Animal Diversity and Evolution - Cnidarians

What does 'Ctenophora' mean?

Named for ctenes – comblike plates of fused cilia

How many species of Ctenophores exist?

~200 species

Where do Ctenophores live?

All marine, mostly warm waters

What type of symmetry do Ctenophores have?

Biradial symmetry

Do Ctenophores have a through gut?

Yes – they have both a mouth and anus

What are colloblasts?

Glue cells unique to Ctenophores (synapomorphy)

Do Ctenophores have nematocysts?

No – only Cnidarians make nematocysts

What organ helps Ctenophores balance?

Statocyst – organ of equilibrium

What type of reproduction do Ctenophores have?

Mostly external fertilization; monoecious (hermaphroditic)

What does 'Cnido-' mean?

Nettle

How many species of Cnidarians exist?

~9,000 species

What is the key synapomorphy of Cnidarians?

Nematocysts

What type of organization do Cnidarians have?

Tissue-level organization

Are Cnidarians diploblastic or triploblastic?

Diploblastic – ectoderm (epidermis) + endoderm (gastrodermis)

Do Cnidarians have a coelom?

No – diploblastic = no mesoderm

What type of gut do Cnidarians have?

Incomplete gut (gastrovascular cavity)

What are cnidocytes?

Specialized cells that house nematocysts

How does a nematocyst discharge?

Triggered by a cnidocil, filament injects venom via osmotic pressure

What are statocytes?

Balance organs in Cnidarians (also in Ctenophores)

What are ocelli?

Photosensitive organs in Cnidarians

Do Cnidarians have a brain?

No – they have a nerve net

How are Cnidarian nerve nets structured?

Two interconnected nets (gastrodermal + epidermal), two-way transmission

Name the main clades of Cnidaria.

Hydrozoa, Scyphozoa, Cubozoa, Anthozoa, Staurozoa, Myxozoans

What is the synapomorphy of Hydrozoa?

Velum

What is unique about Hydrozoa reproduction?

Asexual budding polyps alternate with sexual medusae

What is the immortal jellyfish?

Turritopsis dohrnii

Radiate Animals Q1: Which type of cell is used by Cnidarians to sting/capture prey?

D. Cnidocytes

Radiate Animals Q2: Which organelle is used by Cnidarians to sting/capture prey?

A. Nematocysts

Radiate Animals Q3: The Cnidaria include all of the following animals EXCEPT?

E. Sea urchins