Exam 2 Marine Inverts Test

What type of symmetry do adult cnidarians exhibit?

• A) Bilateral symmetry

• B) Asymmetry

• C) Radial symmetry

• D) Spherical symmetry

Answer: C

What are the two primary body forms found in cnidarians?

• A) Sponge and medusa

• B) Polyp and medusa

• C) Polyp and sessile

• D) Planula and ephyra

B

What do you call the specialized stinging cells used for defense and capturing prey?

• A) Choanocytes

• B) Amoebocytes

• C) Cnidocytes

• D) Nematodes

C

In which class of cnidarians do reef-building corals and sea anemones belong?

• A) Hydrozoa

• B) Scyphozoa

• C) Anthozoa

• D) Cubozoa

C

T/F Cnidarians have a complete one-way digestive tract with a separate mouth and anus.

False (They have a gastrovascular cavity with only one opening serving as both mouth and anus)

T/F The gelatinous middle layer between the ectoderm and endoderm in cnidarians is called the mesoglea.

True

T/F The free-swimming larval stage of a cnidarian is called a planula

True

Explain how a nematocist works.

A nematocyst is a coiled thread that can shoot out of cnidarians to paralyze prey with their poison.

Describe the structural difference between a polyp and a medusa.

Polyps are sessile with a cylindrical body and a mouth pointing upward. Medusae are free-swimming, bell-shaped, and have a mouth pointing downward

How do cnidarians coordinate movement without a true brain?

They possess a decentralized nerve net that transmits signals to simple contractile or muscle-like cells

What type of body cavity do platyhelminthes have?

• A) Hemocoelomate

• B) Pseudocoelomate

• C) Acoelomate

• D) Coelomate

A

• Which structures are used by flatworms for excretion and osmoregulation?

  • A) Nephridia

  • B) Flame cells

  • C) Malpighian tubules

  • D) Choanocytes

B

What type of symmetry do platyhelminthes exhibit?

• A) Radial symmetry

• B) Asymmetry

• C) Spherical symmetry

• D) Bilateral symmetry

D

Which class of flatworms consists entirely of ectoparasitic or endoparasitic flukes?

• A) Turbellaria

• B) Cestoda

• C) Trematoda

• D) Hydrozoa

C

T/F Flatworms possess a complete digestive system with a separate mouth and anus

False (They have an incomplete digestive tract with a single opening, and tapeworms lack a digestive tract entirely)

T/F Platyhelminthes are triploblastic, meaning they have three germ layers

True

T/F Tapeworms (Cestodes) absorb nutrients directly through their body wall

True

What is cephalization, and why is it important for flatworms?

Cephalization is the concentration of sense organs and nerve cells at the anterior (front) end of the body. It allows motile flatworms to sense their environment first as they move forward.

How do flatworms respire without lungs or gills?

Answer: They rely on simple diffusion across their flattened bodies. This high surface-area-to-volume ratio allows gas exchange directly with the environment

Describe the function of a tapeworm's scolex?

The scolex is the head-like anterior end equipped with hooks and suckers, used exclusively to attach itself to the host's intestinal wall.

Which anatomical feature is uniquely responsible for secreting the shell in mollusks?

• A) Visceral hump

• B) Radula

• C) Mantle

• D) Muscular foot

C

Which group of mollusks breaks the general rule of having an open circulatory system?

• A) Bivalves (clams and oysters)

• B) Cephalopods (squids and octopuses)

• C) Gastropods (snails and slugs)

• D) Polyplacophorans (chitons)

B

The rasping, tongue-like organ used by many mollusks to scrape up food is called the:

• A) Radula

• B) Ctenidium

• C) Scolex

• D) Nephridium

A

What is the correct chemical composition of a mollusk shell?

• A) Chitin

• B) Silica

• C) Calcium carbonate

• D) Calcium silicate

C

T/F All classes of mollusks feature a distinct, well-developed head region

False (Bivalves lack a distinct head region entirely).

T/F The unique larval stage that develops directly from or alongside the trochophore stage in many marine mollusks is the veliger larva.

True

Cephalopods use their siphon primarily to filter plankton out of the water column.

False (They use the siphon or funnel for jet propulsion to move rapidly through the water).

How does the coelom of a mollusk differ from its main body cavity?

The true coelom in mollusks is highly reduced. It is restricted to a small space around the heart (pericardial cavity), gonads, and kidneys, while the main body cavity is an open hemocoel filled with blood.

Explain the dual role of the ctenidia (gills) in a typical bivalve

In bivalves, the ctenidia function in respiration for gas exchange and serve as a food-trapping mechanism. Cilia on the gills trap organic particles from the water current and move them toward the mouth.

What evolutionary adaptation allows cephalopods to navigate without an external shell?

Cephalopods lost or internalized their shells to trade heavy armor for speed and agility. They evolved highly developed nervous systems, complex eyes, and dynamic camouflage abilities to avoid predators and hunt effectively.

Describe Torsion

It moves the mantle cavity, gills, and anus from the posterior (rear) end of the animal to the anterior (front) end, directly over the head.

Why might torsion be beneficial, and why may it be harmful?

It allows the snail to retract its sensitive head into the protective shell first, followed by the foot, often sealing the opening with a tough plug called an operculum. Bad because butt over mouth (contamination).

Diploblastic

Having a body derived from only two embryonic germ layers: ectoderm and endoderm.

Triploblastic

Having a body derived from three embryonic germ layers: ectoderm, mesoderm, and endoderm.

Acoelomate

An animal that lacks a fluid-filled body cavity between the digestive tract and outer body wall.

Coelomate

An animal possessing a true coelom, which is a fluid-filled body cavity completely lined by tissue derived from the mesoderm.

Cephalization

The evolutionary trend toward concentrating nervous tissue and sensory organs at the anterior (front) end of the body.

Mesoglea

The translucent, inert, jelly-like substance found between the ectoderm and endoderm in cnidarians.

Gastrovascular Cavity

• A central digestive compartment with a single opening that functions as both the mouth and the anus

Hemocoel

The primary body cavity in most invertebrates, containing circulatory fluid (hemolymph) that directly bathes the organs.

Cnidocyte

A specialized stinging cell unique to cnidarians, used for defense and capturing prey.

Nematocyst

The capsule within a cnidocyte that contains a coiled, barbed, and often poisonous thread.

Flame Cell (Protonephridium)

A specialized excretory cell found in flatworms that filters waste and regulates water balance.

Radula

A rasping, tongue-like organ covered in microscopic chitinous teeth, used by many mollusks to scrape or tear food.

Mantle

A specialized fold of tissue in mollusks that drapes over the visceral mass and secretes the calcium carbonate shell.

Ctenidia

Respiratory gills found in the mantle cavity of mollusks, often used for both breathing and filter feeding.

Scolex

The highly specialized head-like anterior structure of a tapeworm, featuring hooks and suckers for host attachment.

Polyp

The sessile, tubular body form of a cnidarian, typically featuring a mouth and tentacles facing upward.

Medusa

The free-swimming, bell- or umbrella-shaped body form of a cnidarian, typically featuring a mouth and tentacles facing downward (think jellyfish)

Planula

The free-swimming, ciliated larval stage characteristic of most cnidarians.

Trochophore

A small, translucent, free-swimming larva with a ring of cilia, characteristic of marine mollusks and annelids.

Veliger

The second larval stage of many marine mollusks, developing from the trochophore and featuring a tiny shell and a ciliated swimming organ (velum).

Torsion

A 180-degree counterclockwise twisting of the visceral mass during gastropod development, positioning the mantle cavity and anus over the head.