HIGHER CHORDATES 



275 



Suborder SQUALOIDEA (Sharks) 



Diagnosis: gill slits on side of body; body generally 

 torpedo-shaped; pectoral fins not enlarged. 



Although some sharks resemble rays in appearance 

 and habits, most can be considered the wolves of the 

 sea. Prior to the recent and perhaps only temporary 

 warming of eastern Pacific Ocean waters, there was 

 little, if any, danger to Americans from sharks. This 

 fact is emphasized by a 1950 publication, "California 

 Sharks and Rays," of the California Bureau of Ma- 

 rine Fisheries. At that time, the possibly dangerous 

 sharks occasionally were sighted out at sea; there was 

 only one coastal California record, in Morro Bay, of 

 the most dangerous man-eater, the great white shark. 

 Since that time, there have been many incidences of 

 humans being either killed or dismembered, as well 

 as records of close calls, along the California Coast. 

 Now (1963), the shark danger still may be greater 

 along our Pacific shores than along our Atlantic and 

 Gulf coasts; however, fewer attacks in California 

 waters have occurred in the last two years. This 

 lessened danger also seems to be related to a most 

 recent decrease in temperature from the high of a few 

 years ago. 



Sharks are predators of the marine world. In the 

 main they feed upon various kinds of fishes. To ac- 

 complish this they use many rows of small to large, 

 very sharp teeth. Perhaps the most spectacular 

 aspect of their feeding is the so-called "feeding 

 frenzy." If considerable prey is available, a single 

 shark may chop and tear the prey. This releases 

 blood into the water and draws other sharks. Ap- 

 parently if there is enough prey and if sufficient blood 

 is released, the sharks will go into a frenzy, ripping 

 and tearing one another as well as the prey animals. 

 Reports of such frenzies by human observers fre- 

 quently describe a "boiling of blood red water" and 

 sometimes the sharks biting or crashing into the boats 

 of the observers. 



The closest association between small sharks and 

 man probably involves the nuisance value and dam- 

 age brought about by the animals" getting caught in 

 fish nets. The larger sharks are dangerous to swim- 

 mers and small boats. However, the largest sharks, 

 such as the whale shark and basking shark, would 

 not attempt to eat humans. Their teeth are very 

 small and probably incapable of cutting food; feeding 

 is accomplished by filtering microorganisms with the 

 modified gills. Although these giants of 30 or more 

 feet could cause considerable damage if they charged 



swimmers, they are not likely to do so. They tend to 

 stay a little distance offshore and are somewhat slug- 

 gish, seemingly unaffected by the close proximity of 

 boats or swimmers. 



CLASS OSTEICHTHYES (Bony Fishes) 



Diagnosis: common fishes; skin with bony scales 

 of three types (sometimes absent) and with slime or 

 mucus glands; skeleton of bone; fins of variable dis- 

 tribution, but both paired front (pectoral) and rear 

 (pelvic) and unpaired medial fins usually are present; 

 jaws and fin rays present; gills supported by bony 

 arches and covered by a bony flap (operculum); sexes 

 separate, fertilization usually external but may be 

 internal and eggs hatch internally; larva is often 

 present and unlike the adults in form; fresh-water 

 and marine (Figures 16.11 through 16.15). 



The bony fishes, also called true fishes, are not 

 "modern" because they possess a bony skeleton. 

 Bone is a very ancient character in vertebrates. This 

 is the case in spite of there being no bone in living 

 jawless fishes, a condition that can be associated with 

 their tendency towards a parasitic way of life. In this 

 respect, it is very probable that ancient jawless fishes 

 had not only a bony skeleton, but also jaws and fins. 



Another "strange" characteristic of true bony 

 fishes is the ancestral position of the air, or swim, 

 bladder and the lung. The lung was the ancestral 

 feature and was readily available for the offshoot of 

 land vertebrates. Through modification of the lung, 

 the air bladder developed. Modern fishes, having an 

 air bladder, use this structure as a hydrostatic organ 

 to regulate their depth in water. An increase in air 

 content causes the fish to rise and a decrease causes 

 the fish to descend. 



Subclass CHOANICHTHYES (Choanate Fishes) 



Diagnosis: primitively torpedo-shaped and taper- 

 ing at both ends, living forms slender to thick; nos- 

 trils (choanae) connect to the mouth cavity; paired 

 fins with a median lobe; apparently not now found in 

 North America; fresh- water or marine; all living 

 fossils. 



ORDER CROSSOPTERYGII (Lobe-finned Fishes) 



Diagnosis: heavy bodied; marine (Figure 16.11). 

 Until very recently the lobe-finned fishes were of 

 little interest except to students of animal relation- 



