Lab #7 - Phylum Mollusca & Introduction to ... - Biosciweb.net

Phylum Mollusca & Introduction to Digestive Systems 7.1
Lab #7 - Biological Sciences 102 – Animal Biology
The phylum Mollusca is second only to arthropods in the
number of identified species. This phylum consists of the
more than 90,000 living species of chitons, snails, slugs,
clams, oysters, squids, octopuses, cuttlefish, and others.
Molluscs have an extensive fossil record of more than 70, 000
fossilized species and an evolutionary history beginning
during the Precambrian Era. They occupy numerous
ecological niches and are found in the sea, fresh water, and
on land. They range from sedentary herbivores to fastswimming
predators.
Body Plan Features Retained by Molluscans
(seen in previously studied phyla):
‣ bilateral symmetry
‣ cephalization
‣ triploblastic structure
(endoderm, mesoderm and ectoderm)
‣ all organ systems are present
‣ a complete mouth-to-anus digestive system
Prosobranchia by Haeckel
Molluscs are the first group of animals we have studied that are eucoelomates, that is,
they possess a true coelom (body cavity with mesoderm lining all sides).
Molluscs are not metameric (not segmented). They most likely diverged from their common
ancestor with annelids before the advent of metamerism.
Body Plan Features Characteristic of Members of the Phylum Mollusca
1. a specialized, muscular foot, generally used in locomotion
2. a mantle or pallium (fold in the dorsal wall) that surrounds the mantle cavity and
secretes an exoskeleton, or shell
3. a mantle cavity, which usually contains the gills
4. most molluscs have a radula which is a unique rasping organ used for scraping off food
materials (bivalves do not possess a radula)
5. most molluscs have a well-developed head (except for the bivalves and scaphopods)
(many other invertebrate animals also have a well developed head)
6. an open circulatory system with a pumping heart
(many other invertebrate animals also have an open-circulatory system)
7. eucoelomate (as are many other phyla of animals)
A Whelk Shell A Chambered Nautilus Bivalves

Phylum Mollusca & Introduction to Digestive Systems 7.2
Lab #7 - Biological Sciences 102 – Animal Biology
Phylum Mollusca
Classification
Class Monoplacophora (mon'o-pla-kof'o-ra) (Gr. monos, one, + plax, plate, + phora, bearing).
Body bilaterally symmetrical, with broad, flat foot; a single, dome-shaped shell; three to six
pairs of gills in shallow mantle cavity; radula present; separate sexes. Example: Neopilina
Class Polyplacophora (pol'y-pla-kof' o-ra) (Gr. polys, many, + plax, plate, + phora, bearing).
Chitons. Elongated, dorsally flattened body with reduced head; bilaterally symmetrical; radula
present; shell of eight dorsal plates; foot broad and flat; gills multiple, along sides of body
between foot and mantle edge; sexes usually separate. Examples: Mopalia, Katharina
Class Scaphopoda (ska-fop'o-da) (Gr. skaphe, boat, + pous, podo: foot). Tusk shells. Body
enclosed in a one piece, tubular shell open at both ends; conical foot; mouth with radula and
tentacles; head absent; mantle for respiration; sexes separate. Example: Dentalium
Class Gastropoda (gas-trop' o-da) (Gr. gaster, belly, + pous, podos, foot). Snails,
slugs, conchs, whelks, and others. Body asymmetrical, usually in a coiled shell
(shell uncoiled or absent in some); head well developed, with radula; foot large and
flat; one or two gills or with mantle
modified into secondary gills or lung;
dioecious or monoecious.
Examples: Norrisia, Haliotis, Helix, Aplysia
Class Bivalvia (bi-val'vi-a) (L. bi, two, + valva, valve).
Bivalves. Body enclosed in a two-lobed mantle; shell of two lateral valves of variable size and
form, with dorsal hinge; cephalization much reduced; no radula; foot usually wedge-shaped;
gills platelike; sexes usually separate. Examples: Mytilus, Venus, Tagelus, Teredo
Class Cephalopoda (sef'a-lop'o-da) (Gr. kephale, head, + pous, podos,
foot). Squids, nautiloids, and octopuses. Shell often reduced or absent;
head well developed with eyes and radula; foot modified into arms or
tentacles; siphon present; sexes separate. Examples: Loligo, Octopus, Sepia
Class Aplacophora, Subclass Chaetodermomorpha Wormlike; shell, head, and excretory
organs absent; radula usually present; mantle with chitinous cuticle and calcareous scales;
oral pedal shield near anterior mouth; mantle cavity at posterior end with pair of gills; sexes
separate; formerly united with solenogasters in class Aplacophora. Examples: Chaetoderma,
Limifossor
Class Aplacophora, Subclass Neomeniomorpha Wormlike; shell, head, and excretory organs
absent; radula usually absent; rudimentary mantle usually covered with scales or spicules;
mantle cavity posterior, without true gills but sometimes with secondary respiratory
structures; foot represented by long, narrow, ventral pedal groove; hermaphroditic. Example:
Neomenia

Phylum Mollusca & Introduction to Digestive Systems 7.3
Lab #7 - Biological Sciences 102 – Animal Biology
LAB PROCEDURE
NAME:
LAB SCORE:
You must answer ALL questions in the lab procedure for full credit.
Finish them at home if you do not have time to complete them in lab.
Observation of Living Specimens
Class Polyplacophora (chitons)
‣ Observe the specimens and/or diagrams of the chiton, Mopalia muscosa or similar
species.
‣ Record the descriptive information requested at the end of the lab for this species.
Class Gastropoda (snails and slugs)
Subclass Prosobranchia (“sea snails”; nearly all marine)
‣ Observe the specimens and/or diagrams of the prosobranch gastropod,
Norrisia norrisi or similar species.
‣ Record the descriptive information requested at the end of the lab for this species.
Subclass Opisthobranchia (“sea slugs”; nearly all marine)
Order Anaspidea (sea hares)
‣ Observe the specimens and/or diagrams of the opisthobranch gastropod,
Aplysia californica.
‣ Record the descriptive information requested at the end of the lab for this species.
‣ On what organism(s) does the “Sea Hare” predominantly feed?
Subclass Opisthobranchia
Order Cephalaspidea
‣ Observe the specimens and/or diagrams of Navanax inermis.
‣ Record the descriptive information requested at the end of the lab for this species.
‣ On what organism(s) does this species predominantly feed?
Subclass Opisthobranchia
Order Nudibranchia (nudibranchs)
Dorid Nudibranchs – check recent taxonomy on www.itis.gov
‣ Observe the nudibranch specimens.
‣ Record the descriptive information requested at the end of the lab for one dorid
species.
‣ On what organism(s) does this species predominantly feed?

Phylum Mollusca & Introduction to Digestive Systems 7.4
Lab #7 - Biological Sciences 102 – Animal Biology
Subclass Opisthobranchia
Order Nudibranchia (nudibranchs)
Aeolid Nudibranchs - check recent taxonomy on www.itis.gov
‣ Observe the nudibranch specimens.
‣ Record the descriptive information requested at the end of the lab for one aeolid
species.
‣ On what organism(s) does this species predominantly feed?
‣ What defensive structures are housed within the dorsal cerata and how are these
structures acquired by the nudibranch?
Class Gastropoda
(Previously Subclass Pulmonata) - mostly terrestrial and freshwater
- check recent taxonomy on www.itis.gov -
‣ Observe the garden snail specimens.
‣ Record the descriptive information requested at the end of the lab for this species.
Class Bivalvia
‣ Observe the mussel, Mytilus californianus specimen.
‣ Record the descriptive information requested at the end of the lab for this species.
Class Cephalopoda
‣ Observe the Octopus bimaculoides or similar octopus specimen.
‣ Record the descriptive information requested at the end of the lab for this species.
EXAMINATION OF A MOLLUSCAN RADULA
Note the radula from the chiton, Cryptochiton stelleri on display at the front of the
room. This species, found off the west coast of North America, is the world’s largest, reaching
a maximum size of over 30 cm in length. Note the size and shape of the radular teeth, which
are easily visible with the naked eye.
‣ Compare and contrast the characteristic features of a radula obtained from a carnivorous
snail verses that from an herbivorous species using the available microscope slides.
Sketch/diagram the major differences in tooth structure, quantity and general
arrangement on the next page.

Phylum Mollusca & Introduction to Digestive Systems 7.5
Lab #7 - Biological Sciences 102 – Animal Biology
CARNIVORUS SNAIL RADULA SKETCH
Indicate species:
HERBIVOROUS SNAIL RADULA SKETCH
Indicate species:
STUDY OF A BIVALVE: THE CALIFORNIA MUSSEL
‣ Examine the specimens of the California Ribbed Mussel, Mytilus californianus and the
Bay Mussel, Mytilus galloprovincialis or edulis.
Mytilus californianus
Mytilus galloprovincialis or edulis
Briefly
describe some
general
differences in
their
appearance or
texture?
What is the
habitat for
each of these
species and
geographically,
where are they
found?
(look this up
on the
internet)

Phylum Mollusca & Introduction to Digestive Systems 7.6
Lab #7 - Biological Sciences 102 – Animal Biology
DISSECTIONS
Class Gastropoda
Halitois sp. (Abalone)
‣ Refer to Genny Anderson’s (SBCC) Marine Science Website for details on Abalone
including their anatomy (see the abalone introduction) at:
http://www.marinebio.net/marinescience/06future/abindex.htm
‣ Observe the specimens and/or diagrams of the prosobranch gastropod, Haliotis sp.
‣ Record the descriptive information requested at the end of the lab for this species.
‣ Examine the dissected abalone and identify the structures listed below.
Instructor Demonstration
Given the endangered status of abalone we will dissect one
cultured abalone per lab which was not caught in the wild,
but raised for food. Given the expense of abalone, your
instructor will dissect one abalone noting its important
external and internal structures including:
‣ shell
‣ apex
‣ torsion
‣ periostracum
‣ nacre (nacreous layer)
‣ head
‣ foot
‣ lobed epipodium
‣ epipodial tentacles
‣ mantle
‣ mantle cavity
‣ gonad
‣ heart
‣ radula
‣ Briefly describe and/or draw a sketch to show the direction of current flow
through this snail.
‣ Does this species have an operculum?
‣ Is this species dextral (“right handed”) or sinistral (“left handed”)?

Phylum Mollusca & Introduction to Digestive Systems 7.7
Lab #7 - Biological Sciences 102 – Animal Biology
DISSECTIONS
Class Bivalvia
If available, observe the various Tridacna spp. (Giant Clams) on display. This genus
includes the world’s largest bivalve, Tridacna gigas, which can grow to over one meter in length
as an adult. These species are restricted to the tropical Indo-Pacific and have a well developed
mutualistic relationship with their algal endosymbionts similar to that seen in many
hermatypic coral species.
Mytilus californianus (California Mussel)
1. As per the directions given by your instructor, obtain
1 mussel for each 2 or 3 students to dissect.
2. Obtain a dissecting tray and dissecting supplies from the
dissecting cart.
3. Examine the external anatomy of the California Mussel and
identify the following external structures:
‣ growth lines
‣ umbo
‣ excurrent siphon
‣ byssal threads
4. Using a knife, CAREFULLY (so as not to cut your hand!) open the mussel, examine the
internal anatomy and identify the following structures:
‣ foot
‣ mantle
‣ byssal gland (at base of
‣ labial palps
byssal threads)
‣ anterior adductor muscles
‣ gonads
‣ posterior adductor muscles
‣ gills
‣ shell
‣ retractor muscles
‣ Briefly describe and/or draw a simple diagram to show the direction of current flow
through this mussel.
‣ Briefly describe how a mussel gets food into its digestive tract.
Your instructor will be coming around to each dissection group to assist you and ask you
to identify the structures listed in preparation for the invertebrate lab practical.
5. Dispose of the mussel in the container provided.
6. Rinse your dissecting tray and clean your dissecting supplies and return them.

Phylum Mollusca & Introduction to Digestive Systems 7.8
Lab #7 - Biological Sciences 102 – Animal Biology
DISSECTIONS
Class Cephalopoda
Loligo sp. (Squid)
External Anatomy
1. As per the directions given by your instructor,
obtain 1 frozen squid for each 2 students
to dissect.
2. Obtain a clean dissecting tray and dissecting
supplies.
3. Examine the external anatomy of the squid
and identify the following external structures:
‣ mantle
‣ tentacles – how many tentacles does the squid have?
‣ arms – how many arms does the squid have?
‣ lateral fins
‣ mantle
‣ mantle collar
‣ eye
‣ funnel (siphon)
‣ mouth (within circle of arms)
‣ beak (probe inside the mouth to find it)
‣ chromatophores (pigment cells that cause mottling of skin)
Note that squid are “head-footed” because the end which bears the tentacles is homologous to
the ventral side of the clam and the tentacles are a modification of the foot.
The arms of male squid are longer and thicker than those of females. In mature male squid,
the left fourth arm becomes modified for the transfer of spermatophores to a female. On the
fourth arm some of the suckers are smaller and form an adhesion area for holding the
spermatophore.
The funnel (siphon) of the squid is not homologous to the siphon of a clam; the clam siphon is
a modification of the mantle, whereas the squid siphon is a modification of the foot.
‣ Briefly describe and/or draw a simple diagram to show the direction of current flow
through the squid.

Phylum Mollusca & Introduction to Digestive Systems 7.9
Lab #7 - Biological Sciences 102 – Animal Biology
DISSECTIONS
Class Cephalopoda
Loligo sp. (Squid)
Internal Anatomy
4. Obtain a pair of small sharp scissors. Beginning near the funnel, make a longitudinal
incision through the mantle from the collar to the tip. Gently remove any connective
tissue between the mantle and internal structures and pin the mantle down.
5. Examine the internal anatomy of the squid and identify the following internal structures:
(covering the specimen with water will often help visual structures):
‣ mantle cavity (space between the mantle and the visceral mass)
‣ pallial cartilages (if visible; these support the funnel and close space between the neck
and mantle so that water can be expelled out the funnel)
‣ funnel retractor muscles (paired with larger head retractor muscles beneath)
‣ ink sac (do not puncture this – it will make a mess of your dissection)
‣ gills (paired and long)
‣ pen (your instructor will demonstrate the removal of one from one squid)
The structures listed below may be difficult to find and you may not identify all of
them in your particular specimen. However, if someone in class has a particularly
good representative example, please point it out to your instructor so that other
members of the class may view it. Review the available diagrams.
‣ nidamental glands (if visible; only in females)
‣ spermatophoric gland and vas deferens (if visible; only in males)
‣ heart
‣ kidneys (if visible)
‣ esophagus (tube running from the mouth/beak)
‣ liver (if visible)
‣ stomach (if visible)
‣ cecum & intestine
‣ rectum & anus (near the inner opening of the funnel)
‣ stellate ganglia (in the head; if visible)
6. Dispose of the squid in the container provided.
7. Rinse your dissecting tray and clean your dissecting supplies and return them.
Your instructor will be coming around to each dissection group to assist you and ask you
to identify the structures listed in preparation for the invertebrate lab practical.

Phylum Mollusca & Introduction to Digestive Systems 7.10
Lab #7 - Biological Sciences 102 – Animal Biology
Living Specimens Data
Class Polyplacophora
Scientific name: Mopalia muscosa or similar species =
Common name:
Number of shell plates:
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Prosobranchia
Scientific name: Norissia norrisi or similar species =
Common name:
Foot Color:
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Prosobranchia
Scientific name: Haliotis sp.
Common name:
Foot Color:
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.11
Lab #7 - Biological Sciences 102 – Animal Biology
Class Gastropoda
Subclass Prosobranchia
Scientific name:
Common name:
Foot Color:
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Prosobranchia
Scientific name:
Common name:
Foot Color:
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Prosobranchia
Scientific name:
Common name:
Foot Color:
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.12
Lab #7 - Biological Sciences 102 – Animal Biology
Class Gastropoda
Subclass Opisthobranchia
Order Anaspidea
Scientific name: Aplysia californica
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Opisthobranchia
Order Cephalaspidea
Scientific name: Navanax inermis or similar species =
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.13
Lab #7 - Biological Sciences 102 – Animal Biology
Class Gastropoda
Subclass Opisthobranchia
Order Nudibranchia
What is the Suborder or Infraorder for dorid
nudibranchs? (from www.itis.gov):
Scientific name:
Common name:
Body color:
Color of rhinopores:
External gills present?
Cerata present?
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Opisthobranchia
Order Nudibranchia
What is a Family for dorid nudibranchs?
(from www.itis.gov):
Scientific name:
Common name:
Body color:
Color of rhinopores:
External gills present?
Cerata present?
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.14
Lab #7 - Biological Sciences 102 – Animal Biology
Class Gastropoda
Subclass Opisthobranchia
Order Nudibranchia
What is the Suborder or Infraorder for aeolid nudibranchs?
(from www.itis.gov):
Scientific name:
Common name:
Body color:
Color of rhinopores:
External gills present?
Cerata present?
Notes & observations to help you remember and distinguish this group/species:
Class Gastropoda
Subclass Opisthobranchia
Order Nudibranchia
What is a Family for aeolid nudibranchs?
(from www.itis.gov):
Scientific name:
Common name:
Body color:
Color of rhinopores:
External gills present?
Cerata present?
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.15
Lab #7 - Biological Sciences 102 – Animal Biology
Class Gastropoda
What is the Suborder, Infraorder or Family for
garden snails? (from www.itis.gov):
Scientific name:
Common name:
Shell color:
How does this animal obtain oxygen for cell respiration (breathe)?
Notes & observations to help you remember and distinguish this group/species:
Class Bivalvia
Scientific name: Mytilus californianus
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:
Class Bivalvia – any other example
Scientific name:
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.16
Lab #7 - Biological Sciences 102 – Animal Biology
Class Bivalvia – any third different example
Scientific name:
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:
Class Cephalopoda
Scientific name: Octopus bimaculoides or similar species =
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:
Class Cephalopoda – another example that is not an octopus
Scientific name:
Common name:
Color:
Notes & observations to help you remember and distinguish this group/species:

Phylum Mollusca & Introduction to Digestive Systems 7.17
Lab #7 - Biological Sciences 102 – Animal Biology
Homework – Answer the following questions using the internet:
Ammonitida by Haeckel
Ammonites are extinct molluscs that first
appeared 415 million years ago in the form
of a small, straight shelled creature, known
as Bacrites. They quickly evolved into a
variety of shapes and sizes including some
shaped like hairpins. During their evolution
the ammonites faced no less than three
catastrophic events that would eventually
lead to their extinction. The first event
occurred during the Permian (250 million
years ago), where only 10% of ammonite
species survived. These surviving species
went on to flourish throughout the Triassic,
however at the end of this period (206
million years ago) they faced near extinction,
when all but one species survived. This event marked the end of the Triassic and the beginning
of the Jurassic, during which time the number of ammonite species grew once more. The final
catastrophe occurred at the end of the Cretaceous period when all species were annihilated
and the ammonites became extinct. This event coincided with the death of the dinosaurs.
Ammonites are excellent index fossils.
‣ What is an index fossil?
‣ To what class in the phylum Mollusca do ammonites belong?
‣ Briefly describe and/or draw a simple flow chart to show the lifecycle of an oyster or
other bivalve? Be sure to include the names of specific larval stages such as the
trochophore larvae. There is another larval stage involved in the lifecycle.

Phylum Mollusca & Introduction to Digestive Systems 7.18
Lab #7 - Biological Sciences 102 – Animal Biology
‣ Briefly describe and/or draw a simple flow chart to show the lifecycle of any gastropod
snail? Be sure to include the names of specific larval stages such as the trochophore
larvae. There is another larval stage involved in the lifecycle in addition to the trochophore.
What is the name of this second larval stage?
‣ Briefly describe and/or draw a simple flow chart to show the lifecycle of an octopus or
other cephalopod? Do octopi have a larval stage?
‣ List the molluscan classes that contain animals that can be hermaphroditic
(monoecious).

Phylum Mollusca & Introduction to Digestive Systems 7.19
Lab #7 - Biological Sciences 102 – Animal Biology
LABORATORY NOTES:
COPY THE FLOWCHART DIAGRAM OF A GENERALIZED ANIMAL DIGESTIVE SYSTEM
FROM THE BOARD BELOW

Phylum Mollusca & Introduction to Digestive Systems 7.20
Lab #7 - Biological Sciences 102 – Animal Biology
LABORATORY NOTES:
A Keyhole Limpet
- limpets are prosobranchs –