Dichotomous Key

Dichotomous Key

Prior to evolutionary theory, scientists relied on similarity of

physical characteristics to classify organisms. An 18th century

naturalist, Carolus Linneas, developed a taxonomic classification

system. This hierarchical system divides organisms into 5 kingdoms.

Organisms visible to the unaided human eye fall into the plant,

animal, or fungi kingdom. Kingdoms are then divided into phylum.

This division is based body type and skeletal organization. Phylum

are then divided into subphylum. Subphylum are divided into classes,

orders, genus, and then species. This system of classification is

still used by scientists today[1].

In this assignment, seven organisms are presented which are to be

classified into phylum or class based on a dichotomous key. The first

organism presented in this assignment is a starfish. Starfish fall

into the class Asteroidea. Starfish have a regular body shape with

radial symmetry. It has arms which extend from a central disk and has

a knobby body surface. Using these physical characteristics, we would

classify the starfish into the Kingdom Animalia, phylum Echinodermata,

and class Asteroidea.

The second organism is a species of bird. Again using the dichotomous

key, we find that this organism has a regular body shape. The bird

has bilateral symmetry with an internal skeleton. The bird’s

appendages are jointed, not fin-like. The body of the bird is not

covered in scales, the skin is covered with feathers and claws are

present. Using these physical characteristics we find that this

organism falls into the class Aves

The third organism appears to be a type of shark. The shark has a

regular body shape with bilateral symmetry and an internal skeleton.

The body of this animal is not fish-like and appendages are jointed.

The body is not covered by scales and claws are absent. Therefore,

this organism falls into the class Amphibian.

The fourth organism has a regular body shape with bilateral symmetry

and an internal skeleton. The organism has a fish-like body with