Lecture 3- Porifera

Ctenophores, Sponges, basic Phylogeny

Sponge Structure (3 layers)

Choanoderm (water filtering)

Mesohyl (extracellular matrix ECM, gelatinous)

Pinacoderm (outer layer, pinacocytes and porocytes)

Sponge skeletons (and the spicules that they consist of) can be…

calcareous, siliceous, proteinaceous

Scaling

Organisms need a consistent ratio of surface area to volume, so they need different shapes for different sizes

• area increases as square of linear dimensions

• volume increases as cube of linear dimensions

porifera

sponges- they have internal canals and chambers that water flows through

water enters the sponge through the _ and exits through the _

ostia; osculum

most sponges reproduce

sexually- sperm are captured by choanocytes in the incurrent canals

vivipary vs ovipary

vivipary- fertilized eggs develop within the sponge

ovipary- fertilized eggs develop outside the sponge

phases of asexual sponge reproduction

1. Gemmule formation (packets of essential cells)

2. Budding

3. Fragmentation

Physical effects of sponges in coral reefs

1. Filtration

2. Bioerosion (weaken corals, and sediments cause reef growth)

3. Substrate binding (increasing attachment strength when binding to corals)

poriferan phylogeny

calcarea, homoscleromorpha, demospongiae, hexactinellida

what are animals?

• invertebrates

• metazoa

• The MRCA of porifera/ctenophora/bilateria and all of its descendants

LUCA

Last Universal Common Ancestor

First diversion of life (right after Luca)

Split into bacteria and archaea

sponge architecture types

asconoid

syconoid

leuconoid

leuconoid sponge structure

most complex, intricate network of incurrent and excurrent channelsincuincurrent and excurrent

aconoid

most basic sponge structure, tubular body and radial symmetry

syconoid sponge structure

thicker, more complex body wall than asconoid sponges, with folded walls that form radial canals that lead to a central spongocoel

vivipary vs ovipary

fertilized eggs develop inside organism

fertilized eggs decelop outside organism

types of symmetry (know what they mean!

radial, spherical, rotational, bilateral

bonus: directional asymmetry

ways sponges feed

filter feeders, predators, symbiosis, deposit feeders, grazers

osmoregulation

mantaining balance of water and ions by way of internal fluid regulation

Stages of Particle Capture (sponges)

1. Pre-filter: large particles are pagocytized by pinacocytes

2. Primary capture system: mobile archeocytes capture medium particles

3. Secondary particle capture: choanocytes trap smallest particles among microvilli

archeocytes

totipotent stem cells that can transform into any other sponge cell type

• varied function depending on species

pinacocytes

contractile cells that regulate water intake

porocytes

create ostia (pores)

ostia

small pores on sponge body surface that allow water (which carries particles and oxygen) to enter sponge

fertilization 

• sperm enter through incurrent chanals

• captured by choanocytes

• choanocyte becomes amoeboid carrier cell, travels to egg in mesohyl

• sperm in vacuole transferred; fertilization

symbioses with sponges

cyanobacteria often help meet sponge metabolic needs

four main sponge classes

calcarea, homoscleromorpha, demospongiae, hexactinellida

calcarea

• spicules= calcium carbonate

• construction= asconoid, syconoid, and leuconoid

• habitat= marine, often shallow

homoscleromorpha 

• spicules can be siliceous

• construction= epithelium has a basement membrane and cell junctions throughout lifespan

demospongiae (85%+ of all sponges!)

• spicules: siliceous, spongin fibers, or may be absent

• construction: almost entirely leuconoid, some larvae may have basement membrane

• habitat: marine, all depths, and includes all freshwater species

hexactinellida

“glass sponges”

• syncitial

• no pinacoderm

• no cellular choanoderm

• interesting refractory properties

spongin

protein that forms the flexible fibrous skeleton of most sponges

Choanocytes

also called "collar cells"

• specialized cells in sponges that create water currents to filter food from the water and facilitate respiration and excretion. They have a flagellum that beats to pump water and a collar of microvilli that traps food particles like bacteria and plankton.

microvilli

Microvilli are short, non-motile structures made of actin filaments that increase surface area for absorption

• like the non-motile equivalent of cilia