Insert: Textbook cover photo Chapter 15: Marine Animals

Chapter 15 Six Main Concepts Animals could not evolve until atmospheric oxygen was abundant. Photosynthetic autotrophs (mainly cyanobacteria) changed the composition of the atmosphere during the “oxygen revolution.” More than 90% of all living and fossil animals, including all of the earliest multi-cellular animals, are invertebrates – animals without backbones. By nearly any criterion, arthropods – a group that includes lobsters, shrimp, crabs, and insects – are the most successful of Earth’s animals. The Chordates possess a stiffening scaffold – a notochord – on which they are constructed. In vertebrate chordates, this structure persists as a vertebral column. Fishes are Earth’s most abundant and successful vertebrates. Marine mammals include the whales, the largest animals ever to have lived on Earth.

Animals Evolved When Food and Oxygen Became Plentiful The history of animals begins far back in the history of the ocean. Using sunlight, the first primary producers - probably an early form of cyanobacteria - assembled their own food from inorganic molecules and then broke the food down to release energy. As a byproduct, these autotrophs also gave off oxygen sparking the “oxygen revolution.” During the oxygen revolution, the activity of photosynthetic autotrophs changed the composition of the atmosphere from less than 1% free oxygen to its present oxygen-rich mixture of more than 20%. The growing abundance of free oxygen made aerobic respiration practical, speeding the disassembly of food molecules. Ozone derived from this oxygen blocked most of the sun’s dangerous ultraviolet radiation from reaching Earth’s surface.

Animals Evolved When Food and Oxygen Became Plentiful During the oxygen revolution (2 billion to 400 million years ago), photosynthetic autotrophs – mostly bacteria – caused a rapid rise in the amount of oxygen in the air, which made possible the evolution of animals. Animals are thought to have arisen between 900 and 600 million years ago.

Animals Evolved When Food and Oxygen Became Plentiful An animal is a multicellular organism unable to synthesize its own food and often capable of movement. Animals grew in complexity as they became more abundant. Instead of drifting apart after reproduction, some dividing cells stuck together and formed colonies. True animals evolved as these colonies distributed labor among specialized cells, eventually increasing the degree of interdependence among cells within the colony. The colonies ceased to be simple aggregations of individuals and began to take on specific architectures for specific tasks. A group of animals that shares similar architecture, level of complexity, and evolutionary history is known as a phylum.

Invertebrates Are the Most Successful and Abundant Animals More than 90% of all living and fossil animals are categorized as invertebrates. Invertebrates are generally soft-bodied animals that lack a rigid internal skeleton. (RIGHT) Major Animal Phyla with Marine Examples

Phylum Porifera: Sponges All sponges are suspension feeders. Sponges have no digestive, circulatory, respiratory, or nervous systems. Excretion and the movement of gases occur by simple diffusion. A skeletal network of spicules and a fibrous protein called spongin prevents the internal chambers and canals from collapsing.

Phylum Cnidaria: Stinging cells Include jellyfish, sea anemones and corals. They all have large, stinging cells called cnidocytes. They all exhibit radial symmetry. Cnidarians occur in two forms: medusae and polyps. (LEFT) Anatomy of a reef coral polyp.

Advanced Invertebrates Have Complex Bodies and Internal Systems Worms A transition from relatively simple to more advanced organisms is made in the worm phyla. The worm body plan exhibits bilateral symmetry instead of radial symmetry, have some concentration of sensory tissue in what may be termed a head, and many have flow-through digestive systems and systems to circulate fluids and eliminate waste. Mollusca The phyla mollusca includes such diverse members as clams, snails, octopuses, and squid. Most molluscs are marine, and most have an external or internal shell. Molluscs and annelids probably shared a common origin and therefore share a few basic characteristics (bilaterally symmetrical, heads, flow-through digestive tracts, and well-developed nervous systems). (RIGHT) Bivalves are suspension feeders that make their living by filtering the water.

Arthropoda and Echinodermata The phylum Arthropoda includes the lobsters, shrimp, crabs, krill, and barnacles. Arthropods are by far the most successful of Earth’s animal phyla with more than a million known species. They exhibit three remarkable evolutionary advances : exoskeletons, striated muscles, and articulation. Ecinodermata Include sea stars, sea urchins, sea cucumbers and brittle stars. Echinoderms lack eyes or brains, have a radially symmetrical body plan based on 5 sections or projections and move slowly. They also have a water vascular system (RIGHT).

Construction of Complex Chordate Bodies Begins on a Stiffening Scaffold Chordata is the most advanced animal phylum. All chordates have, at some time during development, a notochord. Both invertebrate and vertebrate chordates are represented in ocean environments. In some chordates the notochord is lost during development. These are the invertebrate chordates. Ex: tunicates (RIGHT). Most chordates (about 95%) retain the notochord in some form. These are the vertebrate chordates.

Vertebrate Evolution Traces a Long and Diverse History One proposed family tree for the vertebrates and their relatives, the invertebrate chordates.

Fishes Are Earth’s Most Abundant and Successful Vertebrates Fishes are vertebrates that usually live in water and possess gills for breathing and fins for swimming. There are more species of fishes, and more individuals, than species and individuals of all other vertebrates combined. Fishes have evolved to fit almost every conceivable watery habitat but are most numerous on the bottom or in productive seawater over the continental shelves. Fishes are divided into two major groups based on the material forming their skeletons: Chondrichthyes: The cartilaginous fishes includes sharks, skates, rays, and chimaeras. They have a skeleton made of a tough, elastic tissue called cartilage, jaws with teeth, paired fins, and often active lifestyles. Sharks and rays tend to be larger than bony fishes. Osteichthyes: The bony fishes. About 90% of all living fishes are contained within the Osteichthyan order Teleostei, which contains the cod, tuna, halibut, goldfish, and other familiar species. They are found in almost every marine habitat from tide pools to the abyssal depths.

Fishes Are Earth’s Most Abundant and Successful Vertebrates Example of a cartilaginous fish: the great white shark Some of the diversity exhibited by bony fishes.

Fishes Are Successful Because of Unique Adaptations Movement, shape and propulsion - fish must be able to move through water, which is 1,000 times denser and 100 times more viscous than air Maintenance of level - fish tissue is usually denser than the surrounding water, so fish must have a system to keep from sinking Gas exchange - the problem of extracting oxygen from water Osmotic considerations - fish need a system to maintain proper salt levels in their bodies Feeding and defense - competitive pressure among a large number of fish resulted in the evolution of a wide variety of feeding habits

Gas Exchange Is Accomplished through Gills Cutaway of a mackerel, showing the position of the gills (a). Broad arrows in (b) and (c) indicate the flow of water over the gill membranes of a single gill arch. Small arrows in (c) indicate the direction of blood flow through the capillaries of the gill filament in a direction opposite to that of the incoming water. This mechanism is called countercurrent flow.

Sea Turtle and Marine Crocodiles Are Ocean-Going Reptiles Each of the three main groups or reptiles has marine representatives: turtles, sea snakes and marine lizards (iguanas), and marine crocodiles. Like all reptiles, marine reptiles are ectothermic, breathe air with lungs, are covered with scales and a relatively impermeable skin, and are equipped with special salt glands. (RIGHT) The best known and most successful living marine reptiles are sea turtles. Unlike land turtles, sea turtles have relatively small streamlined shells without enough interior space to retract head or limbs.

Some Marine Birds Are the World’s Most Efficient Flyers Only 270 of the known species of birds, about 3% of known bird species, qualify as seabirds. Seabirds have salt excreting glands to eliminate salt taken in with their food. True seabirds generally avoid land unless they are breeding, obtain nearly all their food from the sea, and seek isolated areas for reproduction. There are four groups of seabirds: Tubenoses Pelicans Gulls Penguins

Marine Mammals Share Common Features The three groups of marine mammals: Cetacea – porpoises, dolphins and whales Carnivora - seals, sea lions, walruses and sea otters Sirenia – manatees and dugongs All marine mammals share four common features: Their streamlined body shape with limbs adapted for swimming makes an aquatic life- style possible. They generate internal body heat from a high metabolic rate, and conserve this heat with layers of insulating fat and, in some cases, fur. The respiratory system is modified to collect and retain large quantities of oxygen. A number of osmotic adaptations free marine mammals from any requirement for freshwater.

Order Cetacea: The Whales Cetaceans are thought to have evolved from an early line of hooved land mammals. Modern cetaceans are further divided into two sub-orders. Suborder Odontoceti: the toothed whales, are active predators and possess teeth to subdue their prey.They search for prey using echolocation. Suborder Mysticeti: the baleen whales, have no teeth and filter small animals out of the water or mud.

Order Carnivora: Oceanic Carnivores The order Carnivora includes land predators ranging from dogs and cats to bears and weasels, but the members of the carnivoran suborder Pinnipedia - the seals, sea lions, and walruses are almost exclusively marine. The suborder Fissipedia has many members (including cats, dogs, raccoons, and bears), but only one truly marine representative, the sea otter

Order Sirenia: Manatees and Dugongs The bulky, lethargic, small- brained dugongs and manatees, collectively called Sirenians, are the only herbivorous marine mammals. Like the cetaceans, they appear to have evolved from the same ancestors as modern ungulates. They make their living grazing on sea grasses, marine algae, and estuarine plants in coastal temperate and tropical waters.