If you are not into biology, nature, animals - then don't bother reading on. If on the other hand, you have an interest in biology, nature and animals, read on if you will. It is nothing complicated, but I am hopeful it will do and make the interviewers think I know my stuff; or at least that I know how to present it. Of course, during my presentation, I plan to have several live examples to exhibit of fish, amphibians, and reptiles. If nothing else, it will keep their interest!
As we learned in class last time, living beings are divided into 5 kingdoms. The kingdoms are then divided into smaller more specialized groups called Phyla. The phyla are divided in more specialized groups called classes.
Of all the phyla, the one with which we may be most familiar is that of Chordata, or animals with a spinal cord. Of these we are probably most familiar with the animals with vertebrae (backbones). In class today we will learn the names of all five classes of vertebrates, and we will also learn how to distinguish between three of the five groups found with the sub-phyla Vertebrata.
All of the vertebrates have some things in common such as: a backbone made up of vertebrae, a spinal chord, and a central nervous system controlled by a brain. Typical vertebrates also have eyes, though in some the eyes have degraded or disappeared due to adaptive changes. Despite these similarities there are many diffrerences among the five different classes of vertebrates. These classes consist of: the true fish, amphibians, reptiles, birds and mammals. The fish, amphibians, and the reptiles are typically ectothermic, or in other words their body temperature is dependent upon the surrounding environment. Birds and mammals are endothermic, and can maintain their internal temperature as a function of their metabolisms. Today will will focus on the ectothermic, or cold blooded, vertebrates.
Fish are aquatic. They are typically ectothermic, or as we commonly call them they are: cold blooded. For the most part they breathe oxygen through internal gills. Most have an outer covering of scales, although some lack scales having tough gritty skin (sharks), or slime covered leathery skin (some catfish). Fish do not have ears, therefore do not have ear openings. A fish's limbs consist of fins. Typical fish have a tail fin, anal fin, dorsal fin, paired pelvic fins, and paired pectoral fins. Some fish can, in addition to breathing through their gills, breathe air through small lungs and or through their skin, and therefore can survive out of water for extended periods, e.g. the walking catfish, and the lungfish. These two fish are easily distinguished from other vertebrates, when they are out of water, because they have fins and gill slits. Most fish have teeth though not all have them. Fish reproduce either by laying eggs or giving birth to live young dependent upon the type of fish.
The amphibian class consists of Sirens, Salamanders, Newts, Frogs and Toads. Amphibians are ectothermic. They all lay eggs to reproduce. Typical amphibians lay their eggs in water, or very near to water where they can remain moist. This typically is in fresh water, but some amphibian eggs may tolerate brackish, slightly salty, water. Many but not all amphibians go through a larval stage wherein they must live in water and breath through external gills during that stage of life. Most mature into a different form as adults, such as a tadpole turning into a frog, or a gilled water breathing larval salamander turning into an air breathing adult. Most adult amphibians will breathe air through lungs, but almost all can also breathe through their skin. For the most part adult amphibians have four legs, a protective slime covering on their skin which is scale-less (some like toads may be drier and have warty skin), and need to live at least the larval part of their lives in water, then the remainder of their lives partially in, or at least near water, in some form. Some types of amphibians never come out of what appears to be a larval stage, and they continue living in the water and breathing through gills such as the mud-puppy, or the axolotl. Some amphibians, the frogs, exhibit what amounts to an external ear, or the tympanum membrane. Salamanders have no external ears or openings. Some amphibians have teeth while others do not, for example most frogs do not have teeth while one species the Argentine Horned frog does have them.
Reptiles - The reptile class consists of the crocodilians, lizards, snakes, turtles and tortoises, and the tuatara. Typical reptiles are ectothermic, though at least one is now believed to be somewhat endothermic (capable of regulating its internal body temperature independent of the outside conditions).All reptiles have scales. All reptiles also have ears, but some such as the snakes have only vestigial ears. These have degraded through evolution to the point where they are useless to detect sound. Lizards have clearly detectable ear openings. All reptiles, with the exception of the Monkey Tailed Lizard, lay eggs in order to reproduce. Although it is a common misconception that some are livebearers as opposed to being egg layers. For example snakes which are referred to as live bearers, such as Garter Snakes, actually lay eggs but the egg membrane is so thin as to burst as soon as it passes out of the mother. These eggs incubate within the mother snake, and the babies are born fully formed but are still born from within, or hatched from, the egg. Many reptiles have fours legs, such as most lizards and all turtles and tortoises. Others do not have legs, such as snakes and legless lizards. Reptiles do not have gills at any stage in their lives after birth. Reptile skin is normally dry to the touch, they do not produce body protective slime as do the fish and amphibians. All reptiles, except turtles and tortoises have teeth; turtles and tortoises have beaks attached to their jaws.
There is a homework assignment being handed out, if you have any questions about it, ask now. Have this assignment ready to be handed in to me in out next scheduled class.
All the best,