Animal Diversity Chapter 32 Which of these organisms are animals? Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers Animals share the same: Nutritional mode Cell structure and specialization Reproduction and development Nutritional mode Animals are heterotrophs that ingest their food (rather than absorb as in fungi) and then use enzymes to break it down Cell structure and specialization Animals are multicellular eukaryotes Cells lack cell walls Collagen provides structural support Have muscle cells or nerve cells, many times organized into tissues 1
Reproduction and development Most animals reproduce sexually, with the diploid stage usually dominating the life cycle After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage Cleavage leads to formation of a multicellular, hollow blastula The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues Reproduction and development The history of animals spans more than half a billion years Most animals have at least one larval stage A larva is sexually immature and morphologically distinct from the adult and eventually undergoes metamorphosis Most animals (and only animals) have Hox genes that regulate the development of body form Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology Neoproterozoic Era (1 Billion 542 mya) Early members of the animal fossil record include the Ediacaran biota (~550 mya) Paleozoic Era (542 251 mya) The Cambrian explosion (~525 mya) marks the earliest fossil appearance of about half of all extant animal phyla There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota Novel predator adaptations led to novel prey adaptations A rise in atmospheric oxygen Origin of the Hox gene complex allowed the evolution of many body forms 2
Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions Animals began to make an impact on land by 460 million years ago Vertebrates made the transition to land around 360 million years ago Mesozoic Era (251 65.5 mya) Coral reefs emerged, becoming important marine ecological niches for other organisms Reptiles returned to the water Dinosaurs were the dominant terrestrial vertebrates The first mammals emerged Flowering plants and insects underwent adaptive radiation Cenozoic Era (65.5 mya to present) Mass extinctions of both terrestrial and marine animals at start of Cenozoic Included the large, nonflying dinosaurs and the marine reptiles Mammals increased in size and exploited vacated ecological niches The global climate cooled, creating more open woodland and savanna Animals can be characterized by body plans Body plan simply describes morphological and developmental features of an organism Body plans have several components: Type of symmetry Organization of tissue Characteristics of body cavities Protostome or deuterostome development modes Type of symmetry Radial symmetry Radially symmetric animals have no front, back, left or right, but have a top and bottom Tend to be sessile or planktonic organisms 3
Bilateral symmetry Dorsal, ventral, left and right sides Anterior and posterior ends Sensory equipment at anterior end cephalization Tend to be mobile organisms Tissues Ectoderm- outer layer Endoderm- lining of digestive tract and some organs Diploblastic animals have only 2 germ layers Cnidarians All bilaterally symmetrical animals have mesoderm (triploblastic) that forms the muscle and organs between digestive tract and ectoderm Body cavities Animals are separated into whether they have a body cavity and what tissues line the body cavity Coelomates are animals that possess a true body cavity or coelom Coelom is derived from mesoderm only Pseudocoelmoates possess a pseudocoelom Pseudocoelom is a body cavity derived from the mesoderm and endoderm 4
Acoelomates lack a body cavity Protostome or deuterostome development Classified in terms of differences in cleavage, coelom formation and fate of the blastopore Cleavage Coelom formation Radial and indeterminate Spiral and determinate Fate of the blastopore Animal phylogeny based on morphology and development 5
Animal phylogeny based on molecular data Points of agreement All animals share a common ancestor Sponges are basal animals Eumetazoa is a clade of animals (eumetazoans) with true tissues Most animal phyla belong to the clade Bilateria Chordates and some other phyla including Echinodermata belong to the clade Deuterostomia Progress in Resolving Bilaterian Relationships The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa Ecdysozoans shed their exoskeletons through a process called ecdysis Lophotrochozoans Some have a feeding structure called a lophophore Others go through a distinct developmental stage called the trochophore larva Construct a dichotomous key for the following organisms: Stovepipe Sponge Pillar Coral Pacific Sea Nettle Octopus Earthworm Crayfish 6
Land animals could be considered to have been common before the time of the A. Cambrian explosion. B. Cenozoic era. C. Ediacaran biota. D. Neoproterozoic era. 25% 25% 25% 25% Cambrian explosion. Cenozoic era. Ediacaran biota. Neoproterozoic era. What should animals with radial symmetry be better able to do than those with bilateral symmetry? A. move quickly in one direction B. detect threats from above or below equally well C. deal effectively with food distributed homogeneously in 360 D. focused attention in a single direction 25% 25% 25% 25% Bilateral symmetry is LEAST associated with A. cephalization. B. the presence of mesoderm. C. an active lifestyle. D. a nervous system with sensory structures concentrated at one end of the animal. E. the sessile condition. 20% 20% 20% 20% 20% move quickly in one dire... detect threats from abov... deal effectively with food... focused attention in a sing.. cephalization. the presence of mesoderm. an active lifestyle. a nervous system with s... the sessile condition. What is true of modern animal phylogenies? A. They take no account of an animal s body plan. B. They portray an animal s place on the scale of nature (scala naturae). C. They rely solely on molecular (genetic) data. D. They are hypothetical. E. They are immune from error due to homoplasy. 20% 20% 20% 20% 20% They take no account of.. They portray an animal s... They rely solely on molec... They are hypothetical. They are immune from e... 7