Chapter 33 Intro to animals

List the characters that define animals

Multicellular and heterotrophs

• Mobility (at least during part of the life cycle)

• Prevalent sexual reproduction

• Unique cell structure:

o No cell wall

o An extensive extracellular matrix provides structural support

o Unique cell junctions hold cells in place and facilitate

communication among them

Invertebrates

invertebrates (evolved first; backbone is

absent)

vertebrates

vertebrates (have a backbone)

Morphological and developmental features traditionally used to classify

animals

Type of body symmetry

• Number of germ layers

• Specific features of embryonic development

Radial symmetry (Radiata)

Can be divided equally by any

longitudinal plane through the central

axis

• Often circular or tubular in shape,

with a mouth at one end

Bilateral symmetry (Bilateria)

Can be divided along a vertical

plane to produce two halves

• Have cephalization and dorsal and

ventral sides

• Have anterior and posterior ends

Do Radiata and Bilateria differ in the number of embryonic cell layers (germ

layers)

YES

Radiata have 2 layers (diploblastic)

o Bilateria have 3 layers (triploblastic)

Cell layers develop during

gastrulation, a stage of embryonic

development

What are the germ layers

nner layer - endoderm

o Outer layer - ectoderm

o Middle layer - mesoderm (3rd layer in bilateral animals)

Forms muscles and most other organs

Embryonic development

Protostome

• Blastopore becomes the mouth

• Cleavage is determinate

o The fate of embryonic cells is determined early

Deuterostome

• Blastopore becomes anus

• Cleavage is indeterminate

o Each cell produced by early cleavage can develop into a complete

embryo

• Humans are Deuterostomes

Why do we think that the Cambrian period fostered animal diversification?

Three possible explanations:

o Favorable environment - warm temperatures, increases in

atmospheric and aquatic oxygen, development of the ozone layer,

and more minerals dissolved in water to make shells

o Evolution of the Hox gene complex

o An evolutionary “arms race”: predators evolved new traits and prey

developed adaptations to escape death

Animals evolved from a

choanoflagellate-like ancestor

the closest living relatives of

animals are choanoflagellates

o Single-celled protists: Have a

single flagellum surrounded by a

collar of cytoplasmic tentacles

o Some are colonial

o Some cells may have taken on

specialized functions

• Choanoflagellates bear a

striking similarity to sponge

choanocytes

What is cephalization

Often associated with bilateral

with cephalization (concentration of sensory organs at the head)

What is segmentation

Body may be divided into regions called segments

• Occurs in annelid worms, arthropods, and chordates

• Allows for specialization of body regions

ecdysis

Ecdysis → molting of an exoskeleton (like insects and arthropods)

Distinguish between radial and bilateral symmetry. Explain how animal symmetry

may match the animal’s way of life.

Radial symmetry

• Body arranged around a center (like a circle)

• Example: jellyfish

• Lifestyle: usually sessile or drifting

• Can sense environment from all directions

Bilateral symmetry

• One left and one right side

• Example: humans

• Lifestyle: active movement

• Often has cephalization

Distinguish between diploblastic and triploblastic development

Diploblastic

• 2 germ layers (ectoderm + endoderm)

• No true organs

• Example: jellyfish

Triploblastic

• 3 germ layers (ectoderm, mesoderm, endoderm)

• Have complex organs and tissues

• Example: most animals

All animals share a

Common Ancestor

Sponges (Porifera) are basal animals with

specialized cells, but NO

TISSUE

Most animal phyla belong to the clade

Bilateria. Bilateral animals

are triploblastic (3 germ layers)

Most animals are

invertebrates, lacking a backbone; Chordata is

the only phylum that includes vertebrates, animals with a backbone

Embryonic development stages

Most animals reproduce sexually, producing a diploid zygote. Embryonic

development typically includes: the blastula stage and the formation of 3 germ

layers (ectoderm, mesoderm, endoderm). Some exceptions are

diploblastic.

Figure 33.3