Invertebrate Zoology
Lecture 5: Phylum Porifera
Lecture outline
Phylum PoriferaOverviewBody structure and the aquiferous “system”Nutrition, excretion and gas exchangeActivity and SensitivityReproductionReaggregationProtectionSponges as habitatSponges and Humans
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
Overview Diversity: three
major groups 2. Hexactinellida:
Glass Sponges Siliceous, 6-rayed
spicules Marine, primarily
deep water
Overview Diversity: three
major groups 3. Demospongiae:
Demosponges Siliceous spicules
(never 6-rayed) and/or spongin for support
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
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”
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
Body structure/aquiferous system
Body structure/aquiferous system
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)
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)
Focus: spicules
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
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
Body structure/aquiferous system
Structural conditions of sponges: Refers to degree of folding and complexity
Ascon Sycon Leucon
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
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
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)
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?
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
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
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
Gas exchange
Oxygen brought in with water
Gas exchange via diffusion (individual cells)
Dissolved carbon dioxide is swept out the osculum via water currents
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
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.
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
Sponge reproduction: asexual
Gemmules (cont.)Good conditions: Archaeocytes migrate out
through the micropyle, reconstruct sponge
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
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
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
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
Sponge reproduction: sexual
Upon settlement, flagellated cells move from outside to inside via invagination
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
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)
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.