What is an Animal? Chapter 25

Characteristics of Animals Animals obtain food  Sessile – Organisms that are permanently attached to a surface  Sessile animals filter feed  Sessile animals are aquatic

Characteristics of Animals Animals digest food  Multicellular organisms digest food in a digestive tract

Characteristics of Animals Animal cell adaptations  Animal cells are differentiated and carry out different functions

Development of Animals Fertilization  The fusing of a sperm cell to an egg cell  Gamete – a sex cell  Zygote – a fertilized egg (2n) (n)

Cell Division Zygotes divide by mitosis Once cell division had begun, the organism is known as an embryo Blastula – a fluid-filled ball covered with cells (2n)

Gastrulation Gastrula – the cells on one side of the blastula move inward

Animal Reproduction Asexual reproduction – requires only one parent  Ex. – bacteria Sexual reproduction – requires two parents Reproduction AsexualSexual External fertilization Internal fertilization

Animal Reproduction Internal fertilization – sperm and egg unite inside the body External fertilization – sperm and egg unite outside the body Reproduction AsexualSexual External fertilization Internal fertilization

Animal Reproduction External fertilization occurs in water Pro: Many offspring can be produced Con: Parental protection is reduced

Animal Reproduction Internal fertilization occurs inside animals Pro: Increased parental protection Con: Low number of offspring produced

Directional Terms Superior – Above; over Inferior – Below; under

Directional Terms Anterior– Toward the front Posterior– Toward the backside

Directional Terms Dorsal – Near the upper surface, toward the backbone Ventral – Toward the bottom, towards the belly

Directional Terms Medial – Toward the midline of the body Lateral – Away from the midline; the outer side of the body

Directional Terms Proximal – Close to Distal – Far from

Directional Terms Cephalic (or cranial) – Towards the head Caudal – Towards the tail

Directional Terms Superior Inferior Anterior Posterior Dorsal Ventral Medial Lateral Proximal Distal Cephalic Caudal

Directional Terms

Symmetry Asymmetry – an animal that has no symmetry  Example: sponge

Symmetry Radial symmetry – divided along a plane, through a central axis, into roughly equal halves

Symmetry Bilateral symmetry – divided down its length into similar right and left halves

Body Cavities Coelom – cavity Cavity – an empty space Body cavities make it possible for animals to grow larger

 Three body cavities  1. Acoelomates – animals that develop from three cell layers but have no body cavities

Body Cavities  2. Pseudocoelomates – a fluid-filled body cavity partly lined with mesoderm  Pseudocoelomate animals are larger and thicker than acoelomate animals

Body Cavities 3. Coelomates – a fluid-filled space that is completely surrounded by mesoderm  More complex animals are coelomates

Animal Protection and Support Exoskeleton – a hard covering on the outside of the body that provides a framework for support Crayfish

Animal Protection and Support Endoskeleton – an internal skeleton within animals

Animal Protection and Support Invertebrate – an animal without a backbone Vertebrate – an animal with a backbone

Animal Classification Animals Invertebrates Vertebrates Sponges Cnidarians Worms Mollusks Arthropods Echinoderms Ectotherms (cold-blooded) Endotherms (warm-blooded) Fishes Amphibians Reptiles Birds Mammals