L3 - Radiata, Bilateria, Acoelomates

Question 1

What are Radiata?

Answer 1

Animals with radial symmetry and diploblastic larvae. Diploblastic - ectoderm (outer layer), endoderm (gut)

Question 2

What is the phylum Cnidaria?

Answer 2

Hydras, jellyfish, sea anemones, corals. All aquatic, mostly marine. Diploblastic, with jelly like mesoglea between germ cell types. Possess a gastrovascular cavity or coelenteron - central digestive cavity with one opening.

Question 3

What are the two basic body plans of the phylum Cnidaria?

Answer 3

Polyp, Medusa

Question 4

What is the Polyp body plan of the phylum Cnidaria?

Answer 4

Sessile, cylindrical. Oral end directed upwards, mouth and tentacles for prey capture. Aboral end attached to substrate

Question 5

What is the Medusa body plan of the phylum Cnidaria?

Answer 5

Free living, bell or saucer shape, aboral end convex and pointed up, oral end concave and pointed down, tentacles hang from oral surface, movement by passive drift or weak bell contractions. Free living medusoid forms are found in all cnidarian classes except the Anthozoa.

Question 6

What does the phylum Cnidaria prey on?

Answer 6

They are carnivorous, prey captured by stinging cells called cnidocytes. These contain a trigger mechanism and nematocysts - possess a long thread within a capsule, when discharged thread is thrown out at great velocity ; some entangle prey but most penetrate the prey and release a toxin. Most are not able to penetrate human skin, but some can : these can be very painful or even fatal.

Question 7

Where are Nematocysts found?

Answer 7

Nematocysts are mainly found in the epidermis of tentacles, around the mouth and lining the gastrovascular cavity.

Question 8

How are nerves arranged in the phylum Cnidaria?

Answer 8

In the form of a net ; Plexus, no brain present, can respond to sensory stimuli and try and move away or towards the stimulus

Question 9

How does movement occur in the phylum Cnidaria?

Answer 9

Fluid filled gastrovascular cavity can be used as a hydrostatic skeleton : simple movement of the bell can cause them to swim

Question 10

What are the Phylum - Cnidaria, Class - Hydrozoa?

Answer 10

Abundant and ubiquitous e.g. Obelia. Most are marine, colonial and alternate between asexual polyp stage and sexual medusoid stage. Some have no medusoid stage, some have no polyp stage. Polypoid form dominates.

Question 11

Phylum - Cnidaria, Class - Hydrozoa. What are the 2 genera of Pleustonic hydroids? What does Pleustonic hydroid mean.

Answer 11

Porpita - known as blue buttons, Velella - know as By-the-wind-sailor, 2-10cm diameter. Hollow gas filled chamber for floating, diagonal fin, gastrozooids hang beneath. They float at the sea surface.

Question 12

Phylum - Cnidaria, Class - Hydrozoa. What is there one order of?

Answer 12

Siphonophores, colonies of medusoid individuals, float and swim, can have long tentacles for feeding, most siphonophores drift beneath the surface, but some float at the surface. E.g. Portuguese man-of-war

Question 13

Where does Hydractinia echinata live?

Answer 13

Only on gastropod snail shells inhabited by hermit crabs

Question 14

What are the Phylum - Cnidaria, Class - Scyphozoa?

Answer 14

True ‘jellyfish’. Polyp stage as larval form, body composed of translucent mesoglea, range from a few cm’s to >2m diameter. Tentacles hang from bell margin (up to 60-70m) Four long extension of the manubrium = oral arms. Nematocysts in tentacles and oral arms, no velum present.

Question 15

What are the Phylum - Cnidaria, Class - Scyphozoa sexual reproduction in the cnidarians?

Answer 15

Free swimming planula larvae develops after fertilisation. Settles as small, benthic, sessile polyp larva = scyphistoma. Can live for several years, feeding and producing more scyphistoma by budding. Produces young jellyfish medusae by budding off at oral end, stacking them like plates, called strobila. They are then released (strobilation) = young jellyfish (ephyra)

Question 16

What are the Phylum - Cnidaria, Class - Cubuzoa?

Answer 16

Box jellyfish. In transverse section the bell is square, either a single or a group of tentacles at each corner. Scyphistoma does not bud, just transforms into ephyra and swims away (no strobila). Strong swimmers, voracious predators (mainly of fish), venom in nematocysts is lethal to humans. Common in australian waters

Question 17

What are the Phylum - Cnidaria, Class - Cubozoa, what can box jellyfish nematocysts cause?

Answer 17

Agonising pain, can lead to cardiac arrest. Vinegar disables the nematocysts that have not yet discharged into the bloodstream. Tentacles will sting if separated from the bell, or after the creature is dead. Removal of tentacles without prior application of vinegar may cause unfired nematocysts to come into contact with the skin. No scientific evidence that urine will disable further stinging, and may even hasten the release of venom.

Question 18

What are the Phylum - Cnidaria, Class - Cubozoa, what are box jellyfish?

Answer 18

Positively phototactic (move toward light). Active during the day and night, although may feed only during the night or the predawn hours. Vision plays a role in both feeding and reproduction. Possess image forming ‘eyes’ - makes them difficult to study because they react to the presence of observers by swimming away

Question 19

What are the Phylum - Cnidaria, Class - Staurozoa?

Answer 19

Stalked jellyfish, unique in that they do not alternate between polyp and medusa life cycle phases. Attached medusa stage, with a life style more resembling that of polypoid forms. Upside down trumpet-shaped body. Tentacles projecting upwards, the stalk located in the centre of the umbrella, members of this class are commonly found in relatively cold waters, close to the shoreline.

Question 20

What are the Phylum - Cnidaria, Class - Anthozoa?

Answer 20

Corals and Anemones ; >6000 spp. Entirely polypoid, no medusae. All marine, solitary or colonial, some supported by skeletons, cylindrical body shape, central mouth surrounded by tentacles. Polyps are very contractile, both in size and shape. Can be very colourful, 2 or 3 subclasses.

Question 21

What are the Phylum - Cnidaria, Class - Anthozoa. What is the subclass of soft corals, sea fans, sea pens?

Answer 21

Octocorallia, always colonial. Polyps have 8 pinnate tentacles in a single cycle. Most contain hard calcerous particles for support = sclerites.

Question 22

What are the Phylum - Cnidaria, Class - Anthozoa. What are soft corals?

Answer 22

Small polyps embedded in a rubbery mass of coenechyme, can be encrusting, erect or cushion like. E.g. Alcyonium (dead men’s fingers)

Question 23

What are the Phylum - Cnidaria, Class - Anthozoa. What are Sea pens and sea fans?

Answer 23

Erect, rod like ; can be several meters tall. Central rod provides support, some have many branches all in one plane. Can be very beautiful and colourful

Question 24

What are the Phylum - Cnidaria, Class - Anthozoa. What are Anemones and true (or stony) corals?

Answer 24

Subclass - Hexacorallia. Solitary or colonial. Polyps have at least 12 tentacles in at least 2 cycles and never pinnate. Anemones have no skeleton, stony corals have a limestone skeleton. Anemones (order Actinaria)

Question 25

What are the Phylum - Cnidaria, Class - Anthozoa. What are Anemones (order Actinaria)?

Answer 25

Large, solitary, usually attached to a hard substrate. Can be brightly coloured, contractile. Carnivorous, using the nematocysts in tentacles. Can reproduce asexually by : pedal laceration, fragmentation, longitudinal fission

Question 26

What are the Phylum - Cnidaria, Class - Anthozoa. What are True or Stony corals (order scleractinia)?

Answer 26

Can be solitary, but mostly colonial, secrete a calcerous skeleton, polyps look like small anemones. Connected to each other by body wall. The living component of the colony is like a sheet overlying the skeleton. Feed on small planktonic animals - carnivorous.

Question 27

What are the Phylum - Cnidaria, Class - Anthozoa. What are True or Stony corals which form coral reefs?

Answer 27

Rate of skeleton growth from 0.5cm to >10cm per year. Continuous growth leads to coral reefs. New polyps settling and growing on skeleton of previous generations. Can produce massive formations, taking carbonates out of sea water and depositing them as calcium carbonate. Great barrier reef can be seen from space. Massive and complex habitat, enormous range of habitats for organisms. Seasonal and synchronous release of gametes.

Question 28

What are the Phylum - Cnidaria, Class - Anthozoa. What are True or Stony corals which form coral reefs? Reproduction?

Answer 28

Gametes fertilise and settle, giving rise to one polyp ; polyp buds to form many colonies. Can keep growing as a single colony for over 100yrs. Most coral polyps contain symbiotic dinoflagellates, usually Symbiodinium. Mostly yellow-brown in colour, making the corals a similar colour. The dinoflagellates require light (photosynthesisers), and the corals require warm water, so coral reefs are only found in warm, shallow, clear water. Up to 50% of the photosynthetic products are transferred to the host. One of the most productive habitats on earth.

Question 29

What are the Phylum - Cnidaria, Class - Anthozoa. Coral bleaching?

Answer 29

A result of - Increasing water temp - Starvation - Changes in salinity - Change in solar irradiance Corals expel the symbiotic dinoflagellates as a stress response. Results in poor growth, and death of coral ; downward spiral, negative feedback loop

Question 30

What is in the phylum Ctenophora?

Answer 30

Comb jellies, Sea gooseberries, Sea walnuts. <100 spp ; mostly pelagic. 8 rows of ciliated bands (combs) used for locomotion. Usually a globose shape, of golf ball size. None have nematocysts. Many have adhesive cells - Colloblasts. Fragile, transparent bodies, bioluminescence, carnivorous on plankton.

Question 31

What do Bilateral animals show?

Answer 31

Bilateral animals show cephalisation, an evolutionary trend towards developing sensory structures at the anterior end. Symmetry may change between larvae and adult. All metazoan embryos undergo gastrulation. As a result, germ cell layers develop which later form tissues and organ.

Question 32

What is Radiata?

Answer 32

Develop 2 germ cells, ectoderm and endoderm. Are termed diploblastic.

Question 33

What is Bilateria?

Answer 33

Develop 3 germ layers, ectoderm (outer layer), mesoderm (connective), endoderm (internal organs). Are termed triploblastic

Question 34

What three major grades of construction (groups) do Bilateria divide into?

Answer 34

Acoelomates, Coelomates, Pseudocoelomates

Question 35

What is an acoelomate?

Answer 35

a = without ; koilos = hollow. Flatworm. Body covering (from ectoderm), Muscle layer (from mesoderm), Mesenchyme (from mesoderm), Digestive tract (from endoderm). The most primitive bilateral metazoans have no coelom, hence are termed Acoelomate, there are only two phyla of acoelomates.

Question 36

What are the two phyla of acoelomates?

Answer 36

Phylum Nemertea, Phylum Platyhelminthes - important parasites of vertebrates.

Question 36

Acoelomates - What is the phylum Nemertea?

Answer 36

650 spp, Ribbon worms, proboscis worms. Free living, mostly marine. Dorsoventrally flattened and ciliated. Most <20cm long, but can be several meters. Have long proboscis to feed on small animals - can be everted to catch prey. Complete digestive tract with mouth and anus. Many are brightly coloured. E.g. Lineus longissimus, the bootlace worm

Question 37

Acoelomates - What is the phylum Platyhelminthes?

Answer 37

>20,000 spp. Platys = flat, helmins = worm, flatworms. Body dorsoventrally flattened, unsegmented worms, gastrovascular cavity has only one opening. Gas exchange via diffusion, no circulatory organs. Excretion via simple tubular excretory system called protonephridium

Question 37

Acoelomates - What are the four classes of the phylum Platyhelminthes ?

Answer 37

Turbellaria (free living flatworms), Monogenea (ectoparasites ; flukes), Trematodes (endoparasites ; flukes), Cestoda (endoparasites ; tapeworms)

Question 38

Acoelomates - What is the phylum Platyhelminthes, class Turbellaria?

Answer 38

Free living ; marine, freshwater and terrestrial. Mostly small ~10mm, either swim by undulation or crawl on cilia on blanket of mucus. Use mouth on mid-ventral surface to eat small organisms. Some are known to stab their prey with the penis, which terminates in a hardened stylet

Question 39

Acoelomates - What is the phylum Platyhelminthes, class Monogenea (10,000 spp) and Trematoda (11,000 spp)?

Answer 39

Often referred to as flukes. Monogenea are mostly ectoparasites of aquatic vertebrates, Trematodes are mostly endoparasite of vertebrates. Many have complex lifecycles involving intermediate hosts

Question 40

Acoelomates - What is the phylum Platyhelminthes, class Cestoda (3,400 spp)?

Answer 40

Tapeworms, all endoparasites, mostly in vertebrates digestive systems. Juveniles often found encysted in vertebrate tissues. Body surface is not ciliated, anterior scolex with suckers, hooks etc. Attached to strobila (body) = ribbon like, made up of many consecutive flattened sections called proglottids. Each proglottid is filled with reproductive organs (both eggs and sperm)

Question 41

Acoelomates - What is the phylum Platyhelminthes, class Cestodes - Echinococcus?

Answer 41

Adults 3-6mm long. In humans the larvae can cause one of two diseases. Cystic echinococcosis CE - E. granulosus. Alveolar echinococcosis AE - E. multicularis