Flashcards in Introduction to Animal Diversity: Form & Function Deck (26):
Five Characteristics that are used to Define Animals
1. Multicellular eukaryotes
2. Heterotrophs that lack cell walls
3. Motile at least some time in their lives
4. Reproduce asexually or (more likely) sexually
5. (Most) have nerve and muscle cells
What is the most likely origin of animals?
Most likely from a colonial unicellular ancestor developed during the Precambrian era (mya) from a flagellated protist.
What happened over time to the flagellated protists?
They gradually became more specialized and layered, forming layers that would eventually become the gut (inner layer becomes a sac).
What is similar to the modern colonial flagellated?
The choanoflagellates, unicellular, cylindrical celled, organisms found in ecosystems. The cells hat form the inner layer of these modern cells (choanocytes) look quite similar to the choanoflagellate.
True or false: each individual cell of the sponge (and choanoflagellate cells) can survive on their own.
The animal kingdom is _____.
Monophyletic. All taxa evolved from a single common ancestor (choanoflagellate).
Animal can be characterized by basic features of their body plan, which may vary in:
1. Embryonic develpooment
2. Specialized tissue types
3. Body cavity type
4. Body symmetry
Overview of Sexual Reproduction
Nearly all animals undergo some form of sexual reproduction, with specialized reproductive cells that undergo meiosis to produce gametes. Females produce ova, males produce sperm. Sperm and eggs fuse to form zygotes, which develop into new individuals.
Overview of Zygote Cleavage
The division of cells in the early embryo. Zygotes undergo rapid cell cycles with no significant growth. The zygote develops into a compact mass of cells termed morula, a ball of rapidly dividing cells. The morula derives into a hollow sphere of single later of cells termed blastula.
What is the blastula?
Exclusive to animals, the blastula invaginates and undergoes further differentiation into three germ layers.
What are the three germ layers?
Ectoderm (skin and nervous system), mesoderm (muscle and skeleton), endoderm (digestive tract).
What do germ layers differentiate to?
Differentiate to form tissues and organs.
What are species with three germ layers termed?
Triploblasts. Most animals will have three germ layers.
What are species with two germ layers termed?
Diplioblasts. The two primary germ layers are the ectoderm and the endoderm. They include simpler animals such as the jellyfish, corals, and hydra. They do not have highly developed internal organ plans because of the lack of a mesoderm.
What does Coelomate mean?
It refers to the presence of the coelum (body cavity) in animals, which is formed within the mesoderm of the embryo. The mesoderm is a membrane-like structure that keeps the organs suspended within the body cavity.
What does Acoelomate mean?
Not hollow, animals without body cavities. Example: Flatworms. The animal may lack a mesoderm or the mesoderm maybe completely packed with cells.
What does Pseudocoelomate mean?
False cavity, the pseudocoelum is a fluid-filled or organ filled space between the endoderm and mesoderm. The cavity is not completely surrounded by the mesoderm lining. Example: Roundworms (Phylum Nematoda)
What are some advantages of having a coelum?
It acts as a layer for shock absorption, and the fluid-filled cavity helps to efficiently move nutrients and waste products throughout the body.
What are the types of body symmetry in animals?
Radial symmetry (can be divided equally by any longitudinal plane passing through the central axis), Bilateral symmetry (can be divided along a vertical plane at the middle to create two identical halves), and Asymmetric (sponges).
Describe Radial Symmetry.
Found in phylum Radiata, consists of diploblastic animals that have a simple body plan an exhibit no left or right sides. They have a top (dorsal) and a bottom (ventral), and are often circular or tubular in shape with a mouth at one end. Examples: Cnidarians and ctenophores.
Describe Bilateral Symmetry.
Consists of phylum Bilateria, animals with a balanced distribution of duplicate body parts or shaped, with specialized head and sensory organs. Triploblastic.
What are some evolutionary advantages of bilateria?
The ability to move through the environment and cephalization, which permits animals to encounter their environment initially with their head.
The localization of sensory structures at the anterior end of the body.
Why should we worry about animal diversity?
1. Understanding animal evolution helps us to learn common principles
2. Understanding patterns of adaptation to environmental constraints helps us to learn common principles
List Patterns of Animal Body System Evolution
1. Multicellularity allows cellular specialization (complex organs and tissues)
2. A complex body requires complex coordination
3. Independent movement allows animals to actively search for food/resources, exploit environments, locate mates/avoid predators
4. Complex skeletal, muscular, and sensory systems are needed
5. No cell walls allows flexibility and assists motility
6. Heterotrophy allows animals to live in environments unsuitable for autotrophs
7. Animals are diverse, but with common principles