Chapter 16 Study Questions - Mollusca

Question 1

How many species of living and fossil molluscs are known?

Answer 1

> 90,000 living species

>70,000 fossil species

Question 2

Briefly discuss the diversity and range of habitats in the members of this phylum?

Answer 2

Extremely diverse - chitons, tooth shells, snails, slugs, nudibranchs, clams, mussels, oysters, squid, cuttlefish, octopus, nautilus
size
< 1mm - smallest snails
giant squid - ~ 20 meters long, weigh up to 1,000 lbs
shells of giant clams - 1.5 m long, 500 lbs, or > 250 kg
ecological relationships
range of habitats - tropics to polar seas
most live in the sea, ponds, lakes, surf, mud

Question 3

List 6 classes of molluscs and give examples of each?

Answer 3

Six classes with characteristics and some representatives

1. Monoplacophora - Neopolina
2. Polyplacophora - the chitons
3. Scaphopoda - tooth shells or tusk shells
4. Gastropoda- snails, slugs
5. Bivalvia (pelecypoda) - clams, oysters, scallops
6. Cephalopoda - squid, octapus, nautilus

Question 4

List some ways that these animals are important to humans?

Answer 4

economic importance/relationships to man
wide variety used for food - oysters, clams, scallops, mussels
pearls - natural and cultured pearls, most valuable from Japan, Eastern Asia
some destructive - burrowing shipworm
roadbuilding - crushed oyster shells
rations for poultry, domestic animals
pearl buttons from shells of freshwater mussels and clams
Shell mounds/Indian relics
cultured pearl industry - big business,
small particle under mantle of marine
oysters or bivalves in cages, harvested later

Question 5

What is the importance of the mantle in bivalves?

Answer 5

mantle and cavity create jet propulsion for locomotion

Question 6

What is the importance of the radula in univalves?

Answer 6

rasping organ used for feeding
. rasping, protrusible tongue-like organ found in all molluscs except bivalves
2. odontophore - supporting cartilages
3. teeth - few or up to 250,000
4. functions
scrape, pierce, tear, cut particles of food
“conveyor belt” to carry food toward the digestive tract

Question 7

Name and describe the two important larval forms of molluscs?

Answer 7

trocophore = free-swimming larval stage
veliger = free-swimming larval stage of snails and has beginnings of a foot, shell, mantle

Question 8

Why do these animals produce such large numbers of larvea?

Answer 8

They serve as food for many other animals so many dont survive

Question 9

8 Characteristics

Answer 9

????????

Question 10

10.Describe the whorls, spire, and the columella in conchs and whelks.

Answer 10

Whorl = inside of squiggles
Spire = hat shape
Columella= inside t shape gives support

Question 11

11.What are the advantages of torsion in gastropods and possible problems resulting from this adaptation?

Answer 11

Torsion = a phenomenon during development which moves and twists the visceral organs and mantle cavity to produce the typical gastropod asymmetry
occurs early in development
brought about by uneven growth of some muscles
results in asymmetry with the anus and the excretory pore positioned above the head
fouling - the curious arrangement that results from torsion poses a serious sanitation problem by creating the possibility of wastes being washed back over the gills
torsion may have some adaptive and selective advantages
consequences of coiling and resulting need to avoid fouling have been very important in the subsequent evolution of gastropods

Question 12

12. Briefly describe the two types of coiling in gastropods.

Answer 12

planospiral coiling - early gastropods were bilaterally symmetrical with shells coiled in whorls lying in one plane
weight distribution was a problem
conispiral coiling = better weight distribution was achieved by shifting the shell upward and posteriorly, in some the shell axis is oblique to the longitudinal axis of the foot
Coiling in most modern gastropods made possible a way to avoid the problem caused by torsion-fouling

Question 13

13.What advantages does the conispiral type of coiling have over planospiral coiling?

Answer 13

Better wieght distribution

Question 14

14.Name some gastropods that feed on other molluscs.

Answer 14

Oyster borer and the moon snail - have extensible proboscis for drilling holes in bivalves, feed on them

Question 15

15.Name and identify the three major groups of gastropods and give examples of each.

Answer 15

1. Prosobranchia – Contains most marine snails and some freshwater and terrestrial gastropods, examples: periwinkles, limpets, whelks, conchs, abalones, slipper shells, oyster borers, cowries
2. Opisthobranchs – nearly all marine, most are shallow-water forms, sea slugs, sea hares, sea butterflies and canoe shells
3. Pulmonata (pulmonates) - land and most freshwater snails and slugs

Question 16

16.What are some of the unique features of bivalves?

Answer 16

1. bivalved = 2-shelled, mussels, clams, scallops, oysters
2. most are filter feeders
3. shell - secreted by the mantle
4. mantle - edges form excurrent and incurrent siphons for regulating water flow
5. locomotion - muscular foot

Question 17

17.What are the glochidia and how are they dispersed from clams?

Answer 17

Bivalve larval stage- Clam can retain fertilized eggs in gills until they become larvea, they are released when they can swim
+progeny can move around find mates
+genetic variation

Question 18

18.Name some typical cephalopods, and list some features of these interesting animals

Answer 18

Cephalopods - “head-footed” molluscs\
most advanced molluscs, invertebrates
squids, octapuses, nautiluses, cuttlefishes
all marine, all active predators
earliest shells were straight cones
the shell
has gas chambers in nautiloids
siphuncle - cord of living tissue, connects chambers
living animal inhabits the last chamber
. locomotion:
force water through a funnel - “jet propulsion”
squids and cuttlefishes are good swimmers
nautilus - active at night
7. features:
octapods have 8 arms
squids and cuttlefishes (decapods) have 10 arms
. Color changes: chromotaphores - special pigment cells, produce color changes
9. Ink production: sepia - a dark pigment contains the pigment melanin
secreted by squids
“smokescreen” for protection
10. Reproduction in cephalopods
sexes are separate
sperm encased in spermatophores
during copulation one arm of the adult male takes a spermatophore from his own mantle cavity and inserts into the female mantle cavity near the opening of the oviduct
males often undergo color displays before mating
eggs are fertilized as they leave the oviduct, usually attached to stones or other objects , some octapods tend their eggs

Question 19

19.What enables communication in cephalopods?

Answer 19

Color changes and smokescreen

Question 20

20.Describe the three layers of the molluscan shell.

Answer 20

1) periostracum - outer, organic layer, made of conchiolin, a resistant protein,
function - protection
prismatic layer - middle layer, made of densely packed prisms of CaCO3 in a protein matrix, secreted by the glandular margin of the mantle
nacreous layer - inner layer, near mantle, secreted continuously, makes shell thicker

Question 21

How does an oyster make a pearl? How are these important to humans?

Answer 21

parasite or grain of sand gets covered with nacre between the mantle and shell- jewlry very rare expensive

Question 22

Calcium comes from?

Answer 22

environment- water, soil, and food

Question 23

Significance of coelom?

Answer 23

primarily serves as the hydrostatic skeleton maintains internal osmotic pressure.