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PART ONE MARINE WORLD



TEXT 1 Introduction Fish are cool-blooded aquatic animals with backbones, gills, and fins. Most fishes are torpedo-shaped (fusiform) for efficient travel through water, but much variation in shape occurs, from flattened and rounded, as in flounders, to vertical and angular, as in sea horses. (1) The living species of fish are usually divided into three classes: the Agnatha, the jawless fishes, comprising the hagfishes and lampreys; the Chondrichthyes, the cartilaginous-skeleton fishes, such as sharks and rays; and the Osteichthyes, the bony-skeleton fishes, comprising all other living fishes. The skeletons of these three groups vary in fundamental ways. In the hagfishes and lampreys, the backbone is basically a notochord, a rod like structure composed of unique notochordal tissue. In sharks and rays the notochord is surrounded and constricted by spaced rings of cartilage, the vertebrae, to form a backbone. The remainder of the skeleton is also cartilaginous, not bony, but in many forms the cartilage is partly calcified, and thereby hardened, by the addiction of calcareous salts. In primitive bony fishes, such as the sturgeon, the vertebrae spaced along the notochord are still largely cartilaginous, but in most advanced bony fishes, the vertebrae are bony and are united to form the backbone, and the notochord is no longer present.



(2) To live, fish must extract oxygen from the water and transfer it to the blood. This is done by gills, lungs, specialized chambers, or skin, any of which must be richly supplied with blood vessels in order to act as a respiratory organ. Gills are made efficient in a number of ways. A large surface area for gaseous exchange means that more oxygen can enter the bloodstream over a given period of time. A single gill of a bony fish consists of a curved gill arch bearing a V-shaped double row of gill filaments. Each filament has many minute folds in its surface, giving it a sort of fuzzy appearance and increasing the amount of surface area along a given length of filament. Consequently, the surface area of the gills is commonly 10 to 60 times more than that of the whole-body surface.



READING COMPREHENSION Exercise a Read again paragraph one and summarize it in the form of diagram below! To complete your summary, you just fill the blank boxes based on the clues given.



hagfishes



Agnatha lampreys



Species of Fish



sharks Chondrichthyes rays Osteichthyes



all other living fishes



Exercise b Answer the three following questions in detail! 1. What is the characteristics of backbone of Agnatha? The characteristics of backbone of Agnatha is basically a notochord, a rod like structure composed of unique notochordal tissue. 2. How do the fish use their respiratory organ based on the text above? The fish use gills, lungs, specialized chambers, or skin, any of which must be richly supplied with blood vessels in order to act as a respiratory organ, specially for extract oxygen from the water and transfer it to the blood. Gills are made efficient in a number of ways. A large surface area for gaseous exchange means that more oxygen can enter the bloodstream over a given period of time. 3. What is the characteristics of gill filament? The characteristics of gill filament is each filament has many minute folds in its surface, giving it a sort of fuzzy appearance and increasing the amount of surface area along a given length of filament. Consequently, the surface area of the gills is commonly 10 to 60 times more than that of the wholebody surface.