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Marine Ecology, Lecture 5
April 16, 2008
I.
Phylum Mollusca, the "soft-bodied" animals
A.
Body organization (hypothetical ancestral mollusc, HAM):
1.
Shell
2.
Mantle
a.
covers body organs, and in some molluscs, serves as only body covering
b.
secretes shell
c.
Associated sensory organs (tentacles, eyespots)
3.
visceral mass
4.
mantle cavity
a.
ctenidia (paired in HAM)

gas exchange

feeding (in Bivalvia)
5.
head and sensory structures at head
6.
radula
7.
foot and epipodial tentacles
B.
Reproduction
1.
Quite variable depending upon class, even species.
C.
Class Polyplacophora: body organization (compare to HAM)
1.
Shell: Eight shell plates (“valves”) rather than a single shell
2.
Mantle: thickened, forms "girdle" around plates which serves as protection
3.
Mantle cavity: expanded along sides, multiple ctenidia
4.
Head reduced
D.
Class Polyplacophora: local species
1.
Cryptochiton stelleri: giant gumboot chiton.
a.
Appearance

Largest chiton in the world (to 1/3 meter)

Rough red mantle completely fused over shell plates
b.
Location

Primarily the low intertidal (maybe up to the low middle
intertidal)

At low tide, it can carry out gas exchange in air as long
as the ctenidia are kept moist.

Found in somewhat shaded areas.
c.
Other interesting details of life history

Feeds on red algae and kelp

Limited movement: Marked Cryptochiton found within 20 m
after 2 years!

Grow slowly. Live 20 years or more.

Commensals live within mantle cavity (a.k.a. "pallial groove"
along edges of foot, containing the ctenidia) and obtain food
brought in by respiratory currents

Scale worms, pea crabs
2.
Katharina tunicata: black Katy chiton
a.
Appearance

Smooth black mantle often pulled far over the shell plates

Able to adjust its mantle position; sometimes completely
closed up.

Plates also black
Page 1 of 6

Foot is orange
Location

Middle intertidal (mostly lower-middle, but venturing to uppermiddle)

Found in areas of moderate to high wave action

Often in areas of sun exposure, although associated with algae
c.
Interesting details of life-history

Feed on brown and red algae, benthic diatoms

Can greatly reduce the amount of kelp in a region (more
on this later)

Ability to pull its mantle over its shell is a defense against other
organisms getting a foothold.
3.
Tonicella lineata
a.
Appearance

Distinct lines on valves

Pink coloration
b.
Location

Lower middle to low intertidal

Protected in crevices, within algae

Often associated with the sea urchin Strongylocentrotus
purpuratus
c.
Interesting details of life-history

Feeds on crustose coralline algae, from which it gets its pink
color

Sometimes exhibit homing behavior
4.
Mopalia spp.
a.
Appearance

Distinctive bristles on its mantle; different species with different
density of bristles
b.
Location

Tolerates wide range of physical conditions

Found from the upper middle intertidal downward (different
species in somewhat different locations)
c.
Interesting details of life-history

Algae eaters
d.
Those which are alternately submerged and uncovered show homing
behavior, but those permanently in tidepools do not.
e.
Ranges of about 50 cm radius (small!)
Phylum Mollusca (cont.)
A.
Class Gastropoda (stomach-footed); snails, slugs, nudibranchs.
1.
Major characteristic: undergo torsion
2.
Mantle cavity and visceral mass twists 180 deg.
3.
Occurs during larval development
a.
Trocophore differentiates into veliger, and then undergoes torsion.
4.
Generally accompanied by loss of symmetry in organs.
5.
Advantages of torsion
a.
Can duck headfirst into mantle cavity
b.
Closes off shell with foot (operculum can serve as trap door)
c.
Sensory system for ctenidium (called the osphradium) now at front
6.
DISADVANTAGE OF TORSION
b.
I.
Page 2 of 6
a.
b.
B.
Possibility of pooping onto heads
Groups of molluscs evolved various ways of dealing with this "sanitation"
problem.

Ex: keyhole limpets
Class Gastropoda: diversity
1.
Diodora aspera: rough keyhole limpet
a.
Appearance

Distinctive keyhole at top

Rough texture and ribbing distinguishes it from other keyhole
limpets
b.
Location

Middle to low intertidal, usually in protected crevices and
underhangs
c.
Other interesting details of life-history

Omnivorous, feeding primarily on bryozoans

Extends mantle over foot and shell, and above keyhole, to prevent
tube foot grip of predatory sea stars.
2.
Lottia gigantea
a.
Appearance

Large limpet of middle to low intertidal

Relatively flat; weathered appearance

Apex near anterior edge
b.
Location

Middle intertidal; can be out on exposed rock
c.
Other interesting details of life-history

Territoriality

Lottia "farms" bare rock area, removing other organisms,
"using its shell like a bulldozer"

Mantle folds for respiration during low tide
3.
Collisella (Lottia) digitalis
a.
Appearance

Recognizable by apex very far forward
b.
Location

High intertidal to upper middle intertidal
c.
Other interesting aspect of life-history

Feeds on microscopic films of algae

Restricted to vertical surfaces in areas of Oystercatcher predation
(why?)

Some individuals home, some don't
4.
Collisella (Lottia) pelta
a.
Appearance

Somewhat high profile, but dependent upon habitat

Apex about 1/3 back from head
b.
Location

Associated with the kelp Egregia when small, and appear black.
Become more ribbed and mottled after moving to rock surfaces

Common in mussel beds
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c.
Other interesting aspects of life-history

Feed on common, erect species of algae

5.
6.
7.
8.
Tidal rhythm of feeding activity
Tectura persona
a.
Appearance

Highest profile compare to other limpets, and a slight hook at the
apex

Apex about ¼ back from head
b.
Location

Most likely to find within crevices
c.
Other interesting aspects of life-history

Feed at night; eats 0.50 m2/year of encrusting algae
Tectura scutum
a.
Appearance

Relatively low profile compared to the others

Apex about 1/3 back, less pointed than others
b.
Location

Mid-intertidal, in areas less exposed to heavy wave action
c.
Other interesting aspects of life-history

Feed on microscopic algae

Tidal rhythm of feeding activity
Tegula funebralis
a.
Appearance

Black shell with flattened bottom and often eroded apex.

Foot black on outside, white on inside, with long epipodial tentacles
b.
Location

Middle intertidal, often in pools are protected in crevices or beneath
algae
c.
Other interesting aspects of life history

Move to tops of rocks during high tide at night only, and orient to
current (perhaps to catch drifting algae?) Will retreat with strong
currents

Often aggregate in groups on rocks and in pools

Negative correlation with algal cover
Littorina sp.
a.
Appearance

Very small; ones here are mostly tiny and black
b.
Location

High intertidal

Littorina planaxis occur higher than any other molluscan
species (can stay out of water for 2-3 mo.)

Can survive submersion in fresh water

Specialized "glue" to stick it to the rock so it can seal itself
off, close operculum
c.
Other interesting aspects of life-history

Feed on diatom films
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
9.
Erosion of tidepools (1 cm/16 yr)
Nucella spp. (dogwinkles)
a.
Appearance

Spiral shells with yellow-orange operculum

N. lamellosa: large (several cm), grayish shell with distinct flattened
areas (i.e. “stepped” appearance)


10.
N. canaliculata: ~1.5 cm: relatively deep channels
N. emarginata: ~1.5 cm: generally with distinct stripes, minimal
channeling.
b.
Location

Upper middle intertidal, primarily within mussel beds but may be
elsewhere in this zone
c.
Other interesting aspects of life-history

Predator on mussels and barnacles

Accessory boring organ on foot: dissolves shells of mussels and
barnacles with acidic secretions, then makes hole with radula and
consumes prey.
Nudibranchs
a.
Undergo detorsion
b.
reduction of shell, or no shell (nudibranchs have no shell)
c.
Feeding: often on toxic sponges, cnidarians, tunicates. Co-opt poisons for
their own use.
d.
dorid nudibranchs (Order Doridacea): rear gill plume, forward
rhinophores (sensory)



Acanthodoris nanaimoensis

Feeds on bryozoans (toxins?)
Archidoris montereyensis

feeds on yellow sponges and stores their toxins
Rostangia pulchra

Feeds on red sponges, camouflaged against them, and
protected with sponge toxins

e.
Discodoris (Dialula) sandiegensis

circles on white body

Feeds on sponges
Aoelid nudibranchs (Order Aeolidacea): extensions of mantle/gut appear
as cerata all over body. Location of gas exchange.

Aeolidia papillosa

Feeds on cnidarians, stores cnidocytes with unfired
nematocysts for later protection. Eats its entire body weight
per day.

f.
Phidiana (Hermissenda) crassicornis

Feeds on cnidarians, stores cnidocytes for later protection
arminacean nudibranchs (Order Arminacea): with cerata as in aeolids
(see above), but cerata are more flattened, and members of this group do not
store cnidocytes

C.
Janolus fuscus

Feeds on hydroids and bryozoans
Class Bivalvia
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D.
1.
laterally flattened
2.
hinged shell
3.
enlarged mantle cavity
4.
enlarged ctenidia: now serves both for respiration and filter feeding
5.
Reduced head
6.
Foot used for digging, more muscular, rather than wide, flat and slimy
7.
Mantle modified as siphons in some bivalves
Class Bivalvia: diversity
1.
Mytilus californianus: California mussel
a.
Appearance

Raised ridges extend along length of shell

Posterior is somewhat angled

Anterior (pointy end) usually weathered

Byssal threads: secreted from foot, used to hold onto rock
b.
Location

Middle intertidal (especially lower middle)

Found in waveswept areas
c.
Other interesting aspects of life-history

Houses a community of organisms

Filter 2-3 l of water/day. Their ingestion of algal spores/invert larvae
may help them in their competition for space

Patchiness: large, old ones rip out, opening up space.
2.
Mytilus trossulus: Pacific blue mussel (M. edulis)
a.
Appearance

Smooth surface, without ridges and less weathered

Posterior end is almost flat, with slightly rounded edges

Byssal threads: secreted from foot, used to hold onto rock

Has fewer and thinner byssal threads
b.
Location

Found in less turbulent water than M. californianus. This species is
collected off docks and in bays.
Study questions
1.
Know the basic features of the ancestral mollusc, and the functions of these major parts. Also, be
able to compare these features between the “hypothetical ancestral mollusc” (HAM) and each of the
major classes of the phylum, noting both similarities and differences. Also, be able name each of
the major molluscan classes, and list typical members of each class.
2.
What is torsion? Which class of phylum Mollusca has members which undergo torsion? Describe
the process, and discuss the major advantages and disadvantages of torsion.
3.
Know the differences among dorid, aoelid and arminacean nudibranchs.
4.
Know aspects of the life histories of common intertidal organisms as discussed in class (and
included on this and previous, outlines.) For example, be able to describe what the Nucella species
eat and how they penetrate the shells of their prey. You might also have to name a particular
animal, given its description. You will have the list of scientific names (in alphabetical, not
phylogenetic, order) to help you. Common names not allowed on exams.
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