and symmetry and highly specialized cellsare simplest animals ialized cells embedded in gellike Cellular level of organization with no tissues or organs 1 The only major animal group phyla to lack ID: 396827
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Key development genes are ancient: Homeotic genes Direct embryological development Produce groups of proteins that turn genes on and off during development Found in every eukaryote analyzed so far; yeasts, plants, earthworms, frogs, chickens, mice and humans Parthenogenesis zation to internal Embryo development external to internal Evolution of Nervous System lack definite symmetry and tissues organized into Dominated by sponges (Porifera). and symmetry and highly specialized cellsare simplest animals. ialized cells embedded in gel-like Cellular level of organization with no tissues or organs 1. The only major animal group phyla to lack nerve cells 2. External fertilization no specialized gametes (male and female gametes appear similar Asexual and sexual reproduction Key evolutionary advance: symmetry and tissues. (~3000 species); 1. Have no head, no centralized nervous system (only a nerve net 2. Exhibit alternation of asexual polypoid and sexual medusoid generations. Fertilization and development is external to the body Phylum Cnidaria corals, sea anemones, jelly fish, hydra etc. Key evolutionary advance: symmetry and tissues. 1. Have no head, no centralized nervous system (only a nerve net 2. Exhibit alternation of asexual polypoid and sexual medusoid generations. Fertilization and development is external to the body Key evolutionary advance: internalAre hermaphroditic, with coHave cephalization of the Phylum Annelida segmented worms Key evolutionary advance: innovatisegmentation. Nervous system well developed many centralnervous system and peripheral nerves) trochophore larva Fertilization external - some species have a specialized structure to introduce the gametes into the reproduction dioecious - many dimorphic oviparous, or ovoviviparous metamorphosis - complete / incomplete some parthenogenic development from a unfertilized ovum. yolk sac. nourishment directly from mothers blood. Evolution of Vertebrate Brain Evolution of Vertebrate Reproduction Eggs of most bony fish fertilizyolk sac. Development divided into stages. Evolution of Vertebrate Reproduction Most reptiles are oviparous, and lay amniotic eggs. Most males use penis to introduce sperm into the cloaca of Evolution of Vertebrate Reproduction Evolution of Vertebrate Reproduction Give birth to incompletely developed fetuses that Evolution of Vertebrate Reproduction Placental Mammals - Retain young for relatively long period of development within mothers uterus. Not all mammals are alike