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BIOLOGY OF ANIMALS LABORATORY
LAB # 5-A (Supplement Spring09) (Written by Dr. Olson, Professor Emeritus; Modified by Dr. Alan D. Christian and J.D. Wilhide)
PHYLUM: MOLLUSCA ("molluscs")
LAB. MAN.: EXERCISE #11-A; Pages 171-
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.
GENERAL MOLLUSCA CHARACTERISTICS:
- 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.
- 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.
- 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) that 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) (3) Nacreous (inner) made of many thin layers of calcium carbonate and commonly called "mother of pearl".
GENERAL MOLLUSCA TAXONOMY
(condensed for this lab)
PHYLUM: MOLLUSCA ("soft")
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 "tuskshells" 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).
-Includes the "squid", "octopus", "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 ).
EXERCISES:
- "Freshwater Clam/mussel" ( Anodonta )
**Examine the external structure of a preserved clam and know the structures/terms ( hinge ligament, umbo, growth line s) found also on page 173 of your laboratory manual.
**Complete a dissection of a freshwater clam BY READING AND FOLLOWING DIRECTIONS FOUND IN LAB MANUAL starting on page 173 (right column).
*Know the structures/terms (EXTERNAL STRUCTURE: THE SHELL: nacreous layer, prismatic layer, anterior adductor muscles, posterior adductor muscles, hinge ligament, pallial line, pseudocardinal teeth, lateral teeth; INTERNAL STRUCTURE: THE MANTLE: mantle, incurrent aperture, excurrent aperture; INTERNAL STRUCTURE: THE MANTLE CAVITY: gills, mantle cavity, visceral mass, foot, labial palps, mouth ; INTERNAL STRUCTURE: RESPIRATION AND THE GILLS: lamellae, filaments, suprabranchial chamber; INTERNAL STRUCTURE: CIRCULATORY SYSTEM: pericardial sac, heart, anterior aorta, posterior aorta, coelmic cavity; INTERNAL STRUCTURE: DIGESTIVE SYSTEM: labial palps, mouth, esophagus, stomach, digestive glands, crystalline style, intestine, anus; INTERNAL STRUCTURE: REPRODUCTIVE SYSTEM: gonad, zygotes, glochidium ; INTERNAL STRUCTURE: NERVOUS SYSTEM: ganglia, cerebropleural ganglia, pedal ganglia, visceral ganglia ) found on pages 173-183 and Figures 11-02 through 11-08) of your laboratory manual. Also, study Figures 11-2, 11-3, 11-4, and 11-5.
*Observe demonstration slide of a glochidium larva stage of the freshwater clam.
BY READING IN YOUR LABORATORY MANUAL OR TEXTBOOK, YOU SHOULD BE ABLE TO ANSWER THE FOLLOWING QUESTIONS CONCERNING THE ORGANISMS LISTED BELOW:
Phylum?
Class?
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?
- "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.
FOR THE PRACTICAL, KNOW WHAT CLASS THEY BELONG TO AND THEIR KEY “MOLLUSK” FEATURE(S)
-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.
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")
- The "marine annelids".
- The largest and the most successful annelid class.
- Typically possess numerous long setae (often in tufts).
- Cephalization is distinct (tentacles, eye spots, etc. often present).
- Parapodia present (often with tufts of setae).
- Are dioecious with temporary gonads (only present during breeding season).
- No clitellum present at any time.
CLASS: OLIGOCHAETA ("few setae")
- The terrestrial "earthworms" and the "freshwater annelids".
- Possess relatively few short setae (never in tufts).
- Cephalization greatly reduced or absent.
- Parapodia lacking.
- Are monoecious with permanent gonads.
- Clitellum present and permanent.
CLASS: HIRUDINEA ("leech habit")
- The freshwater and the terrestrial "leeches".
- No setae present.
- Cephalization reduced.
- Parapodia lacking.
- Are monoecious with permanent gonads.
- Clitellum present, but temporary (only during breeding season).
- 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 hirudinin their saliva. EXERCISES:
- "Common Earthworm" ( Lumbricus terrestris )
**Examine a preserved earthworm specimen and note its external structures as described on pages 193 of your laboratory manual and know the following structures/terms ( peristomium, mouth, prostomium, anus, clitellum ). Draw the external structures on the figure provided to you on page 199 of your lab manual to include the above structures.
**Complete a dissection of an earthworm FOLLOWING INSTRUCTIONS GIVEN IN THE LAB MANUAL EXCEPT THAT YOUR SPECIMEN IS PRESERVED. FOR MORE INFORMATION ASK YOUR LAB INSTRUCTOR !! (Page 193-199)
**Know the following structures/terms ( digestive tract, seminal vesicles, seminal receptacles, nephridia, dorsal blood vessel, aortic arches, esophagus ; DIGESTIVE SYSTEM: mouth, pharynx, crop, gizzard, intestine, anus, typhlosole; CIRCULATORY SYSTEM: dorsal vessel, aortic arches, ventral vessel, subneural vessel, lateroneural vessel ; REPRODUCTIVE SYSTEM: seminal vesicles, testes, seminal receptacles, ovaries; Excretory system: nephridia, nephrostome; NERVOUS SYSTEM: cerebra ganglia, circumpharyngeal connectives, ventral nerve cord ) found on pages 194-198 and Figure(s) 12-03 of your laboratory manual. Also, study Figure 12-3.
**Examine a microscope slide of a cross-section through the earthworm body. Know the following structures/terms ( Cuticle, epidermis, circular muscle layer, longitudinal muscle layer, peritoneum, setae, coelom, alimentary canal, ventral nerve cord, dorsal vessel, ventral vessel, septa, mesenteries ) found on pages 197-198 and Figure(s) 12-05 of your laboratory manual.
*Briefly observe demonstration slides of an earthworm cross-section showing setae and a nephridiopore (see Fig. 12-5 in lab manual).
*Observe preserved earthworm cocoons (Figure 12-4) and understand the mating and reproduction (Page 196) BY READING IN YOUR LABORATORY MANUAL OR TEXTBOOK, YOU SHOULD BE ABLE TO ANSWER THE FOLLOWING QUESTIONS CONCERNING THE ORGANISMS LISTED BELOW: Phylum? Class?
