Animals are heterotrophs that ingest their food Animals are multicellular eukaryotes

1. Animals are heterotrophs that ingest their food • Animals are multicellular eukaryotes • Their bodies are held together by structural proteins such as collagen • Nervous tissue and muscle tissue are unique to animals • Most animals reproduce sexually, with the diploid stage usually dominating the life cycle

2. In most species, a small flagellated sperm fertilizes a larger, non-motile egg. • The zygote undergoes cleavage, a succession of mitotic cell divisions, leading to the formation of a multicellular, hollow ball of cells called the blastula. • During gastrulation, part of the embryo folds inward, forming layers of embryonic tissues that will develop into adult body parts. • The resulting development stage is called a gastrula.

3. Blastocoel Cleavage Cleavage Cross section of blastula Eight-cell stage Zygote Blastula Blastocoel Endoderm Ectoderm Gastrula Gastrulation Blastopore

4. Animals can be categorized according to the symmetry of their bodies, or lack of it • Some animals have radial symmetry

5. The two-sided symmetry…bilateral symmetry

6. Bilaterally symmetrical animals have: • Dorsal (top side) • Ventral (bottom side) • Anterior (head) • Posterior (tail) • Cephalization (development of a head) • A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis, transforming the animal into an adult.

7. Animal embryos have concentric layers called germ layers that form tissues and organs • Ectoderm is the germ layer covering the embryo’s surface • Endoderm is the innermost germ layer • Diploblastic animals have ectoderm and endoderm • Triploblastic animals also have an intervening mesoderm layer

8. In triploblastic animals, a body cavity may be present or absent • A true body cavity (a fluid-filled space separating the digestive tract from the outer body wall) known as a coelom and by the structure of the body cavity.

9. A true coelom forms from tissue derived from mesoderm. • The inner and outer layers of tissue that surround the coelom connect dorsally and ventrally and form mesenteries that suspend the internal organs. • Animals that possess a true coelom are known as coelomates.

10. Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Coelomate

11. A pseudocoelom is a body cavity derived from the blastocoel, rather than from mesoderm Body covering (from ectoderm) Muscle layer (from mesoderm) Pseudocoelom Digestive tract (from endoderm) Pseudocoelomate

12. Acoelomates are organisms without body cavities Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) Acoelomate

13. Protostome and Deuterostome Development • In protostome development, cleavage is spiral (in which planes of cell division are diagonal to the vertical axis of the embryo) and determinate (fate of each embryonic cell is determined early in development) • In deuterostome development, cleavage is radial (cleavage planes are parallel or perpendicular to the vertical egg axis) and indeterminate (embryo cells retain the capacity to develop into a complete embryo)

14. Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Cleavage Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate

15. In gastrulation, the developing digestive tube of an embryo initially forms as a blind pouch, the archenteron. • In protostome development, the splitting of solid masses of mesoderm to form the coelomic cavity is called schizocoelous development • In deuterostome development, mesoderm buds off from the wall of the archenteron and hollows to become the coelomic cavities, enterocoelous development

16. Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annnelids, arthropods) Coelom formation Coelom Archenteron Coelom Blastopore Mesoderm Mesoderm Blastopore Schizocoelous: solid masses of mesoderm split and form coelom Enterocoelous: folds of archenteron form coelom

17. In protostome development, the blastopore becomes the mouth In deuterostome development, the blastopore becomes the anus Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annnelids, arthropods) Fate of the blastopore Mouth Anus Digestive tube Mouth Anus Mouth develops from blastopore Anus develops from blastopore

18. Animations and Videos • Chapter Quiz Questions – 1 • Chapter Quiz Questions - 2