Chapter 6 Porifera - Biology PDF

 **Chapter 6 Porifera ** **Metazoa **- Animal clade  32--34 extant phyla  \~95% of animal sp. are invertebrates  **Multicellularity ** Specialization among cells  Different cell types have different functions  Some cells types just do reproduction  Arisen in \>20 lineages  [Colonial unicell...

 **Chapter 6 Porifera ** **Metazoa **- Animal clade  32--34 extant phyla  \~95% of animal sp. are invertebrates  **Multicellularity ** Specialization among cells  Different cell types have different functions  Some cells types just do reproduction  Arisen in \>20 lineages  [Colonial unicells]: connected and coordinated but lack specialization  **Origin of Sponges ** **Phylum Porifera (Sponges) ** **Canal Types ** - Large with thick body wall  - Flagellated radial canals  - Fold back and forth -- where the choanocytes, inside of the passages in the body wall - Water enters canals through prosopyles: toward, opening - Empties through apopyles: apo = away, opening - empty into the spongocoel and then out the osculum - Spongocoel lack choanocytes  - Clusters of flagellated chambers  - Filled from incurrent canals  - Discharge to excurrent canals leading to osculum  - Can have many oscula  - Lack true spongocoel  - Broader canal - Increased flagellated surface-to-volume ratio  - More surface covered in choanocytes - Most sponges  - That are around today (over ½) - Intermediate in complexity  - Transitional step - Ostia without choanocytes lead to radial choanocyte canals  - Choanocytes that are inside the canals, but not tight clusters - More true spongocoel - Modified leuconoid chambers  - Internally connected feeding tubes  - All tubes are connected, choanocyte tubes - Only tube walls have choanocytes  **Cell layers --** occurring in most sponges [Choanoderm]: internal layer of choanocytes  - Surrounding the spongocoel, or clusters [Pinacoderm]: external, flat cells (**pinacocytes**)  - [Mesohyl]: gelatinous extracellular matrix containing spicules and other cell types  - True tissues have distinct germ layers and structural integration - These are not structurally integrated enough to be considered true tissues, need more distinct layers of cells (endoderm, ectoderm, etc.) - Sponges lack true tissues **Other Cell Types ** - [Porocytes]: Tubular cells in body wall that allow water flow  - Can be created by infoldings - - [Archaeocytes/Amoebocyte]: ameboid cells -- "ameba shaped" - Move in mesohyl  - Receive engulfed food  - Differentiate into other types  - Changes into a different type of cell, stem cell - [Collencytes]: secrete collagen for the spicules - Collagen is the main structural protein - [Sclerocytes]: secrete silica  - Taking in silicon and secreting silica - Use that as well for spicules -- "glassy" - [Spongocytes]: secrete spongin  - Modified collagen that makes sponges flexible, spongy texture **Asexual Reproduction ** - Fragmentation and budding  - *Gemmules*: internal buds  - inside the sponge the gemmules form and are filled with archaeocytes - archaeocytres are stem cells and then will have the potential to be other cells when they are released - Dormant mass of archaeocytes  - Survive harsh conditions  - Produces clones -- same DNA, mitosis - Ability to regenerate -- not reproduction, but similar - Mitosis repairing damaged or broken parts **Sexual Reproduction ** - *Fertilization*: internal or external  - Sperm develop from choanocytes  - Makes sense because they have the flagella - External = would swim out to find egg - Internal = fertilizes egg inside the mesohyal - Oocytes develop from archaeocytes  - [Hermaphroditic]: produce sperm and eggs  - Both sexes - Most of the time they cross fertilize - Make sperm and egg at different times of years - Do not fertilize themselves **Development ** - Free-swimming larvae are ciliated  - Attach to substrate - Undergo simple development steps - Flagellated cells migrate inwards to line chambers **Porifera Clades ** 1. Homoscleromorpha: "same stiff form" a. Mostly nearshore, shallow b. Simple or no spicules  i. Encrusting on other structures ? ii. Do not need skeleton due to that c. Leuconoid  iii. More complex sponge, flagellated chambers d. Pinacoderm has a basal lamina (incipient epithelium)  iv. The outer layer is more complex, still not a true tissue 2. Calcarea:  e. Calcerous spicules  v. Spicules are made out of calcium carbonate f. Asconoid, syconoid, and leuconoid forms  3. Demospongiae:** --** largest group g. 80% of living sponge species h. Leuconoid -- more complex i. Spicules: silica and many with spongin  - High oxygen ponds and springs  - Encrust stems and submerged wood  - Die in fall but leave gemmules  - Seasonal - Leave behind the gemmules that are packed with archeocytes - Bath sponges  - Spicules have spongin, modified collagen (flexible), and no silica  - soft - Can be farmed  - Fragments of them and suspend them at the right height and area, they will filter feed and grow into the right size for a bath sponge - Recently discovered  - Deep water caves  - Hook-like spicules entangle prey  - Lack choanocytes and internal canals  - Unique carnivorous feeding mode  - Considered sponges because of their ancestral history, have arisen from this group, but have lost characteristics **4. Hexactinellida ** - '6-rayed sponges' or 'glass sponges'  - Siliceous (have silica) - May be the longest-lived animal (up to 15k years)  - Indeterminant growth -- do not stop growing, compare known ages and their size to larger size - Sponges have their skeleton of spicules has growth rings to look at like trees - Usually deep and cold sea  - Extensive *syncytium*: multinucleated cytoplasm  - Two layers of choanocytes and other cells within those layers - Also known as the tribecular reticulum - A bunch of cells fused together, that is why there are a lot of nuclei **Ecological Relationships --** can be noxious or smell bad - Prey for predators  - Turtles, parrot fish, nudibranch - Hosts for parasites  - Polykeet (segmented worm, lots of branches), fungal and bacteria parasites - Hosts for commensals -- symbiotic organism, organism will benefit but no impact on host, +0 - live on the sponge, but sponge does not benefit - Christmas tree worm, sea anemones - Commensals/Mutualists - A sponge living on a giant clam - Can also be mutualistic, crab decorating the shell - Beneficial to both -- sponge camouflages the crab, the crab will defend predators from eating the sponge - Competitors  - Competitors with other sponges and other sessile organisms - Competing for space as well **Human Connections ** - Chemical extracts and bacterial isolates: *medicinal* *properties*  - Lots of review papers that look at these compounds - Mediterranean sponges -- tested 50 sponges and half have anti-tumor properties - Fibrous elements: *scaffold for tissue engineering*  - Use the spicules for tissue engineering - Bone or cartilage regrowth - Glass spicules: *fiber optic properties*  - Transmit light, discovered due to the sponges have photosynthetic endosymbionts deep inside of them, the spicules transmit that - Spongin: *removal of chemical pollution*  - Ex\] remove chemical byproduct of making plastic (absorb) END OF SPONGES **Placozoa -** 'Plate animal' 'Flat' *Slide* *example*: sticky hairy plate - Small (20 microns thick)  - One of the smallest animals - Marine and free-living  - Not parasitic - No fixed shape or symmetry  - Flat bob shape - Dorsal and ventral cilia  - Sister taxon obscure  - They don't know who their closest relative is - Usually put by sponges, but not for sure - 6 cell types:  1. Gland cells -- digestive enzymes 2. Dorsal epithelial cells - cilia 3. Ventral epithelial cells -- cilia 4. Lipophil -- lipids 5. Shiny sphere cells - ? 6. Fiber cells - Eat by engulfment  - Reproduce by fission or budding