Aquatic Lophotrochozoans, Flatworms, Annelids, Nematodes, and Cnidarians: Key Concepts and Structures

What is a trochophore?

A specialized, free-swimming larval stage common to aquatic lophotrochozoans.

Why do Platyhelminthes not require a coelom for gas exchange?

Their flattened bodies ensure cells are near enough to the surface to exchange gases directly with the environment.

How do free-living flatworms process food?

They use a muscular pharynx at the body midpoint to deliver food to a highly branched, incomplete digestive system.

How do parasitic flukes and tapeworms protect themselves from host defenses?

They possess a tough outer layer that protects against the host's digestive enzymes and immune system.

What are proglottids in tapeworms?

Repeated body segments that contain fertilized eggs and break off to leave the host in feces.

What is the primary function of the saddle-like thickening in Annelida?

It secretes a protective cocoon for fertilized eggs during reproduction.

How do earthworms move through soil?

They use bristles on each body segment to provide traction while burrowing.

What distinguishes Polychaeta from other Annelids?

They are marine worms with fleshy, paddle-like appendages containing many bristles (chaetae) for locomotion.

Why are earthworms vulnerable to drying out?

They lack specialized respiratory systems and must exchange gases via diffusion across a moist body surface.

What is the medical use of leeches?

They provide blood-thinning chemicals to stimulate circulation in reattached digits and remove excess blood after nervous system damage.

What is the body structure of Nematoda?

Unsegmented, cylindrical worms with a pseudocoelom.

Why are Nematoda limited to back-and-forth thrashing motions?

They possess only longitudinal muscles, preventing them from crawling or lifting their bodies.

What is ecdysis?

The process of shedding and replacing a tough external covering, shared by nematodes and arthropods.

What is the primary difference between protostomes and deuterostomes?

In protostomes, the mouth forms first; in deuterostomes, the anus forms first.

What is the advantage of a complete digestive tract?

Food passes in one direction through specialized compartments, increasing nutrient absorption efficiency.

What is the evolutionary benefit of segmentation?

It allows for increased body flexibility and the potential development of specialized body parts.

What is the difference between direct and indirect development?

Direct development lacks a larval stage, while indirect development involves passing through one or more larval stages.

What are spicules in sponges?

Tiny, sharp minerals made of silica or calcium carbonate that provide structural support.

What is the function of collar cells in sponges?

They trap and partially digest food particles.

What is the function of amoebocytes in sponges?

They digest food, distribute nutrients, and secrete skeletal components.

What are the two body forms of Cnidaria?

The sessile polyp and the free-swimming medusa.

What are cnidocytes?

Stinging cells containing tiny harpoons used to sense, grab, and paralyze prey.

How do sponges distribute nutrients and oxygen?

Water enters and leaves the body through pores, circulating through the organism.

What is the gastrovascular cavity?

A dead-end digestive chamber that secretes enzymes and distributes nutrients throughout the animal.