Remember…all animals are “multicellular, heterotrophic eukaryotes”.

In most animals, cells interact at three levels of organization.

tissues

organs

organ systems

Animal bodies are organized at the basic level of the cell, which in combination (of similar cells) creates tissues, which work together to form organs, which work together to form organ systems…which make up the organism.

• Epithelial tissue covers the body’s surface and lines its internal tubes.• Connective tissue provides support and connects body parts.• Muscle tissue moves the body and its parts.• Nervous tissue detects internal and external stimuli and coordinates responses.

Epithelial TissueConnective Tissue

Muscle Tissue

Nervous Tissue

Parazoa

• • Literally translates “besides the animals”• Unlike true animals (or Eumetazoa) these organisms have no distinct tissues.

The only surviving parazoans are the sponges, which belong to the phylum Porifera, and one surviving species (Trichoplax adhaerens) in the phylum Placozoa

Organs and organ systems help animals to organize and compartmentalize the tasks of survival and reproduction for the body as a whole. Organs may belong to multiple systems.

The primary tissue layers that form in the early embryo (ectoderm, mesoderm, and endoderm) give rise to various organs and organ systems.

• ectoderm• mesoderm• endoderm

Three tissue (germ) layers that form during gastrulation develop into many different tissues.

Organisms with three tissue layers of development are triploblastic.

Organisms with only two tissue layers of development are diploblastic.

Tissue formation begins in an embryo. The simplest animals are diploblastic. They have only ectoderm, and endoderm.Cnidaria are invertebrates that are diploblastic.

What similarities do you notice about all these animals?

Platyhelminthes are another invertebrate phyla with diploblastic development.

When embryonic development involves the formation of three tissue layers, (as is the case with most animals) we have triploblastic development.

Most animal embryonic development follows this plan:• Zygote (fertilized egg)• Cleavage (division to 8 cells)• Blastula (hollow ball stage)• Gastrulation (pinching in of blastula, to form blastopore)• Gastrula formation, and independent tissue formation.

In animals, the dominant generation is 2n. What generation would you compare this to in the plant kingdom, and why?

What would the only exception to that rule be in the plant kingdom?

Sporophyte; gametophyte is (n), and sporophyte is 2n

Bryophytes (mosses),which have a dominant n (gametophyte) generation.

Asymmetrical animals (sponges) have no general body plan or axis of symmetry that divides the body into mirror-image halves.

Radially symmetrical animals (such as coral and jelly fish) have body parts organized about a central axis and tend to be cylindrical in shape. This feature is normally associated with a sedentary or sessile life style, rather than motile.

Bilateral Symmetry in animals (such as humans and fish) have only a single plane of symmetry that produces mirror halves.

• Organisms that are radially symmetrical have only a top and a bottom (or front and back).• Organisms that are bilaterally symmetrical have a top and bottom (dorsal, ventral), and a head and tail end (anterior, posterior)

Whenever you see this word…think “head”. Increased cephalization occurs in higher level animals with bilateral symmetry, from a collection of ganglia (nervous tissue) to brains.

What type of body plan, or symmetry does a sea anemone exhibit?

Does a sea anemone exhibit cephalization?

Name an organism that exhibits bilateral symmetry, and prove it by naming its planes of symmetry, (or surfaces).

Raidal

No…animals without bilateral symmetry do not have “heads”.

Dogs (any vertebrate). Dorsal, ventral, anterior, posterior

Whenever you see this phrase, think “guts”. Simple animals have a mouth that doubles as an anus. In more advanced organisms the cavity is through.

Acoelomate animals, like Platyhelminthes, have no body cavity at all. Organs have direct contact with the epithelium. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.

Pseudocoelomate animals have a pseudocoel, which is a fully functional body cavity. Tissue derived from mesoderm only partly lines the fluid filled body cavity of these animals. Thus, although organs are held in place loosely, they are not as well organized as in a eucoelomate. (true coelomate)

Nematodes and Rotifers (two invertebrate phyla) are the only pseudocoelomate animals. These also represent the first animals of triploblastic development.

Eucoelomates have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm. The complete mesoderm lining allows organs to be attached to each other so that they can be suspended in a particular order while still being able to move freely within the cavity. Most animals with bilateral symmetry are coelomates. This fluid filled sac allows for the growth and movement of internal organs.

Some cells migrate upward into the blastula to form a blastopore. This opening eventually forms the mouth of animals called protostomes.If the opening does not form the mouth, but instead forms the anus, the animals are deuterostomes.

During embryonic development, many organisms show tendencies to either be protostomes, or deuterostomes.Deuterostomes are the more complex of the organisms

Two major lineages of bilaterally symmetrical animals differ in how their digestive systems form.

• Protostomes: blastopore becomes a mouth

• Deuterostomes: blastopore becomes an anus

PlatyhelminthesNematodesRotifersAnnelidsArthropodsMollusks

EchinodermsChordates/Vertebrates

Only a few animals are able to reproduce asexually. When it occurs, asexual reproduction in animals usually occurs in one of three ways:

• Parthenogenesis: Modified sexual reproduction, in which eggs develop without fertilization

•Polyembryony: internal production of propagules, which are released and develop into new organisms (identical twins)

•Budding: splitting to produce new individuals