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SUBPHYLUM VERTEBRATA: 



vertebrates'" presents difficulties because many am- 

 phibians (especially certain salamanders), certain 

 reptiles (the sea snakes), and many mammals 

 (whales, seals and their close relatives) are strictly 

 marine or essentially so. "Tetrapods," literally, 

 "four-legged," probably is no better than "land 

 vertebrates," because some (the snakes) are legless; 

 some (the sirens) have only front legs; and some (the 

 seals and whales) have the legs modified into flippers. 

 Therefore, for those not familiar with the limits of 

 amphibians, reptiles, birds, and mammals, it is criti- 

 cal to diagnose the group. 



Superclass TETRAPODA (Land Vertebrates) 



Diagnosis: mostly terrestrial, but sometimes 

 aquatic, vertebrates; body streamlined generally only 

 in aquatic species; usually with two sets of paired 

 limbs, but often with one pair, none, or modified 

 limbs; when the body is covered with scales there 

 are no gills; specialized, generally mobile, neck bones 

 and a neck region usually present; distinct joint 

 between head and neck (or neck bones). 



The above diagnosis gives a general description of 

 usual features, but is so interlaced with exceptions 

 or things difficult to determine as to be exasperating 

 to the reader. Unfortunately, any characters that are 

 truly diagnostic are difficult to observe and, as a rule, 

 require the study of internal features. Therefore, for 

 full appreciation of the limits of the Tetrapoda one 

 must make such studies or become familiar with a 

 number of representative species. 



CLASS AMPHIBIA (= BATRACHJA) (Amphibians) 



Diagnosis: skin moist and glandular, without 

 scales; usually two pairs of legs, without paired fins; 

 paired nostrils lead to the mouth; respiration by gills, 

 mouth, throat, lungs and/or skin; sexes separate, 

 eggs with jelly envelopes, laid in water or moist places 

 (rarely retained), larvae usually aquatic (often meta- 

 morphose within the egg when eggs are laid on 

 land); adults restricted to moist places, often aquatic; 

 larvae herbivorous or carnivorous, adults typically 

 carnivorous. 



This class includes four living orders, the salaman- 

 ders, the sirens, the frogs and toads, and the tropical 

 caecilians. The amphibians, literally meaning "dual 

 or double life," are named for the tendency of a great 

 many to spend their developmental stages in water 

 and their adult life on land. Typically, they have a 



moist, slimy skin owing to the presence of mucus and 

 poison glands. Most salamanders, frogs, and toads 

 have two pairs of limbs; sirens have only a single pair 

 of limbs, the front legs; and caecilians are limbless, 

 usually blind, worm-like animals. 



The habitat of amphibians can be related to their 

 moist skin and body temperature and to environmen- 

 tal temperature and humidity. Because their skin 

 tends to lose water and water evaporation causes 

 cooling, amphibian body temperature on land often 

 is slightly below the environmental temperature. The 

 lower the relative humidity of the atmosphere, the 

 greater the water loss and body cooling of these ani- 

 mals. Amphibians have no internal mechanisms to 

 control body temperature; actual body temperature, 

 then, is the consequence of lack of internal tempera- 

 ture control mechanisms, environmental temperature 

 and humidity, and the cooling due to loss of water. 

 In addition, the loss of water when they are on land 

 places amphibians in constant danger of death from 

 drying. The above conditions indicate the reason 

 why the best land habitat for amphibians is a moist, 

 humid area. Moreover, owing to their dependence 

 upon environmental temperature, amphibians usually 

 are not found in perpetually cold or hot areas. In 

 addition, because their skins are permeable to water, 

 there are no marine amphibians. In spite of these 

 various limitations on habitat, especially those of 

 temperature and water, amphibians are fairly wide 

 ranging, being found in moist areas from the deserts 

 (including Death Valley) to the proximity of glaciers. 



Because of environmental limitations and the fact 

 that amphibians cannot move great distances, it 

 might seem that only a few habitats would be suitable 

 for them throughout a year. However, there are 

 various ways in which these animals can exist in 

 places that seem to be unfavorable. Since they need 

 not spend their entire annual cycle on the surface of 

 the land, some can retreat to water during the dry 

 season. However, most go underground to a depth 

 having relatively constant conditions of temperature 

 and moisture throughout the year. Also, many am- 

 phibians go into coma-like states (summer aestivation 

 and winter hibernation) that reduce their physical 

 requirements (e.g., for food). Other amphibians 

 avoid unfavorable environments by burrowing into 

 the mud bottoms of ponds and streams or by moving 

 into springs, caves, or deep cracks in rocks. The 

 duration of their subsurface existence depends upon 

 local conditions such as temperature and amount of 

 moisture present. 



