1. Phylum Porifera Sponges
Ancient group of animals that dates back to the late Precambrian about 600 million years ago

2. Phylum Porifera (sponges)
Sessile, aquatic, benthic, suspension feeders on bacteria and protists
Mainly marine (~7000 species), but some in freshwater (~300 species).
~27 freshwater species in North America.

3. Defining Characteristics of Phylum
Cellular level of organization
No true tissues
No true embryological germ layers
Cells are not connected to each other by basement membrane as seen in true tissues
Adults asymmetrical or radially symmetrical; no fixed body shape
Cells are totipotent
Can change form and function
Unique flagellated cells – choanocytes
drive water through pores, canals and chambers constituting the aquiferous system

4. Defining Characteristics of Phylum
Adults are sessile (immobile) suspension feeders (a few are carnivorous)
Larval stages are motile
Mesohyle - middle layer:
variable, but always includes motile cells and usually some skeletal material.
Skeletal elements
Spicules composed of calcium carbonate, silicon dioxide and/or collagen fibers (protein = spongin)

5. Phylum Porifera
Bauplan

6. Two Unique Characteristics
Aquiferous System
Water current channels
Choanocytes
Cells are totipotent
Most able to change many times
Reproductive cells and those that make spicules differentiate irreversibly
These two features define sponges and have played major roles in poriferan success.
Sponge diversity is largely derived from these two characteristics.

7. Compensating for Simplicity of Form in Sponges
Increasing size/surface area comes from folding body wall in variety of patterns.
Plasticity of form and totipotency of sponge cells compensate for lack of tissues and organs
Aquiferous system
Brings water close to the cells responsible for food gathering and gas exchange.
Removes excretory and digestive wastes and reproductive products are expelled
1 x 10 cm Leucosolenia filters 22.5 liters daily

8. What is “A” Sponge Old idea: individual sponge was one cell
Later – one choanocyte chamber = one sponge
Currently two ideas:
Each excurrent opening (osculum) = one sponge
Preferred: each “sponge” in its entirety = individual
Any and all sponge material bounded by a continuous outer cellular covering.

9. Bauplan - Body Structure
Outer squamous surface cells make up the pinacoderm (single cell thick)
Cell = Pinacocyte
Pinacoderm is perforated by small holes
Incurrent pores = dermal pores or ostia
Pinacocytes lining internal canals are endopinacocytes vs. exopinacoderm
Inner surface is the choanoderm (single cell thick)
Cell = Choanocyte

10. Sponge Anatomy

11. Bauplan - Body Structure
Between pinacoderm and choanoderm is the mesohyle
Various thicknesses
Contains amoeboid cells, collagen, spicules
Plays roles in digestion, gamete production, transport of nutrients and waste products (via amoeboid cells) and secretion of the skeleton
Water movement is driven by beating of choanocyte flagella
Pump large volumes of water at low pressure = water current (aquiferous) system

12. Bauplan - Body Structure
Body covered in holes (ostia)
Pores lined with porocytes
Pores - hence the name Porifera
“Pore bearer”
Skeleton made of spicules
Silica
CaCO3
Or Spongin – protein

13. Sponge Anatomy

14. Porifera Bauplan
Cell Types

16. Pinacocytes (“tablet cells”) - form the pinacoderm, the outermost layer of sponge; equivalent of epidermis

17. Water enters thru prosopyle, exits thru apopyle
Porocytes (pore cells) - line the pores (or ostia) of the sponge; provide channels to spongocoel
Water enters thru prosopyle, exits thru apopyle
prosopyle
apopyle

18. Sponge Cell Types
Microvillae form collars around flagella of Collar cells = Choanocytes
Functions of choanocytes
Generate currents that maintain water flow throughout sponge.
Capture small food particles on sticky contractile collar.
Capture sperm for fertilization/may produce sperm
nucleus
microvillus
Flagellum
Collar

19. Choanocytes - flagellated collar cells that pump water through the sponge, capture prey, capture sperm

20. Choanocytes –, form the choanoderm. Similar to choanoflagellates.
Collect food matter on sticky contractile collar; may also produce sperm.

21. Sponge Cell Types
Amoebocytes (or Archaeocytes) are amoeba-like cells that are totipotent, in other words each is capable of transformation into any other type of cell.
Have important roles in feeding, reproduction and in clearing debris that blocks the ostia.
Store, digest and transport food, excrete wastes, secrete skeleton
Amoebocytes wander through the central jelly or mesohyle
Form gametes
May give rise to buds in asexual reproduction.
Several different types.

22. Amoebocytes

23. Functions of Amoebocytes
Transfer food from cells that do the feeding to cells that have other functions
Produce spicules, collagen and other mesyhyle components.
Replace missing cells
Act as immune response cells
Become gametes

24. Amoebocyte Types
Large Amoebocytes- distribute food to other cells of sponge; move by way of pseudopods
Archeocytes- undifferentiated sponge cells that can give rise to more differentiated cells such as pinacocytes, porocytes or oocytes. Play major role in digestion, transport excretory activities.
Chromocytes – pigmented amoebocytes
Trophocytes – nurse cells (provide nutrients) involved in gemmule formation
Sclerocytes - produce spicules - the mineralized spicules that form the skeletons of many sponges and in some species provide some defense against predators.
Calcoblasts – make calcium carbonate spicules
Silicoblasts – make silicious spicules

25. Other types of cells within the mesohyl
Lophocytes – are amoeba-like cells that move slowly through the mesohyl and secrete collagen fibers.
Collenocytes – are another type of collagen-producing cell.
Rhabdiferous cells – secrete polysaccharides that also form part of the mesohyl.
Thesocytes - resting archaeocytes in gemmules of freshwater sponges
Myocytes ("muscle cells") regulate the opening and closing of the ostia and osculum .
"Grey cells" act as the equivalent of an immune system for the sponge.
Oocytes and spermatocytes are reproductive cells.

26. Other types of cells within the mesohyl
In addition to or instead of sclerocytes, demosponges have spongocytes that secrete a form of collagen that polymerizes into spongin, a thick fibrous material that stiffens the mesohyl.
No specialized cellular communication. Cells signal each other by diffusion of chemical messages
Cell aggregation – cells can reaggregate after mechanical disruption.
Can identify self from non-self
If two different species’ cells are mixed, each species reaggregates only with its own cells.

27. Mesohyl Middle layer of sponge Acellular matrix Contains archaeocytes
Gelatinous
Nonliving
Acellular
Contains archaeocytes
Contains spicules and spongin

28. Sponge Skeletal Materials
Spicules and spongin fibers are
Structural
Used in defense against predators
Also important for identification of sponges

29. Sclerocytes - derived from amoebocytes; produce spicules

30. Growth of a sponge spicule
Sclerocytes - derived from amoebocytes; produce spicules
Spicule
Founder cell
Thickener cell

33. Additional spicule shapes
Figure 4.2
Additional spicule shapes

34. Massive calcium carbonate supports evolved several times independently in the Demospongiae and the Calcarea.
Massive calcium carbonate supports evolved several times independently in the Demospongiae and the Calcarea

36. Generalized Sponge Anatomy
Osculum
H2O
inhalant pore (ostium)
spongocoel(atrium)

37. Cell Layers Pinacoderm made of pinacocytes Ostia lined by porocytes
Mesohyle with
amoebocytes
Choanoderm with choanocytes

39. Mesohyle

42. Sponge Body Plans Asconoid Syconoid Leuconoid
See handout for details of water flow and anatomy
for practice, label the following diagrams

43.    
   
   
Asconoid
Syconoid
Leuconoid
Choanocytes
Mesohyl
Pinacocytes
Water flow

47. Leucosolenia
Pinacoderm

48. Leucosolenia
Asconoid sponge

49. Leucosolenia

50. Asconoid Body Plan Simplest body type Found only in the Calcarea
Choanoderm is simple and continuous
Water:
enters through pores
and flows into spongocoel
then out through osculum.

51. Structure and organization of an asconoid sponge.
Spicule
Pinacoderm
Porocyte
Osculum
Spongocoel
Mesohyl
Amoebocyte
Choanocyte in
choanoderm
Inhalant pore

53. Syconoid Body Plan More complex body type
Choanoderm is folded into many radial canals
Water:
enters through pores
and travels through radial canals to spongocoel
then out through osculum.
radial canals
spongocoel

54. Grantia = Scypha = Sycon See following slides for anatomy

55. Grantia = Scypha = Sycon

57. Structure and organization of a syconoid sponge.
Spongocoel
Spicule
Osculum
Pinacoderm
Incurrent Pore
Choanocyte
Incurrent Canal
Radial Canal
Amoebocyte
Internal
water canal
Mesohyl

58. Sycon (Grantia, Scypha) Asconoid sponge

59. Grantia longitudinal section; water flow shown by arrows

62. Amphiblastula larva

63. apopyle

65. prosopyles

66. Grantia cross section; water flow shown by arrows.

67. Grantia
Details of radial canal

68. Structure and organization of a leuconoid sponge

73. Leuconoid Body Plan Most common and most complex type of sponge body
Water:
flows in through pores into inhalant canals.
It then enters choanocyte lined chambers…
…and finally travels the excurrent canals to the osculum.

74. Detailed organization of the leuconoid sponge
Apopyle
Prosopyle

78. Hexactinellida

80. Hexactinellida

81. Hexactinellida Live in deep water
Habitat favored possibly because body structures are so fragile.

82. Hexactinellida
Glass sponge community in Antarctica's eastern Weddell Sea, in an area not covered by ice shelves

83. Syncitia Hexactinellid sponges
No pinacoderm covering body wall and lining aquiliferous system
Instead the tissue is arranged in three-dimensional cobweb-like strands called a trabecular syncitium or network
No choanoderm, have a choanosyncitium instead
Collar bodies (no nucleus) rise of the surface of the choanosyncitium.
Each group of collar bodies occupies a syconoid- like pocket supported by the trabecular network.
Each group of collar bodies comes from out growths of stem cell - choanoblast

84. Flagellated cells lack nuclei, and are called collar bodies.
Choanosyncitium
Trabecular Syncitium
Major components of the body are the trabecular syncytium and Choanosyncitium.
Flagellated cells lack nuclei, and are called collar bodies. 
Produced by nucleated choanoblasts.

85. Trabecular Syncytium
Is the largest example of a syncytium known in the animal kingdom.
Comes from fusion of early embryonic cells.
Embryos are cellular until gastrulation
SO - Hexactinellid sponges may have evolved from cellular sponges

86. Possesses multiple nuclei Is bilayered
Choanosyncitium
Trabecular syncitium
Syncytium
Is Cytoplasmic
Lacks cell walls
Possesses multiple nuclei
Is bilayered
Extends through the entire body of the sponge.
Syncytium
Connects through cytoplasmic bridges to various cells in the sponge, such as choanoblasts and archaeocytes.

90. Trabecular Syncytium
Choanosyncitium encloses and supports the collar bodies and the choanoblasts
Trabecular syncitium branches from the primary reticulum and forms a kind of barrier around the collars of the collar bodies. 
Nuclei are scattered within the two reticula.
Water is drawn through openings, or prosopyles, and moves through the microvilli of the collar bodies then through the excurrent canals to the outside through apopyles.
Some water passes directly through the prosopyles into the flagellated chamber

91. prosopopyle

92. Collar body

93. Syncytia Cytoplasm within the syncytium flows bidirectionally.
Food products may be distributed through the sponge via the syncytium and not via cellular transport as in other sponges.