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Diversity of Life
Taxonomy
All known life forms are systematically arranged and placed in various groups. This
process is called taxonomy. The following example illustrates why this is important for
communication among biologists. Europeans call the European house sparrow, now
common in the United States, many different names:
England
Germany
Denmark
Norway
House sparrow
Haussperling
Graaspurv
Graaspurv
France
Italy
Spain
Holland
Moineau domistique
Passera oltramontana
Gorrion
Musch
It is clear that the above can lead to confusion when scientists of different countries are
trying to communicate with each other. Another example is the burrowing rodent called
a gopher found throughout the western United States. In the southeastern United States
the term gopher refers to a burrowing turtle very similar to the desert tortoise found in the
American southwest. One final example; two North American mammals known as the
elk and the caribou are known in Europe as the reindeer and the elk. We never sing
“Rudolph the Red-nosed elk”! Confused? This was the reason for creating an
internationally recognized system of naming organisms. To avoid confusion, living
organisms are assigned a scientific name based on Latin or Latinized words. The English
sparrow is Passer domesticus or Passer domesticus (italics or underlining these two
names is the official written representation of a scientific name). Using a uniform
naming system allows scientists from all over the world to recognize exactly which life
form a scientist is referring to. The naming process is called the binomial system of
nomenclature. Passer is comparable to a surname and is called the genus, while
domesticus is the specific or species name (like your given name) of the English
sparrow. Now scientists can give all sparrow-like birds the genus Passer but the species
name will vary. All similar genera (plural for genus) can be grouped into another,
“higher” category (see below). Study the following for a more through understanding of
taxonomy.
Taxonomy
Analogy
Kingdom: Animalia
Country
Phylum: Chordata
State
Class: Aves
City
Order: Passeriformes
Street
Family: Ploceidae
Genus: Passer
Species: domesticus
House number
Surname
Given name
Today there are over 1 million known and named species of animals. The majority of
scientists believe that there are 10 to 50 million additional species not yet described and
named. In Zoology 5 we will confine our study to the most common animal phyla.
In addition to eliminating confusion, taxonomy allows us to identify most kinds of
animals without ever seeing them before or without knowing their names using a
dichotomous key. Given an animal, the key presents a pair of statements (occasionally
3). We select the statement that best describes the animal under question. At the end of
the statement is a number directing the key’s user to proceed to the next pair of
statements. Continue this process until a taxon (phylum, class, etc.) rather than a number
appears at the end of a statement. If done correctly you will have discovered the correct
taxon for the animal in question.
Most of us know what a lobster looks like
(see drawing at right). Look at statements 1 and 1’
on the key. 1’ is correct and directs us to go to 2.
The lobster is bilaterally symmetrical, hence 2’
directs us to go to 16. The lobster lacks 8
calcareous plates so 16’ directs us to 17. The
lobster is not worm-like, so we go to 20. There is
an external skeleton thus the lobster is in the
Phylum Arthropoda as well as the fact that we
should continue on to 21. Antennae are present
Figure
so we must go to 22. Since there are 2 pair of
antennae, gills and 5 pairs of jointed appendages
the lobster is in the class Crustacea.
As you proceed record the number for each
successive step so that you can go back if you made
a mistake. For the above example the steps were
1’,2,’ 9,’ 16’, 17, 20, 21, 22. More complicated keys
exist allowing a determination of genus and species,
however we will not use them in this course.
The exercise today will be two-fold.
1. Identification of specimens found in lab beginning with yourself. Record the
numbered steps you followed for each specimen. List a few key characteristics and
indicate the phylum and class (if given) of each animal keyed out. Your instructor will
indicate how many animals to key in this exercise.
2. Go to the seawater tank and key out the animals present List the phyla and classes
present.
Morphological Terms
Microscopic
-
Organisms whose gross structures can only be seen with the aid of a
microscope or other magnifying instrument.
Macroscopic Organisms whose gross structures can be seen with the unaided eye.
Unicellular
Organisms consisting of only a single cell.
Multicellular Organisms composed of many cells. Many are microscopic.
Asymmetry - Organisms that cannot be divided into identical halves.
Radial symmetry - Organisms that are circular or cylindrical in form and can be
divided into identical halves or mirror images in several different
ways.
Bilateral symmetry -Organisms that can cut along only one plane to achieve equal
halves.
Body Orientation - The portion of a bilaterally symmetrical animal that moves forward
and contains the mouth is anterior. Opposite anterior is termed
posterior. The upper surface or back is dorsal and the underside (or
belly) is ventral. Structures toward the center are medial and those
toward the sides are lateral.
Example: Microscopic, unicellular
animal, asymmetrical
Figure
Figure
Figure
Radial
Bilateral
Example: Macroscopic, multicellular animals, symmetry indicated (note orientations).
Segmentation – Many animals have structures or body parts, which are linearly repeated
analogous to the individual pieces in a loaf of sliced bread. The repeated
units are called segments, somites or metameres. Segments may be
external as well as internal. Internal segmentation may not be
accompanied by external segmentation so one must exercise care when
deciding if an animal is or is not segmented. Furthermore, serial
repetition of structures found on individual appendages (i.e.suckers on
the arms of an octopus) is not considered segmentation.
Figure
Example: Externally segmented animal
Appendages - structures, or parts that extend out
from the animal’s body and serve
various functions such as (1) sensory antennae, (2) offense/defense,
(3) locomotion, (4) sperm transfer
in males, (5) aid in respiration and
carrying eggs in females, (60 backward swimming, and (not shown)
food handling, gills, etc.
Figure
Figure
Example: Internally segmented
animal with an exoskeleton.
Example: External segmentation with an endoskeleton.
Skeleton – a skeleton is the hardened framework of an animal’s body which serves in
support, protection and muscle attachment. Some animals have external skeletons or
exoskeletons while others have internal skeletons or endoskeletons.