Invertebrate Zoology Lecture 5: Phylum Porifera. Lecture outline Phylum Porifera Overview Body structure and the aquiferous “system” Nutrition,

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.