Bracket key and indented key

Mariam Zaheer
Assistant Professor
Zoology Department
Govt. Graduate College of Science Wahdat Road,
Lahore

Taxonomic Keys
 A key is a device by which each specimen in a group of
specimens may be identified.
 This can be achieved by presenting diagnostic characters in a
series of alternative choices.
 The worker finds the correct name of his specimen by making
the appropriate choice in a series of consecutive steps.
 Types of dichotomous keys
1. Bracket key
2. Indented key
3. Pictorial key

How to construct key?
 A good key is strictly dichotomous, not offering more than
two alternatives at any point.
 The style of key is telegraphic.
 Alternatives should be precise.
 The key does not has words such as is, are, was, were,
has have etc.
 No abbreviation is used in the key.

Bracket Key
Advantage
 It is most commonly used.
 the couplets are composed of alternatives which are side by side
for ready comparison.
 It is also economical in space.
 It may be run forward or backward with equal facility by following
the numbers .
 The numbers in brackets are responsible for running backward in
the key.
Disadvantage
 It has disadvantage that the relationship of the divisions is not
apparent to eye.

Indented Key
Advantage
 To indent means to begin a line at greater or less distance
from the margin.
 The relationship of the various divisions is apparent to the
eye.
Disadvantage
 The alternatives may be widely separated and wasteful of
space.
 It is generally used only for short keys, keys to higher taxa
or comparative keys.

Pictorial Key
Advantage
 The critical characters are illustrated.
 It can be used by non-technical persons, field workers,
engineers as well as entomologists.
 These keys have also been employed as field guides to
higher taxa, vertebrates and flowering plants.
Disadvantage
 It is too lengthy.

Taxa
Characters
Salticidae Lycosidae Oxyopidae Tetragnathidae Pholcidae
No. of eyes 8 8 8 8 6
No. of rows of
eyes
3ss 3 2 2 2
Spinnerets
position
End of
abdomen
End of
abdomen
End of
abdomen
Centre of
abdomen
End of
abdomen
AME>ALE Yes No No No No
Eyes in
hexagonal
arrangement
No No Yes No No

Bracket Key
1. Six eyes present…………………………..………......Pholcidae
Eight eyes present …………...….....……….................2
2.(1) Spinnerets are present at the
end of abdomen………………………………….........3
Spinnerets are present at the
centre of abdomen……………………………….........Tetragnathidae
3. (2) Anterior median eyes greater
than anterior lateral eyes……………………………....Salticidae
Anterior median eyes not
greater than anterior lateral eye……………………….4
4. (3) Eyes present in hexagonal
arrangement…………………………………….............Oxyopidae
Eyes not present in hexagonal
arrangement……………………………………………..Lycosidae

Indented Key
A. Six eyes present. . ……………………………..................................Pholcidae
AA. Eight eyes present
B. Spinnerets present at
the end of abdomen
C. Anterior median eyes greater
than anterior lateral eyes…………………………..Salticidae
CC. Anterior median eyes not
greater than anterior lateral eyes
D. Eyes present in hexagonal
arrangement………………………........Oxyopidae
DD. Eyes not present in hexagonal
arrangement……………………….......Lycosidae
BB. Spinnerets present at
the centre of abdomen………...........................................Tetragnathidae

Cladogram
 A diagram depicting taxonomic relationship between
organisms on the basis of shared derived characters.
Out group
 A group of organism not belonging to the group whose
evolutionary relationships are being investigated.
 Such a group is used for comparison to assess which
characteristics of the group being studied are more widely
distributed and may therefore be older in origin.

Insect Fish Amphibian Bird Chimpanzee Human
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Amniotic egg
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Bracket key and indented key

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