25 2 ANIMAL BODY PLANS AND EVOLUTION Miss

25. 2 ANIMAL BODY PLANS AND EVOLUTION Miss Grant Kaimuki Christian School

What is a body plan? � � A unique organization of structures Features include � Levels of organization � Body symmetry � Differentiation of germ layers � Formation of body cavities � Patterns of embryological development � Segmentation � Cephalization � Limb formation

Levels of Organization � � � � Body Organ systems Organs Tissues Cells Organelles Molecules Atoms

Body Symmetry � � Radial symmetry (sea anemone) Bilateral symmetry (lobster)

Differentiation of Germ Layers � Make up three layers of cells during embryological development � Endoderm (develop linings of digestive tract and respiratory system) � Mesoderm (muscles and most of the circulatory, reproductive, and excretory systems) � Ectoderm (sense organs, nerves, outter layer of skin)

Formation of Body Cavity � � � Fluid-filled space between the digestive tract and body wall Space where internal organs are suspended and can grow Most complex animals have a true coelem � Body cavity that develops within the mesoderm and is completely lined with tissues from the mesoderm � � Acoelomate: lack a body cavity Pseudocoelomate: only partially lined with mesoderm

Patterns of Embryological Development � � Zygote: fertilized egg Blastula: hollow ball of cells Blastopore: single opening in the digestive tract Efficient digestive tract needs two opening � Why? � � Protostomes: blastopore becomes the mouth Deuterostomes: blastopore becomes the anus (chordates and echinoderms)

Segmentation (Repeating Parts) � � Worms, insects, vertebrates At least some internal and external body parts that repeat on each side of the body Bilateral symmetry and segmentation found in many of the most successful animal groups How can a simple mutation in the genes of an organism affect segmentation?

Cephalization � � Concentration of sense organs and nerve cells at the anterior end Exhibited by most animals with bilateral symmetry Most successful animal groups Heads are formed by fusion and specialization of several body segments during development

Limb Formation � � � � Segmented, bilaterally symmetrical animals typically have appendages on both sides Bristles in worms Jointed legs in spiders Wings in dragonflies Bird wings Dolphin flippers Monkey arms

Cladogram of Animals � � Based on characteristics of living species Evidence from fossils comparative genomic studies Animals phyla defined according to body plans and patterns of embryological development

Differences Between Phyla � � Cladogram shows the sequence in which body plan features evolved Every phylum has a unique combination of ancient traits inherited from ancestors