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Comparing Invertebrates What is an Animal? Animals, members of the kingdom Animalia, are multicellular, eukaryotic heterotrophs whose cells lack cell walls Invertebrates are animals that have no backbone, or vertebral column Includes over 95% of all animal species Vertebrates are animals that have a backbone Includes 5% of all animal species Modern Evolutionary Relationships Cladogram indicating the sequence in which important invertebrate features evolved What Animals Do to Survive Animals carry out the following essential functions: 1. 2. 3. 4. 5. 6. 7. Feeding – herbivores, carnivores, omnivores, detritivores Respiration – take in O2 and give off CO2 Circulation – diffusion, closed/open circulatory system Excretion – ridding the body of liquid and solid wastes Response – nervous systems Movement – sessile or mobile Reproduction – asexual or sexual Trends in Animal Evolution Complex animals tend to have high levels of cell specialization and internal body organization, bilateral body symmetry, a front end or head with sense organs, and a body cavity Trends in Animal Evolution mollusks echinoderms roundworms flatworms cnidarians sponges annelids arthropods chordates Early Development Animals that reproduce sexually begin life as a zygote (fertilized egg) The zygote undergoes a series of divisions (cleavage) to form a blastula (hollow ball of cells) The blastopore leads to a central tube that becomes the digestive tract A protostome is an animal whose mouth is formed from a blastopore (most invertebrates) A dueterostome is an animal whose anus is formed from the blastopore (most vertebrates) Body Symmetry With the exception of sponges, all animals exhibit some type of body symmetry Radial symmetry: body plan in which body parts repeat around the center of the body Bilateral symmetry: body plant in which only a single imaginary line can divide the body into 2 equal parts Cephalization Animals with bilateral symmetry usually exhibit what is called cephalization Cephalization is the concentration of sense organs and nerve cells at the anterior, or front, end of the body Evolutionary Trends Specialized Cells, Tissues, and Organs The evolution of larger and more complex animals involved specialized cells joining together to form tissues, organs, and organ systems Body Symmetry All invertebrates except sponges exhibit some type of body symmetry Asymmetry: sponges Radial: cnidarians and echinoderms Bilateral: worms, mollusks, and arthropods Evolutionary Trends Cephalization The evolution of a body plan for feeding, defense, and other functions was accompanied by the trend toward cephalization Invertebrates with cephalization can respond to the environment in more sophisticated ways than simpler invertebrates Evolutionary Trends Segmentation Most inverts with bilateral symmetry also have segmented bodies specialized for specific functions Coelom Formation A coelom is a body cavity that forms between germ layers Most complex animal phyla have a true coelom that is lined completely with mesoderm About the Coelom Coelom means body cavity (a tube within a tube). Acoelomates Have NO TRUE body cavity! Pseudocoelomates Have a fluid filled cavity BUT – it is not lined like that of higher-order animals. Coelomates Have a body cavity that separates the body into an inner and outer tube (fully lined). Coelom Formation pseudocoelom digestive cavity digestive tract coelom digestive tract acoelomate pseudocoelomate coelomate KEY TERMS TO KNOW Early Development During early development, the cells of most animal embryos separate into three layers called germ layers: 1. 2. 3. ENDODERM: innermost layer; develops into the lining of the digestive tract & much of the respiratory system MESODERM: middle layer; develops into muscles and much of the circulatory, reproductive, and excretory systems ECTODERM: outermost layer; develops into the sense organs, nerves, and outer layer of the skin Evolutionary Trends Early Development In most inverts, the zygote divides repeatedly to form a blastula (a hollow ball of cells) In protostomes, the opening of the blastula (blastopore) develops into a mouth Includes worms, arthropods, and mollusks In deuterostomes, the blastopore forms an anus Includes echinoderms and deuterostomes KEY TERMS TO KNOW Early Development Protostomes are organisms that develop a mouth first and then an anus. Most invertebrates are protostomes Deuterostomes are organisms that develop an anus first and then a mouth. Echinoderms and all vertebrates are deuterostomes Form and Function in Inverts Feeding and Digestion The simplest animals break down food primarily through intracellular digestion Food is digested in the cells More complex animals use extracellular digestion Food is broken down outside the cells in a digestive cavity and then absorbed into the body Patterns of Extracellular Digestion Simple animals such as cnidarians and flatworms ingest food and expel wastes through a single opening More complex animals digest food in a tube called the digestive tract Food enters mouth and wastes leave through the anus These are characteristics of a one way digestive tract Roundworms, annelids, mollusks, arthropods, echinoderms Patterns of Extracellular Digestion Form and Function in Inverts Respiration Respiratory organs have large surface areas that are in contact with the air or water For diffusion to occur, the respiratory surfaces must be moist Aquatic v/s Terrestrial Respiration Many aquatic animals respire through their skin (cnidarians and flatworms) Aquatic mollusks, arthropods, and annelids exchange gases through gills Spiders respire using book lungs In insects, air enters the body through openings called spiracles, travels through tracheal tubes and then diffuses in and out of surrounding fluids Invertebrate Respiratory Structures Form and Function in Inverts Circulation Most complex animals move blood through their bodies using one or more hearts and either an open or closed circulatory system OPEN: blood is only partially contained within a system of blood vessels Arthropods and most mollusks CLOSED: vessels extend throughout the body and blood remains contained within these vessels Annelids and some mollusks Open v/s Closed Circulatory System Form and Function in Inverts Excretion Most animals have an excretory system that rids the body of metabolic wastes while controlling the amount of water in the tissues Aquatic: ammonia diffuses from the body tissues into the surrounding water Terrestrial: convert ammonia into urea before elimination In annelids and mollusks, urine forms in tube-like structures called nephridia Some insects and arachnids have Malpighian tubules (saclike organs that convert ammonia into uric acid) Invertebrate Excretory Systems Form and Function in Inverts Response: Inverts show 3 trends in the evolution of the nervous system: 1. 2. 3. Centralization – in flatworms and roundworms, the nerve cells are more concentrated, or centralized with a few clumps of ganglia (nerve tissue) in the head Cephalization – in mollusks and arthropods, ganglia are organized into a brain at one end of the body that controls the nervous system Specialization – complex animals, such as insects and echinoderms, have a variety of specialized sense organs that detect light, sound, chemicals, and movement Invertebrate Nervous Systems Form and Function in Inverts Movement & Support: invertebrates have one of 3 main kinds of skeletal systems 1. Hydrostatic skeleton: muscles surround a fluid filled body cavity that supports the muscles 2. Exoskeleton: external body covering made of chitin 3. Annelids & some cnidarians arthropods Endoskeleton: structural support located inside the body Echinoderms and vertebrates Form and Function in Inverts Reproduction: most invertebrates reproduce sexually during at least part of their life cycle Many, however, may also reproduce asexually Sperm and egg may meet in 2 ways: External fertilization: eggs are fertilized outside the female’s body (usually in water) Internal fertilization: eggs are fertilized inside the female’s body “Radiata” Eumetazoa Metazoa Ancestral colonial flagellate Deuterostomia Protostomia Bilateria Nematoda Nemertea Rotifera Arthropoda Annelida Mollusca Platyhelminthes Chordata Echinodermata Brachiopoda Ectoprocta Phoronida Ctenophora Cnidaria Porifera