Ch16 | Molluscs – Complete Test Bank – 18th Ed

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CHECK ALL THE APPLY. Choose all options that best completes the statement or answers the question.
1) If you were keeping clams in an aquarium, what should you do to be sure that their shells do not become too thin? Check all that apply.

A) Make sure the pH does not become too low
B) Make sure calcium levels are adequate
C) Make sure that the carbon dioxide level in the tank is high
D) Make sure the acidity does not become too low

MULTIPLE CHOICE - Choose the one alternative that best completes the statement or answers the question.
2) Which correctly describes the evolutionary origin and adaptive radiation of molluscs?

A) Molluscs originated in freshwater and invaded both terrestrial and marine environments.
B) Molluscs originated on land, all classes then invaded both freshwater and marine environments.
C) Molluscs originated on land, all classes then invaded freshwater and the bivalves and gastropods invaded marine environments.
D) Molluscs originated in the sea, both bivalves and gastropods invaded marine environments and the land.
E) Molluscs originated in the sea, bivalves and gastropods invaded brackish and freshwater environments, and just gastropods invaded the land.

3) Where would you locate the coelomic cavity when dissecting a mollusc such as a clam?

A) The coelom is between the mantle and the shell.
B) The coelom is all of the area enclosed by the two shells.
C) The cavity around the heart, the kidneys, and the lumen of the gonads form the limited coelom.
D) The cavities inside the siphon are the coelom.
E) The coelom is the space inside the small tubules that form the gills.

4) The radula

A) not only rasps off fine food particles but also serves as a conveyor belt to carry food toward the digestive tract.
B) replaces worn teeth by secreting new teeth at the posterior end.
C) varies in number, pattern, and form of teeth, allowing species to be classified by this trait.
D) may be modified to bore through hard materials.
E) All of the choices are correct.

5) To prevent taking back in the wastes it has just expelled, a standard sediment-inhabiting bivalve mollusc should position itself

A) with the incurrent siphon upstream.
B) with the excurrent siphon upstream.
C) in any direction, since it can control which way the water flows in either siphon.
D) either with the incurrent siphon upstream or with the excurrent siphon upstream, but not in any direction, since it can control which way the water flows in either siphon.
E) None of the choices is correct.

6) Imagine a clam that grows but is unable to produce sufficient thickness in the newest regions of the shell. These thinner regions of shell would occur

A) on the outside so the periostracum is the newest material.
B) on the inside so the inside nacreous layer is the newest.
C) both directions outward from the central prismatic layer.
D) all at once; all layers of shell are the same age.
E) None of the choices is correct.

7) Because shells require it, land snails are limited to soils that contain some level of

A) aluminum.
B) silica.
C) calcium.
D) sodium.
E) carbon.

8) Clams burrow by using

A) adductor muscles.
B) cilia action.
C) gills for jet propulsion.
D) a modified radula.
E) a foot.

9) In some molluscs, the free-swimming larva is a trochophore while in others, it is a veliger with the beginnings of a foot, shell and mantle. What is the relationship of these molluscan juvenile stages?

A) A veliger is found strictly in terrestrial molluscs.
B) The trochophore is considered ancestral and the veliger is a derived larval stage.
C) The two larval forms represent two early and distinct branches of molluscs.
D) The veliger is ancestral and the trochophore is a derived larval stage.
E) Only the cephalopods have the veliger stage; all other molluscs have a trochophore stage.

10) The solenogasters

A) live free on the sea bottom and feed on cnidarians.
B) have a shell of eight articulating plates.
C) resemble the squids.
D) are called chitons.
E) have the primitive radula and gill mollusc plan.

11) The caudofoveates

A) are mostly worm-like, burrowing, marine organisms.
B) possess an oral shield associated with food selection and intake.
C) possess a radula (reduced in some species).
D) may have more features in common with the common ancestor of all molluscs than any other living group.
E) All of the choices are correct.

12) The Monoplacophora

A) lack a shell.
B) live in fresh water.
C) lack a foot.
D) have several internal organs that are serially repeated.
E) All of the choices are correct.

13) The Polyplacophora

A) have a coiled shell.
B) live in the ocean, especially in intertidal areas.
C) lack gills.
D) lack a radula.
E) All of the choices are correct.

14) The Scaphopoda

A) lack a shell.
B) lack a mantle.
C) live in fresh water.
D) pursue prey in a manner similar to squid.
E) lack gills.

15) The central axis around which the shell of a snail coils is called the

A) aperture.
B) columella.
C) sinistral.
D) dextral.
E) torsion.

16) Torsion

A) involves movement of the shell independent of visceral movements.
B) rotates the shell between 90 and 180 degrees.
C) begins with the contraction of an asymmetrical foot retractor muscle.
D) shifts the anus from posterior to the right side of the body.
E) All of the choices are correct.

17) Early gastropods had a coiled shell that did not twist to the right or left; this bilaterally symmetrical shell is called

A) sinistral.
B) planospiral.
C) conispiral.
D) dextral.
E) scaphopodal.

18) The genus __________ contains some members that have a toxin strong enough to kill humans.

A) Tegelu
B) Cyphom
C) Halioti
D) Conus
E) Neopilina

19) Some prosobranchs have only one _____________ in their mantle cavity.

A) Shell
B) Foot
C) Gill
D) Radula
E) Tentacle

20) The nudibranchs belong to the

A) scaphopoda.
B) pelecypoda.
C) prosobranchia.
D) opisthobranchia.
E) pulmonata.

21) The mantle cavity of a pulmonate snail is used

A) for propulsion.
B) to produce pearls.
C) as a lung.
D) to store wastes.
E) All of the choices are correct functions.

22) Cultured pearls are made by

A) cutting spherical balls from the thick shell of oysters and polishing them into circular beads.
B) dropping a grain of sand into the incurrent siphon of a pearl oyster.
C) tying off the labial palps.
D) growing oysters in high-calcium waters where they produce the pearls as unfertilized eggs.
E) placing an irritating particle under the shell mantle.

23) Of all of the freshwater organisms, more freshwater clams are becoming endangered than other species. What is the likely reason?

A) They are a primitive animal and they are due for natural extinction.
B) The shellfish industry has moved inland and we are over harvesting them for human food.
C) Clams are more heavily parasitized than any other molluscan group.
D) As filter-feeders, they concentrate pollutants and are more likely to be harmed by water pollution.
E) All of the choices are correct.

24) Most freshwater clams have a bivalve __________ stage that attaches to the gills and lives as a parasite for a few weeks.

A) veliger
B) trochophore
C) brachial
D) miracidia
E) glochidia

25) The main structures that taste food and direct it into the mouth of a clam are

A) the gills.
B) labial palps.
C) the siphons.
D) the gastric mill.
E) adductor muscles.

26) Cephalopods feed on

A) microscopic organisms.
B) fish, molluscs, crustaceans, and worms.
C) seaweed.
D) whales and porpoises.

27) The water current in the body of a cephalopod mollusc provides

A) oxygen for respiration.
B) jet power for rapid locomotion.
C) a means of carrying wastes and gametes out of the body.
D) All of the choices are cephalopod uses for their body water currents

28) The cephalopod nervous system is best described as

A) absent.
B) primitive and very little advanced from that of a cnidarian.
C) the most advanced among molluscs.
D) more complex than ours.

29) The intromittent organ of male cephalopods is the

A) pedipalp, a modified labial palp.
B) hectocotylus, a modified arm.
C) aedeagus, a modified beak.
D) penis, the first structure homologous to the mammalian reproductive structure.
E) baculum, a modified piece of internal shell.

30) Although snails and some other molluscs are hermaphroditic, most molluscs are either male or female, which means they are

A) asexual.
B) sexual.
C) monoecious.
D) dioecious.
E) parthenogenetic.

31) Which of the following statements is NOT TRUE of cephalopods?

A) Most cephalopods have color vision.
B) The underwater visual acuity of cephalopods surpasses that of humans.
C) Cephalopods can be taught to discriminate between shapes.
D) The sensory systems pf cephalopods are more elaborate than those of other molluscs.
E) The cephalopod brain is the largest of any invertebrate.

32) Gaseous exchange in gastropods may involve

A) gills.
B) lungs.
C) mantle.
D) body surface.
E) All of the choices are correct.

33) The circulatory system of cephalopods is more efficient than that of other molluscs because

A) it places the systemic circulation before the gills.
B) it is a closed network of vessels.
C) all blood is circulated through the gill filaments.
D) accessory or brachial hearts increase blood pressure before blood flows through the gills.
E) All of the choices are correct.

34) When cephalopods hatch from their eggs, they are

A) trochophore larvae.
B) glochidial parasites.
C) helpless, sessile larvae that must metamorphose into adult forms.
D) juveniles that resemble small adults.
E) All of the choices occur among the various cephalopods.

35) As part of your laboratory assignment, you must identify the class of a shelled mollusc. You believe that the animal is a nautilus, but your lab partner believes that the animal is a large snail. What feature of this animal would both support your idea and disprove your lab partner's idea?

A) Division of the shell into internal chambers
B) Coiling of the shell
C) Mantle
D) Radula

36) A cephalopod that could no longer produce sepia would be unable to

A) utilize a decoy to elude a predator.
B) digest food.
C) form egg cases.
D) communicate visually.

37) A snail without a radula would be

A) unable to eat.
B) unable to move.
C) unaffected, as a snail never has a radula.
D) unable to sense the presence of a food source.

38) Predict would what occur if the mantle cavity of a mollusc did not open to the external environment.

A) Gases could not be exchanged via the gills.
B) Gases could not be exchanged via the lining of the mantle cavity.
C) Wastes could not be eliminated.
D) All of the choices are correct.

FILL IN THE BLANK. Write the word or phrase that best completes each statement or answers the question.
39) The internal organs in coelomates are covered with a mesodermal epithelium called the __________.

40) The membranes that hold the internal organs in place in coelomates are called __________.

41) The tongue-like, rasping organ in the head of many molluscs is the __________.

42) The __________ is the layer on the outside of the clam or mussel shell that provides protection from acidic water and may be colored to hide the clam in the mud.

43) A pair of __________ serve as sense organs for sampling water and are found in the mantle grooves near the anus of many chitons.

44) Among living molluscs, the ancestral condition is most nearly approached by the class __________.

45) The shell of a polyplacophoran is divided into eight __________ valves.

46) Molluscs with a tubular shell that opens at both ends are in the class __________.

47) The shell of a bivalve grows in concentric rings around the __________, which is the oldest part of the shell.

48) The crystalline __________ projects into a bivalve stomach to keep the contents whirling while releasing digestive enzymes.

49) Accessory or __________ hearts at the base of each gill help to maximize the efficiency of the cephalopod circulatory system.

ESSAY. Write your answer in the space provided or on a separate sheet of paper.
50) Describe five morphological or developmental features that would most likely be found in the earliest ancestral mollusc.

51) The scaphopods have a shell that resembles a straightened gastropod shell. Why are they not classified with the gastropods?

52) How are scaphopod tentacles different from the tentacles of cephalopods? Are these two types of tentacles homologous?

53) How does torsion differ from coiling? Fully explain your answer.

54) Cephalopod eyes and vertebrate eyes are anatomically similar. Evaluate whether or not the similarity is a case of homology or analogy.

55) What are the morphological features that distinguish the ammonoids from the nautiloids?

56) Opisthobranchs and pulmonates are both gastropods. What are their main distinguishing features?

57) How do you account for the enormous radiation of the molluscs?

58) What surface (e.g., dorsal, ventral, anterior, posterior) of the squid faces forward as the animal moves by jet propulsion? What surface faces forward in a swimming cuttlefish? Explain your answers.

59) Give the supporting evidence that shows that the molluscs share a common ancestor with the annelids.

60) How has the problem of "fouling" been resolved by the various groups of molluscs?