Invertebrates

CHAPTER ONE

1.0              INTRODUCTION

Invertebrates are animals without a vertebral column. This has led to the conclusion that invertebrate are a group that deviates from the norm, invertebrate. This has been said to be due to the fact that researchers in the past, such as lamark’s theory of evolution, he evolution, he believed that characteristics acquired through the evolutionary process involved  not only survival, but also progression toward a “higher form”, to which humans and vertebrates were closer than invertebrate were in any event in the 2000 (Barnes etal; 2001) edition of invertebrate zoology, it is noted that “division of the animal kingdom in to vertebrates and invertebrates is artificial and reflects human bias in favor of mains own relatives. The book also point out that the group lumps a vast a vast number of species together, so that no one characteristics describe all invertebrates. In addition, some species included are only remotely related to one another, with some more related to vertebrates than other  invertebrate (Barns and Robert, 1968) for many centuries, invertebrates , invertebrates have been neglected by biologist, in favor of big vertebrates and “useful” or charismatic species (Ducarme, 2015) During the 20^th century, many discoveries made invertebrate zoology, one of the major fields of natural sciences with prominent discoveries of medicine, genetics, ecology. (Ducarme 2015).

Invertebrates are also used by scientists in the field of aquatic biomonitoring to evaluate the effect of water pollution and climate change. (Lawrence et al 2010). The trait that is common to all invertebrates is the absence of a vertebral column. This creates a distinction between invertebrates and vertebrates. The distinction is one of convenience only. It is not base on any clear biologically homologous trait any more than the common trait of having wings functionally unites insects, bats, and birds, or than not having wings unit’s tortoises, snails and sponges.  Being animals invertebrate are heterotrophs and require of sustenance in the form of the consumption of other organisms with a few exception, such as porifera, invertebrate generallyhave body composed of differentiated tissues. There is also typically a digestive chamber with one or two opening to the exterior. Most invertebrates reproduce at least partly through sexual reproduction. They produce specialized reproductive cells that undergo meiosis to produce smaller motile spermatozoa or large, non-motile ova (Schwartz et al; 2010) which fuse to form zygotes, which develop in to new individual reproduction or sometimes both methods of reproduction.

1.1       CLASSIFICATION OF INVERTEBRATE

Invertebrate can be classified in to several main categories, some of which are taxonomically obsolescent or debatable, but still used as terms of convenience. Each however appears in its own article at the following links protozoa (like the worms, an arbitrary grouping of convenience link to their article for details). The word “invertebrate” comes from the form of the latin word vertebra. Vertebra means a joint in general and sometimes specifically a joint from the spinal column of a vertebrate. In turn the jointed aspect of vertebra divided from the concept of turning, expressed in the root verto or vorto to turn. (Turker, 1931). The term invertebrates is not always precise among non-biologiests since it close not always describe a taxon in the same way that Arthropoda, Vertebrate or Manidae do. Each of these terms descrbes a valid taxon phylum, subphylum or family. “Invertebra” is a term of convenience not a taxon, it has very little circumscriptional significance except within the chordata. The vertebrate as a subphylum comprises such a small proportion of the metazoan that to speak of the kingdom animalia in terms of “vertebrata” and invertebrate” has limited practicality. In the more formal taxonomy of animalia other altributes that logically should precede the presence of a notochord. However, even the notocord would be a less fundamental criterion than aspects of embryological development and symmetry (pecheniket el; 1996) or perhaps bauphanbrusa (Brusa et al; 1990) of the million more animal species in the word more than 98% are invertebrates.

Invertebrate don’t have a skeleton of bone, either internal or external. They include hugely varied body plans. Many have fluid filled, hydrostatic skeleton, like jelly fish or worms. Others have hard exo-skeletons, outer shell like those of insect and crustaceans. The most familiar invertebrats include the protozoa, porifera, coelenterate, protyhelminthes, nematode, Annelida, Echinodermata, mollusca and Arthropoda.

Arthropoda include insect, crustaceaus and arachnids.

-          Sponges (Porifera)

-          Stinging jelly fish (Cnidaria)

-          Comb jellies (Ctenophora)

-          Flatworm (Platy helminthes)

-          Round or thread worms (Nematoda)

-          Segmented worms (Annelida)

-          Insect, spiders, crabs and their kin (Arthropoda)

-          Cuttle fish, snails, mussels and their kin (Mollusca)

-          Starfish, sea-cucumbers and their kin  (Echinodermata)

1.2         AIM AND OBJECTIVES

-          To collect and preserve some invertebrate for further study.

-          To examine the morphological feature of the organisms.

CHAPTER TWO

2.0.      LITERATURE REVIEW

Invertebrate are animals lacking a back bone such as an arthropod, muscles, annelid and coelenterate. The invertebrate constitute an artificial division of the animal kingdom comprising 95 percent of animal species and about thirty different phyla. All living things are place in to group depending on common characteristics. The animal kingdom is informally divided into two groups, the vertebrate and invertebrates. Invertebrate are a group of animals that have no backbone unlike animals such as reptiles, amphibians, fish, birds, and mammals who all have backbone. (Schwart et al; 2010).

Invertebrate are animals that neither posses nor develop a vertebral column, derived from notochord. This include all animals apart from the subphylum vertebrata, familiar examples of invertebrate include insects, crabs, labsters, and their kin, snails clams, octopuses and their kin, starfish, sea-urchins and their kin and worms. The majority of animal species are invertebrate. One estimate puts the figure at 97%. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of vertebrata. Some of the so called invertebrate, such as the chaetognatha, Hemichordata, Tunicate and Cephalochordata are more closely related to the vertebrates than to other invertebrate. This makes the term “Invertebrate” almost meaningless for taxonomic purposes. The word “Invertebrate” come from the form of the spinal column of a vertebral derived from the concept of turning expressed in  the root verto or vorto to turn. (Riley et al; 2005)

2.1.      GENERAL CHARACTERISTICS OF INVERTEBRATE

The main characteristics that separates invertebrates from other organisms is the absence of the spinal column and backbone. The trait that is common to all invertebrates is the absence of vertebral column. This creates a distinction between invertebrates and vertebrates. The distinction is one of convenience only; it is not based on any clear biologically homologous trait any more than the common trait of having wings functionally unites insects, bats, and birds or than not having wings unites tortoises, snails and sponges. Being animals invertebrates are heterotrophs, and require sustenance in the form of the consumption of other organisms. With few exception such as the porifera, invertebrate generally have bodies composed of differentiated tissues. There is also typically a digestive chamber with one or two openings to the exterior.

-          They are multicellular organism, then completely lack cell wall.

-          They are devoid hard bony endoskeleton

-          Due to the lack of complex skeletal systems, some invertebrates tend to be slow and small in nature.

-          Due to the lack of back bone and complex nervous system the invertebrate cannot occupy of multiple environment though they are found in the harshest of the environments.

-          Invertebrate live all over the world in various habitats.

-          Body is divided into three part head, thorax and the abdomen.

-          They do not have lungs for respiration

-          Respiration is through skin

-          Some invertebrate groups possess a hard chitinous exoskeleton.

-          Most of them have tissue, that are specific organization of cells

-          Most of them reproduce sexually by the fusion of the male and female gametes.

-          Few invertebrate like sponges are sedentary, but most of the organism are motile.

-          Most invertebrate are organized with symmetric body organization (Hamiton et al; 2009)

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