Zoology - PHYLUM MOLLUSCA

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Things you need to know from this chapter.

  1. Why is Phylum Mollusca so important?
    1. What type of animals does the phylum include?
  2. Know about the following mollusc body parts & their functions…
    1. Eucoelom
    2. Foot
    3. Visceral mass
    4. Mantle
    5. Radula
    6. What are the metanephridium?
    7. Circulatory system

                                          i.    What type of heart do they have?

                                        ii.    Describe an open circulatory system.

                                       iii.    Describe a closed circulatory system.  Which molluscs have this system?

    1. Reproductive system  - Are they monoecious or dioecious?  Do they self-fertilize or cross fertilize?
    2. Review the layers of their shells
  1. Know the following  class names, example animals of the class, where you find them, and how they make their living (if we discussed it).
    1. C.  Gastropoda

                                          i.    What’s torsion?

    1. C.  Bivalvia

                                          i.    How do marine & freshwater bivalves reproduce differently?

    1. C.  Cephalopoda

                                          i.    What are some of the interesting species of cephalopods?

                                        ii.    How are they more complex than the other molluscs?

    1. C.  Polyplacophora
    2. C.  Scaphopoda
    3. C.  Monoplacophora
    4. C.  Caudofoveata (included in C. Aplacophora)
    5. C.  Solenogastres (included in C. Aplacophora)

 

I.  Compared and Contrasted to Pseudocoelomate Animals

 

            A.  They are like the pseudocoelomate animals in that…

                        1.  They lack _________________________.

                        2.  They are _________________________ and generally mobile.

                        3.  They have well developed sense organs.

 

            B.  They are more complex than the pseudocoelomate animals in that …

                        1.  They are our first group of animals with a true coelom.  They are

                        _________________________.

                        2.  All organs – including respiratory & circulatory – are present.

                        3.  They have a fleshy _________________________ that often

                        secretes a _________________________.

                        4.  They have a rasping organ – the _________________________

                        – with which to feed.

                        5.  Cephalopods have a highly developed eye.

 

II.  Characteristics of Phylum Mollusca

 

            A.  Contains nearly _________________________ living species and

            35,000 fossil species.

1.  This rivals the arthropods in diversity of body forms & sizes

2.  Also rivals arthropods in terms of ecological success.

            a.  Found in almost all environments:  marine, freshwater,

            terrestrial   

 

B.  Includes snails, slugs, clams, octopuses, squids


C.  Members of the phylum are bilateral and unsegmented.

 

D.  Have a reduced eucoelom usually located around the

_________________________ (pericardial cavity)

1.  Eucoelom sometimes surrounds the lumen of the gonads & part

of kidney

 

E.  Molluscan Body Plan:
            1.  _________________________  - used for locomotion, digging,

            or modified for feeding

2.  _________________________-  contains digestive, circulatory,

respiratory, and reproductive organs
            3.  _________________________  - formed by two folds of skin.

                        a.  Provides protection

                        b.  Increases surface area for gas exchange

                        c.  Secretes the shell in those molluscs that have one

                        d.  Provides locomotion in the ________________________

                        e.  Creates the mantle cavity between the mantle and the

                        visceral mass which houses the ______________________

                        4.  _________________________  - rasping tongue

a.  Not all molluscs have a radula, but if an animal does have

one, it is a mollusc.

 

F.  All organ systems are present

·         Digestive System -  complete (from mouth to anus) with radula

·         Respiratory System -  gills, lungs, mantle, epidermis

·         Skeletal System -  shell in most, usually external, internal in some

·         Muscular System - complex system, not just longitudinal or circular

·         Excretory System - _________________________ (kidneys); distinct organs not just scattered cells as are protonephridia

·         Nervous System -  is a complex of several ganglia; plus have specialized sense organs for touch, smell and vision

·         Circulatory System – usually with a ______________________

                                 _________________________________________________

o    _________________________ system -  no capillaries - just sinuses, with a dorsal heart

o    _________________________ system  - capillaries present (found only in _________________________)

·         Reproductive System - usually dioecious, monoecious in some 


G.  Molluscan shell structure

1.  _________________________ layer - outer horny layer; organic

material

2.  _________________________ layer - middle layer, calcium

carbonate
3.  _________________________ layer - mother of pearl molluscan classes

 

II.  MOLLUSCAN CLASSES

 

A.  Class Gastropoda - _________________________

                  1.  The largest of all molluscan classes, most of the ~40,000 living

                  spp.

a.  Shelled forms are called snails, forms w/o shells are

called slugs.

2.  Tentacles with eyes; 2 pair in terrestrial species
3.  Head well developed, anterior
4.  Well developed ventral foot
5.  Most species show _________________________- twisting of

body to the right (it is not coiling)

a.  Primitive condition- no torsion

b.  Advanced condition – torsion

c.  Really advanced – detorsion

d.  Adults asymetrical due to torsion

e.  Torsion results in:

1) loss or reduction of organs on right side

2) allows for snail to withdraw into shell in the

following order:  ____________________________

___________________________________________

__________________________________________

6.  Feeding - well developed radula

a.  in some radula modified; i.e., cone shells

b.  most are scrapers, a few are predators
7.  Respiration  -  in most species gastropods have well developed

_________________________ in mantle cavity

a.  terrestrial snails have functional

_________________________ in mantle cavity
8.  Reproduction  -  most gastropods are

_________________________, but cross-fertilization is the rule

a.  Some are dioecious

b.  Usually rely upon internal fertilization

c.  Marine species have trochophore larvae

d.  Freshwater and terrestrial species have direct

development

 

B.  Class _________________________ (= Pelecypoda) -  clams,

scallops, oysters

            1.  ~8,000 living spp., mostly marine

a.  There are many freshwater spp.

b.  There are NO terrestrial spp.

                        2.  Shell is divided into two parts (valves) and is hinged

                        3.  Body is laterally compressed

                        4.  No head or radula

5.  Large hatchet shaped foot

6.  Filter feeders

7.  Their gills have multiple functions

            a.  Respiration

            b.  Feeding

            c.  Reproduction

8.  Most are _________________________ (e.g., oysters) or very

slow movers (clams);

            a.  A few move actively (scallops)

9.  Their heart is situated in pericardial cavity (=coelom)

a.  Moves blood around to kidney, gills, and mantle

b.  There are a limited number of true blood vessels

10.  Reproduction in bivalves -  They are

_________________________

11.  Marine species life cycle; e.g., oysters

a.  Eggs are produced by females & released

b.  Fertilization is mostly external

c.  The embryo develops through a

_________________________, then

            _________________________, and

            _________________________ stage to reach adulthood.

            d.  Very high reproductive potential (50,000,000 eggs/yr)

12.  Some freshwater species life cycle; e.g. mussels
                        a.  Females produce eggs which are kept internally

            b.  Internal fertilization

c.  They develop in mother’s water tubes into bivalved

            _________________________

d.  Glonchidium larva live as a parasite on

_________________________ (attached to gills or skin) for

several weeks.

e.  They disengage & sink to the bottom to live as

independent adults

f.  High reproductive potential


octopus handshake.JPG

 

B.  Class _________________________ -  octopods, squids and chambered nautilus

1.  Most of the 650 living spp. are active swimmers.

a.  Most spp. of octopus have secondarily assumed a

_________________________ lifestyle.

b.  Includes _________________________– largest known

invertebrate (up to 20 meters long with tentacles)

c.  Includes the most intelligent & the fastest swimming

aquatic invertebrates (_________________________)

                        d.  Includes forms with external shells

                        (_________________________) & internal hard shells

                        (_________________________)

2.  All are marine _________________________
            3.  All have extreme modification of the foot

a.  i.e., _________________________ and

_________________________ homologous to molluscan

foot

4.  Shows highest development in molluscs of:

a.  Brain

b.  Eyes  -  have cornea, lens, retina; sees real images

c.  Nerves

d.  Locomotion (with _________________________)

e.  Circulatory system (_________________________) with

developed blood vessels; complex heart (an adaptation to an

active lifestyle

f.  Radula is modified into _________________________ -

for predation

g.  Has _________________________ for protection

5.  Reproduction -  dioecious

a.  Show some sexual _________________________

b.  Males have modified tentacles for sperm transfer and

holding female in copulation

c.  Fertilization is internal

d.  No free living larvae; egg hatches into a juvenile

e.  Some (e.g., octopus) show maternal care

f.   Due to higher survivability of offspring, they show lower

reproductive potential

9.  Respiration

a.  Well developed pair of gills

b.  Gills with well developed blood vessels

 

D.  C. Polyplacophora – _________________ -  "_____________ plates"

            1.  Usually have 8 overlapping dorsal plates or shells

            2.  Reduced head, no eyes or tentacles

            3.  All marine

            4.  Usually live on rocky shores

            5.  Have radula, gills

            6.  External fertilization

            7.  Scrape algae

            8.  Approximately 600 described species are generally flattened &

            elongated antimals

 

E.  C. Scaphopoda - _________________________

                        1.  slender, tubular shells open at both ends

                        2.  ~350 described species, all marine, between 3 & 6 cm long

                        (max. of a living spp. 15 cm)

                        3.  Lie buried in soft sediments, in shallow to moderately deep

                        water (usually < than 2,000 meters deep), the larger end facing

                        downward & the smaller aperture projecting above the surface.

4.  Mouth is surrounded by tentacles bearing adhesive knobs,

which capture small organisms
5.  No defined head
6.  No gills, respiration across mantle

 

F.  C. Monoplacophora -    "_________________________"
                        1.  Until _____________, they were known only from fossils.  There

            are only 11 described living species

2.  All Monoplacophorans are known from deep marine waters

(>12,000 feet)
3.  They have a single circular (cap-like) shell with radula.

4.  They possess many primitive features & studies of their internal

anatomy have provided much fuel for debates about molluscan evolution.

 

G.  C.  [Aplacophora] - "without plates"

            1.  deep marine, not much is known about them

            2.  Many zoologists divide these animals into two separate classes:

                        a.  C.  _________________________ – small worm-like

                        molluscs that live buried head down in the sea floor.  ~70

                        described living species

                        b.  C.  _________________________ – small worm-like

                        molluscs that live symbiotically (or feed upon) cnidarians. 

                        They have no shell,             eyes, or tentacles.  ~250 described

                        species, usually living over 200 meters deep, where they are

                        sometimes quite abundant