Unit II - Populations
|Topic 8 - Brief Survey of Animals
Refer to Chapters 32 to 35
Zoology is the study of animal life.
All animals are multicellular, heterotrophic organisms. Since they can not produce their own food they have evolved elaborate adaptations for food getting. In the majority of animals, these adaptations include sensory organs for the detection of food, danger, and sexual mates. Most animals have systems for support and locomotion, digestion, excretion, nervous, endocrine, respiratory, circulatory, and reproduction.
Vertebrates are animals that have a backbone as a major support frame for their muscles. Invertebrates are animals that do not have a backbone. Vertebrates belong to Phylum Chordata, subphylum Vertebrata. Not all chordates are vertebrates. The members of the two subphyla, Urochordata and Cephalochordata, have no vertebrae and are therefore considered to be invertebrates (invertebrate chordates). All vertebrates are chordates, but not all chordates are vertebrates
An animal with radial symmetry generally has dorsal (top) and ventral (bottom) surfaces, but no right or left sides. Any plane cut through the axis (the length of their body) produces two symmetrical halves. Examples of an animals with radial symmetry include the hydra, jellyfish and starfish (seastar). The proportional arrangement of similar parts of a body around a central axis, as in the case of jellyfish or starfish, is known as radial symmetry. Cross sections at different levels are not alike, but any lengthwise cut down the center divids the animal into matching halves. The jellyfish shows radial symmetry. One end of the animal has a mouth and tentacles. The other end is closed and rounded. Any lengthwise cut down the center divides the jellyfish into matching halves, like the halves of a vase. Most animals showing radial symmetry either drift with the water currents, like the jellyfish, are very slow moving, like the seastar, or are sessile, living attached to a stationary object, like a hydra.
Bilaterial symmetry is common to the vast majority of animal species. These animals have distinct left and right sides, front and rear, top and bottom surfaces. With bilateral symmetry, there is only one plane that can divide the organism into two symmetrical halves. In this type symmetry, there is only one way to divide the body into two symmetrical halves. Each half is a mirror image of the other. Bilaterally symmetrical animals have fixed right and left sides. There are special terms that describes positions other than right and left on bilaterally symmetrical animals. The dorsal refers to the upper side or the back of the animal. Ventral is the lower, or belly side of the animal. The front or head is the anterior and the rear, or tail, end is posterior.
The bodies of protozoans, such as those of the order Radiolaria, which have a round form about a central point or nucleus, are said to have spherical symmetry. Any plane that passes through the central point will divide the organism into two symmetrical halves. These organisms have no left or right, and no top or bottom.
A few organisms are said to be asymmetrical, which means that they can not be cut or divided into two egual or similar halves. Examples include the amebas and most sponges.
The term dorsal means top or upper surface. Ventral is the lower surface. Anterior is toward the front or head end of the organism, and posterior is toward the rear of the animal.
The body cavity or coelom first appears as a pseudocoelom (false coelom) in the roundworms (Phylum Nematoda). The false coelom is not surrounded by a membrane (peritoneum) as is the true coelom. The pseudocoelom is only partly covered on the outer side by mesoderm. The first true coelom appears in the segmented worms (Phylum Annelida). The true coelom is surrounded by mesoderm and covered by a lining known as the peritoneum.
The true coelom provides the organism with a "tube within a tube" body plan. This gives the organism greater movement or flexability without crushing or distorting the internal organs.
Invertebrates are the animals without a backbone and include the following phyla: Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata, and two of the three chordate subphyla (Urochordata and Cephalochordata) which are invertebrate chordates.
The sponge has no true organs or systems. It is organised at the tissue level of organization. It has no respiratory, circulatory, nervous, musculo-skeletal, digestive, or excretory systems.
Reproduction can be asexual or sexual. Asexual reproduction occurs by budding and by the formation of gemules. Sexual reproduction involves the formation of sperm and eggs. Sperm are released into the water and generally fertilize eggs in another sponge.
Most adult coelenterates have radial symmetry. Coelentrates have two cell layers, a outer layer called the ectoderm and an inner layer called the endoderm. The two layers are separated by a jellylike material called mesogla. Medusas tend to drift with the water to move because the contractile fibers in their ectoderm cells don't have strong enough contractions to overcome the movement of the water. Coelenterates are unlike the sponges in that the coelenterates have nerves. Not only do they have nerves but the nerve signals travel both ways. In their bodies they have an evenly distributed nerve net. This causes a reaction from the entire body when one part is touched. This is why when you touch one tentacle all the tentacles react and pull in. They also have specialized stinging cells called cnidoblasts. Inside the cnidoblasts are nematocysts which are small, fluid-filled capsules containing a coiled thread. When the cord on a tentacle is touched the cnidoblasts are discharged. The thread then uncolis and captures the prey and paralyzes it. Once the prey is captured the tentacles bring it into the mouth of the coelentrate. Because they eat their food in chunks they are known as chunk feeders. The internal body cavity is called the gastrovascular cavity and functions like a stomach. The single opening to the cavity serves as both a mouth and an anus. Enzymes secreted into the cavity by some of the cells of the endoderm begin the process of extracellular digestion. Because coelentrates can be both female and male they can reproduce sexually, but they also reproduce asexually. The process in which coelentrates reproduce asexually is known as budding.
Planaria is a flatworm in the class Turbellaria. The head of these organisms have eyespots which detect light but can not see an image. The planarian uses the eye spots to avoid the sunlight. The muscular pharynx is a tube that can be extended through the mouth opening for eating. Planaria have no skeletal, circulatory, or respiratory system. Oxygen and carbon dioxide diffuse into and out of individual cells. A series of tubules that run the length of the body make up the excretory system of the planaria. Side branches of the tubules have cells called flame cells. These cells remove excess water and liquid wastes from the body and passes them into ducts. The contents of the ducts pass out of the worm through small excretory pores on the dorsal surface.
The planaria has a small brain beneath the eyespots. Connected to the brain are two
parallel nerves that run the length of the body. Transverse nerves branch from the
parallel nerves to form a ladder-like nervous system. Planaria have well developed
reproductive systems. They are hermaphroditic, which means that each individual has both
ovaries and testes. The planaria can regenerate an entire animal from a fairly small
segment. It can also reproduce asexually by fission, seperating its tail end from its head
end. Each half regenerates the missing structures.
Tapeworms are parasitic flatworms of the class Cestoda.
Flukes are parasitic flatworms of the class Trematoda. Because the food obtained from the host has already been broken down, flukes do not need well-developed digestive systems. In humans this parasite causes a disease called schistosomiasis. The fluke lives in the blood vessels of the human intestine. Here it lays eggs that pass out of the body with digestive wastes. If the eggs land in water, they hatch into free-swimming larvae. They then enter the bodies of snails, where they reproduce asexually.
The worms in Pylum Annelida are the most familiar worms. There are two classes, the earthworm, class Oligochaeta, and the leech, class Hirudinea. Segmented worms are also called the annelids. The body of these worms can separate into separate sections, also called segments. These worms can be found in both salt water and fresh water and on land. Most types of these worms are free living, however some worms, such as the leech are parasites. Segmented worms vary in length from less than 1mm to more than 2m.
Segmented worms are bilaterally symmetrical. The segmented worms are the simplist of the invertibrates that have a closed circulatory system. They have a tube within a tube body plan. The digestive tract is the inner tube and the body wall makes up the outter tube. The coelom,which is a fluid filled cavity is found between the two tubes. The segmented worms are the simplest worms that have true coeloms. The marine sandworm Nereis is very similar to the earthworm. But there are afew differences. Nereis lives at tide level,in the intertidal zone. Nereis is composed of almost 200 similar segments. The first two form a distinct head. The first segment is called the peristomium.
There are three major classes belonging to Phylum Mollusca. b>Class Bivalvia have two shells and include the muscles, clams, and oysters. Class Gastropoda have only a single shell or no shell at all, and include animals such as the snails and slugs. Class Cephalopoda include the squid and octapus which have arms (tentacles) attached to their head.
Arthropods are the most successful and abundant out of all animal groups. They are the most advanced invertebrates, are bilaterally symmetrical, and have a small coelom. All arthropods have jointed legs that are made of seveal pieces connected at hinged joints. Arthropods have exoskeletons composed of protein and chitin. It is waterproof, prevents waterloss, and protects soft body parts. Arthropods undergo molting as the grow, to shed and replace a new exoskeleton. All arthropods are segmented. The body segments are modified and fused to form specific body regions. Arthropods also have a well developed nervous and circulatory system.Of the various classes of arthropods, the insects are the most successful form of animal life on earth for a number of reasons. Insects are capable of flying, this enables them to fly great distances in search of food. There is also a tremendous variation in how they adapt for feeding and reproduction. This allows them to exist in many environments and get nourishments from many sources. Insects have a high rate of reproduction and a short life cycle. They produce hundreds even thousands off eggs, this helps them adapt. Insects are very small organisms, so they do not need a large environment in which to live.
Discuss developmental trends and the increasing complexity demonstrated by invertebrates in terms of form and function (e.g. symmetry, body cavity, separate sexes, number of tissue layers, lifestyle, body system function).
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The three main characteristics of chordates are the dorsal nerve cord, which is hollow; they have a notochord which is a flexible rod that is used to support the body organs for at least part of their lives; chordates have gill slits for at least part of their life; and most have a post anal tail. *There are three subphyla of the chordates: Urochordata, Cephalochordata, and Vertebrata. The subphyla Urochordata and Cephalochordata are invertebrate chordates since they do not develop a backbone at any time of their life. TUNICATES (Subphylum Urochordata) The tunicates are soft-bodied animals, found in marine, or saltwater, environments. Adult tunicates are sessile animals that obtain food and oxygen from water that flows through their bodies. LANCELETS (Subphylum Cephalochordata) The lancelets are marine animals. The most common member of this group is amphioxus. Lancelets usually live buried in the sand with only their anterior end exposed. Adult lancelets show the three characteristic chordate structures. VERTEBRATES (Subphylum Vertebrata) In addition to the development of a backbone, vertebrates share a number of additional characteristics: *The anterior part of the dorsal, hollow nerve cord is enlarged into a brain. *The body usually is divided into a head, neck, and trunck. The head contains the brain and various sense organs. *In most vertabrates, a tail is present at some stage of development. *There is a jointed, internal skeleton. *There are two jointed appendages. *There is a heart with two to four chambers. The circulatory system is closed, and the red blood cells contain hemoglobin. *In aquatic vertebrates, gas exchange takes place in the gills. In land vertebrates, it occurs in the lungs. *There is a large body cavity, or coelom, containing the organs of digestion, excretion, and reproduction, as well as the heart and lungs. *The body covering, the skin, is made of at least two layers. The skin often forms other structures, such as glands, scales, feathers, hair, nails, horns, and hoofs. The vertebrates are divided into eight classes. These classes are lampreys, hagfishes, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, and mammals. Fishes, amphibians, and reptiles are cold blooded, or ectothermic, animals. Their body temperature changes with the temperature of their environment. Birds and mammals are warm-blooded, or endothermic animals. Their body temperature remains fairly constant regardless of the temperature of their environment. To save energy, some warm-blooded animals hibernate in cold weather. When an animal goes into hibernation, the body temperature drops, and the animal becomes inactive.
The Vertebrate is of the subphylum chordate. They are the animals with backbones, for example the mammals, birds, reptiles, amphibians and various classes of fish.The vertebrates are the most numerous and complex of the chortdates. The main characterstic distiguishing vertebrates from other animals is the spinal column or backbone which is the basis for internal supporting sketelon and it allows flexibility and movement. Some other characterstics of vertebrates are as follows: 1) the anterior part of the dorsal, hollow nerve cord is enlarged into a brain. 2) the body usually is divided into a head, neck, and a trunk. 3) in most vertebrates a tail is present at some stage of developement. 4) there is a jointed, internal sketelon. 5) there are two pairs of appendages. 6) There is a two to four chambered heart, containing a close circulatory system and red blood cells that contain hemoglobin. 7) the aquatic vertebrates have gas exchnage which takes place in the gills, where as in land vertebrates it takes part in the lungs. 8) there is a large body cavity, or coelom, containing the organs of digestion, excretion and reproduction. 9) the skin (body covering) is made of at least two layers, it often forms other structures such as glands, scales, feathers, hair, nails, claws, horns and hoofs.
The frog (amphibian) has a three chambered heart, with two atria and one ventricle. The advantage of the amphibian circulatory system is that blood returns to the heart and is pumped under full pressure to the systemic circulation. As a result, the rate of blood flow through the systemic system is much higher in the amphibians than in the fish. The only problem that occurs as a result of the three chambered hear seems to be that there is some mixing of the oxygenated and deoxygenated blood within the single ventricle.
Reptiles are in interesting group of animals that seem to lie between the amphibians and the warm blooded birds and mammals. Many of the smaller reptiles have a three chambered heart. There is a partial septum that forms within the ventricle of some. This helps to reduce the mixing of the oxygenated and deoxygenated blood, as seems to occur within the amphibians. The larger reptiles (crockodilians) have a four chambered heart which totally eliminates the mixing problem
Birds and mammals have four chambered hearts, with two atria and two ventricles. An advantage is that of rapid circulation caused by high pressure. There is no mixing between oxygenated and deoxygenated blood.
Omnivores are animals that can eat both plant and animal food types. This ability to live on a great variety of food sources is an advantage to them in a changing environment. It can be expected that during a changing environment, there will be great fluctuation in the variety of plants and animals present. An organism that eats only one variety of plant as its only food source will have a real problem surviving if its food source is lost. The omnivore however would simply shift its eating habits to another available food. This is why the omnivore is more likely to survive ecological change.
The omnivre is also likely to have a variety of food digesting enzymes to digest the wide variety of foods. This too enables the omnivore to better exploit ecological and evolutionary changes to its food sources, even if new food sources should appear in the environment as a result of the change.