Download Ch 10: Classification

Z202- Unit 1
Chapter 12
Mesozoa and Parazoa
Review:
Major Subdivisions of Animal Kingdom
(Chapter 10)
I.
Advent in Multicellularaity
A. Advantages
- Increasing the size of a cell causes problems in
exchange
- Multicellularity avoids surface area-to-volume problems
B. Position in the Animal Kingdom
1. Multicellular organisms divided into 3 grades:
a. Mesozoa
b. Parazoa
c. Eumetazoa
(phylum Porifera & Placozoa)
(all other animal phyla)
2. Mesozoa and Parazoa are multicellular but lack
germ layers
II. Origin of Metazoa
3 Theories of their Origins
1. Syncytical Ciliate Hypothesis
Arose from multinucleated ciliated protozoans
2. Colonial Flagellate Hypothesis**
Arose from colonial flagellated protozoans
(biochemical evidence support Choanoflagellates)
3. Polyphyletic Hypothesis
Metazoans are polyphyletic
III. Phylum Mesozoa
A. Mesozoa
“Middle Animals”
- named in 1876 by van Beneden
(link between protozoa & metazoa)
- minute(1/2 to 7mm long) ciliated wormlike animals
- all are parasites in marine invertebrates
- small (20-30 cells) with 2 cell layers (but not germ)
- outer layer of somatic cells, inner layer of reproductive
- 2 classes:
1. Rhombozoa (kidney’s of Cephalopods)
2. Orthonectida (invertebrate parasite)
B. Phylogeny
- debated:
a. maybe ciliate protozoans
b. perhaps primitive/degenerate flatworms (Phylum
Platyhelminthes) (molecular support)
IV. Phylum Porifera
(aka Parazoa)
A. General Features
- 5,000 species (most marine, 150 freshwater)
- Porifera = “pore-bearing” sac-like body
- Sessile (dependent on water currents) filter feeders
- Body = mass of cells embedded in gelatinous matrix &
stiffened by spicules & collagen
- Spicules of calcium carbonate or silica
- No organs or tissues, nervous or sense organs
- Morphology changes w/ stratum, speed of water current
- Ancient, fossils extend earlier than Cambrian
B. Form & Function
- Sac-like body:
Ostia (small incurrent pores)
Oscula (few excurrent pores)
Choanocytes (lining flagellated collar cells)
Keep water flow, trap & phagocytize food
Archaeocytes (move w/in mesohyl, phagocytize,
secrete spicules/spongin/collagen)
Pinacocytes (flat epithelial-like cells, regulate water flow)
- Type of Skeleton:
*All have Collagen fibrils
- some have spongin
- some secrete siliceous spicules
- some secrete calcium carbonate spicules
- Physiology
(*large sponges filter 1500 Liter/day)
- radial to asymmetrical
- digest intracellular by Choanocytes & Archaeocytes
- no excretory, respiratory organs (diffusion)
- no nervous system
(only behavior – pore open/close)
C. Reproduction
1. Asexual
- external buds break off
- internal buds (gemmules) form by Archaeocytes
(also aid surviving adverse environmental conditions)
2. Sexual
- monoecious (both male & female individuals)
- sperm arise from transformed choanocytes
- oocytes arise develop from choanocytes or
archaeocytes
- sperm may enter adult sponge to fertilize or free-swim
- zygote supported by adult or released as ciliated larvae
3. Regeneration
- regenerate wounded portions
- fragments may aggregate into new structures
D. Three types of Canal Systems (Fig. 12-7)
1. Asconoids (Flagellated Spongocoels)
2. Syconoids (Flagellated Canals)
3. Leuconoids (Flagellated Chambers)
V. Phylogeny & Classification
- Sponges appeared PreCambrium
- Biochemical evidence suggest sponges arose from
choanoflagellates (though collar cells also seen in some
corals & echinoderms)
- Classification:
• Class Calcarea (calcium carbonate spicules)
• Class Hexactinellida (6 ray siliceous spicules)
• Class Demospongiae (95% of living sponges)
(siliceous spicules or no spicules – spongin only)
Ch 13: Radiate Animals
VI.
Position & Contributions
A. Position in Animal Kingdom
- Radiate animals = Phylum Cnidaria & Ctenophora
- Radial symmetry may be limited (several planes)
- Tissue level of organization only
B. Biological Contributions
- 2 well-defined germ layers (Ectoderm & Endoderm)
though mesoderm may be present (ectoderm derived)
- simplest animals w/ nerve cells & sense organs
- polyp & medusa stages present
- Nematocysts unique
- ecologically diverse & widespread
VII. Phylum Cnidaria
A. Life History
- over 9,000 species, originated over 700 mya
- specialized cells (Cnidocytes) contain unique stinging
organelle (Nematocyst)
- most common in shallow marine environments, some
freshwater = all aquatic
- some live symbiotically: coral reef formation & algae
B. Characteristics
- Radial (biradial) = oral & aboral end
- 2 Body types:
1. free swimming Medusa (bell-shaped/umbrella)
- oral end downward surrounded by tentacles
- form dominant in true jellyfish
2. sessile polyp
- tubular body (oral end up) surrounded by
tentacles
- aboral end attach to substrate by pedal disc
- colonial forms (segregate jobs)
- sea anemones & coral have no medusa stage
- exo & endoskeletons of chitinous, calcareous, or protein
- Gastrovascular cavity w/ 1 opening (extracellular
incomplete digestion)
(may be lined with Nematocysts)
- Nematocysts in epidermis
(20 Different types, important in taxonomy)
*filaments vary – poisonous or barbed to grasp
*after discharged, cnidocyte absorbed & another
develops
- Nerve net w/ some sensory organs
- Unique neural transmission
(bidirectional – neurotransmitters)
- Muscular system (primitive)
- Reproduction either asexual or sexual
- No excretory, respiratory systems or coelomic cavity
VIII. Phylogeny & Classification
A. Phylogeny
- most likely theory – Radiates arose from a radial
symmetric protozoan ancestor
B. Classification
Class Hydrozoa
(hydra)
(most colonial marine)
Class Scyphozoa
(open ocean)
(most of large jellyfish)
Class Cubozoa
(sea wasp, square umbrellas)
Class Anthozoa
(lack medusa, marine)
(sea anemone, corals)
IX. Phylum Ctenophora
A. Life History
- fewer 100 species
- all marine
- eight rows of comb-like plates used for free swimming
- lack nematocysts
- most luminesce
- body design similar to Cnidarians