Module 4

Question 1

What is the sponge?

Answer 1

sponge is the simplest animal
- it undergoes blastulation during embryogenesis
- heterotrophic but lack a gut – digestion is intracellular
- osmotrophic – feed on organic dissolved matter as well as phagotrophic – feed on particulate organic matter
- hermaphroditic – release both sperm and eggs

Question 2

Sponge

Answer 2

Invertebrate
Part of Phylum Porifera

Question 3

Sponge diversity

Answer 3

barrel sponge - large sponge structures
encrustring sponge - encrust over the seabed
- can be a major form of erosion by eroding the top few centimetres of coral skeleton

Question 4

Sponge development

Answer 4

ovum –> 16-cell-stage –> stomoblastula –> amphiblastula –> metamorphosis –> mature syconold sponge

Question 5

Multicellularity of sponges

Answer 5

micromeres
pinacocytes
porocytes
myocytes
archaeocytes
choanocytes

Question 6

Micrometers

Answer 6

micrometers can differentiate into choanocytes as they develop collars
- these line the pseudo-gut, where water is drawn in through incurrent press – Ostia – and an exit pore – osculum

Question 7

Porocytes

Answer 7

tubular cells found between pinacocytes that let water into the sponge
- these pores are known as the Ostia

Question 8

Myocytes

Answer 8

a form of pinacocytes that can contract and open or close the porocytes

Question 9

Archaeocytes

Answer 9

amoeboid cells that carry out a variety of functions as they move about in the mesohyl
- can phagocytose particles in the pinacoderm and receive particles too digestion from the choanocytes
- can differentiate into other types of cells as needed, including those part of the structures in the mesohyl

Question 10

Choanocytes

Answer 10

collar-like cells with a flagellum
- important for moving food, water, and oxygen into the sponge and removing waste
- food particles that are too large become trapped in the mucus and are passed two the choanocyte cell where they are phagocytose
- this creates a food vacuole which is transported across the cell and then passed onto an amoeboid archetype which digests it

Question 11

Pinacocytes

Answer 11

thin and elastic layer of cells that cover sponges and keeps water out
- also ingest food, which is passed to the archaeocyte

Question 12

Multicellularity of sponges

Answer 12

sponges limit sexual reproduction to certain cells
- these cells are held together by an extracellular matrix called the mesohyl

Question 13

Mesohyl cells

Answer 13

sclerocytes - secrete spicules
spongocytes - secrete spongin
collencytes - secrete collagen

Question 14

Internal structure of sponges

Answer 14

can be fibrous and/or rigid
- rigid skeletons consist off calcareous or siliceous support structures called spicules
- the fibrous structure of skeletons comes from collagen fibres within the mesohyl of all sponges – spongin is one of the main types of collagen fibres used

Question 15

Sclerocytes

Answer 15

specialised cells which secrete spicules of siliceous or calcium carbonate

Question 16

Spongocytes

Answer 16

secrete collagen, including spongin

Question 17

Cyanobacteria

Answer 17

photosynthetic organisms found on the surface and deep inside the bodies of sponges

Question 18

Body plans of sponges

Answer 18

asconoid
syconoid
leuconoid

these increase in complexity and size
- the body wall folds into itself to create increasingly complex structures with a greater ratio of surface area to volume

Question 19

Sponge behaviour

Answer 19

sponges do not have tissues yet the oscular – major pores – can close slowly if the water fills with sediment

Question 20

Associated bacteria

Answer 20

sponges have secondary metabolites and bacteria
- bioprospectors target sponges in search for new antibacterial and antiviral compounds
- products from sponges can help treat herpes and parasitic infections
- some are effective against e.coli

Question 21

Reproduction in sponges

Answer 21

archaeocytes - totipont cells which can develop into any other cell type
choanocytes - can differentiate into archaeocytes if needed

Question 22

Asexual reproduction in sponges

Answer 22

internal formation of gemmules - clumped archaeocytes surrounded by spongin that forms a test
- these are small seed-like structures which remain dormant while in the living spong and continue to live following the death of the sponge
- at this point the archaeocytes exit through the micropyle to form a new sponge

Question 23

Sexual reproduction in sponges

Answer 23

• sperm and oocytes are derived from choanocytes archaeocytes
• when sperm arrive from another individual and enter the sponge through ostia, the choanocytes phagocytose it and transform it to the archaeocytes
• the archaeocytes transfer it through the mesohyl to the oocytes where fertilisation can occur

Question 24

4 major sponge lineages

Answer 24

Homoscleromorpha
Hexactinellida
Demospongiae
Calciospongiae

Question 25

Sponges on coral reefs

Answer 25

high biodiversity of sponges in the tropics
found throughout the world’s oceans – more than 8500 species

Question 26

Ecological roles of sponges on the reef

Answer 26

• provide reef structures that act as habitats for other organisms
• contribute to filtering the water both inside and on top of the reef

can have natural but negative impacts
- bioerosion – the growth of sponges over dead coral erodes the surface, converting hard limestone into sand
burrowing sponges – can grow through even live corals, causing an erosive impact
–> these forms of erosion contribute to a gradual flattening of the reef

Question 27

Sponge loop

Answer 27

40% of the carbon fixed by corals is lost as dissolved organic carbon
- some sponges can absorb this dissolved organic carbon as it allows for high levels of cellular turnover

Question 28

Homoscleromorpha

Answer 28

leuconoid design
reduced and poorly organised siliceous skeleton
flagellated pinacocytes

Question 29

Hexactinellida

Answer 29

have a six-rayed siliceous spicules usually bound together to form glass-like networks
- their soft adult tissues are syncytial, meaning majority of the cells are fused, creating one large multinucleate mega-cell that is wrapped around the mineral skeleton

Question 30

Calispongiae

Answer 30

can be asconoid, syconoid, or leuconoid
have spicules composed of CaCO3

Question 31

Demospongiae

Answer 31

when present, the spicules are siliceous but not six-rayed and held together with spongin
- mostly leuconoid
- some carnivorous species can trap tiny crustaceans on the outer sponge, overgrow and digest them