Phylum Platyhelminthes, Cnidaria, and More

Practice questions covering the biological characteristics, classes, and life cycles of Platyhelminthes, Cnidarians, and related phyla as described in the lecture notes.

In simple Platyhelminthes, what structure acts as both the entrance for food and the exit for waste?

The pharynx

What is the function of 'flame cells' in freshwater Platyhelminthes?

They act as kidneys for osmoregulation and filter out nitrogenous waste using flagellum beatings.

What type of nervous system do Platyhelminthes possess?

A basic ladder-like nervous system featuring a cerebral ganglion, lateral nerve cords, and transverse nerves.

What distinguishes Class Turbellaria from other Platyhelminthes?

They are the only group with a ciliated epidermis, which helps with movement such as sliding, crawling, and swimming.

What is a specific characteristic of the stem cells in Planaria regarding regeneration?

They can regrow a head even if the organism is cut to $1/260^{th}$ of its original size.

What is a 'syncytial tegument' in Clade Neodermata?

A skin where cells have merged into one continuous layer with many nuclei but no cell membranes separating them, helping to evade the host immune response.

Which class of Platyhelminthes is characterized as endoparasites with oral and ventral suckers?

Class Trematoda (The flukes)

What are the intermediate and definitive hosts for Schistosoma (blood flukes)?

Snails are the intermediate hosts, and humans are the definitive hosts.

What structure allows Class Monogenea to attach to the gills of fish?

The opisthaptor (a ring of hooks)

What are proglottids in Class Cestoda?

Reproductive structures that can break off and produce eggs.

What does 'diploblastic' mean in the context of Phylum Cnidaria?

They have only two layers of tissue: the ectoderm and the endoderm, with no mesoderm.

Which specialized organelle in cnidocytes acts as a 'lasso' to grab prey?

Spirocyst

What are the two primary body forms of Cnidarians?

The polyp (sessile) and the medusa (free-swimming).

What sensory structures are used for light detection in Cnidarians?

Ocelli

What is the function of a 'statocyst' in Cnidaria?

It is used for gravity sensing and orientation, containing stone material and cilia.

In Class Anthozoa, what is a 'siphonoglyph'?

A ciliated groove in the pharynx that helps move water down into the gastrovascular cavity.

Why do hard corals (Order Scleractinia) have a symbiotic relationship with dinoflagellates?

The dinoflagellates provide food and color to the coral, while the coral provides protection.

What occurs during coral 'bleaching'?

When temperatures increase by $1-2^{\circ}C$, the coral expels its zooxanthellae (which produce toxins under heat stress), leaving the white calcium carbonate skeleton exposed.

What are the eight unpaired internal septa a characteristic of?

Subclass Octocorallia (soft corals)

List the stages of the Class Scyphozoa life cycle in order from larva to adult.

Ciliated planula larva $\rightarrow$ Scyphistoma (polyp) $\rightarrow$ Strobila $\rightarrow$ Ephyra $\rightarrow$ Adult medusa

What type of eyes do Cubozoans (box jellies) possess?

Complex, image-forming eyes kept in rhopalia.

In Class Hydrozoa, what are 'gastrozooids' and 'gonozooids'?

Gastrozooids are feeding polyps with mouths and tentacles; gonozooids are reproductive polyps that produce medusae.

Which genus of Hydrozoa is known for its 'biological immortality' and lack of a medusa stage?

Hydra

How do the gonads of hydromedusae differ from those of scyphomedusae?

Hydromedusa gonads are epidermal (outside), while Scyphomedusa gonads are located in gastripouches (stomach).

What structure in Class Myxozoa is homologous to cnidarian nematocysts?

Polar capsules

What are 'ctenes' in Phylum Ctenophora?

Rows of cilia on the outside of the body used for slow locomotion.

What chemical reaction produces bioluminescence in organisms?

The protein luciferin binds with $O_2$ in the presence of the enzyme luciferase, releasing light as a byproduct.