Invertebrate Evolution

Introduction

Animal classification is an issue of arranging out likenesses and differences, of putting animals in groups and then shattering those assemblies apart into subgroups. The whole endeavor conceives the structure—a hierarchy in which large high-level groups sort out bold and obvious dissimilarities, while low-level groups tease apart subtle, nearly imperceptible, variations. This arranging process enables scientists to recount evolutionary relationships, identify distributed traits, and focus exclusive characteristics down through various grades of animal assemblies and subassemblies.

Among most rudimentary criteria by which animals are sorted is if or not they own the backbone. This lone trait places an animal into one of just two groups: vertebrates or invertebrates and comprises the basic partition amidst all animals living today as well as those that has long before disappeared. If we are to understand anything about an animal, we should first aim to work out whether it is an invertebrate or the vertebrate. We'll then be on our way to comprehending its place inside animal world.

Difference between Vertebrates and Invertebrates

Vertebrates

Vertebrates (Subphylum Vertebrata) are animals that own an interior skeleton (endoskeleton) that encompasses the backbone made up of the column of vertebrae (Keeton, 1986:1150). The Subphylum Vertebrata is an assembly inside Phylum Chordata (commonly called 'chordates') and as such inherits characteristics of all chordates:

* Bilateral symmetry

* Body segmentation

*Endoskeleton (bony or cartilaginous)

*Pharyngeal pouches (present throughout some stage of development)

* Complete digestive system

* Ventral heart

* closed blood system

*follow (at some stage of development)

In addition to traits recorded above, vertebrates possess one added trait that makes them exclusive amidst chordates: presence of the backbone. There are the couple of assemblies of chordates that do not own the backbone (these organisms are not vertebrates and are rather than referred to as invertebrate chordates).

The animal categories that are vertebrates include:

*Jawless fish (Class Agnatha)

*Armored fish (Class Placodermi) - extinct

*Cartilaginous fish (Class Chondrichthyes)

*Bony fish (Class Osteichthyes)

* Amphibians (Class Amphibia)

* Reptiles (Class Reptilia)

* Birds (Class Aves)

* Mammals (Class Mammalia)

Invertebrates

Invertebrates are the broad assemblage of animal assemblies (they do not pertain to the single subphylum like vertebrates) all of which lack the backbone. Some (not all) of animal assemblies that are invertebrates encompass:

* Sponges (Phylum Porifera)

*Jellyfish, hydras, ocean anemones, corals (Phylum Cnidaria)

*Comb jellies (Phylum Ctenophora)

* Flatworms (Phylum Platyhelminthes)

* Molluscs (Phylum Mollusca)

* Arthropods (Phylum Arthropoda)

*Segmented worms (Phylum Annelida)

* Echinoderms (Phylum Echinodermata)

Evolution of Invertebrate

Evolution is method by which all dwelling things have developed from primitive organisms through alterations happening over billions of years, method that encompasses all animals and plants. Exactly how evolution happens is still an issue of debate, but there are numerous distinct ideas and that it occurs is technical fact. Biologists acquiesce that all dwelling things arrive through long annals of alterations formed by personal and chemical processes that are still taking place. It is possible that all organisms can be traced back to origin of Life from one celled organism. The most direct verification of evolution is research of Paleontology, or study of life in past through fossil continues or impressions, generally in rock. Changes occur in living organisms that serve ...