Porifera are the simplest multicellular animals and include sponges. They live in both freshwater and marine environments and filter feed by circulating water through their bodies using flagellated cells. Sponges have no tissues or organ systems. They exist in three main classes defined by their skeletal elements, with demosponges being the largest and most diverse class. Sponges reproduce both sexually and asexually, with larvae developing from fertilized eggs and fragments also able to regenerate into new individuals.

1. Phylum Porifera

2. Porifera Characteristics
• Freshwater and marine
• Simplest of all animals
• Asymmetrical
• No systems for repro, digestion,
respiration, sensory, excretion

3. Porifera Characteristics
• ~ 5,500 extant species
• Highest abundance in unpolluted littoral
and tropical reefs
• ~ 75% benthic biomass

4. Porifera Characteristics
• Sessile (Adults)
• Suspension-feeders (Adults)
• Multicellular
• Flagellated cells = choanocytes circulate
water through water canals
• No tissues
• Cells totipotent

5. Porifera Characteristics
• Outer and inner cell layers lack basement
membrane
• Middle layer (mesohyl) has motile cells and
skeletal material
• Skeletal elements (when present) are calcium
carbonate, silicon dioxide and/or collagen fibers

6. Taxonomy and classification
• Taxonomy based on skeletal elements
• Now embryological, biochemical,
histological, and cytological methods to
diagnose sponge taxa

7. Three classes (Calcarea,
Demospongiae, Hexactinellida)
• Class Calcarea: Calcareous sponges
• Shallow, tropical water, near shore
Leucetta

8. Class Calcarea
• Spicules = calcium carbonate
• Calcarean spicules lack hollow canals =
strong
Clathrina

9. Class Hexactinellida (Glass
sponges)
– Silica spicules
– Spicules join at right angles, sponge appears
artificial

10. Class Demospongiae
(Demosponges)
• Largest and most diverse class of
sponges, ~ 90 percent of sponges
• Spicules either spongin, an organic
substance; or silica, a mineralized
substance
Oscarella

11. Class Demospongiae
• Genera Adocia, Halisarca, Myxilla

12. Aquiferous system
• Brings water to cells
• 1 x 10 cm sponge pumps 22.5 l water daily
• Large sponge filters body mass every 10-20 s

13. Sponges are single individuals
• Grow by continually adding cells that
differentiate as needed

14. Body structure and aquiferous
System
Outer layer
– Perforated by small holes - dermal pores or
ostia
• Choanoderm: innermost layer of
flagellated cells = choanocytes
• Mesohyl: middle layer

15. Body structure: 3 shapes

16. Asconoid sponges
• Asconoid: one-cell thick choanoderm is
simple and continuous
– ~10 cm height
– Thin walls enclose central cavity; atrium
opens outside via osculum
– Pinacoderm has specialized cells; porocytes
– External opening of porocyte canal is ostium
or incurrent pore

17. Asconoid sponges

18. Syconoid sponges
• Syconoid: choanoderm folded
– Mesohyl two layers thick:
• Outer region is cortex (contains skeletal material)

19. Leuconoid Sponge
• Leuconoid: choanoderm subdivided into
separate flagellated chambers

21. Flow rate
• Flow rate not uniform throughout
• Water must move slowly over choanoderm
– Exchange nutrients, gases, and wastes
• Water leaving osculum must be carried far
enough away to prevent fouling

22. Cells that line surfaces
• Pinacocytes
• Porocytes
• Choanocytes

23. Cells that line surfaces
• Porocytes
– Form ostia
– Cylindrical tube-like cells
– Contractile - open and close pore to regulate
diameter

24. Cells that line the surface
• Choanocytes
– = choanoderm
– Create currents
– Not coordinated in movement

25. Cells that secrete skeleton
• Fibrillar collagen
– Collencytes
– Lophocytes
– Spongocytes
• Calcareous and siliceous spicules
– Sclerocytes

26. Contractile cells
• Myocytes
– Contractile cells
– Filament arrangement
homologous with smooth
muscle cell
– Unlike neurons and true
muscle fibers

27. Cell Aggregation
• Atlantic sponge (Microciona prolifera)
– Pieces pressed through fine cloth
– Separated cells reorganize
– 2-3 weeks
– Self-recognition

28. Support
• Skeletal elements
– Organic - collagenous
– Inorganic – siliceous (hydrate silicon dioxide)
• Sponges only animals that use hydrated
silica as skeletal material

29. Sponge Harvest
• Harvested for thousands of years
• Greeks harvested sponges
• Sponge fishery south of FL, Bahamas,
Mediterranean
– 1938: 2.6 million lbs

30. Sponge Harvest
• Hippospongia
• Spongia

31. Spicules
• Microscleres
• Megascleres
– Demosponges and
Hexactinellids have both
– Calcareous sponges
have only megascleres

32. Nutrition, Excretion, and Gas
Exchange
• Intracellular digestion
• Continuously circulate water
– Size selective feeders
• Food capture
– Phagocytosis and pinocytosis

33. Excretion
• Ammonia and gas exchange
– Diffusion

34. Activity and Sensitivity
• Respond to environmental stimuli:
– Close ostia or oscula, canal constriction,
backflow

35. Reproduction and Development
• Sexual and asexual reproduction
– All sponges capable of sexual and asexual repro
– Processes unknown due to lack of distinct, localized
gonads (gametes, embryos occur throughout
mesohyl)
– Asynchrony of reproductive activity w/in populations

36. Reproduction and Development
• Asexual Reproduction
– All sponges produce viable adults from fragments
– Cellular reorganization “pinches off” branch ends
which regenerate into new adults – branching
species

37. Reproduction and Development
• Asexual Reproduction
– Common in Florida’s sponge farms - cuttings attached
to cement structure
– Other processes include formation of gemmules,
budding

38. Reproduction and Development
• Gemmules
– Produced in winter as dormant bodies
– Coat and supportive cells protects from
freezing and desiccation

39. Reproduction and Development
• Gemmules

40. Reproduction and Development
• Budding
– Squat or elongate club-shaped protrusions from
sponge surface
– Buds drop, carried by current, adhere to substratum
– Marine species

41. Reproduction and Development
• Sexual Processes
– Majority are hermaphroditic; produce sperm and eggs
at different times
• = Sequential hermaphroditism
– Protogyny or protandry may occur once or many
times during life

42. Reproduction and Development
• Sexual reproduction
• Sperm from choanocytes; eggs from choanocytes
and archaeocytes

43. Reproduction and Development
• Sexual process (Demospongiae and Calcarea)
• Sperm and oocytes released into environment via
aquiferous system
– Sperm release -”smoking sponges”
– Fertilization in open water (oviparous)
– Few viviparous: sperm into nearby sponge’s aquiferous
system; sperm to oocyte for fertilization

44. Reproduction and Development
Madsen sponge
releasing sperm

45. Reproduction and Development
• Release of larvae (vivipary)
– Through aquiferous system or ruptured wall
– Larvae swim hours or days, or crawl along
substratum before settling
– Larvae are lecithotrophic = use stored yolk

46. Reproduction and Development
• Larval development

47. Distribution and Ecology
• Calcareous sponges abundant in shallow
waters < 200 m
• Hexactinellids deeper
• Demosponges at all depths

48. Distribution and Ecology
• Sensitive to suspended sediments
• Resistant to hydrocarbon and heavy metal
contamination
– Why?

49. Symbioses
• Commensalism common (small inverts,
fishes)
• Protection, habitat, water currents for
suspended food particles
• Some organisms utilize sponge for
camouflage, small piece on shell or
carapace

50. Boring Demosponges - harmful to
corals and mollusc shells
• = bioerosion; chemical and mechanical removal
of fragments by etching cells