1. Porifera and cnidaria

Question 1

Describe sponges (porifera).

Answer 1

15000 extant species
Mostly marine, some freshwater. In shallow, abyssal water
Sessile as adults
4 classes, none monophyletic
No muscle cells or nerve cells
Connective materials well developed, usually form complex skeletal lattice
Few mm to 1 m in diameter and height
Radial or asymmetrical body symmetry
Many brightly coloured, we aren’t sure why

Question 2

What does monophyletic mean?

Answer 2

Group of organisms classed in same taxon with shared most recent common ancestor

Question 3

Describe structure of sponges.

Answer 3

No true tissues or organs
System of water canals
Surface perforated, incurrent pores or ostia, where water enters
Pores open into interior cavity (atrium)
Water leaves atrium through osculum (constant flow)
Carries food particles, oxygen and excretion products, including carbon dioxide
Outer surface covered by pinacocytes, which make up the pinacoderm
Pores are formed by porocytes, closed or open by contraction
Beneath pinacoderm is the mesohyl, a gelatinous protein matrix containing skeletal material and amoeboid cells
Skeletal components: spicules of calcium carbonate or silica

Question 4

What are the 3 sponge body designs?

Answer 4

Asconoid: hollow cylinder
Syconoid: interdigitating inpockets and outpockets
Leuconoid: complex network of water vessels

Question 5

What is suspension feeding (sponges generally use this)?

Answer 5

Filter feeding

Capturing suspended food particles from water by passing a current of water through the body

Question 6

Some sponges harbour photosynthesising mutualists, give some examples.

Answer 6

Green algae
Dinoflagellates
Cyanobacteria

Question 7

Why is the sponge family Cladorhizidae unusual?

Answer 7

They are carnivores

Typically feed by capturing and digesting whole animals, like small crustaceans with their spicules

Question 8

What skeleton do sponges have?

Answer 8

Usually an endoskeleton, but can also be exoskeletal region

Fibrous, made of spongin (flexible collagen protein)

Question 9

How do sponges reproduce?

Answer 9

Sexual (hermaphrodites)

Or asexual through producing buds

Question 10

Why are sponges ecologically and economically important?

Answer 10

Water filters
Organiser of communities
Food for other animals
Used as tools by humans and bottlenose dolphins

Question 11

Describe the phylum Cnidaria.

Answer 11

2 layered animals: diploblasts
Muscles and nerve cells
Stinging cell: cnidocyte
Around 10000 extant spp.
Mostly marine, some freshwater
Found from polar regions to tropics

Question 12

What is the basic ‘sac’ body plan of Cnidaria.

Answer 12

Gastrovascular cavity can act as a hydrostatic skeleton
Endodermal
Ectodermal

Question 13

What are the two variants of the Cnidaria body plan?

Answer 13

Medusa: mouth and tentacles face downwards
Polyp: mouth and tentacles face upwards

Question 14

What is mesoglea?

Answer 14

Translucent, jelly-like substance found between the 2 epithelial cell layers in the bodies of Cnidaria and Porifera
Mostly lacking cells but there are muscle bundles and nerve fibres and wandering amoebocytes
Thinner than either of the other layers
Elastic properties help animal restore shape after deformation by muscular contraction

Question 15

How do Cnidaria move?

Answer 15

Contraction of ‘bell’ part of body

Also passive movement: carried by currents or wind

Question 16

How do Cnidaria eat?

Answer 16

Cnidocytes on tentacles and other structures discharge Cnidae
Prey is paralysed by venom injected by each Cnidae
Cnidae may also inject a proteolytic enzyme
Amino acids and other chemicals released by stung prey stimulate mouth-opening and the tentacles convey prey to mouth
Cnidaria can also harbour mutualistic dinoflagellate algae in gastroderm

Question 17

What are colonial cnidarians?

Answer 17

Superorganisms that comprise many zooids
Zooids may differ in structure and function
Example: corals

Question 18

What are zooids?

Answer 18

A single animal that is part of a colonial animal

e.g. coral

Question 19

What are the major features of Cnidaria?

Answer 19

Sac body plan
Tentacles surrounding mouth
Radial symmetry around mouth-foot axis 
Muscles present
Nervous system: net or lattice
Skeleton in some
Epidermis contains cnidocytes (nematocytes): harpoon like stinging cells
Extracellular digestion
Some have colonial growth form
3 stem cell lineages

Question 20

Why are ecologically and medically important cnidarians?

Answer 20

Coral reefs: provide environment with high diversity of life, highly productive, barrier against wave action
Jellyfish stings: dangerous, can be lethal