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Mollusca
Bio 1413: General Zoology Lab
(Ziser, 2008)
Exercise 11 (p 171)
Identifying Characteristics of Phylum:
-triploblastic with true coelom
-bilateral symmetry; some with secondary assymetry
-soft, usually unsegmented body consisting of anterior head, ventral foot and dorsal
visceral mass
-body usually enclosed by thin fleshy mantle
-mantle usually secretes hard external shell
-complete digestive tract, many with a radula; a rasping or scraping feeding organ
-respiratory system consists of gills in aquatic forms or "lung"-like chamber in terrestrial forms
-most with open circulatory system; body cavity (coelom) a haemocoel
-marine forms with characteristic trochophore larva
Cell Types and Characteristic Structures:
-shell consists of three layers, from outside - in, periostracum, prismatic layer
and nacreous layer
-characteristic trochophore larva
- distinctive radula used as main feeding tool in most groups
Body Organization:
-body usually consists of anterior head with radula, ventral muscular foot and dorsal visceral
mass containing most internal organs,and gills
-almost all molluscs have the basic molluscan features; shell, mantle, foot, gills, radula and head
but they have been variously modified in each class
Classification:
Class:
Class:
Class:
Class:
Class:
Class:
Class:
Class:
Monoplacophora
Caudofoveata
Solenogastres
Polyplacophora (Chitons)
Scaphapoda (Tusk Shells or Tooth Shells)
Bivalvia (Clams)
Gastropoda (Snails)
Cephalopoda (Octopi and Squid)
Lab Activities:
1. Read description and discussion of molluscs in the lab manual
beginning on page 169
2. The Freshwater Clam, Class Bivalvia (p 172)
-external structure (p173): know: hinge, umbo,
growth lines
preserved: clam
3. The Mollusc Shell (p 175)
preserved: clam shells
-know and distinguish between: periostracum, prismatic
layer, nacreous layer
4. Clam, internal structure (p173): know: anterior and posterior
adductor, pallial line, teeth, mantle, incurrent &
excurrent siphons, aperture (siphons),
pericardium, visceral mass, foot, gills,
labial palps
5. Bivalve Gills (p 175)
-note structures in preserved clam as assigned
-make wet mount of transverse section if time permits
slide: mussel gills, cs
6. Bivalve Reproduction (p179)
slides: mussel glochidia,
-note structures in preserved clam as assigned
wm
-be able to recognize a marsupium or brood chamber,
Patella trochophore
if present in any preserved clams
-make a wet mount of gonadal tissue and determine whether
eggs or sperm are present
-recognize the glochidia larva of freshwater clams
-be able to recognize a trochophore larva from slide
7. Dissection of Oyster (if available; see handout)
know: shell, adductor muscle, gills, mantle, mouth,
anus, palpus, intestine, pericardium, heart
8. Class Gastropoda (Ex 11B):
a. Pulmonate Land Snail, Helix (p180)
-note structures and behaviors as described if live
specimens are available
-surface anatomy: know: shell, apex, growth lines,
head, foot, tentacles, eyes, mouth
b. Slug, Limax
-use fig 11-9 to find: eyes, tentacles, mantle,
pneumostome
9. Radula (p181)
-recognize radula as characteristic molluscan feeding
structure
fresh(if available):oyster
preserved: Helix
preserved: Limax
slide: snail radula wm
10. A Squid: Loligo; Class Cephalopoda Ex 11D; (p184)
preserved: squid
a. External anatomy (p 184)
fresh(if available): squid
-know: head, arms, fins, mantle, eyes, suckers,
tentacles, mouth, funnel, beak
-be able to distinguish between the male and female and
know associated structures
b. Internal Anatomy (p 186)
-know: mantle cavity, gills, hearts, ovaries, testes,
ink sac, stomach, cecum with spiral valve,
pen
-which structures are easier to see in the fresh squid (if available)?
In the preserved squid?
11. Chiton Ex 11C (p 183)
-know: mantle, girdle, head, mouth, gills, foot
shell plates
preserved: Katharina
Demonstrations:
• Mollusc anatomy: use the additional figures to help identify the anatomical
features you are responsible for.
• Diversity of Molluscs: be able to recognize the classes of each of the figures,
preserved and fresh specimens and shells available
Notebook Suggestions:
 Observe and describe the movement, feeding and behaviors of living
representatives as available
 Make a table indicating how the basic molluscan anatomical features vary among the different
classes