Reproduction- external fertilization to internal. - Embryo development external to internal. ⢠Oviparous. ⢠Ovovivip
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Evolution of the Animal Phyla Chapter 19 General Features of Animals All animals are multicellular heterotrophs. Invertebrates account for 99% of all species. Animal Kingdom includes about 36 phyla. Most occur in the sea. Three phyla dominate animal life on land. - Arthropoda (spiders and insects) - Mollusca (snails) - Chordata (vertebrates) Phylogeny of Kingdom Animalia 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
Trends in the evolution of animals •
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Reproduction Asexual – mitosis - Reproduction by fission or budding - Parthenogenesis Sexual – meiosis - Reproduction- external fertilization to internal - Embryo development external to internal ¾ Oviparous ¾ Ovoviviparous ¾ Viviparous
Evolution of Nervous System Sponges Kingdom Animalia has two subkingdoms: Parazoa - lack definite symmetry and tissues organized into organs. - Dominated by sponges (Porifera).
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Eumetazoa - have definite shape and and symmetry and highly specialized cells.
Sponges are simplest animals.
Bodies consist of masses of specialized cells embedded in gel-like matrix. Phylum Porifera
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. (~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 Platyhelminthes –flat worms Key evolutionary advance: internal organs and bilateral symmetry. Are hermaphroditic, with complex reproductive systems Fertilization and development external Have cephalization of the nervous system
Phylum Annelida – segmented worms
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Key evolutionary advance: innovation to arise in coelomates was segmentation.
Nervous system well developed many central ganaglion grouped together (central nervous system and peripheral nerves)
Annelida •
reproduction monoecious / dioecious trochophore larva asexual - budding Fertilization external Gametes passed into the coelom (body cavity) stored until eggs are laid. - some species have a specialized structure to introduce the gametes coelom.
into the
Arthropoda •
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reproduction dioecious - many dimorphic oviparous, or ovoviviparous metamorphosis - complete / incomplete some parthenogenic – development from a unfertilized ovum. - Fertilization can be internal- males have an ovipositor
Evolution of Reproduction Three Strategies of Internal Fertilization: Oviparity - Eggs are fertilized internally and deposited outside mother’s body to complete development. Ovoviviparity - Fertilized eggs are retained within mother to complete development, but all nourishment gained from yolk sac.
Viviparity - Young develop within mother and obtain nourishment directly from mother’s blood. Evolution of Vertebrate Brain Evolution of Vertebrate Reproduction
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Fish Eggs of most bony fish fertilized externally, and eggs contain small yolk sac. Fertilization in most cartilaginous fish is internal. Amphibians Fertilization is usually external. Eggs of most species develop in water. Development divided into stages.
Evolution of Vertebrate Reproduction •
Reptiles Most reptiles are oviparous, and lay amniotic eggs. - Other species are ovoviviparous, or vivaparous. Most males use penis to introduce sperm into the cloaca of females. Evolution of Vertebrate Reproduction
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Birds All birds practice internal fertilization. - As eggs pass along oviduct, glands secrete albumin proteins and hard calcareous shell. Homeothermic - Must keep eggs warm. Young cared for and nurtured by parents. Evolution of Vertebrate Reproduction Monotremes - Oviparous (duck-billed platypus). - Incubate eggs - Lack nipples Marsupials - Give birth to incompletely developed fetuses that complete development in mother’s pouch. Evolution of Vertebrate Reproduction
Placental Mammals - Retain young for relatively long period of development within mother’s uterus. - Nourished by placenta. Male Reproductive Organs Female Reproductive System Not all mammals are alike
