1. Diagram and discuss the schizocoel and
enterocoel hypotheses of coelom development.
2. Define the terms protostome and deuterostome.
Discuss the differences between the two forms of development.
3. Summarize the evidence which places the
mollusks where they are in relationship to the annelids on the phylogenetic
tree.
4. Compare the size and diversity of the Phylum
Mollusca with other phyla.
5. List the seven classes of mollusks, give
any common names for each class, and representatives of each class.
6. List and briefly describe the molluscan
characteristics of shell, mantle, radula and foot in each of the seven classes.
7. Diagram and describe the three layers of
a typical molluscan shell.
8. Describe the formation of a pearl.
9. Use the variation within the mollusks to
illustrate what is meant by adaptive radiation, and relate the success of
the mollusks in adaptive radiation to the new phylum characteristics and
the conditions at the time the phylum evolved.
10. Compare the mollusk circulatory system
and oxygen-combining pigment with those of earlier phyla.
11. Detail the benefits that mollusks provide
man, particularly the economic benefits. Contrast the economic benefits
of this group with the economic impacts of the previous groups discussed
in this class.
12. Describe gastropod torsion and the conditions
that result from this process.
13. Define operculum and radula.
14. Describe coiling in gastropods. Identify
the differences between conispiral and planospiral coiling.
15. List characteristics of the three subclasses
of gastropods, the Prosobranchia, the Pulmonata and the Opisthobranchia.
16. Outline the life cycle of a typical freshwater
clam.
17. Briefly describe the anatomy and functioning
of the respiratory system, digestive system, circulatory system, excretory
system and reproductive system of the clam.
18. Describe the foot in each class, and the
general arrangement of the digestive tract.
19. Name the unique organ in the mollusk mouth
which is used for feeding.
20. Detail the role of the crystalline style
in the digestive system of a clam. Trace the route of a food particle through
the digestive system of a clam starting with entry into the clam and ending
with exiting of waste.
21. Briefly describe the method of movement,
activities in general and the feeding method of members of each class.
22. Summarize the ways in which cephalopods
are more complex than the other kinds of mollusks.
23. Compare the circulatory system of the cephalopods
to that of the bivalves and higher organisms such as chordates.
24. Describe the unique features of reproduction
in the cephalopods.
Resources: Text: Animal Diversity, Chapter
10
Internet Resources:
http://www.austmus.gov.au/
http://www.mhhe.com/hickmanad4e
Eucoelomata
Coelom- mesentaries, mesodermal lining (peritoneum)
Advances/Problems so far.
Advances Problems
multicellular internal
transport
specialization respiration
diplo and triplo waste
removal
circulatory system nutrient
transfer
(Nemertea)
protonephridia
branching gut
Eucoelomates: 1. peritoneum,
ciliated
2. body
wall, visceral wall
3. blood
vessels in mesentaries
4. excretory
system and gonadoducts held in place
How coelomates are formed today.
1. Schizocoelomates- annelids,
arthropods, mollusca
-coelom appears as a space in mesoderm
2. Enterocoelomate- echinoderms,
chordates
-coelom appears as pockets of gut
Phylum Mollusca
-second only to Arthropoda in named
species (50,000 living; 35,000 extinct)
Classes
Monoplacophora- one plate,
Neopilina, thought to be extinct
Polyplacophora- many plates (8), chitons Tonicella
***Gastropoda- belly foot; snails, nudibranchs
***Bivalvia- (Pelecypoda) two doors; clams, oysters, mussel/Mytilus
***Cephalopoda- head foot; squid,
octopus (Loligo)
GENERAL FEATURES OF MOLLUSKS:
Mantle- -"skin" surrounding
visceral mass
-outer surface secretes
shell
-houses respiratory organs (gills in aquatic, lungs in terr.
-into cavity is
dumped products from digestive, excretory,
reproductive
systems
-water currents bring
food, flush water (bivalves)
-adapted for swimming
in cephalopods
Foot- -major characteristic
used for classification
-adapted for locomotion/attachment
-usually ventral, broad, flat, muscular
Radula- (absent in bivalves)
-rasping tongue
-teeth backwards
on conveyor belt, scrape food into mouth/pharynx
Shell- -bivalve (clam,
univalve (snail), 8 plates in chitons, rod (pen) in
squid; divided
in Nautilus, absent in slugs and nudibranchs
3 Layers
Periostracum- outer
layer, protects against erosion and boring animals,
secreted by mantle only
at outer edge. UMBO oldest part of shell.
Prismatic layer- calcium carbonate, thick, secreted by mantle at outer edges
Nacreous layer-
calcium carbonate in thin sheets, secreted continuously
by mantle surface, grows
w/animal. Responsible for pearl formation.
ALL BODY SYSTEMS PRESENT!!
Respiratory- diffusion still occurs
(through mantle) but specialized gills, lungs
present (derived from mantle)
Circulatory- pumping heart, vessels
and sinuses; open system in all but cephalopods;
Hemocyanin- "blood"- oxygen
combining pigment, contains
copper ---> bluish when
combined w/O2
Digestive- complete and complex
Excretory- 2 kidneys (nephridia) empty into mantle cavity
Nervous- ganglia and connecting nerve cord; specialized eye in ceph.
Reproductive- most dioecious, some gastropods monoecious
HUMAN IMPORTANCE (economic benefit
rather than liability)
-food source; pearls
-damage to warves; snails/slugs damage
greens; parasite host
Class Gastropoda
most successful class ~35,000 living
(named): marine, freshwater,
terrestrial (snails/slugs)
-bilaterally symmetric, basically,
However. . . .very early and abruptly in
larval (veliger) stage TORSION
occurs
*twisting of internal organs
at least 180o because of uneven development
of right and left muscles that
attach the head/foot complex to shell
*outcomes of torsion:
-head can be withdrawn into
shell; OPERCULUM
-right becomes left and visa
versa
-anus is moved anterior and
dorsal
-reduces visceral volume
-foot large, ventral, (slugs-
slime trail aids movement)
-head well developed w/eyes,
sensory tentacles and a RADULA
-respiration by gills except
for terrestrial, due to torsion usually only one
gill present
*pulmonate snails hava a
lung, mantle cavity functions in this capacity by
trapping air in pneumostome.
-because of torsion, usually only one auricle, one nephridia
-both mono & dioecious,
insemination often preceeded by courtship; sperm
exchanged using spermatophores
, self fertilization is avoided.
COILING (not torsion), winding
of shell
primitive- planospiral, coiling
in one plane, not compact
conispiral
, shell tapers, more compact but unbalanced. Shell axis
perpendicular
to foot axis.
shell eventually shifted up and back w/ shell axis not perp (or parallel) to axis of foot.
-weight pressed on right side
effectively reducing organs on that side leading to
bilateral asymmetry.
THREE SUBCLASSES:
Prosobranchia
Pulmonata Opisthobranchia
-largest group
-land and freshwater -undergo detorsion
-anus remains forward -lack
gills, mantle -gills and anus
cavity acts as lung return to posterior
-aquatic 1pr of still only have one
tentacles gill, one nephridia
-terrestrial 2pr of -nudibranch no shell
tentacles -naked gill
-use nematocysts
from cnidarians for
defense
Class Bivalvia (Pelecypoda = hatchet foot) `20,000 named
-2 lateral shells (valves), hinged dorsally
-foot typically bladelike, adapted for burrowing,
operated by muscles working against
hydrostatic pressure of blood within
the hemocoel.
(exceptions: Mytilus is sessile,
attaches to substrate, oysters secrete cement,
scallops capable of swimming)
-mantle modified posterior to incurrent
& excurrent siphons, control flow of water into shell
-filter feeders: mucus on ciliated gill,
grooves, palps seperate particles
-basis for classification: hinge teeth, adductor muscles, gills
-digestion in stomach, long style sac
containing a crystaline style composed of
solidified mucus and enzymes
*style rotated, reels in food laden
mucus, style projects into stomach where it is
worn away liberating digestive
enzymes.
*stomach contains ciliated sorting
area, large particles to intestine, smaller to
digestive gland
-dorsal heart pumps blood from gills
(oxygenated) out to anterior and to kidney for
waste removal.
-ganglia, 3prs.
-sense organs include eyes (scallops) w/
cornea, lens and retina
*many bivalves have a gravity sensing
statocyst embedded in foot
-most bivalves dioecious, gametes shed externally through excurrent
*freshwater fert. internal, larva
develop into glochidium that becomes parasitic
on gills of fish until it can
resist being washed away
*marine embryo have three free swimming
stages; trochophore, veliger,
spat ---> adult
Class Cephalopods (head foot) squid,
octopus, Nautilus
foot becomes siphon (funnel) ~650
living species
-highly mobile and most advanced
invertebrate
-giant squid up to 16m in length.
delicacies for sperm whale which usually
bear scars ~25cm in diameter
inflicted by sucker that has a chitinous claw.
SHELL
-present in Nautiloids- series of
gas chambers allow bouyancy septa divide
chambers (diff from gastro)
animal inhibits newest chamber, all others
connected by siphuncle
-reduced to chitinous pen in squid,
absent in octopus
HEAD
-mouth ringed with tentacles (90+
in Nautilus, 8 in octopus, 10 in squid)
-mouth equipped w/ chitinous beak and radula, saliva more or less venomous
-eyes large and closely resemble
vertebrate eyes even to the extent of being
able to adjust pupil and change
focal length
-movement by jet propulsion, siphon
directs, octopus crawls
-water movement multipurpose
(waste expulsion, oxygenate, locomotion,
gamete expulsion)
-brain highly developed w/millions
of nerve cells, one lobe of brain dedicated entirely
to bringing about color changes.
CHROMATOPHORES are pigment
sacs, expanding or contracting changes color,
defensive or behavioral w/ courtship
All cephalopods are predacious
DIGESTION
-Y shaped tract, large ceacum
(cecum) occupying apex of Y, mouth and anus
located anterior
-digestion extracellular in stomach; enzymes secreted by "pancreas" and "liver"
-cecum folded and sorts out indigestible particles for elimination
CIRCULATORY SYSTEM
-closed system w/3 hearts
-median systemic heart pumps
blood through body through arteries into capillary
beds, vein delivers deoxygenated
blood to pair of branchial hearts at base of
each gill
-hemocyanin respiratory pigment
RESPIRATORY SYSTEM
-gills not ciliated, therefore,
cannot create currents
-mantle muscle contraction draws water in and out
REPRODUCTION
-most dioecious
-mating preceeded by courtship
-sperm packaged into bundles (
spermatophores) and stored
-during mating male transfers
spermatophores w/ hectocotylized arm to edge of
females mantle or directly into
genital duct
-eggs fertilized as they leave
oviduct and attach to fixed surface to develop
(octopus tends eggs)