LAB # 4-A (Supplement)

(Written and provided by Dr. Olson, Professor Emeritus)

PHYLUM: MOLLUSCA ("molluscs")

LAB. MAN.: EXERCISE #11-A; Pages 169-178

TEXT: CHAPTER #16; Pages 325-354

Evidence suggests molluscs (MOLLUSCA) evolved from a flatworm (PLATYHELMINTHES) ancestor and are closely related to both the segmented worms (ANNELIDA) and the arthropods (ARTHROPODA). Although molluscs originated in the sea, today’s species exhibit great diversity and occur in marine, freshwater, and terrestrial habitats. The scientific study of molluscs is known as malacology.


1. The phylum Mollusca is quite large and ranks second to arthropods in number of known species. Molluscs have retained most of the "advances" introduced in earlier phyla including: organ-system level, bilateral symmetry, triploblastic, and cephalization.

2. Molluscs are the first to possess a eucoelom (or, true body cavity) which, unlike a pseudocoel, has a lining of mesodermal peritoneum. Eucoelom "advantages" include:

a. Source of mesenteries which support or suspend body organs.

b. Provides space for organ/system development.

c. Fluid in coelom acts as a hydrostatic (liquid) skeleton for body support.

d. Fluid in coelom aids transport/circulation of nutrients and metabolic wastes.

3. The "typical" mollusc features the following major body structures (each of which may be variously modified within a particular class):

a. Visceral Mass (visceral hump)

-The main body mass or grouping of body organs.

b. Head

-Extends anteriorly from the visceral mass.

-Is the main sensory and food intake body area and, in most, features a rasping tongue-like, feeding structure called the radula.

c. Foot

-Usually extends ventrally from the visceral mass.

-Its functions may include locomotion, attachment, and/or food capture.

d. Mantle (pallium)

-A fleshy sheath of tissue that typically covers the visceral mass on all sides and encloses the mantle cavity (space between mantle and visceral mass) which houses the respiratory organs (gills or lung).

-Important mantle functions include:

(1) Protection of visceral mass.

(2) Secretion of shell.

(3) Formatin of siphons (water in/out openings).

(4) Water circulation within the mantle cavity.

(5) Formation of gills, or lung.

(6) Sensory ("reads" water chem.)

e. Shell

-Present and well-developed in most, but is greatly reduced or absent in some.

-Is secreted by the mantle and may be double (in bivalves) or single (in univalves).

-The 3 main shell layers include: (1) Periostracum (outer), (2) Prismatic (middle), and (3) Nacreous (inner) made of many thin layers of calcium carbonate and commonly called "mother of pearl".

GENERAL MOLLUSCA TAXONOMY (condensed for this lab)


CLASS: POLYPLACOPHORA ("many plate bearing")

-Commonly called the "chitons" and are marine, intertidal, and attached to rocks.

Head: Greatly reduced; Tongue-like radula extended to scrape algae off rocks.

Foot: Broad and muscular; Used for attachment to, or creeping over, rocks.

Mantle: Thick/fleshy; Lies under shell valves or may completely surround them.

Shell: Composed of 8 overlapping valves (basis for class name).

CLASS: SCAPHOPODA ("boat foot")

-Commonly called the "tooth shells" or "tusk shells" and are marine, intertidal, and found partially burrowed into sand or mud bottom in shallow water.

Head: Modified into feeding tentacles; Radula present.

Foot: Extends from larger end of shell; Is used for burrowing and generally resembles a ship’s keel (basis for class name).

Mantle:Wraps around visceral mass forming a tube; Circulates water and handles all gas exchange (are no gills in these small aquatic molluscs).

Shell: 1-piece (univalve); Tooth or tusk-shaped; Open at both ends.

CLASS: GASTROPODA ("stomach foot")

-Commonly called the "snails", "slugs", etc.

-Is the largest, most-successful, and most-diverse class of molluscs! Most species are marine, but some are freshwater, and a few are terrestrial.

-Their bilateral larva undergoes torsion (twisting of body within shell) to become an asymmetrical adult. Torsion "advantages include: (1) Makes room for retraction of head, (2) Improves respiration (gills/lung moved to front).

Head: Well-developed with tentacles and eyes usually present; Radula present and variously modified for different food habits within the class.

Foot: Large and muscular; For creeping or attachment.

Mantle:Covers visceral mass under the shell; Encloses the mantle cavity, forms the gills (aquatics) or is modified to form a lung (land snails and slugs).

Shell: Present in most and is of 1-piece (univalve) and coiled; Is reduced in slugs and absent in nudibranchs (sea slugs) and in sea hares.

CLASS: BIVALVIA ("2 valves")

-Includes the "clams" and "oysters"; Most are marine, but some are freshwater; Most have either a burrowing, or a sedentary, lifestyle.

Head: Absent; No radula (only molluscs without one); All are "filter feeders".

Foot: Large and muscular; Extended anteriorly for burrowing into soft substrate.

Mantle:Covers visceral mass as a "thin curtain"; Forms siphons (incurrent and excurrent); Forms pearls (esp. in certain oyster species).

Shell: Clams and oysters possess 2 hinged valves (basis for class name) held together by anterior and posterior adductor muscles.

CLASS: CEPHALOPODA ("head foot")

-Includes the "squid", "octupus", "nautilus", and "cuttlefish". Are considered to be the "most-advanced molluscs" and are all active, marine predators.

Head: Especially-well developed; Modified to form long tentacles and arms; The radula is beak or jaw-like; Eyes are advanced in structure (like vert. eyes).

Foot: Found in head region; Modified into a siphon for "water-jet propulsion".

Mantle:Thick and muscular; Covers entire body and encloses shell in some.

Shell: Well-developed in nautilus; Absent in octopus; Reduced in squid (pen) and cuttlefish (cuttlebone).


1. "Freshwater Clam/mussel" (Anodonta)



How does this organism move?

Do clams/mussels and other "bivalves" possess a radula? How do they feed?

What is the correct name for the larval stage of the freshwater clam? (See page 177)

How does this larval form become widely distributed in a stream, lake, or pond?

**Examine the external structure of a preserved clam and know the structures/terms found in heavy print on page 171 of your laboratory manual.

**Complete a dissection of a freshwater clam BY READING AND FOLLOWING DIRECTIONS FOUND IN LAB MANUAL starting on page 171 (right column).

*Know the structures/terms found in heavy print on pages 171-177 of your laboratory manual. Also, study Figures 11-2, 11-3, and 11-5.

*Observe demonstration slide of a glochidium larva stage of the freshwater clam.

2. "Other Molluscs"

*Briefly "tour" and observe the preserved demonstration specimens representing the major molluscan classes (at back of room). As you view members of each class, note the presence/absence and the appearance/location of the "key mollusc features" (i.e. head, foot, etc.) itemized under each class name in this handout.



LAB # 4-B (Supplement)

(Written and provided by Dr. Olson, Professor Emeritus)

PHYLUM: ANNELIDA ("segmented worms")

LAB. MAN.: EXERCISE #12-A,B C; Pages 187-199

TEXT: CHAPTER # 17; Pages 356-374

Members of the phylum ANNELIDA are commonly called the "segmented worms" and are considered close relatives of both molluscs (MOLLUSCA) and arthropods (ARTHROPODA). All 3 of these phyla likely evolved from a common flatworm (PLATYHLEMINTHES) ancestor.


1. Despite their somewhat primitive, worm-like appearance, annelids are quite advanced in body design (organ-system level; bilateral symmetry; triploblastic; eucoelomate).

2. The phylum Annelida’s major contribution to animal evolution is metamerism (division of the body into true segments). The significance of metamerism is that it:

a. Favors specialization of individual segments ("division of labor") for better efficiency.

b. Improves locomotion by permitting better control of localized body areas.

c. Allows fluid in the coelom to act as a hydrostatic (liquid) skeleton.

Note: In annelids, individual body segments are set apart externally by grooves called annuli, and internally by thin mesoderm partitions called septa.

3. Distinctive Body Features:

a. Digestive System:

-Is complete (with mouth, intestine, anus). The intestine features a dorsal, longitudinal fold called the typhlosole which greatly increases surface area for digestion efficiency.

-As in the pseudocoelomates (like Ascaris), there is no muscle in the gut wall so there is no peristalsis activity.

b. Excretory System:

-Most annelid body segments possess paired kidney units called nephridia. Metabolic wastes in the coelom enter each nephridium through a ciliated nephrostome and exit through a lateral external pore called the nephridiopore.

c. Circulatory System:

-Have a "closed" system (blood remains within "tubing" at all times) with a dorsal vessel, paired aortic arches, and ventral vessel.

d. Reproductive System:

-Most annelids are monoecious. However, marine annelids are dioecious.

-Non-marine annelids feature a clitellum which produces cocoons for eggs. In some the clitellum is permanent and in others only temporary.

Page 2 ("segmented worms")

e. Miscellaneous:

-Most annelids (except leeches) possess chitinous, lateral projections called setae. These may be short and relatively sparse (in earthworms) or may be long and numerous forming distinct tufts (in marine annelids). Setae may aid locomotion, anchor annelids to their burrow walls, or be used for defense.

-Marine annelids possess segmentally-paired, lateral body projections called parapodia. These structures typically bear tufts of long setae and contain numerous blood vessels. The 2 main functions of parapodia thus are locomotion and respiration.

-It should be noted that only marine annelids exhibit distinct cephalization.

GENERAL ANNELIDA TAXONOMY (condensed for this lab)

PHYLUM: ANNELIDA ("little rings")

CLASS: POLYCHAETA ("many setae")

1. The "marine annelids".

2. The largest and the most successful annelid class.

3. Typically possess numerous long setae (often in tufts).

4. Cephalization is distinct (tentacles, eye spots, etc. often present).

5. Parapodia present (often with tufts of setae).

6. Are dioecious with temporary gonads (only present during breeding season).

7. No clitellum present at any time.

CLASS: OLIGOCHAETA ("few setae")

1. The terrestrial "earthworms" and the "freshwater annelids".

2. Possess relatively few short setae (never in tufts).

3. Cephalization greatly reduced or absent.

4. Parapodia lacking.

5. Are monoecious with permanent gonads.

6. Clitellum present and permanent.

CLASS: HIRUDINEA ("leech habit")

1. The freshwater and the terrestrial "leeches".

2. No setae present.

3. Cephalization reduced.

4. Parapodia lacking.

5. Are monoecious with permanent gonads.

6. Clitellum present, but temporary (only during breeding season).

7. Blood-feeding leeches are considered "temporary parasites" because they spend little of their time on a host. They have anterior and posterior suckers for host attachment and possess the anticoagulant hirudin in their saliva.


1. "Common Earthworm" (Lumbricus terrestris)



Where do they live and when are they most active?

What is their ecological value?

**Examine a preserved earthworm specimen and note its external structures as described on pages 191-192 of your laboratory manual.

**Complete a dissection of an earthworm FOLLOWING INSTRUCTIONS GIVEN BY YOUR LAB INSTRUCTOR !!

**Know the structures/terms found in heavy print on pages 192-194 of your laboratory manual. Also, study Figure 12-3.

**Examine a microscope slide of a cross-section through the earthworm body.

Know any structures/terms found in heavy print on pages 195-196 of your laboratory manual . Also, study Figures 12-5 and 12-6.

*Briefly observe demonstration slides of an earthworm cross-section showing setae and a nephridiopore (see Fig. 12-6 in lab manual).

*Observe preserved earthworm cocoons.

2. "Freshwater Oligochaetes"



Where do they live and of what ecological importance are they?

Observe preserved demonstration specimens.

3. "Leeches"



Where do most leeches live and what do they eat?

Observe preserved demonstration specimens.

4. "Marine Annelids"



In what ways are they distinct from other annelids?

Observe preserved demonstration specimens of various species. Note their distinct class features (setae, parapodia, cephalization, etc.).

Briefly view demonstration slide showing a parapodium.