27: Introduction to Animal Diversity Flashcards
Features of the Animal Kingdom, Features Used to Classify Animals, Animal Phylogeny, the Evolutionary History of the Animal Kingdom
How many species of animal are there?
Although over one million extant species of animals have been identified, scientists are continually discovering more species as they explore ecosystems around the world. The number of extant species is estimated to be between 3 and 30 million.
How are animals classified?
The animal classification system characterizes animals based on their anatomy, morphology, evolutionary history, features of embryological development, and genetic makeup.
What is a blastula?
16-32 cell stage of development of an animal embryo.
What is a body plan?
Morphology or constant shape of an organism.
What is cleavage?
Cell division of a fertilized egg (zygote) to form a multicellular embryo.
What is the gastrula?
Stage of animal development characterized by the formation of the digestive cavity.
What is a germ layer?
Collection of cells formed during embryogenesis that will give rise to future body tissues, more pronounced in vertebrate embryogenesis.
What is a Hox gene?
Master control gene that can turn on or off large numbers of other genes during embryogenesis. AKA homeobox gene.
What is organogenesis?
Formation of organs in animal embryogenesis.
What features distinguish animals from other organisms?
All animals are eukaryotic, multicellular organisms, and almost all animals have a complex tissue structure with differentiated and specialized tissues. Most animals are motile, at least during certain life stages. All animals are heterotrophic, and may be carnivores, herbivores, omnivores, or parasites. Most animals reproduce sexually, and the offspring pass through a series of developmental stages that establish a determined and fixed body plan.
How are animal cells different than other multicellular organisms?
They don’t have cell walls, they may be embedded in an extracellular matrix (such as bone, skin, or connective tissue), and they have unique structures for intercellular communication (such as gap junctions).
What kind of tissues distinguish animals?
Animals are characterized by specialized connective tissues that provide structural support for cells and organs. This connective tissue constitutes the extracellular surroundings of cells and is made up of organic and inorganic materials.
What role does epithelial tissue play?
Epithelial tissues cover, line, protect, and secrete.
What are some examples of epithelial tissues?
Epithelial tissues include the epidermis of the integument, the lining of the digestive tract and trachea, and make up the ducts of the liver and glands of advanced animals.
What are the two major divisions of the animal kingdom?
The animal kingdom is divided into Parazoa (sponges, “beside animal”) and Eumetazoa (all other animals, “true animals”).
How do tissues distinguish Parazoa?
As very simple animals, the organisms in group Parazoa do not contain true specialized tissues; although they do possess specialized cells that perform different functions, those cells are not organized into tissues.
Why are Parazoans considered animals?
They are considered animals because they lack the ability to make their own food.
What is an example of tissue specialization that has contributed to the evolutionary success of Eumetazoans?
The evolution of nerve tissues and muscle tissues has resulted in animals’ unique ability to rapidly sense and respond to changes in their environment. This allows animals to survive in environments where they must compete with other species to meet their nutritional demands.
What are some examples of haploid animals?
In bees, wasps, and ants, the male is haploid because it develops from unfertilized eggs.
What are some examples of animals that perform asexual reproduction?
A few groups, such as cnidarians, flatworms, roundworms, sea stars and sea anemones, and some insects, reptiles, and fish undergo asexual reproduction, although nearly all of those animals also have a sexual phase to their life cycle.
What are some forms of asexual reproduction in animals?
The most common forms of asexual reproduction for stationary aquatic animals include budding and fragmentation. In contrast, a form of asexual reproduction found in certain insects and vertebrates is called parthenogenesis (“virgin birth”), where unfertilized eggs can develop into new male offspring.
What are the advantages and disadvantages of asexual reproduction in animals?
Asexual reproduction produces genetically identical offspring, which is disadvantageous from the perspective of evolutionary adaptability because of the potential buildup of deleterious mutations. However, for animals that are limited in their capacity to attract mates, asexual reproduction can ensure genetic propagation.
What are some examples of complete and incomplete metamorphosis?
Some animals, such as grasshoppers, undergo incomplete metamorphosis, in which the young resemble the adult. Other animals, such as some insects, undergo complete metamorphosis where individuals enter one or more larval stages that may differ in structure and function from the adult. For the latter, the young and the adult may have different diets, limiting competition for food between them.
What are the first stages of animal development?
The process of animal development begins with the cleavage, or series of mitotic cell divisions, of the zygote. Three cell divisions transform the single-celled zygote into an eight-celled structure. After further cell division and rearrangement of existing cells, a 16-32-celled hollow structure called a blastula is formed. Next, the blastula undergoes further cell division and cellular arrangement during a process called gastrulation. This leads to the formation of the next developmental stage, the gastrula, in which the future digestive cavity is formed. Different cell layers are formed during gastrulation. These germ layers are programmed to develop into certain tissue types, organs, and organ systems during a process called organogenesis.
Which genes determine animal structure?
The genes that determine animal structure are called “homeotic genes” or Hox genes, and they contain DNA sequences called homeoboxes.
What are some examples of responsibilities of Hox genes?
Hox genes are responsible for determining the general body plan, such as the number of body segments of an animal, the number and placement of appendages, and animal head-tail directionality.
How were Hox genes discovered?
The first Hox genes to be sequenced were those from the fruit fly, Drosophila melanogaster. A single Hox mutation in the fruit fly can result in an extra pair of wings or even appendages growing from the “wrong” body part.
How do Hox genes serve as master control genes?
They code transcription factors that control the expression of numerous other genes.
How are Hox genes similar and different across the animal kingdom?
Hox genes are homologous in the animal kingdom, that is, the genetic sequences of Hox genes and their positions on chromosomes are remarkably similar across most animals because of their presence in a common ancestor. One of the contributions to increased animal body complexity is that Hox genes have undergone at least two duplication events during animal evolution, with the additional genes allowing for more complex body types to evolve.
What is an acoelomate?
An animal without a body cavity.
What is bilateral symmetry?
Type of symmetry in which there is only one plane of symmetry, so the left and right halves of an animal are mirror images.
What is a blastopore?
An indentation formed during gastrulation, evident in the gastrula stage.
What is a coelom?
A lined body cavity.
What is determinate cleavage?
Developmental tissue fate of each embryonic cell is already determined.
What is a deuterostome?
The blastopore develops into the anus, with the second opening developing into the mouth.
What is a diploblast?
An animal that develops from two germ layers.
What is enterocoely?
When the mesoderm of deuterostomes develops as pouches that are pinched off from endodermal tissue, cavity contained within the pouches becomes coelom.
What is a eucoelomate?
An animal with a body cavity completely lined with mesodermal tissue.
What is indeterminate cleavage?
Early stage of development when germ cells or “stem cells” are not yet pre-determined to develop into specific cell types.
What is a protostome?
Blastopore develops into the mouth of protostomes, with the second opening developing into the anus.
What is a pseudocoelomate?
An animal with a body cavity located between the mesoderm and endoderm.
What is radial cleavage?
When cleavage axes are parallel or perpendicular to the polar axis, resulting in the alignment of cells between the two poles.
What is radial symmetry?
A type of symmetry with multiple planes of symmetry, with body parts (rays) arranged around a central disk.
What is schizocoely?
When, during development of protostomes, a solid mass of mesoderm splits apart and forms the hollow opening of the coelom.
What is spiral cleavage?
When cells of one pole of the embryo are rotated or misaligned with respect to the cells of the opposite pole.
What is a triploblast?
An animal that develops from three germ layers.
What is a prominent feature of true animal body plans?
They are morphologically symmetrical.
How are true animals classified?
True animals are primarily classified according to morphological and developmental characteristics, such as body plan. 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.
How can animals be classified according to the symmetry of their body plan?
At a very basic level of classification, animals can be largely divided into three groups based on the type of their body plan: radially symmetrical, bilaterally symmetrical, and asymmetrical. Asymmetry is a unique feature of Parazoa, and only a few animal groups display radial symmetry.
