1. Invertebrate Zoology Lecture 5: Phylum Porifera

2. Lecture outline  Phylum Porifera  Overview  Body structure and the aquiferous “system”  Nutrition, excretion and gas exchange  Activity and Sensitivity  Reproduction  Reaggregation  Protection  Sponges as habitat  Sponges and Humans

3. Overview  Considered to be plants until 1765.  Diversity: three major groups  1. Calcarea: Calcareous sponges  Calcium carbonate (calcite) spicules  Primarily shallow water and tropical (some exceptions) Photo: www.meer.org

4. Overview  Diversity: three major groups  2. Hexactinellida: Glass Sponges  Siliceous, 6-rayed spicules  Marine, primarily deep water

5. Overview  Diversity: three major groups  3. Demospongiae: Demosponges  Siliceous spicules (never 6-rayed) and/or spongin for support

6. Overview  Simplest multicellular animals  Considered "multicellular" rather than colonial because there are different cell types.  Key cell type, the choanocyte, resembles a cells of a choanoflagellate (Protista) Choanoflagellate

7. Overview  Key characteristics (see Box 6A)  Metazoa  No true tissues or body systems of any type  Not much, if any. coordination among cells  Layers lack basement membrane  Adults are asymmetrical or superficially radially symmetrical  Totipotent cells: like stem cells!  Choanocytes drive water through the various canals and chambers: “aquiferous system”

8. Overview  Key characteristics (cont.)  Almost all species are sessile suspension feeders  Larvae are motile, usually lecithotrophic (dispersed, not brooded; carry significant yolk supply; non-feeding)  Mesohyle (middle “layer”) includes motile cells plus supporting material (i.e. spicules, spongin)  Skeletal elements composed of calcium carbonate, silicon dioxide and/or collagen

9. Body structure/aquiferous system

10.  Surface:  Pinacocytes  cover outside & line pores/passageway  flattened, single cell width  No basement membrane  Collagen, may cover sponge instead  ostia (pores) perforate the pinacocyte “layer” (tiny)  Porocytes in some sponges  osculum: main exit (large)

11. Body structure/aquiferous system  Main matrix of sponge: mesohyle  Non-cellular, colloidal matrix  Skeletal elements  Collagen (spongin)  Spicules  composed of calcium carbonate or silicon dioxide  Often used in sponge ID  myocytes:  contractile cells that surround major openings and channels (not shown)

12. Focus: spicules

13. Body structure/aquiferous system  Main matrix of sponge: mesohyle  Amoebocytes (= “archaeocytes”)  Move in amoeboid fashion  highly mobile  Secrete spicules & spongin  Complete the process of digestion  Store food  Transport waste to excurrent pore  Totipotent  Control of flow rates (How?)  May leave parent sponge and then return  Can move the entire sponge

14. Body structure/aquiferous system  Choanocytes: key cell type, inner surface  Provides water current by beating its flagellum  Beating of flagella is not coordinated  Captures and engulfs food particles  intracellular digestion

15. Body structure/aquiferous system  Structural conditions of sponges:  Refers to degree of folding and complexity Ascon Sycon Leucon

16. Body structure/aquiferous system  Structural conditions of sponges:  Trend from one large chamber to numerous small chambers.  Ascon: one main chamber (spongocoel) lined with choanocytes  Sycon: choanocyte chambers off the spongocoel  Leucon: has multiple layers of choanocyte chambers

17. Body structure/aquiferous system  Consequences of increased complexity  More surface area for…?  Higher flow rates (overall)  Causes?  Advantages of higher flow rates?  Potential problems of flow?  Where in sponge must flow rates drop and why?  What causes this slowing?  NOTE: Water current adds to internal current created by flagella

18. Nutrition  Water flow brings in food  Size selectivity at several levels  Ostia, ~5-50 µm = small phytoplankton, bacteria, detritus  Ameobocytes, ~2-5 µm (smaller phytoplankton, bacteria, detritus)  Choanocyte collar: ~0.5 – 1.5 µm (bacteria, viruses, larger organic molecules)

19. Nutrition  Food capture by choanocytes  Beating of flagellum creates negative pressure inside collar, draws food to outside of mucus- covered microvilli of collar  What are microvilli made of?

20. Nutrition  Food capture by choanocytes (cont.)  Food particles caught in mucus, moved via cilia (?) or undulations of the collar to cell body  Food phagocytosed, digested  Food capture by amoebocytes  Directly  Transfer from choanocytes

21. Nutrition  Carnivorous sponges: Family Cladorhyzidae!  Stalked; tentacle-like extensions covered with hook- like spicules capture prey  Individual cells engulf and digest prey (intracellular)  Symbionts provide nutrients to some sponges  Methanotrophic bacteria (in some carnivorous sponges!)  Photosynthetic protists Photo: Michel Phlibert

22. Excretion/osmoregulation  Excretion (ammonia) via diffusion over individual cells  Dissolved ammonia is swept out the osculum via water currents  Water expulsion vesicles (WEV) in freshwater sponges

23. Gas exchange  Oxygen brought in with water  Gas exchange via diffusion (individual cells)  Dissolved carbon dioxide is swept out the osculum via water currents

24. Activity and Sensitivity  No nervous system or discrete sense organs  Respond to touch (some will close off ostia/osculum)  Respond to excessively high particle concentration  Close off ostia (via myocytes);  flagellar beating  Some have endogenous rhythmicity  Takes a few minutes for the entire sponge to change rates  Cells communicate mechanically and chemically   current generation: reorganization or reproduction  Class Hexactinellida have a syncytium which can conduct electrical signals along its membrane  Much slower than true neurons.  Apparently controls water flow into the sponge

25. Activity and Sensitivity  Movement  Most species are sessile as adults  Cells frequently move and rearrange themselves  Amoebocytes are highly mobile  One species, Tethya seychellensis, Red Sea, has sticky, filamentous extensions  Filaments contract and pull sponge along.

26. Sponge reproduction: asexual  Fragmentation  Regeneration  Budding  buds fall & develop into a new sponge  Gemmules: resting stage  Family Spongillidae (freshwater)  Withstand freezing & drying  Gemmule structure  Archaeocytes aggregate  Layer of spongin and spicules  Micropyle: small opening

27. Sponge reproduction: asexual  Gemmules (cont.)  Good conditions: Archaeocytes migrate out through the micropyle, reconstruct sponge

28. Sponge reproduction: sexual  Overview  Most sponges are protandrous or protogynous hermaphrodites  A few are gonochoristic  Some species have both hermaphroditic and gonochoristic individuals in the same population  No gonads  Sperm production: choanocytes transform into spermatogonia (in choanocyte chambers or after migrating into the mesohyle.  Egg production: choanocytes or amoebocytes transform into oocytes

29. Sponge reproduction: sexual  Location of fertilization  In the water column (both eggs and sperm are spawned)  Within the body of the sponge (sperm spawned, eggs retained)  Gametes are released via the osculum  Example: Sperm release, barrel sponge

30. Sponge reproduction: sexual  Specifics of fertilization (for retained eggs)  Sperm enters choanocyte, loses tail, is encased in a vesicle inside choanocyte  Choanocyte is transformed (loses collar & flagellum)  Transfer choanocyte moves, attaches to an egg, transfers the sperm to the egg  Fertilization occurs

31. Sponge reproduction: sexual  Zygote  larva: one type is an amphiblastula larva  Flagellated cells inside first, then the whole larva turns inside out  Larvae released with flagellated cells on outside  Leaves via osculum

32. Sponge reproduction: sexual  Upon settlement, flagellated cells move from outside to inside via invagination

33. Reaggregation of sponges:  Dissociated cells find each other, reform a functional sponge  Can learn about cell-cell recognition; development & cell differentiation  Some only reaggregate with members of same species, others more flexible  May help us to understand tissue rejection

34. Protection  Spicules  Toxins/warning coloration  Toxic secondary metabolites within spherulous cells (type of amoebocyte)  Some sponge toxins useful to humans  anti-cancer, anti-viral and anti-bacterial  NOTE:Nudibranch predators co-opt sponge defenses (toxins, spicules)  Regenerative ability  Camouflage (if not toxic)  Bore into shells (parasitic)

35. Sponges and humans  Medical uses (just mentioned)  Bath sponges  Sponge farms in some regions  Sponges over-harvested in Greece, Bahamas  Declines due to fungal and viral diseases in some regions.