BIO 172 Exam 2

• Multicellular eukaryotes

• Heterotrophs

• Motile for at least part of the lifespan

Distinguishing Features of an Animal

• Choanoflagellates

• Animals are multicellular parazoans and eumetazoans

descended from unicellular colonial protozoans (protists)

• ~100 phyla appeared during Cambrian Explosion (~530 MYA)
• ~34 extant phyla (75% arthropod species!)

Animal Kingdom Overview

Levels of organization- Parazoans

Cellular (placozoans, sponges)

Levels of organization- Eumetazoans

• Tissue (comb jellies, cnidarians)
  • Organ (“bilaterians”) = most successful plan

Tissues

groups of differentiated cells that work together to
perform specific functions

Epithelial

Thin sheets of tightly joined cells = linings

Connective

Sparse cells in matrix material = connection and support

Muscular

• Contractile cells = produces movement

• NOTE: most abundant tissue type (collagen dominates)

Nervous

Chemically and electrically excitable cells = receives sensory inputs,
integrates/analyzes and sends motor outputs

Collagen

the most abundant protein in animals’ bodies

Body Symmetry: None

placozoans + most sponges (sessile)

Body Symmetry: Radial

allows interaction from all sides

• Primary: Cnidarians, Ctenophores, few sponges

• Secondary: Echinoderms

Body Symmetry: Bilateral

best for unidirectional interaction

• All other phyla (incl. echinoderm larvae), called “Bilaterians”

Oral

Aboral

Central

Peripheral

Anterior

Posterior

Dorsal

Ventral

Medial

Lateral

Animal Reproduction

Mostly sexual = biggest genetic advantage

Animal Reproduction

Lots of asexual too, including parthenogenesis = faster

Animal Reproduction

Multicellular diploids (no multicellular haploids!)

cell cleavage

Zygote undergoes rapid ____ ______

blastula

ball of cells hollows out

gastrulation → gastrula. Gastrula develops 2 or 3 “germ layers”
that develop into tissues (via cell
migration & differentiation):

Blastula undergoes _____ ______

Ectoderm

embryo’s outer layer

Endoderm

innermost layer = lining of primitive gut (archenteron)

• Mesoderm

  • Protostomes

  • Deuterostomes

middle layer
(only forms in Bilaterians!)

Protostome

Cell proliferation following fertilization is by spiral cleavage

Deuterostome

Cell proliferation following fertilization is by radial cleavage

Protostome

Coelom (body cavity) forms within the middle tissue germ layer

Deuterostome

Coelom forms from outpocketing of the middle tissue germ layer

Protostome

Initial opening into the gut becomes the mouth

Deuterostome

Initial opening into the gut becomes the anus

Embryos develop into larvae or juveniles
○ Sexually immature (vs adults)
○ Larvae very diff. form vs adult; must undergo
metamorphosis (1+) to take on adult form
○ Juvenile ~ small adult

Animal Development

coelom

body cavity

Parazoa

• Porifera

• Placozoa

710 MYA

Chemical evidence of first sponges

choanoflagellate

Best candidate ancestor

Modern choanoflagellates

are animals’ closest living relatives

Cellular level parazoans
• Asymmetrical (a few radial)
• All aquatic
– Porous body wall allows filter-feeding
• Endoskeleton of spongin
– Most contain calcareous or siliceous spicules
– Many are toxic
• Asexual and sexual reproduction
– Motile larvae → (metamorphosis) → sessile adults

Phylum Porifera (Sponges)

Spongin Spicules

(calcareous or siliceous) = sharp structures that often deliver TOXINS

Collar cells (choanocytes) create feedings currents
using flagella

Cell level of organization: no true tissues

Amoebocytes

cruise around and do lots of stuff, including:

• intracellular digestion + feeding of other cells

• immune & sexual repro functions

• repair = STEM CELLS! (blender...)

Amoebocytes

digest food particles filtered from the water
by collar cells (choanocytes)

hermaphrodites

Most sponges are

by broadcast spawners

Eggs may be released

by brooders

or retained

Phylum Placozoa: Plaque Animals

Only ONE known species
- No symmetry but motile!
– Muscle-like cells
– Walk with cilia !

Some cells act “tissue-ish”
– DNA evidence suggests
between Porifera & Cnidaria

Cell Level of org - only 6 cell types

Placozoans: Interesting Moltility

Use contractile “muscle-ish” cells + cilia