Introduction to Animal Diversity Packet #37 Chapter #32

Animal Diversity Biologists have identified 1.3 million living species if animals. Estimates put the range much higher 10 – 200 million

Characteristics Most Common to Animals Eukaryotic Multicellular Heterotrophic Animals use enzymes to digest their food after they have ingested it.

Characteristics Common to Most Animals Reproduction Most animals reproduce sexually and have a diploid stage that is dominant in the life cycle. Sperm and egg unite to form a zygote Zygote undergoes cleavage Multiple cell divisions result in the development of a hollow ball of cells Blastula Blastula undergoes gastrulation. Embryonic tissues are formed Developmental stage is called the gastrula.

Characteristics Common to Most Animals Reproduction Some animals develop directly into adults After transient stages of maturation However, life cycle of many animals include larval stages. Larva Sexually immature form of an adult Morphologically distinct Usually eats different food Inhabits different areas than the adult Must undergo metamorphosis to become an adult

Characteristics Common to Most Animals Reproduction Animals share a unique homeobox Family of genes Hox genes The number of hox genes is correlated with the complexity of the animal’s anatomy.

The “Evolution” of Animals

Figure 32.4

Introduction I Animal diversification, according to the theory of evolution, began more than one billion years ago. Most systematists believe that the Kingdom Animalia is monophyletic. Theory is that a colonial flagellated protist, related to today’s chanoflagellates, was the start of the Animal Kingdom.

Introduction II Ediacaran fauna is considered to be the first generally accepted fossil of animals. According to the theory of evolution they are 542 to 525 million years old Cambrian Explosion Ecological causes Predator/prey relationships Geological causes Rise in atmospheric oxygen Genetic causes Evolution of the Hox gene complex At the end of the period, developmental patterns, that constrained evolution, caused no additional phyla to evolve after that period.

Grades vs. Clades Grade Clade A group of animal species that share the same level of organized complexity. Does not have a monophyletic ancestor Body Plan Set morphological and developmental traits that define a grade. Basic structure of the body used to infer evolutionary relationships. Clade Group of species that includes ancestral species and all of its descendents Have a monophyletic ancestor

Body Plans Symmetry

Symmetry Radial Symmetry Describes how the parts of an animal radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images. Sea anemones have a top (oral, mouth) side and a bottom (aboral) side.

Symmetry II Bilateral Symmetry Describes a two sided body plan. Animal has a left side and right side Imaginary slice can only be placed in one location in order to divide the animal mirror images. Lobster has a dorsal (top) side, a ventral (bottom) side, a left and right side, an anterior (head) with a mouth and a posterior (tail) end.

Symmetry III Animals can be categorized according to the symmetry of their bodies or lack of it. Sponges lack symmetry It was hypothesized that cnidarians and ctenophores were closely related because they share radial symmetry. Symmetry Reflects Lifestyle Radial animals are sessile or planktonic Bilaterial animals more actively from one place to another The nervous system enables these organisms to move.

Relationships Via Tissue

Tissue I Embryonic Tissue, called germ layers, are produced via gastrulation Germ Layers Ectoderm Outer layer Gives rise to the body covering and the nervous system Endoderm Inner layer Gives rise to the lining of the gut (archenteron) and other digestive organs Mesoderm Middle layer Gives rise to most other body structures. Including muscle

Diploblastic vs. Triploblastic Animals with only two layers Ectoderm and Endoderm Jellies Corals Comb jellies Triploblastic Animals with all three layers Include all bilaterally symmetric animals.

Body cavities

Body Cavity I Triploblastic animals have traditionally been classified as Acoelomates No body cavity Lack a coelom. Pseudocoelomate Body cavity not completely lined with mesoderm Body cavity formed from the blastocoel. Coelomate True coelom Body cavity completely lined with mesoderm.

Functions of Body Cavities Provides protection to internal organs Allow organs to grow and move independently of the outer body wall.

Formation of the Coelom During gastrulation, developing digestive tube forms the archenteron. Protostomes Development of the coelom forms from splits in the mesoderm Schizocoelous Development Deuterostomes Development of the coelom forms from outpocketing of the mesodermal tissue of the archenteron. Enterocoelous Development

Evolutionary Branches of Coelomates

Introduction I Protostomia Deuterostomia Mollusks Annelids Arthropods Enchinoderms Chordates

Protosomes Blastopore develops into the mouth Undergo spiral and determinate cleavage Spiral cleavage Describes how the planes of cell division are diagonal to the vertical axis of the embryo. Smaller cells lie in the grooves between larger, underlying cells Determinate cleavage Indicates that the developmental fate of each embryonic cell is determined at fertilization. If cell is isolated it will form an inviable embryo.

Deuterostomes Blastopore typically becomes the anus. Undergo radial and indeterminate cleavage. Radial cleavage Cleavage planes are either parallel or perpendicular to the vertical axis of the egg Indeterminate cleavage Each cell produced by early cleavage divisions has the capacity to develop into a complete embryo.