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Name _____________________________ Period _________ Living Environment / Biology Date ______________________ 1 of 6
LAB ____. CLASSIFICATION & DICHOTOMOUS KEYS
As we have discussed in class, with the help of Carolus Linnaeus, scientists have developed a hierarchical organizing and naming system for all organisms — from Kingdom all the way down to Genus and Species. They have also detailed the characteristics by which organisms are clustered into those groups. For example, all organisms which are warm-blooded, have hair, give birth to live young, and produce milk are considered Mammals. Now that we have this organized system, we can classify all living creatures into these groups. And we also can use the characteristics and groups to identify unknown specimens. Like “What bird is that?” or “What kind of bug is that How does one go about identifying the species, genus, etc., of a specimen whose identity is unknown (to the person who wishes to identify the specimen)? The most useful tool for such identifications is the dichotomous classification key. A dichotomous key contains information useful in identifying unknown organisms, and is arranged in a way that allows the information to be used quickly. It is the most widely used type of key in biological sciences. In a dichotomous key, the user is presented with a sequence of choices between paired statements based on characteristics of the organism. By always taking the correct choice the identity of the organism will eventually be revealed. Let’s begin with a brief exercise to illustrate this.
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FRUIT IDENTIFICATION
We will practice using a dichotomous key with some items we are familiar with: fruit. To use a dichotomous key, one begins with the first couplet of paired statements, deciding which statement is true for a specimen. The key may then tell you what organism or group you have, or it may direct you to another couplet. Choose the fruits at your lab bench one at a time and follow the key until you have arrived at an identification for each. 1a. Fruits occur singly ........................................................................... Go to 3 1b. Fruits occur in clusters of two or more ........................................... Go to 2 2a. Fruits are round ................................................................................ Grapes 2b. Fruits are elongate .........................................................................Bananas 3a. Thick skin that separates easily from flesh .................................. Oranges 3b. Thin skin that adheres to flesh ........................................................ Go to 4 4a. More than one seed per fruit .............................................................Apples 4b. One seed per fruit ............................................................................ Go to 5 5a. Skin covered with velvety hairs ..................................................... Peaches 5b. Skin smooth, without hairs ................................................................Plums Note that the overall organization of the key is very important. One cannot simply read through a key to find characteristics that apply to a specimen. For example, statement 3a above ( thick skin that separates easily from meat ) is true of both oranges and bananas. Correct identification of bananas depends on couplet number 1, which separates clustering vs. non-clustering fruits. You must walk through a dichotomous key step-by-step and not jump around until the key tells you to.
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CLASSIFICATION KEY FOR COMMON FRESHWATER FISH OF NEW YORK STATE
Questions Identify/Go To 1a. Body noticeably covered with scales 2 1b. Scales not covering body or too small to be seen 12 2a. Dorsal fin single 3 2b. Dorsal fins two or more, joined or separated 6 3a. Body more than four times as long as broad (top to bottom): front edge of dorsal fin far back on body; mouth large, hinge back of eye
3b. Body less than four times as long as broad: front edge of dorsal fin about midway between head and tail; mouth not large, hinge in front of eye
4a. Dark lines forming netted design on body: fins not spotted Pickerel 4b. Body covered with yellow spots; fins spotted Northern Pike 5a. Mouth turned downward: barbels absent; dorsal fin not elongated White Sucker 5b. Mouth not turned downward: barbels present; dorsal fin elongated Carp 6a. Two dorsal fins separated, the anterior spiny and the posterior soft 7 6b. Two dorsal fins united, forming an anterior spiny portion and a posterior soft portion
7a. Top of head concave, forming a hump in front of dorsal fin; dark vertical bars on body Yellow Perch 7b. Top of head not concave, body sloping to dorsal fin and not forming a hump; dark blotches on body Walleye 8a. Body more than three times as long as broad 9 8b. Body less than three times as long as broad 10 9a. Hinge of jaws behind the eye: notch between spiny and soft dorsal fin deep and nearly separating into two fins Large Mouthed Bass 9b. Hinge of jaws below the eye; notch between spiny and soft dorsal fin not nearly separating into two fins Small Mouthed Bass 10a. Mouth large, hinge below or behind eye 11 10b. Mouth small, hinge in front of eye Bluegill 11a. Five to seven spines in dorsal fin; dark spots forming broad vertical bars on sides, Red/orange earspot on gill covering Pumpkinseed 11b. Ten or more spines in dorsal fin: sides flecked with dark spots Rock Bass 12a. Body much elongated and snakelike: dorsal, caudal, and anal fins continuous American Eel 12b. Body not elongated and snakelike: dorsal, caudal, and anal fins separate; adipose fin present
13a. Barbels growing from lips arid top of head; head large and broad 14 13b. Barbels lacking; head not large and broad 16 14a. Caudal fin deeply forked; head tapering 15 14b. Caudal fin rounded or slightly indented but not forked: head blunt Bullhead 15a. Dorsal fin rounded at top: body silvery, speckled with black markings Channel Catfish 15b. Dorsal fin long and pointed at too: body bluish-gray without speckles Blue Catfish 16a. Caudal fin deeply forked: back not mottled and with few spots Atlantic Salmon 16b. Caudal fin square or slightly indented; back mottled or spotted 17 17a. Back and caudal fin spotted: broad horizontal band along sides Rainbow Trout 17b. Back mottled with dark lines: caudal fin not spotted; fins edged with white Brook Trout
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Data: The following data were collected during this activity:
Fish # Identified as
Identification pathway
(list numbers & letters separated by commas)
