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of the Phyla Chapter 19 General Features of • All animals are multicellular heterotrophs. • account for 99% of all . • Animal includes about 36 phyla. ™ Most occur in the . ™ Three phyla dominate animal on land. - Arthropoda (spiders and ) - (snails) - Chordata ()

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 analyzed so far; , , earthworms, , chickens, mice and humans

Trends in the evolution of animals • Reproduction ™ Asexual – mitosis - Reproduction by fission or budding - ™ Sexual – meiosis - Reproduction- to internal - development external to internal ¾ Oviparous ¾ Ovoviviparous ¾ Viviparous

Evolution of • Kingdom Animalia has two subkingdoms: ™ Parazoa - lack definite and tissues organized into organs. - Dominated by sponges (Porifera). ™ - 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 (male and female gametes appear similar Asexual and

Key evolutionary advance: symmetry and tissues.

(~3000 species);

1. Have no head, no centralized nervous system (only a ),

2. Exhibit alternation of asexual polypoid and sexual medusoid generations. Fertilization and development is external to the body

Phylum , sea anemones, jelly , 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 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

• 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 ™ asexual - budding ™ Fertilization external ™ Gametes passed into the (body cavity) stored until are laid. - some species have a specialized structure to introduce the gametes into the coelom.

Arthropoda • reproduction ™ dioecious - many dimorphic ™ oviparous, or ovoviviparous ™ - complete / incomplete ™ some parthenogenic – development from a unfertilized ovum. - Fertilization can be internal- males have an ovipositor

Evolution of Reproduction • Three Strategies of : ™ - 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 sac. ™ - Young develop within mother and obtain nourishment directly from mother’s blood.

Evolution of Brain Evolution of Vertebrate Reproduction • Fish ™ Eggs of most bony fish fertilized externally, and eggs contain small yolk sac. ™ Fertilization in most cartilaginous fish is internal. • ™ Fertilization is usually external. ™ Eggs of most species develop in water. ™ Development divided into stages. Evolution of Vertebrate Reproduction • ™ Most reptiles are oviparous, and lay amniotic eggs. - Other species are ovoviviparous, or vivaparous. ™ Most males use penis to introduce into the cloaca of females.

Evolution of Vertebrate Reproduction • Birds ™ All birds practice internal fertilization. - As eggs pass along , glands secrete albumin proteins and hard calcareous shell. ™ Homeothermic - Must keep eggs warm. ™ Young cared for and nurtured by parents.

Evolution of Vertebrate Reproduction ™ - Oviparous (duck-billed platypus). - Incubate eggs - Lack nipples ™ Marsupials - Give 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 . - Nourished by . Male Reproductive Organs Female Not all mammals are alike