In a parasitic worm, why would it be useful to be hermaphroditic? 14. Give a possible reason why bivalves have not tended toward cephalization. 15. Why have more complex organisms such as molluscs had to develop gills? 33. How is the circulatory system of most molluscs different from the annelids? Is this unexpected? 34. Describe feeding in the gastropods, bivalves, and cephalopods. 35. How are cephalopods different from other mollusks? 36. Explain how the gills of bivalves perform two separate functions? 37. How is the closed circulatory system an advantage to cephalopods? 38. List some characteristics of arthropods. 39. Why does the presence of an exoskeleton require the presence of jointed appendages? 40. Why is molting necessary? 41. What are the advantages and disadvantages of an exoskeleton? 42. What factors limit the size of the insects?
Pages to are hidden for
"The 20Invertebrates"Please download to view full document