MBE 230-Chapter 8: Metazoa

Advantages for Multicellular

- Size reduces predation
- Size increases food options
- Size increases speed
- Cellular differentiation

Disadvantages for Multicellular

- Size decreases S/V ratio
- Sinking (meiofauna)
- O2 Uptake (Cambrian Explosion)
- Internal transport -- Internal Structure

First Metazoans were:

More than 650 million years ago (mya)

Ediacarian Fauna:

Experiment with body plans

Cambrian Explosion:

Roughly 570-600 million years ago (shells)

Metazoan Meiofauna:

- Nematodes
- Tardigrades
- Placozoa
- Gastrotrichs

"Miniaturized" Metazoans

- Flatworms
- Annelids
- Tunicates
- Hydrozoa
- Rotifers
- Bryozoa
- Molluscs
- Brachiopods
- Crustaceans
- Echinoderms
- Ascidians

Ediacarian Period (670-570 mya)

- Multicellular organisms
- Morphological evolution begins
- Dramatic decline in acritarchs and stromatolites
- Soft bodied invertebrates appear
- Many odd groups went extinct

Cambrian body plan survivors:

- Sponges
- Radiata
- Protostomes
- Deuterostomes

- They had spiral or radial cleavage
- Partial or complete cleavage
- Equal or unequal cell size
- Blastopore (opening of central cavity of an embryo) ---> mouth or anus
- They also had an ectoderm, endoderm, and mesoderm.

Mobility of Metazoa:

- Cilia
- Hydrostatic body (light body underwater)
- Skeletal system (chitin, CaCO3)(Opposing muscles)

Metazoa feeding on microbes:

- Cilia
- Filtering
- Mucus
- Mucus Filtering

Metazoa feeding on larger food:

- Engulfing
- Bites
- Sucking
- Poisoning

Respiration and Excretion of Metazoa:

- S/V Ratio: size, flattened shape
- Gills
- Coelomic cavity
- Open and closed circulation
- Heart
- Hemoglobin (red, Fe)
- Hemocyanin (blue, Cu)
- Haemerythrin (purple, Fe)
- Chlorocruorin (green, Fe)

Physical Sensory systems:

- Gravity
- Touch
- Vibration
- Hearing
- Echolocation
- statoliths (helps with balance and orientation in invertebrates)
- hairs

Light Sensory systems:

- Intensity
- Direction
- Patterns
- Image
- Bioluminescence
- Black and white, grays, colors, IR visible, UV

Polarized eyespot - lenses - compound eye - camera eye

Chemical Sensory systems:

- Taste
- Smell

Chemoreception SLIDE 1 (ability to perceive specific chemical stimuli):

Taste:
- few, broad receptors
Food evaluation (copepods, biggest metazoans on earth)

Smell:
- many, specific receptors
Food evaluation, predator detection, and communication

Chemoreception SLIDE 2

Within body - hormones (endocrine disruptors)
Within population - communication, pheromones
Within community - detect predators and prey
Within ecosystem - orientation

Metazoan Reproduction:

- Isogamy or anisogamy (sexual reproduction by the fusion of similar gametes)
- Separate sexes and hermaphrodites
- Internal and external fertilization
- Direct development of larvae
Larvae -- usually planktonic, sometimes series of larvae.
- Sometimes alternation of body plans (sexual and asexual)
- Reproductive plans evolve in response to environmental situations

Reproductive characteristics of:

Macrofauna (larger):
- Many eggs
- External Fertilization
- Usually separate sexes
- Planktonic larvae
- Seasonal reproduction
- Long generation time
- Large temporal variability

Meiofauna (smaller):
- Few eggs
- Internal Fertilization
- Often hermaphroditic
- Direct development, brooding
- Continuous Reproduction
- Short generation time
- Relative population stability

Meiofauna vs Macrofauna:

Meiofauna increases in diversity and importance with depth (higher diversity in deep sea)

Macrofauna become less important, have restricted diversity with depth

(Higher speciation and extinction rates on shelves)
(Lower speciation and extinction rates in the deep sea)