Chapter 15Marine Animals

OceanographyOceanographyAn Invitation to Marine Science, 7thAn Invitation to Marine Science, 7th

Tom GarrisonTom Garrison

Chapter 15 Study Plan

• Animals Arose Near the End of the Oxygen Revolution• Invertebrates Are the Most Successful and Abundant Animals• The Worm Phyla Are the Link to Advanced Animals• Advanced Invertebrates Have Complex Bodies and Internal

Systems• Construction of Complex Chordate Bodies Begins on a

Stiffening Scaffold• Vertebrate Evolution Traces a Long and Diverse History• Fishes Are Earth’s Most Abundant and Successful Vertebrates• Fishes Are Successful because of Unique Adaptations• Sea Turtles and Marine Crocodiles Are Ocean-Going Reptiles• Some Marine Birds Are the World’s Most Efficient Flyers• Marine Mammals Include the Largest Animals Ever to have

Lived

Chapter 15 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 Arose near the End of the Oxygen Revolution

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.

Phylum Porifera Contains the Sponges

The body plan of a simple sponge.

Fig. 15-3b-d, p. 406

Water out

Central cavity

Water inCollar cell

Flagellum

Flattened surface cells

MesogleaPore

Amoeboid cell

Spicules

Stepped Art

NucleusMicrovilli

Stinging Cells Define the Phylum Cnidaria

Anatomy of a reef coral polyp, with enlarged detail showing a cross section of the outer covering and tissue. The symbiotic photosynthetic zooxanthellae are crucial to the survival of this type of coral.

Advanced Invertebrates Have Complex Bodies and Internal Systems

Bivalves are suspension feeders that make their living by filtering the water for edible particles. In this diagram (showing a bivalve with its left shell removed), water and tiny bits of food are swept into the animal by the movement of tracts of cilia on the gills. Food settles onto the gills and is then driven toward the mouth and swallowed.

The water-vascular system in a sea star (shown in blue). (a) Water enters the animal’s body through a sieve plate, which excludes material that might clog the tubes and valves, and circulates through canals.

Sea Stars Are Typical of the Phylum Echinodermata

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.

• 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.

Class Osteichthyes Comprises the Familiar 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.

(left) Some of the diversity exhibited by teleost (bony) fishes. These fishes are not all drawn to the same scale.

Fishes Are Well Adapted to Their Environment

• What are some problems posed by living in a marine environment?

• 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

Turbulence and drag. At the same speed, with the same frontal area, shape (a) will have about 15 times as much drag as shape (c). Shape (b) shows only a small improvement in drag over the disk.

Fishes Are Well Adapted to Their Environment

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.

Successful Fishes Quickly Adapt to Their Osmotic Circumstances

Osmoregulation in freshwater and marine fishes.

Like All Birds, Marine Birds Evolved from Dinosaur-Like Ancestors

• Only 270 of the known species of birds qualify as seabirds. Seabirds have salt excreting glands to eliminate salt taken in with their food.

• There are four groups of seabirds:– Tubenoses - this group includes the albatrosses and

petrels– Pelicans - this group includes relatives of the

penguins that have webbed feet and throat pouches– Gulls - these birds are found along the shore, where

they scavenge for food.– Penguins - these birds have lost the ability to fly, but

are excellent swimmers

Marine Mammals Share Common Features

• What are the three groups of marine mammals?

• Cetacea – porpoises, dolphins and whales

• Carnivora - seals, sea lions, walruses and sea otters

• Sirenia – manatees and dugongs

Marine Mammals Share Common Features

A few of the marine mammals of the Order Cetacea. Suborder Mysticeti (mystidos = unknowable) whales are known for having no teeth and instead use baleen for filter feeding.

Some representatives of the order Cetacea. Suborder Odontoceti (odontos = tooth) whales are known for being active predators who use teeth for feeding. The toothed whales search for food using echolocation, a biological equivalent to sonar.

Marine Mammals Share Common Features

Marine animals have evolved effective adaptations for capturing prey, avoiding danger and maintaining thermal and fluid balance with their environment.

(above) Echolocation, used by toothed whales to locate and perhaps stun their prey.

The Order Cetacea Includes the Whales

The Order Cetacea Includes the Whales

A plate of baleen and its position in the jaw of a baleen whale. For clarity, the illustration shows an area of the mouth cut away.

Chapter 15 in Perspective

In this chapter you learned that animals must ultimately depend on primary producers (autotrophs) for nutrition. Animals could not exist on Earth until increasing levels of free oxygen in the atmosphere permitted them to metabolize food obtained from autotrophs. And remember, it was the photosynthetic autotrophs themselves that contributed huge quantities of oxygen to the environment. True multi-cellular animals arose between 900 and 700 million years ago, near the end of this “oxygen revolution.” Their variety is astonishing – a tribute to millions of years of complex interplay between environment, producer, and consumer.

Our survey of marine animals followed the course of their evolution. The complexity of animals increased as we moved from groups (phyla) whose basic structure seems to have solidified relatively early in the history of animals to groups that evolved more recently. Every marine animal has evolved effective adaptations for capturing prey, avoiding danger, maintaining thermal and fluid balance with their surroundings, and competing for space, and our survey of marine animals stressed these adaptations.

In the next chapter you will learn how these animals interact with one another and with their environment. The organisms you met in the last two chapters do not live alone. They are distributed throughout the marine environment in specific communities: groups of interacting producers, consumers, and decomposers that share a common living space. The types and variety of organisms found in a particular community depend on the physical and biological characteristics of that living space.