ZOO201 Complete Handouts 2022

ZOO – 201 ANIMAL DIVERSITY (INVERTEBRATES) · Architecture Patterns of Animals (Patterns of Organization) · Symmetry

➢ It describes how parts of an animal are arranged around a point or an axis.

1. Radial symmetry
2. Bilateral symmetry

Asymmetry

➢ Absence of a central point or axis around which body parts are equally distributed ➢ e.g. Protists and many sponges.

Other patterns of Organization:

1. Unicellular organization

2. Diploblastic organization (a. two germ layered gastrula)
3. Triploblastic organization (b. three germ layered gastrula)

I. The Triploblastic Acoelomate Pattern II. The Triploblastic Pseudocoelomate III. The Triploblastic Coelomate

1. Unicellular organization

Characteristics:

➢ Consist of single cell ➢ Also known as “Cytoplasmic” ➢ They are not simple ➢ They provide function of locomotion, food acquisition, digestion, Water and ion regulation, sensory perception and reproduction. ➢ They can also form cellular aggregates i.e., colonies

2. Diploblastic organization

➢ IT is simplest tissue level organization ➢ Body parts are organized into two layers i.e.

Ectoderm and Endoderm · Ectoderm · Endoderm

Give rise to gastrodermis, the tissues that line gut cavity

Taxonomy

The binomial system of nomenclature is universal and clearly indicates the level of classification involved in any description. No two kinds of animals have the same binomial name, and every animal has only one correct name. The entire scientific name is italicized or underlined because it is derived from Latin or is latinized. Thus, the scientific name of humans is written Homo sapiens. When the genus is understood, the binomial name can be abbreviated H. sapiens.

KINGDOMS OF LIFE

In 1969, Robert H. Whittaker described a system of classification that distinguished between kingdoms according to cellular organization and mode of nutrition.

According to this system, members of the kingdom Monera are the bacteria and the cyanobacteria. They are distinguished from all other organisms by being prokaryotic. Members of the kingdom Protista are eukaryotic and consist of single cells or colonies of cells. This kingdom includes Amoeba, Paramecium, and many others. Members of the kingdom Plantae are eukaryotic, multicellular, and photosynthetic. Plants have walled cells and are usually nonmotile. Members of the kingdom Fungi are also eukaryotic and multicellular. They also have walled cells and are usually nonmotile. Mode of nutrition distinguishes fungi from plants. Fungi digest organic matter extracellularly and absorb the breakdown products. Members of the kingdom Animalia are eukaryotic and multicellular, and they usually feed by ingesting other organisms or parts of other organisms. Their cells lack walls and they are usually motile. The emerging picture is that the five previously described kingdoms do not represent distinct evolutionary lineages. Ribosomal RNA is excellent for studying the evolution of early life on earth. Evolutionary conservation of this molecule means that closely related organisms (recently diverged from a common ancestor) are likely to have similar ribosomal RNAs. Distantly related organisms are expected to have ribosomal RNAs that are less similar, but the differences are small enough that the relationships to some ancestral molecules are still apparent. Studies of ribosomal RNA have led systematists to the conclusions that all life shares a common ancestor and that there are three major evolutionary lineages. Each of these lineages is called a domain.

The Archaea are prokaryotic microbes that live in extreme environments, such as high-

temperature rift valleys on the ocean floor, or high-salt or acidic environments. All members of the Archaea inhabit anaerobic environments.

Animal Systematics

The goal of animal systematics is to arrange animals into groups that reflect evolutionary relationships. Ideally, these groups should include a single ancestral species and all of its descendants. Such a group is called a monophyletic group. A character is virtually anything that has a genetic basis and can be measured—from an anatomical feature to a sequence of nitrogenous bases in DNA or RNA. Polyphyletic groups have members that can be traced to separate ancestors. A paraphyletic group includes some, but not all, members of a lineage. Evolutionary systematics is the oldest of the three approaches, sometimes called the “traditional approach,”. A basic assumption is that organisms closely related to an ancestor will resemble that ancestor more closely than they resemble distantly related organisms. Homologies are resemblances that result from common ancestry and are useful in classifying animals. Analogies are resemblances that result from organisms adapting under similar evolutionary pressures. The latter process is sometimes called convergent evolution. Numerical taxonomy emerged during the 1950s and 1960s and represents the opposite end of the spectrum from evolutionary systematics. The founders of numerical taxonomy believed that the criteria for grouping taxa had become too arbitrary and vague. Numerical taxonomists use mathematical models and computer-aided techniques to group samples of organisms according to overall similarity. They do not attempt to distinguish between homologies and analogies. Phylogenetic systematics (cladistics) is a third approach to animal systematics. The goal of cladistics is similar to that described for evolutionary systematics–the generation of hypotheses of genealogical relationships among monophyletic groups of organisms. Cladists contend, however, that their methods are more open to analysis and testing, and thus are more scientific, than those of evolutionary systematists. Characters that all members of a group share are referred to as symplesiomorphies (Gr. sym, together plesio, near morphe, form). Characters that have arisen since common ancestry with the outgroup are called derived characters or synapomorphies (Gr. syn, together apo, away morphe, form). Taxa that share a certain synapomorphy form a subset called a clade (Gr. klados, branch).

Phylogeny

Depicting phyla or classes as ancestral is misleading because evolution occurs in species groups (populations), not at higher taxonomic levels. Also, even though phyla or classes are depicted as ancestral, modern representatives of these “ ancestral phyla” have had just as long an evolutionary history as animals in other taxonomic groups that may have descended from the common ancestor. All modern representatives of any group of animals should be visualized at the tips of a “tree branch,” and they may be very different from ancestral species. Zoologists use modern representatives to help visualize general characteristics of an ancestral species, but never to specify details of the ancestor’s structure, function, or ecology. In addition to these problems of interpretation, evolutionary trees often imply a ladderlike progression of increasing complexity. This is misleading, because evolution has often resulted in reduced complexity and body forms that are evolutionary failures. In many cases, evolution does not lead to phenotypes that permit survival under changing conditions, and extinction occurs. Further, the common representation of a phylogeny as an inverted cone, or a tree with a narrow trunk and many higher branches, is often misleading. This implies that evolution is a continuous process of increasing diversification. The fossil records show that this is often wrong. For example, 20 to 30 groups of echinoderms (sea stars and their relatives) are in the fossil record, but there are only five modern groups. This evolutionary lineage, like many others, underwent rapid initial evolutionary diversification. After the initial diversification, extinction—not further diversification—was the rule. Contemporary paleontologist Stephen J. Gould uses the term contingency to refer to rapid evolutionary explosion followed by a high likelihood of extinction.