Chapter 34 - Animals34.2 Animal Bodies

Body Structure

Morphology is◦the branch of biology dealing with the form and

structure of organisms.

Symmetry is◦the proper proportion of the parts of a body

with respect to one another and with regard to size and form.

Patterns of Symmetry

Radial SymmetryBasic body plan where the organism can

be divided into similar halves by passing a plane at any angle along a central axis.

Characteristic of sessile and bottom-dwelling animals, as the sea anemone and starfish.

Bilateral Symmetry – most animals…

Bilateral SymmetryBasic body plan where the left and right

sides of the organism can be divided into approximate mirror images of each other along the midline.

Dorsal - backVentral - tummyAnterior - headPosterior – rear end

Bilateral Symmetry…

Cephalization◦specialization of the body with sensory and neural organs in an anterior head

Patterns of Symmetry

Germ Layers – layers formed during very early development of most animals

1. ectoderm = outside layer

2. endoderm = inside layer

3. mesoderm = layer in between the above two

Body Cavities…

Most animals have some type of body cavity.

Body Cavity◦Fluid-filled space between the digestive tract

and the outer wall of the body during development.

Examples:FLATWORM: three germ layers; solid

body – lack a body cavity.ROUNDWORM: Body cavity aids in

movement by providing a firm structure against which muscles can contract.

Body Cavities…

A body cavity also allows some movement of the exterior part of the body in respect to the internal parts of the body. ◦more freedom of movement for the animal

The fluid in the cavity acts as a reservoir and medium for the transport for nutrients and wastes.◦these diffuse in/out of the animal’s body cells.

Animal Diversity…

ANIMAL DIVERSITYAnimal phyla shown on the same branch

of the phylogenetic tree are thought to be more closely related to each other than they are to other animals.

They are characterized by important similarities in morphology.

Likewise, animals shown in different parts of the tree are thought to be more distantly related.

Animal Diversity…

Multicellularity and a limited degree of cell specialization – characterize sponges

Sponges have no organized body shape and no true tissues.

True tissues in two layers – found in the cnidarians (hydra, jellyfish, etc.) and the ctenophores (exclusively marine, invertebrates)

True tissues in three layers and bilateral symmetry – characterize all of the other animal phyla

phylogenetic categories are based on◦ the absence or presence and type of body cavity◦ fundamental patterns of development

Animal Diversity…

InvertebratesAbsence of a backboneGreatest number of animal speciesMost of the animals alive today

Animal Diversity…

ChordatesRefers to the notochord

◦A firm, flexible rod of tissue located in the dorsal part of the body (the back).

◦At some stage of development, all chordates have a notochord, dorsal nerve cord, pharyngeal pouches, and a post anal tail.

Dorsal nerve cord◦Hollow tube lying just above (dorsal to) the notochord.

Pharyngeal pouches◦Small outpockets of the anterior part of the digestive

tract.Postanal tail

◦Consists of muscle tissue and lies behind the posterior opening of the digestive tract.

Animal Diversity…

In most vertebrates…The dorsal nerve cord develops into the

brain and the spinal cord.This runs within the hollow backbone in

aquatic vertebrates (fishes and amphibians).Pharyngeal pouches evolved into gills –

used for breathing.In most vertebrates, the notochord is seen

only in the embryonic stage.It is replaced by the backbone early in

development.

Animal Diversity…

Vertebrates…Make up only one subphylum of the

phylogenetic tree of all animals.Humans are vertebrates.Humans interact extensively with many other

vertebrates.◦fishes◦birds◦mammals

All of these are primary food sources for humans.