Animal Diversity: Gastrulation and Development

• Animal diversity highlights gastrulation as the most important event, according to Lewis Wolpert

Nutrition, Cell Structure, and Specialization

• Animals are heterotrophs, they ingest their food
• Animals are multicellular eukaryotes lacking cell walls and held together by structural proteins such as collagen
• Nervous and muscle tissues are unique to animals
• Around 1.3 million living animal species have been identified

Reproduction and Development

• Most animals reproduce sexually, with the diploid stage dominating the life cycle
• After fertilization, the zygote undergoes rapid cell division called cleavage leading to the formation of a blastula
• The blastula undergoes gastrulation, forming a gastrula with distinct embryonic tissue layers

Larval Stages

• Many animals have a larval stage
• The larval stage is sexually immature and morphologically distinct from the adult stage
• Larvae undergo metamorphosis to transform into adults

Cell Division

• Mitosis generates two genetically identical cells from a single parent cell
• Meiosis produces genetically unique cells with half the DNA of the parent cell.
• Identical (monozygotic) twins come from a single fertilized egg splitting into two, resulting in identical genetic information
• Fraternal (dizygotic) twins come from two eggs fertilized by two sperm, creating genetically unique offspring

Specialized Animal Cells

• Specialized animal cells possess components that allow them to serve a specific purpose
• Examples include red blood cells, sperm, eggs, nerve cells, muscle cells, ciliated cells, and villi
• Cytokinesis in animal cells begins with a cleavage furrow appearing on the cell surface
• The furrow deepens and spreads until the cell divides into two
• Plant cells cannot form cleavage furrows due to their rigid cell walls; they use a phragmoplast to transport cell wall materials to the center

Hox Genes

• All animals possess Hox genes, which regulate the development of body form
• Hox genes are highly conserved and responsible for animal morphological diversity

Characterization by Tissues

• Ectoderm is the germ layer covering the embryo’s surface
• Endoderm is the innermost germ layer lining the developing digestive tract (archenteron)
• Diploblastic animals have endoderm and ectoderm
• Triploblastic animals have a mesoderm layer between the ectoderm and endoderm, includes all bilaterians

Body Cavities

• Acoelomates are triploblastic animals lacking a body cavity (coelom) and usually have an uncompleted digestive system
• Pseudocoelomates have a body cavity derived from the mesoderm and endoderm which are still triploblastic
• Most triploblastic animals have a body cavity
• Coelomates possess a true coelom, which is a body cavity derived from the mesoderm

Hernias

• A hernia is when an internal body part protrudes through a weak spot in muscle or surrounding tissue
• Hernias often develop between the chest and hips
• Many hernias have few or no symptoms, though swelling or a lump may be noticeable in the abdomen or groin

Explore animal diversity, emphasizing gastrulation's significance as highlighted by Lewis Wolpert. Animals, being heterotrophs, ingest their food and are multicellular eukaryotes lacking cell walls. Reproduction predominantly occurs sexually, with the diploid stage dominating the life cycle. After fertilization, the zygote undergoes rapid cell division.