Millar Harley Zoology INVERTEBRATES Phylum Porifera.pdf

1. INVERTEBRATES (Zool-02506)
3(2-1)
Presented by: Nabeel Tahir
M.Phil. Zoology
Class: ADP 5 Semester
Lecture: 3-4

2. Animal-Like Protists: The Protozoa

3. Introduction
 The term protozoa has traditionally referred to chemoorganotrophic protists.
 Zoologists who specialize in the study of protozoa are called protozoologists, and the study of all protists,
regardless of their metabolic type, is called protistology.
Definition: a protozoan (Gr. proto, first + zoa, animal) is a complete organism in which all life activities are
carried on within a single plasma membrane.
Some characteristics of protozoans.
• Lack collagen and chitinous cell walls.
• display unicellular (cytoplasmic) eukaryote organization.
• Complex organisms.
• form colonies.
• Reproduce asexually or sexually.
• Contain chloroplasts (Photoautotrophs).
• Absorb organic molecules/ ingest food particles (Heterotrophs)
• Photosynthesis and heterotrophic nutrition ex: species of euglenoids (Mixotrophs).

4. Origin of Protozoan
• The first evidence of what appears to be a protist is found in tiny fossils in
rock 1.5 billion years old.
• These fossils are much larger than bacteria and contain small membrane-
bound structures.
• The fossil record indicates that virtually all Protist and animal phyla living
today were present during the Cambrian period, about 550 million years
ago.
• The Eubacteria and Archaea diverged from a common ancestor about 1.5
billion years ago.
• Ancient members of the Archaea (extremophiles) were the first living
organisms on this planet.
• The Archaea and Eubacteria probably contributed to the origin of the
protists about 1.5 billion years ago.

6. Evolution of Protozoan
The endosymbiont theory is one of a number of explanations of how
protozoan have evolved.
Endosymbiont Theory:
• proposed by Lynn Margulis (1938–2011).
• Eukaryotes formed when large, nonnucleated cells engulfed smaller and
simpler cells.
• Endosymbiont: is an organism that can live only inside another organism,
forming a relationship that benefits both partners (Symbiosis).
• Symbiogenesis: The merging of different species to produce evolutionarily
new forms.
• Mitochondria evolved by endosymbiosis of an aerobic prokaryote.
• Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium.

8. Secondary
endosymbiosis
• When a eukaryotic cell engulfs a
cell that has already undergone
primary endosymbiosis.
• plastid-bearing lineage of protists-
red algae and green algae.
• During eukaryotic evolution- red
and green algae underwent
secondary endosymbiosis, in
which they were ingested by a
heterotrophic eukaryote.

9. Classification of protozoan
• Based on morphological, biochemical, and physiological analysis, the
International Society of Protistologists recognizes six
phylogenetically coherent protist clusters called supergroups.
• The protists as a whole represent a polyphyletic assemblage, and the
monophyly of each supergroup lineage is being evaluated by ongoing
research.
• Some protists are plantlike because they are primarily autotrophic
(they produce their own food). Others are animal-like because they
are primarily heterotrophic (they feed on other organisms).

10. Six supergroups
• Excavata
• Chromalveolata
• Rhizaria
• Archaeplastida
• Ameobozoa
• Opisthokonta

11. Multicellular and Tissue Levels of Organization

12. Multicellular and Tissue Levels of Organization
• After the first eukaryotes appeared, a great range of unicellular forms
evolved, giving rise to the diversity of single-celled eukaryotes that
continue to flourish today.
• Another wave of diversification also occurred: Some single-celled
eukaryotes gave rise to multicellular forms, whose descendants
include a variety of algae, plants, fungi, and animals.

13. Origins of Multicellularity
• The oldest known fossils of multicellular eukaryotes are of relatively small red algae that
lived 1.2 billion years ago.
• Larger and more diverse multicellular eukaryotes do not appear in the fossil record until
about 600 million years ago.
• These fossils, referred to as the Ediacaran biota, were of soft-bodied organisms—some
over 1 m long—that lived from 600 to 535 million years ago.
• The Ediacaran biota included both algae and animals, along with various organisms of
unknown taxonomic affinity.
Advantage in multicellular existence
Defense: Larger size was less vulnerable to predation by predatory protists.
Exchanges with the environment: were more efficient in organisms made of more,
smaller cells.
Division of labor in an organism: Cells can be specialized for specific functions like
reproduction, feeding and digestion, sensory perception, and communication.

14. Two hypotheses of origin of multicellularity
Colonial hypothesis
• cells of a dividing protist remained together.
• Cellular differentiation and invagination could have formed a second cellular
layer.
• There are many examples of colonial organisms that form in a manner similar to
that depicted by the colonial hypothesis, including the choanoflagellates.
Coencytial hypothesis
• Formation of cell boundaries within a coencytial protist.
• The primary support for this hypothesis comes from the observation that the
development of insects, like the fruit fly (Drosophila melanogaster), proceeds by
nuclear divisions of the zygote followed by the formation of cell membranes
between nuclei.

16. Animal Origins
Monophyly of Animalia
 The animal kingdom as being monophyletic— derived from a common ancestor.
This hypothesis is supported by impressive similarities within the Animalia as regards certain cellular
structures that are common to animals.
• The presence of flagellated cells, especially monoflagellated cells, is characteristic of animals.
• Asters form during mitosis in most animals,
• certain cell junctions are similar in all animal cells, and the proteins that accomplish movement are
similar in most animal cells.
Ancestral protists
 The choanoflagellates are a group of protists that possess a basket-like collar surrounding the base of a
flagellum that is used in feeding. These cells are virtually identical to one kind of sponge(animal) cell used
in feeding—the choanocyte.
There are also impressive similarities between choanoflagellate and animal genes.
• cell adhesion proteins,
• Extracellular matrix proteins
• cell surface receptors

17. Evolutionary perspective
• Evolutionary Relationships of the Ctenophora, Porifera, and Cnidaria to
other members of the animal kingdom.
• Evidence for these relationships is based on modern developmental and
molecular biology.
Members of the phylum Porifera are probably derived from ancestral
choanoflagellate stocks.
Members of the phylum Cnidaria arose very early in animal evolution—
probably from radially symmetrical ancestors.
Members of the phylum Ctenophora are the comb jellies. New
information suggests that ancestral members of the phylum Ctenophora
may be closest to the root of this animal phylogeny.

18. Phylum Porifera

19. Phylum Porifera
• The Porifera (po-rif9er-ah) (L. porus, pore 1 fera, to bear),
or sponges,
• Primarily marine animals consisting of loosely organized
cells.
• 9,000 species of sponges.
Characteristics of the phylum Porifera include:
1. Asymmetrical or superficially radially symmetrical
2. Three cell types: pinacocytes, mesenchyme cells, and
choanocytes
3. Central cavity, or a series of branching chambers, through
which water circulates during filter feeding
4. No tissues or organs

20. Cell Types
• Have a division of labor
• Pinacocytes: thin, flat cells that line outer surface, may contract and change
shape of sponge.
• Porocyte: some pinacocytes are specialized into tubelike, contractile cells, which
can regulate water circulation.
• Mesohyl: jellylike layer below pinacocyte layer.
• Mesenchyme Cells: ameboid cells moving about in mesohyl; for reproduction,
secreting structures, food transport and storage.
• Choanocytes: flagellated cells below mesohyl that line inner chamber(s); create
water current and filter microscopic food.
• Spicules: thorn-like projections that provide structural support and protection;
made of calcium carbonate by ameboid cells.
• Some species make a fibrous protein of collagen - spongin

22. Water Currents
• Choanocytes use their flagella to create water currents through
external pores called – ostia (sing. ostium,); incurrent pores.
• Bring food (bacteria, protists, etc.) and oxygen and remove metabolic
wastes from the center of the sponge – spongocoel.
• Choanocytes use collar-like rings to filter food.
• Wastes and water flow out a central osculum (plural, oscula); an
excurrent pore.

23. Sponge Anatomy

24. 1. Ascon Body Form
• The simplest and least common
sponge body form is the ascon
• Ascon sponges are vaselike.
• Ostia are the outer openings of
porocytes and lead directly to a
chamber called the spongocoel.
• Choanocytes line the spongocoel, and
their flagellar movements draw water
into the spongocoel through the ostia.
• Water exits the sponge through the
osculum, which is a single, large
opening at the top of the sponge.

25. 2. Sycon Body Form
• In the sycon body form, the sponge wall
appears folded. Water enters a sycon
sponge through openings called dermal
pores.
• Dermal pores are the openings of
invaginations of the body wall, called
incurrent canals.
• Pores in the body wall connect incurrent
canals to radial canals, and the radial
canals lead to the spongocoel.
• Choanocytes line radial canals (rather
than the spongocoel).
• The beating of choanocyte flagella moves
water from the ostia, through incurrent
and radial canals, to the spongocoel, and
out the osculum.

26. 3. Leucon Body Form
• Leucon sponges have an extensively
branched canal system.
• Water enters the sponge through ostia
and moves through branched
incurrent canals, which lead to
choanocyte- lined chambers.
• Canals leading away from the
chambers are called excurrent canals.
• Proliferation of chambers and canals
has resulted in the absence of a
spongocoel, and often, multiple exit
points (oscula) for water leaving the
sponge.

28. The Importance of Water Currents
• Respiration (gas exchange), Metabolism, and Excretion all done by
direct diffusion with water.
• No nervous system – no responsiveness.
• Defenses – may produce some irritating chemicals if touched;
chemical defense against predators, fish, sea stars, etc.
• Choanocytes filter microscopic food and trap in collar.
• Placed into food vacuole and digested by lysosomes.
• Digested food is passed to amoeboid cells for transport to other cells
– beginnings of specialization.

29. Reproduction
• Sponges are monoecious (both sexes in the same individual – hermaphrodite).
• Do not self-fertilize. Why?
• Choanocytes become sperm.
• Other choanocytes and amoeboid cells become eggs.
• Released from oscula and exteranl fertilization.
• Early development occurs in the mesohyl.
• Cleavage of a zygote results in the formation of a flagellated larval stage.
• A larva is an immature stage that may undergo a dramatic change in structure before
attaining the adult body form.
• The larva breaks free, and water currents carry the larva out of the parent sponge. After
no more than two days of a free-swimming existence, the larva settles to the substrate
and begins to develop into the adult body form.
• Larvae are free-swimming.

30. Free-swimming
larvae settle to the
bottom and ….
…become sessile
(attached to the
bottom) adults

31. Larval stage
Parenchymula larva
• 0.2 mm.
• Flagellated cells cover most of the
larva’s outer surface.
• After the larva settles and
attaches, the outer cells lose their
flagella, move to the interior, and
form choanocytes.
• Interior cells move to the periphery
and form pinacocytes.
Amphiblastula larva
• 0.2 mm.
• Hollow and has half of the larva
composed of flagellated cells.
• On settling, the flagellated cells
invaginate into the interior of the
embryo and form choanocytes.
• Nonflagellated cells overgrow the
choanocytes and form the
pinacocytes.

32. Parenchymula larva Amphiblastula larva

33. Alternatives to Sex
• Asexual reproduction from internal,
resistant capsules – gemmules.
• Gemmules – are masses of ameboid
cells that are released when parent
dies.
• Dormant stage - resistant to freezing
and drying.
• Pieces broken off can become a new
sponge – fragmentation.
• Grow new pieces – budding.

34. THANK YOU