Download 5 SYSTEMATICS AND MORPHOLOGY Objectives After completing

5 SYSTEMATICS AND MORPHOLOGY
Objectives
After completing this exercise you should be able to
1. Know the hierarchical classification of animals and the binomial nomenclature system.
2. Study the animals according to the levels of organization using morphology of symmetry,
grade of tissue construction, body cavity and development.
Introduction
Biosphere is rich and diverse with the biota consisting of many ancient and newly evolved
organisms. This diversity of animals and a keen desire to understand the evolutionary
relationships has shaped up the discipline of systematics.
Systematics
Systematics is a scientific approach of classifying animals and assigning them a position in the
evolutionary tree. This discipline of biology is described as taxonomy. Almost 1.6 million species
have already been described and named of the existing biota. A Swedish botanist Carl von Linne,
introduced a scientific naming method to plants, called as the binomial nomenclature system.
According to this method the organisms would have a unique combination of two Latin words,
one expressing the genus and the other its species, eg Homo sapiens (man), Panthera pardus
(leopard). The animals are also categorized into different broader groups such as family order,
class, phylum, kingdom and domain.
Common name:
Man
Leopard
Species:
sapiens
pardus
Genus:
Homo
Panthera
Family:
Hominidae
Felidae
Order:
Primates
Carnivora
Class:
Mammalia
Mammalia
Phylum:
Chordata
Chordata
Kingdom:
Animalia
Animalia
Domain:
Eukarya
Eukarya
Levels of organization
Although animals express a tremendous diversity in morphology, exhibit a basic body plan at
specific grade levels. A body plan is a set of morphological and developmental traits integrated
into the living body. These levels of organization can be studied on the basis of morphology of
symmetry, grade of tissue construction, body cavities and development.
Symmetry
Symmetry is the balanced arrangement of body parts along common axis or different planes.
There are three different patterns of symmetry:
1) Asymmetry – Is irregular arrangements of body parts, thus the body cannot be divided into
two equal halves through any axis or plane. eg Amoeba, Sponges.
Observe
Sketch
2) Radial symmetry – Is arrangement of body parts around one central axis, thus the body can be
divided into two equal halves through that axis along any plane. eg. Sea anemone, Sand dollar.
Observe
Sketch
3) Bilateral symmetry – Is arrangement of body parts such that the body can be divided into two
equal halves through an axis along one plane. eg. Fish, Frog, Fox.
.
Observe
Grade of Tissue Construction
Multicellular organisms with different types of cells forming tissues at different grades of
arrangements. There are three different grades of construction:
1) Tissue grade – Multicellular organisms with different cell types aggregating to form simple
tissues but not organs or organ systems. eg Sponges - Porifera
Observe
Sketch
2) Diploblastic construction – Multicellular organisms with different cell types forming two tissue
layers, ectoderm and endoderm derived from embryonic germ layers. eg Hydra - Cnidaria.
Observe
3) Triploblastic construction – Multicellular organisms with different cell types forming three
tissue layers, ectoderm, mesoderm and endoderm derived from embryonic germ layers.
eg Earthworm - Annelida.
Observe
Body Cavity
The triploblastic animals possess an air or water filled space separating the digestive system from
the body wall. This is called as the body cavity or coelom.
There are three different groups of organisms on the basis of arrangements of these layers :
1) Acoelomate – Do not have any body cavity as the region between the ectoderm and endoderm
gets filled with mesenchyme. eg Planaria - Platyhelminthes.
2) Pseudocoelomate – Do have a cavity, but this cavity is not entirely lined by mesoderm.
eg. Roundworms - Nematoda.
3) Coelomate – Have a body cavity within the mesoderm, and a specialized mesodermal
peritoneum line the digestive system. eg Earthworm – Annelida.
Observe
Body Development
Evolution of bilaterian into diverse forms of higher animals involved many changes over millions
of years. However the bilateral animals diverged into two main groups, the Protostomes and the
deueterostomes.
There are two different groups of organisms on the basis of development :
1) Protostomes – In these animals the blastopore develops into mouth. eg the invertebrate phyla
such as, Platyhelminthes, Rotifers, Nematodes, Molluscs, Annelids and Arthropods.
2) Deuterostomes – These animals have their blastopore developed into anus. eg Echinoderms,
Hemichordates and Chordates.
EXERCISE
1) List the organisms into the correct columns based on their body symmetry pattern.
Asymmetry
Radial
Bilateral
2) Identify the body symmetry pattern of the given animal and sketch its figure.