Animal Body Plans and Evolution

Zoology Mrs. Rushing

Features of Body Plans• Each animal phylum has a unique organization of particular

body structures that is often referred to as a body plan.

• Features of body plans include:– Levels of organization (slide 3)– Body symmetry (slides 4-14)– Differentiation of germ layers– Formation of body cavities– Patterns of embryonic development– Segmentation– Cephalization– Limb formation

Levels of Organization• Animals have specialized cells that are organized into tissues. Cell

specialization ensures survival because each cell performs a specific function.

• There are several types of tissues found in animals:– Epithelial tissues- cover body surfaces inside and out, are also

thin and flat. • Example: epithelial tissues line lungs and allow gases to easily

diffuse through– Muscle tissues– Connective tissues

• Tissues combine during growth and development to form organs and organ systems to carry out complex functions

Body Symmetry (AL COS 3)

• Bodies of most animals exhibit some sort of symmetry

• There are three different forms of symmetry– Radial symmetry: any number of imaginary planes

drawn through the center of the body could divide into equal halves. Example: Sea anemone

– Bilateral symmetry: a single imaginary plane divides the body into left and right sides that are mirror images of each other. Example: Human

– Asymmetrical: Arrangement without a central axis or point. Example: Sponge

Radial Symmetry

• Body parts are repeated around a central axis like spoke on a wheel.

• Can be cut in half in many ways and still get equal halves

• Advantage- can capture prey from all directions or can see predators coming from all directions.

• Disadvantage- Very slow or sessile (stuck in one place).

• **No head region

Bilateral Symmetry• Can only be cut in one way to get

equal halves

• Most animals fit into category

• Many parts are paired with one on each side of the body

Advantage: Leads to cephalization (sensory organs and the brain get moved to the head end of the animal)

Disadvantage: Hard to detect predators chasing them.

Asymmetry• Structurally simplest

• Represents oldest group on earth

• Not identical on both sides of central line(two halves of something don’t match or are unequal).

• Common example are corals and sponges

Anatomical Terms of Direction (AL COS 1)

• Caudal- The plane going towards the hind end. The rear portion.• Cranial- The plane going towards the head end (front). The front portion• Distal- Further away from the main part of the body, furthest. Example: The hoof

is the most distal part of the leg.• Dorsal- Back surface or topline • Lateral- Away from the median (middle line) plane. It is also the outside or

external surface. • Medial- Towards the middle (median plane) of the body. The inner or more

internal part.• Plantar- The sole of the hind hoof continuing up to the back of the hock (tarsus)• Proximal- Closer to the body, or point of attachment. Example: The knee is

proximal to the ankle• Rostral- Towards the nose• Ventral- Underneath or belly side

Anatomical Terms

• Anterior- Toward the front • Posterior- Toward the back• Superior- above (back)• Inferior- below (belly)• Superficial- close to the surface• Deep- internal, below the muscles• Quadruped- 4 legged• Biped- 2 legged• aboral- opposite of mouth, anus• Oral- mouth

Anatomical Planes of Reference• Sagittal Plane- Divides the body into right and left parts

• Median Plane (Midsagittal) Divides the body into equal right and left parts

• Transverse Plane- Divides body into cranial end and caudal end. (head- tail)

• Dorsal Plane- Divides the body into dorsal and ventral ( back- belly)

Quadruped or Biped?

Differentiation of Germ Layers• During embryological development the cells of most

animal embryos differentiate into 3 germ layers . This is a triploblastic organism because it is derived from 3 embryological layers

– 1. Endoderm: the innermost germ layer, develops into linings of the digestive tract and much of the respiratory system

– 2. Mesoderm: the middle layer, gives rise to the muscles and much of the circulatory, reproductive, and excretory organ systems

– 3. Ectoderm: the outermost layer, produces sense organs, nerves, and the outer layer of skin

– Most have organ- system level of organization

Advantages of Body Cavities(AL COS 2)

• Provides more room for organ development

• Provides more surface area for diffusion of gases, nutrients, and wastes into and out of organs

• Provides an area for storage

• Facilitates increased body size

Acoelomate• The mesoderm forms a solid mass of cells between the endoderm and

ectoderm

• An animal that lacks a coelom or a body cavity. Acoelomates, which include the flatworm, fluke, tapeworm, and ribbon worm, exhibit bilateral symmetry and possess one internal space, the digestive cavity.

Pseudocoelomate• Has a false body cavity not entirely lined by mesoderm

• Pseudocoelomate lack a circulatory system, and the pseudocoelom itself lacks the endothelial lining of a coelom. The hydrostatic pressure of the pseudocoelom gives the body a supportive framework that acts as a skeleton. Nematodes or roundworms are Pseudocoelomate.

Coelomate

• A true body cavity or coelom that is lined by mesoderm

• Mollusks and vertebrates

• short video on different body cavities

*Take Notes

Patterns of Embryological Development

• Every animal that reproduces begins as a zygote (a fertilized egg)

• At the beginning of development a zygote forms a blastula, which is a hollow ball of cells like an inflated balloon

• The blastula develops into the digestive tract by folding in on itself and developing a long elongated tube that runs from one end to the other

• In the beginning the digestive tract has only one opening, called the blastopore

Patterns of Embryological Development

• An efficient digestive system needs two openings: a mouth through which food enters and an anus through which waste exits

• Protostomes: the blastopore becomes the mouth first and the anus becomes the second opening, which develops at the opposite end of the tube

• Examples: flatworms, earthworms, snails, clams, spiders, and insects

• Deuterotomes: the blastopore becomes the anus and the mouth is formed from the second opening that develops– Chordates and echinoderms (sea stars) are deuterotomes, which

indicates that echinoderms are closely related to chordates

Segmentation: Repeating Parts• Segmentation occurs as many bilateral symmetrical animals

develop, their bodies become divided into numerous repeated parts, or segments

• Segmented animals such as worms, insects, and vertebrates have at least some internal and external body parts that repeat on each side of the body

• The most successful animals, including humans, have bilateral symmetry and segmentation

Cephalization: Head Formation• Animals with bilateral symmetry typically exhibit cephalization-

the concentration of sense organs and nerve cells at their anterior end

• The most successful animals including arthropods and vertebrates exhibit pronounced cephalization

• Insect and vertebrate embryos heads are formed by fusion and specialization of several body segments during development – As the segments fuse the external and internal parts combine in ways that

concentrate sense organs in the head, such as the eyes– Nerve cells that process information and “decide” what an animal should

do are also found in the head– Animals with a head move in a head first direction because this way the

concentration of sense organs and nerve cells come in contact with the new environment first

Limb Formation: Legs, Flippers, and Wings

• Segmented, bilaterally symmetrical animals typically have appendages on both sides of the body.

• The types of appendages vary depending on the animal. Examples:

• Bristles in worms * Flippers in dolphins• Jointed legs in spiders * Wings in dragonflies

• These different kinds of appendages have evolved several times, and have been lost several times, in various animal groups

• Limb formation and segmentation have evolved to allow animals to be more flexible and have improved movement

Limb Formation: Legs, Flippers, and Wings

Animal Type:

Levels of organization Cells, tissues, organs?Body symmetry Bilateral, radial?Germ layers 1,2,3..?Body Cavity Coelom, Pseudocoelom,

Acoelom..?Embryological Development Protostomes, DeuterostomeSegmentation Absent, Present?Cephalization Present, Absent?

Animals to include on chart: •Sponges *Cnidarians•Flatworms *Roundworms•Annelids *Mollusks•Arthropods *Echinoderms•Chordates

CnidariansLevels of organization

Specialized cells, Tissues

Body symmetry Radial symmetryGerm layers TwoBody Cavity AcoelomateEmbryological Development

___

Segmentation AbsentCephalization Absent

25.2 Body Plans and Evolution Vocabulary

• Radial Symmetry: any number of imaginary planes drawn through the center of the body could divide into equal halves.

• Bilateral Symmetry: a single imaginary plane divides the body into left and right sides that are mirror images of each other.

• Endoderm: the innermost germ layer, develops into linings of the digestive tract and much of the respiratory system

• Mesoderm: the middle layer, gives rise to the muscles and much of the circulatory, reproductive, and excretory organ systems

• Ectoderm: the outermost layer, produces sense organs, nerves, and the outer layer of skin

• Coelom: a body cavity that develops within the mesoderm and is completely lined with tissue derived from the mesoderm

25.2 Body Plans and Evolution Vocabulary

• Pseudocoelom: which is only partially lined with mesoderm • Zygote: a fertilized egg• Blastula: a hollow ball of cells like an inflated balloon that

develops into the digestive tract by folding in on itself and developing a long elongated tube that runs from end to the other

• Protostomes: the blastopore becomes the mouth and the anus becomes the second opening, which develops at the opposite end of the tube

• Deuterostomes: the blastopore becomes the anus, and the mouth is formed from the second opening that develops

• Cephalization: the concentration of sense organs and nerve cells at their anterior end