Cnidarians

Question 1

Give the phylogeny of the Cnidarians

Answer 1

Hydrozoa (hydrozoans)

Scyphozoa (jellyfish)

Cubozoa (box jellyfish)

Anthozoa (sea anemones, corals)

Anthozoas are regarded as a sister group to the other cnidarians

Question 2

What can most of the Cnidarian phylogeny be grouped as?

Answer 2

Medusazoans

Due to them having a medusa stage in their life

Question 3

What are some of the features of Cnidarians?

Answer 3

Have 2 body layers - epidermis (outside) and the gastrodermis (lies the gastrovascular cavity)

The mesoglea lies between the two layers

Have one opening - mouth/anus

Limited organ development

Question 4

Name some of the cell types present in the Cnidarians

Answer 4

Epitheliomuscular cell - forms the muscle layer

Interstitial cells - totipotent

Cnidocytes - stinging cell aka nematocyst

Question 5

What Cnidarian is blooming in the Mediterranean? Why is this causing issues?

Answer 5

Pelagia noctiluca

Decreases tourism and causing issues for fisheries

Question 6

What animal inherits a nematocyst from the Cnidarians? How?

Answer 6

Glaucus (a sea slug) aka the blue sea dragon

Eats jellyfish and uses their nematocyst as a defense mechanism rather than digesting them

Question 7

What polymorphisms can the Cnidarians be?

Answer 7

Polyp (asexual form)

Medusa (sexual form)

Question 8

What are the polymorphisms of the Cnidarian phylogeny?

Answer 8

Anthozoans - no medusa stage, only polyp

Hyrozoans - can have both or just medusa stage

Cubozoans and scyphozoans - mainly medusa stage, they spend little time in the polyp stage

Question 9

Which Cnidarian phylogeny undergoes secondary polymorphism?

Answer 9

Hydrozoans

Can asexually produce a medusa bud (whilst in polyp form) which can then bud off into a free-swimming form to sexually reproduce

Question 10

What are the types of polyps in Hydrozoans?

Answer 10

Gonozoid - for reproduction

Dactylozoid - for defence (contains the nematocyst)

Gastrozoid - for feeding

Question 11

What type of fertilisation do Cubozoans show?

Answer 11

Internal fertilisation

Question 12

Give the reproductive cycle of an Anthozoan

Answer 12

Release gametes into the sea - although some can internally fertilise

This then forms a planula

The planula develops into a polyp

The polyp develops into a young sea anemone polyp

This then forms adult stage sea anemone

Question 13

What is the rhopalium made from?

Answer 13

Ocellus - acts as the eye

Statocyst - lets animal know where it is in the water e.g. the right way up

Question 14

What does the rhopalium act as (other than a sense organ)?

Answer 14

A pacemaker

Question 15

Give the different eyes found on a Cubozoa

Answer 15

24 eyes in total

6 sets of 4 different types

Upper lens eyes - used to detect mangroves

Lower lens eyes - detect objects

Pit eyes

Slit eyes