Sponges, Corals and Pre-Bilaterian Life

Question 1

A species can be defined as

Answer 1

a group of organisms which can interbreed to produce viable offspring

Question 2

Phylum rank can be defined as

Answer 2

• organisational clade that has a unique body plan
• exhibit similarly-placed, similar structures
• found together on the phylogenetic tree

Question 3

Give examples of animal Phyla

Answer 3

• Porifera (sponges)
• Cnidaria
• Arthropoda
• Mollusca
• Nematoda
• Annelida (roundworms)
• Chordata

Question 4

Describe the phylogeny the ‘early branches’ of the Animalia

Answer 4

• originating roughly 550-570Mya on the time sequence tree
• Porifera, Placozoa, Ctenophora and Cnidaria

Question 5

Describe Porifera morphology

Answer 5

• globe-like
• two germ layers
• pore cells which punctuate these two layers
• actin-conjoined choanocytes infiltrating the inner germ layer and pressing against the pinacocytes
• active and sticky supporting tentacles

Question 6

Describe Porifera germ layers

Answer 6

• pinacocytic outer germ layer
• convoluted inner germ layer

Question 7

Choanocytes

Answer 7

• sometimes exist in chambers
• aka collar cells

Question 8

Describe Porifera feeding

Answer 8

• filter feeding mechanism
• water is wafted away from the cell by choanocytic flagella, setting up a water current that allows the tentacles to contract bacterial food
• water expelled from the Porifera through their anterior osculum, expunging planktonic competition
• efficiency mediated by germ convolution and choanocytic abundance

Question 9

Describe Poriferan symmetry

Answer 9

none

Question 10

Describe Poriferan nerve cells

Answer 10

none

Question 11

Describe carnivorous Porifera

Answer 11

• harp-shaped deep-sea Porifera in the Family Cladorhizidae
• ping-pong tree sponge
• harp sponge
• spicule-and-envelope mediated carnivory of shrimp
• adaptation to a lack of environmental planktonic food source

Question 12

Describe Placozoa

Answer 12

• marine
• approximately 20 species
• e.g. Trichoplax adhaerens

Question 13

Describe Placozoa morphology

Answer 13

• double germ layer structure
• semi-ciliated upper germ layer
• lower germ layer exhibiting some secretory gland cells, separated by contractile fibre cells
• no symmetry
• no nerve cells
• very disorganised, amorphous shape
• small size of 3-4mm

Question 14

Describe Placozoan feeding

Answer 14

• grazers
• secrete enzymes over the reef rock in tropical seas
• crawling over algae and absorbing digestants

Question 15

Describe Placozoan taxonomy

Answer 15

four Classes:
- Anthozoa (the sea anemones and corals)
- Cubozoa (the box jellies)
- Hydrozoa (the hydroids)
- Scyphozoa (the jellyfish).

Question 16

Describe Cnidarian morphology

Answer 16

• body plan is extremely diverse
• 2 germ layers
• mesoglea
• blind-ending gut cavity
• approximately radial symmetry
• nerve net

Question 17

Describe mesoglea in Cnidaria

Answer 17

• intermediate
• jelly-like
• allows a few cells to crawl through

Question 18

Describe the Cnidarian germ layers

Answer 18

• epidermis and gastrodermis
• unspecialised actin and myosin contractile and extensile cells in both layers.

Question 19

Describe Cnidarian dual morphology

Answer 19

• sedentary Polyps and mobile Medusas
• alternation of generations as two different morphs in the same Cnidarian’s life cycle

Question 20

Describe Polyps

Answer 20

• anterior double mouth and anus surrounded by tentacles and leading to the gastrovascular cavity
• rest of the body is stalked

Question 21

Describe the Medusa

Answer 21

• more active
• posterior double mouth and anus, still surrounded by tentacles and leading into the gastrovascular cavity
• outer layer fibres more contractile
• mesoglea more stiff to generate more power for its motile swimming lifestyle

Question 22

Describe Medusa mesoglea

Answer 22

almost skeletal

Question 23

Describe slow-moving Cnidarian feeding adaptations

Answer 23

• predatory feeding behaviours
• nematocysts contained within the cnidocyte, and store the nematocyte cells

Question 24

Describe nematocysts

Answer 24

stinging organelles that allow predation upon fast-moving fish and crustaceans

Question 25

Describe nematocyst cells

Answer 25

• contain a hollow, tightly wound venom-delivering thread coil and barb
• fired on mechanical activation of their touch-sensitive hairlike projection

Question 26

Describe the hydrozoan Portuguese man o’war

Answer 26

polyps bud to form genetically identical but individually specialised colonial entities

Question 27

Describe the photosynthetic dinoflagellates

Answer 27

• polyps bud to form genetically identical but individually specialised colonial entities
• provides symbiotic corals with photosynthates harvested from the energy of the sun

Question 28

Describe the myxozoans

Answer 28

• parasitic
• anomalous vermiform morphology of just a few mms
• nematocyst-like cell

Question 29

Describe the Ctenophores

Answer 29

• dual germ layering
• approximate radial symmetry
• nerve net
• shimmering appearance
• predatory
• slow motility achieved by synchronous beating of their cilia
• colloblasts

Question 30

Describe colloblasrs