Which Characteristics Are Utilized When Differentiating Animals From One Another?

Introduction to Animal Diversity

Features Used to Classify Animals

OpenStaxCollege

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Learning Objectives

By the terminate of this section, you will be able to:

• Explain the differences in animal body plans that support basic animal classification
• Compare and contrast the embryonic development of protostomes and deuterostomes

Scientists have developed a classification scheme that categorizes all members of the brute kingdom, although in that location are exceptions to nearly "rules" governing fauna classification ([link]). Animals are primarily classified according to morphological and developmental characteristics, such as a body plan. 1 of the most prominent features of the body plan of truthful animals is that they are morphologically symmetrical. This means that their distribution of body parts is balanced along an axis. Additional characteristics include the number of tissue layers formed during development, the presence or absence of an internal body cavity, and other features of embryological development, such as the origin of the mouth and anus.

Art Connexion

The phylogenetic tree of animals is based on morphological, fossil, and genetic evidence.

Which of the following statements is false?

1. Eumetazoans have specialized tissues and parazoans don't.
2. Lophotrochozoa and Ecdysozoa are both Bilataria.
3. Acoela and Cnidaria both possess radial symmetry.
4. Arthropods are more closely related to nematodes than they are to annelids.

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Animal Characterization Based on Body Symmetry

At a very basic level of nomenclature, truthful animals can be largely divided into three groups based on the type of symmetry of their body programme: radially symmetrical, bilaterally symmetrical, and asymmetrical. Asymmetry is a unique feature of Parazoa ([link]a). Only a few creature groups display radial symmetry. All types of symmetry are well suited to meet the unique demands of a detail animate being's lifestyle.

Radial symmetry is the arrangement of body parts around a central axis, as is seen in a drinking glass or pie. It results in animals having elevation and bottom surfaces just no left and correct sides, or front end or back. The two halves of a radially symmetrical animal may be described every bit the side with a mouth or "oral side," and the side without a oral cavity (the "aboral side"). This class of symmetry marks the trunk plans of animals in the phyla Ctenophora and Cnidaria, including jellyfish and adult sea anemones ([link]bc). Radial symmetry equips these ocean creatures (which may exist sedentary or only capable of wearisome movement or floating) to feel the environment as from all directions.

The (a) sponge is asymmetrical. The (b) jellyfish and (c) anemone are radially symmetrical, and the (d) butterfly is bilaterally symmetrical. (credit a: modification of work by Andrew Turner; credit b: modification of work by Robert Freiburger; credit c: modification of work by Samuel Chow; credit d: modification of work past Cory Zanker)

Bilateral symmetry involves the division of the animal through a sagittal airplane, resulting in two mirror image, correct and left halves, such every bit those of a butterfly ([link]d), crab, or human body. Animals with bilateral symmetry have a "head" and "tail" (inductive vs. posterior), front end and back (dorsal vs. ventral), and correct and left sides ([link]). All true animals except those with radial symmetry are bilaterally symmetrical. The evolution of bilateral symmetry that allowed for the formation of inductive and posterior (head and tail) ends promoted a miracle called cephalization, which refers to the collection of an organized nervous organisation at the animal's anterior end. In contrast to radial symmetry, which is best suited for stationary or express-motion lifestyles, bilateral symmetry allows for streamlined and directional move. In evolutionary terms, this simple form of symmetry promoted active mobility and increased sophistication of resource-seeking and predator-casualty relationships.

The bilaterally symmetrical human body tin be divided into planes.

Animals in the phylum Echinodermata (such equally sea stars, sand dollars, and sea urchins) display radial symmetry every bit adults, but their larval stages showroom bilateral symmetry. This is termed secondary radial symmetry. They are believed to have evolved from bilaterally symmetrical animals; thus, they are classified as bilaterally symmetrical.

Link to Learning

Spotter this video to see a quick sketch of the dissimilar types of body symmetry.

Animal Characterization Based on Features of Embryological Development

Most animal species undergo a separation of tissues into germ layers during embryonic development. Recall that these germ layers are formed during gastrulation, and that they are predetermined to develop into the animal's specialized tissues and organs. Animals develop either two or three embryonic germs layers ([link]). The animals that display radial symmetry develop ii germ layers, an inner layer (endoderm) and an outer layer (ectoderm). These animals are called diploblasts. Diploblasts take a non-living layer between the endoderm and ectoderm. More complex animals (those with bilateral symmetry) develop three tissue layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). Animals with three tissue layers are called triploblasts.

Art Connexion

During embryogenesis, diploblasts develop two embryonic germ layers: an ectoderm and an endoderm. Triploblasts develop a tertiary layer—the mesoderm—between the endoderm and ectoderm.

Which of the following statements about diploblasts and triploblasts is false?

1. Animals that brandish radial symmetry are diploblasts.
2. Animals that display bilateral symmetry are triploblasts.
3. The endoderm gives rising to the lining of the digestive tract and the respiratory tract.
4. The mesoderm gives rising to the central nervous system.

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Each of the 3 germ layers is programmed to requite rise to detail body tissues and organs. The endoderm gives rise to the lining of the digestive tract (including the stomach, intestines, liver, and pancreas), equally well as to the lining of the trachea, bronchi, and lungs of the respiratory tract, along with a few other structures. The ectoderm develops into the outer epithelial roofing of the torso surface, the central nervous arrangement, and a few other structures. The mesoderm is the tertiary germ layer; information technology forms betwixt the endoderm and ectoderm in triploblasts. This germ layer gives rise to all muscle tissues (including the cardiac tissues and muscles of the intestines), connective tissues such as the skeleton and blood cells, and most other visceral organs such as the kidneys and the spleen.

Presence or Absence of a Coelom

Farther subdivision of animals with three germ layers (triploblasts) results in the separation of animals that may develop an internal body cavity derived from mesoderm, chosen a coelom, and those that practise not. This epithelial cell-lined coelomic cavity represents a space, usually filled with fluid, which lies between the visceral organs and the trunk wall. It houses many organs such as the digestive organisation, kidneys, reproductive organs, and center, and contains the circulatory system. In some animals, such as mammals, the part of the coelom called the pleural cavity provides space for the lungs to expand during animate. The evolution of the coelom is associated with many functional advantages. Primarily, the coelom provides cushioning and stupor absorption for the major organ systems. Organs housed within the coelom tin can grow and move freely, which promotes optimal organ development and placement. The coelom also provides space for the improvidence of gases and nutrients, every bit well every bit body flexibility, promoting improved animal motion.

Triploblasts that practise not develop a coelom are chosen acoelomates, and their mesoderm region is completely filled with tissue, although they practise still have a gut cavity. Examples of acoelomates include animals in the phylum Platyhelminthes, also known as flatworms. Animals with a true coelom are called eucoelomates (or coelomates) ([link]). A truthful coelom arises entirely within the mesoderm germ layer and is lined by an epithelial membrane. This membrane also lines the organs within the coelom, connecting and belongings them in position while allowing them some gratuitous motion. Annelids, mollusks, arthropods, echinoderms, and chordates are all eucoelomates. A 3rd grouping of triploblasts has a slightly different coelom derived partly from mesoderm and partly from endoderm, which is establish between the two layers. Although still functional, these are considered simulated coeloms, and those animals are called pseudocoelomates. The phylum Nematoda (roundworms) is an example of a pseudocoelomate. True coelomates tin can be further characterized based on sure features of their early embryological development.

Triploblasts may be (a) acoelomates, (b) eucoelomates, or (c) pseudocoelomates. Acoelomates have no body cavity. Eucoelomates accept a body crenel within the mesoderm, called a coelom, which is lined with mesoderm. Pseudocoelomates also have a torso cavity, only it is sandwiched betwixt the endoderm and mesoderm. (credit a: modification of work past Jan Derk; credit b: modification of work by NOAA; credit c: modification of work by USDA, ARS)

Embryonic Evolution of the Mouth

Bilaterally symmetrical, tribloblastic eucoelomates can be further divided into two groups based on differences in their early embryonic evolution. Protostomes include arthropods, mollusks, and annelids. Deuterostomes include more than complex animals such as chordates but also some simple animals such as echinoderms. These two groups are separated based on which opening of the digestive cavity develops first: oral cavity or anus. The give-and-take protostome comes from the Greek discussion significant "rima oris first," and deuterostome originates from the word significant "oral fissure second" (in this case, the anus develops commencement). The mouth or anus develops from a construction called the blastopore ([link]). The blastopore is the indentation formed during the initial stages of gastrulation. In afterwards stages, a second opening forms, and these 2 openings volition eventually give rising to the oral cavity and anus ([link]). It has long been believed that the blastopore develops into the oral fissure of protostomes, with the second opening developing into the anus; the opposite is true for deuterostomes. Contempo evidence has challenged this view of the evolution of the blastopore of protostomes, however, and the theory remains nether contend.

Some other stardom between protostomes and deuterostomes is the method of coelom formation, beginning from the gastrula stage. The coelom of nearly protostomes is formed through a process called schizocoely, meaning that during development, a solid mass of the mesoderm splits apart and forms the hollow opening of the coelom. Deuterostomes differ in that their coelom forms through a procedure chosen enterocoely. Here, the mesoderm develops as pouches that are pinched off from the endoderm tissue. These pouches somewhen fuse to form the mesoderm, which then gives ascension to the coelom.

The earliest stardom betwixt protostomes and deuterostomes is the type of cleavage undergone by the zygote. Protostomes undergo spiral cleavage, meaning that the cells of 1 pole of the embryo are rotated, and thus misaligned, with respect to the cells of the opposite pole. This is due to the oblique angle of the cleavage. Deuterostomes undergo radial cleavage, where the cleavage axes are either parallel or perpendicular to the polar axis, resulting in the alignment of the cells between the two poles.

Eucoelomates can exist divided into 2 groups based on their early embryonic evolution. In protostomes, function of the mesoderm separates to grade the coelom in a procedure called schizocoely. In deuterostomes, the mesoderm pinches off to form the coelom in a process called enterocoely. It was long believed that the blastopore developed into the oral fissure in protostomes and into the anus in deuterostomes, but recent evidence challenges this belief.

At that place is a second distinction between the types of cleavage in protostomes and deuterostomes. In improver to spiral cleavage, protostomes as well undergo determinate cleavage. This means that fifty-fifty at this early stage, the developmental fate of each embryonic cell is already determined. A cell does not have the ability to develop into any cell type. In dissimilarity, deuterostomes undergo indeterminate cleavage, in which cells are not yet pre-determined at this early stage to develop into specific prison cell types. These cells are referred to as undifferentiated cells. This feature of deuterostomes is reflected in the existence of familiar embryonic stem cells, which have the ability to develop into any cell type until their fate is programmed at a later developmental stage.

Evolution Connectedness

The Evolution of the CoelomOne of the beginning steps in the nomenclature of animals is to examine the fauna'south body. Studying the body parts tells us not only the roles of the organs in question simply also how the species may have evolved. One such structure that is used in classification of animals is the coelom. A coelom is a body cavity that forms during early embryonic development. The coelom allows for compartmentalization of the trunk parts, so that different organ systems can evolve and nutrient transport is possible. Additionally, considering the coelom is a fluid-filled cavity, it protects the organs from shock and compression. Uncomplicated animals, such as worms and jellyfish, do not take a coelom. All vertebrates have a coelom that helped them evolve complex organ systems.

Animals that do not have a coelom are called acoelomates. Flatworms and tapeworms are examples of acoelomates. They rely on passive improvidence for nutrient transport across their body. Additionally, the internal organs of acoelomates are not protected from crushing.

Animals that have a true coelom are called eucoelomates; all vertebrates are eucoelomates. The coelom evolves from the mesoderm during embryogenesis. The intestinal cavity contains the breadbasket, liver, gall bladder, and other digestive organs. Another category of invertebrates animals based on torso cavity is pseudocoelomates. These animals take a pseudo-cavity that is not completely lined by mesoderm. Examples include nematode parasites and small worms. These animals are thought to have evolved from coelomates and may accept lost their power to form a coelom through genetic mutations. Thus, this step in early on embryogenesis—the formation of the coelom—has had a large evolutionary bear on on the diverse species of the animate being kingdom.

Department Summary

Organisms in the animal kingdom are classified based on their torso morphology and evolution. True animals are divided into those with radial versus bilateral symmetry. Generally, the simpler and often not-motile animals display radial symmetry. Animals with radial symmetry are also generally characterized by the development of two embryological germ layers, the endoderm and ectoderm, whereas animals with bilateral symmetry are generally characterized by the development of a third embryological germ layer, the mesoderm. Animals with three germ layers, called triploblasts, are further characterized by the presence or absenteeism of an internal torso cavity chosen a coelom. The presence of a coelom affords many advantages, and animals with a coelom may exist termed true coelomates or pseudocoelomates, depending on which tissue gives ascension to the coelom. Coelomates are further divided into one of two groups called protostomes and deuterostomes, based on a number of developmental characteristics, including differences in zygote cleavage and method of coelom formation.

Fine art Connections

[link] Which of the following statements is imitation?

1. Eumetazoans have specialized tissues and parazoans don't.
2. Lophotrochozoa and Ecdysozoa are both Bilataria.
3. Acoela and Cnidaria both possess radial symmetry.
4. Arthropods are more closely related to nematodes than they are to annelids.

[link] C

[link] Which of the post-obit statements virtually diploblasts and triploblasts is false?

1. Animals that display radial symmetry are diploblasts.
2. Animals that display bilateral symmetry are triploblasts.
3. The endoderm gives rise to the lining of the digestive tract and the respiratory tract.
4. The mesoderm gives ascension to the central nervous organization.

[link] D

Review Questions

Which of the post-obit organism is most probable to exist a diploblast?

1. sea star
2. shrimp
3. jellyfish
4. insect

C

Which of the post-obit is not possible?

1. radially symmetrical diploblast
2. diploblastic eucoelomate
3. protostomic coelomate
4. bilaterally symmetrical deuterostome

B

An animal whose evolution is marked by radial cleavage and enterocoely is ________.

1. a deuterostome
2. an annelid or clam
3. either an acoelomate or eucoelomate
4. none of the above

A

Gratuitous Response

Using the post-obit terms, explain what classifications and groups humans autumn into, from the most full general to the most specific: symmetry, germ layers, coelom, cleavage, embryological evolution.

Humans accept body plans that are bilaterally symmetrical and are characterized by the evolution of three germ layers, making them triploblasts. Humans have true coeloms and are thus eucoelomates. As deuterostomes, humans are characterized by radial and indeterminate cleavage.

Explain some of the advantages brought most through the development of bilateral symmetry and coelom formation.

The evolution of bilateral symmetry led to designated head and tail body regions, and promoted more efficient mobility for animals. This improved mobility allowed for more adept seeking of resource and casualty escaping from predators. The appearance of the coelom in coelomates provides many internal organs with stupor assimilation, making them less prone to physical damage from bodily set on. A coelom as well gives the torso greater flexibility, which promotes more efficient motion. The relatively loose placement of organs within the coelom allows them to develop and grow with some spatial freedom, which promoted the evolution of optimal organ organisation. The coelom also provides space for a circulatory arrangement, which is an advantageous way to distribute body fluids and gases.

Glossary

acoelomate

animal without a torso cavity

bilateral symmetry

type of symmetry in which there is merely one plane of symmetry, then the left and right halves of an animal are mirror images

blastopore

indentation formed during gastrulation, evident in the gastrula stage

coelom

lined trunk cavity

determinate cleavage

developmental tissue fate of each embryonic cell is already determined

deuterostome

blastopore develops into the anus, with the second opening developing into the mouth

diploblast

animate being that develops from 2 germ layers

enterocoely

mesoderm of deuterostomes develops as pouches that are pinched off from endodermal tissue, cavity contained inside the pouches becomes coelom

eucoelomate

animal with a body crenel completely lined with mesodermal tissue

indeterminate cleavage

early stage of evolution when germ cells or "stem cells" are non nonetheless pre-determined to develop into specific cell types

protostome

blastopore develops into the rima oris of protostomes, with the second opening developing into the anus

pseudocoelomate

brute with a torso crenel located betwixt the mesoderm and endoderm

radial cleavage

cleavage axes are parallel or perpendicular to the polar axis, resulting in the alignment of cells betwixt the two poles

radial symmetry

blazon of symmetry with multiple planes of symmetry, with body parts (rays) arranged around a key deejay

schizocoely

during development of protostomes, a solid mass of mesoderm splits autonomously and forms the hollow opening of the coelom

spiral cleavage

cells of 1 pole of the embryo are rotated or misaligned with respect to the cells of the opposite pole

triploblast

creature that develops from iii germ layers

Source: http://pressbooks-dev.oer.hawaii.edu/biology/chapter/features-used-to-classify-animals/

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