What Characteristics Do Animals Share At The Class Level

Learning Objectives

Past the end of this section, you volition be able to:

• List the features that distinguish the creature kingdom from other kingdoms
• Explain the processes of brute reproduction and embryonic development
• Describe the hierarchy of basic animal nomenclature
• Compare and dissimilarity the embryonic development of protostomes and deuterostomes

Even though members of the animal kingdom are incredibly diverse, animals share common features that distinguish them from organisms in other kingdoms. All animals are eukaryotic, multicellular organisms, and almost all animals have specialized tissues. Most animals are motile, at least during certain life stages. Animals crave a source of food to grow and develop. All animals are heterotrophic, ingesting living or dead organic matter. This grade of obtaining free energy distinguishes them from autotrophic organisms, such equally most plants, which make their ain nutrients through photosynthesis and from fungi that digest their food externally. Animals may be carnivores, herbivores, omnivores, or parasites (Figure 15.2). Near animals reproduce sexually: The offspring pass through a series of developmental stages that establish a adamant trunk programme, unlike plants, for example, in which the verbal shape of the body is indeterminate. The body programme refers to the shape of an animal.

Figure 15.2 All animals that derive energy from nutrient are heterotrophs. The (a) black bear is an omnivore, eating both plants and animals. The (b) heartworm Dirofilaria immitis is a parasite that derives energy from its hosts. It spends its larval phase in mosquitos and its adult stage infesting the hearts of dogs and other mammals, equally shown hither. (credit a: modification of piece of work by USDA Forest Service; credit b: modification of work past Clyde Robinson)

Complex Tissue Structure

A hallmark trait of animals is specialized structures that are differentiated to perform unique functions. Every bit multicellular organisms, nearly animals develop specialized cells that group together into tissues with specialized functions. A tissue is a drove of similar cells that had a common embryonic origin. There are four main types of animal tissues: nervous, musculus, connective, and epithelial. Nervous tissue contains neurons, or nerve cells, which transmit nerve impulses. Muscle tissue contracts to cause all types of body movement from locomotion of the organism to movements within the body itself. Animals likewise have specialized connective tissues that provide many functions, including send and structural support. Examples of connective tissues include blood and bone. Connective tissue is comprised of cells separated by extracellular fabric made of organic and inorganic materials, such equally the poly peptide and mineral deposits of bone. Epithelial tissue covers the internal and external surfaces of organs inside the beast body and the external surface of the body of the organism.

Link to Learning

Concept in Action

View this video to watch a presentation by biologist E.O. Wilson on the importance of animal diversity.

Creature Reproduction and Evolution

Nearly animals have diploid body (somatic) cells and a minor number of haploid reproductive (gamete) cells produced through meiosis. Some exceptions exist: For example, in bees, wasps, and ants, the male is haploid considering it develops from an unfertilized egg. Almost animals undergo sexual reproduction, while many as well have mechanisms of asexual reproduction.

Sexual Reproduction and Embryonic Development

Almost all fauna species are capable of reproducing sexually; for many, this is the only fashion of reproduction possible. This distinguishes animals from fungi, protists, and bacteria, where asexual reproduction is mutual or exclusive. During sexual reproduction, the male and female person gametes of a species combine in a process called fertilization. Typically, the small, motile male sperm travels to the much larger, sessile female egg. Sperm form is diverse and includes cells with flagella or amoeboid cells to facilitate move. Fertilization and fusion of the gamete nuclei produce a zygote. Fertilization may be internal, especially in country animals, or external, every bit is common in many aquatic species.

After fertilization, a developmental sequence ensues as cells divide and differentiate. Many of the events in development are shared in groups of related animal species, and these events are one of the main ways scientists classify high-level groups of animals. During development, creature cells specialize and class tissues, determining their future morphology and physiology. In many animals, such every bit mammals, the immature resemble the adult. Other animals, such every bit some insects and amphibians, undergo complete metamorphosis in which individuals enter one or more than larval stages. For these animals, the young and the developed have unlike diets and sometimes habitats. In other species, a process of incomplete metamorphosis occurs in which the immature somewhat resemble the adults and go through a serial of stages separated by molts (shedding of the skin) until they achieve the final adult form.

Asexual Reproduction

Asexual reproduction, different sexual reproduction, produces offspring genetically identical to each other and to the parent. A number of animal species—peculiarly those without backbones, but even some fish, amphibians, and reptiles—are capable of asexual reproduction. Asexual reproduction, except for occasional identical twinning, is absent in birds and mammals. The almost common forms of asexual reproduction for stationary aquatic animals include budding and fragmentation, in which office of a parent private tin dissever and grow into a new private. In contrast, a form of asexual reproduction institute in certain invertebrates and rare vertebrates is called parthenogenesis (or "virgin beginning"), in which unfertilized eggs develop into new offspring.

Nomenclature Features of Animals

Animals are classified according to morphological and developmental characteristics, such equally a body plan. With the exception of sponges, the animal body plan is symmetrical. This means that their distribution of torso parts is balanced along an axis. Additional characteristics that contribute to creature nomenclature include the number of tissue layers formed during development, the presence or absence of an internal body cavity, and other features of embryological development.

Visual Connection

Visual Connexion

Figure 15.three The phylogenetic tree of animals is based on morphological, fossil, and genetic evidence.

Which of the following statements is false?

1. Eumetazoa take specialized tissues and Parazoa do not.
2. Both acoelomates and pseudocoelomates have a body cavity.
3. Chordates are more than closely related to echinoderms than to rotifers co-ordinate to the figure.
4. Some animals take radial symmetry, and some animals have bilateral symmetry.

Body Symmetry

Animals may be asymmetrical, radial, or bilateral in form (Figure fifteen.4). Asymmetrical animals are animals with no pattern or symmetry; an example of an asymmetrical animal is a sponge (Figure 15.4a). An organism with radial symmetry (Figure 15.4b) has a longitudinal (up-and-down) orientation: Any plane cut along this up–down centrality produces roughly mirror-image halves. An example of an organism with radial symmetry is a sea anemone.

Figure 15.four Animals showroom different types of body symmetry. The (a) sponge is asymmetrical and has no planes of symmetry, the (b) sea anemone has radial symmetry with multiple planes of symmetry, and the (c) caprine animal has bilateral symmetry with i plane of symmetry.

Bilateral symmetry is illustrated in Figure 15.ivc using a goat. The goat as well has upper and lower sides to it, but they are not symmetrical. A vertical aeroplane cut from forepart to back separates the animal into roughly mirror-paradigm right and left sides. Animals with bilateral symmetry also take a "head" and "tail" (anterior versus posterior) and a back and underside (dorsal versus ventral).

Link to Learning

Concept in Activity

Watch this video to encounter a quick sketch of the different types of trunk symmetry.

Layers of Tissues

Nigh animal species undergo a layering of early tissues during embryonic evolution. These layers are called germ layers. Each layer develops into a specific set of tissues and organs. Animals develop either two or iii embryonic germs layers (Figure fifteen.5). The animals that brandish radial symmetry develop 2 germ layers, an inner layer (endoderm) and an outer layer (ectoderm). These animals are called diploblasts. Animals with bilateral symmetry develop three germ layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). Animals with three germ layers are chosen triploblasts.

Figure 15.5 During embryogenesis, diploblasts develop two embryonic germ layers: an ectoderm and an endoderm. Triploblasts develop a third layer—the mesoderm—betwixt the endoderm and ectoderm.

Presence or Absenteeism of a Coelom

Triploblasts may develop an internal body cavity derived from mesoderm, called a coelom (pr. see-LŌM). This epithelial-lined cavity is a space, commonly filled with fluid, which lies between the digestive system and the body wall. It houses organs such as the kidneys and spleen, and contains the circulatory system. Triploblasts that do non develop a coelom are called acoelomates, and their mesoderm region is completely filled with tissue, although they accept a gut cavity. Examples of acoelomates include the flatworms. Animals with a true coelom are called eucoelomates (or coelomates) (Figure 15.half-dozen). A true coelom arises entirely within the mesoderm germ layer. Animals such as earthworms, snails, insects, starfish, and vertebrates are all eucoelomates. A third group of triploblasts has a body cavity that is derived partly from mesoderm and partly from endoderm tissue. These animals are chosen pseudocoelomates. Roundworms are examples of pseudocoelomates. New information on the relationships of pseudocoelomates suggest that these phyla are not closely related and so the evolution of the pseudocoelom must take occurred more than once (Figure 15.3). True coelomates can be farther characterized based on features of their early on embryological evolution.

Figure xv.six Triploblasts may be acoelomates, eucoelomates, or pseudocoelomates. Eucoelomates have a trunk cavity within the mesoderm, called a coelom, which is lined with mesoderm tissue. Pseudocoelomates have a similar body crenel, but information technology is lined with mesoderm and endoderm tissue. (credit a: modification of work by Jan Derk; credit b: modification of work by NOAA; credit c: modification of work by USDA, ARS)

Protostomes and Deuterostomes

Bilaterally symmetrical, triploblastic eucoelomates can be divided into two groups based on differences in their early embryonic development. Protostomes include phyla such as arthropods, mollusks, and annelids. Deuterostomes include the chordates and echinoderms. These two groups are named from which opening of the digestive crenel develops first: oral cavity or anus. The give-and-take protostome comes from Greek words meaning "mouth showtime," and deuterostome originates from words significant "mouth second" (in this case, the anus develops first). This divergence reflects the fate of a construction called the blastopore (Effigy 15.seven), which becomes the oral fissure in protostomes and the anus in deuterostomes. Other developmental characteristics differ between protostomes and deuterostomes, including the mode of germination of the coelom and the early jail cell division of the embryo.

Figure 15.7 Eucoelomates can be divided into two groups, protostomes and deuterostomes, based on their early on embryonic development. Two of these differences include the origin of the mouth opening and the fashion in which the coelom is formed.

Source: https://openstax.org/books/concepts-biology/pages/15-1-features-of-the-animal-kingdom

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