Bracket key and indented key

Bracket key and indented key

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

2. BRACKET KEY AND INDENTED KEY

3. 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

4. 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.

5. 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.

6. 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.

7. 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.

8. 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

9. 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

10. 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

11. 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.

12. Insect Fish Amphibian Bird Chimpanzee Human Bipedal locomotion Hair Amniotic egg Tetrapod Vertebrae Development from Blastula