Mollusca - Chitons, Snails, Clams, Octopus, and More! Domain

Mollusca - Chitons, Snails, Clams,
Octopus, and More!
Domain: Eukarya
Kingdom: Animalia
Phylum: Mollusca
molluscus = soft bodied
~100,000 described living species (2nd to Arthropods)
California
Locals
Intertidal to abyss (land, too!)
All latitudes
Mostly marine
Around since Cambrian Period (570 mya)
Long evolutionary history
Long evolutionary history
Kimberella - Precambrian
•  Rich fossil record
•  Bilaterally symmetrical
•  Over 35,000 extinct species
•  Probably had a shell
Snail
Ammonite (cephalopod) - index species
Seven major taxa (classes) - share a common, general
design, but each has modified aspects of design
Squidward belongs in which class?
1
Morphology
Bilateral symmetry
Hypothetical Ancestral Mollusk
Shell - Inner Layer
Mantle - body wall over
visceral mass
1.  Secretes mucus
2.  Sensory function
Shell
•  Formed of calcareous
material
Nacreous (CaCO3)
1.  Crystalline (very resistant to
fracture)
•  Secreted by mantle
2.  Resists or entombs
parasites
Shell - Inner Layer
Hypothetical Ancestral Mollusk
Circulatory System
•  Hemocyanin
•  Open system (most mollusks)
- blood empties into sinuses
Abalone pearls
•  Closed system - squid,
octopus
Nervous System
Golden pearls
Black pearls
2
Gills
Radula
•  Ribbon of teeth supported by muscular structure
•  Used to scrape algae, small, sessile organisms,
and detritus off hard substrata.
Gas exchange
Cilia – water flow, move particles, cleaning
Reproduction
•  External and internal fertilization
•  Released from mantle cavity by exhalant current
Reproduction
Gastropod and bivalve development
•  Some are hermaphroditic
Larva
•  Cilia move water and particles
plates
Class:
Polyplacophora
Polyplacophora
Plates
Chitons
•  ~800 species
•  Marine only (abundant intertidally)
•  Adapted to adhering to rocks and shells
•  Indistinct head
girdle
442
Fig. 2 Diversity of eye types in
four molluscan classes.
a Dorsal view of the shell plates
and ocelli of a chiton
(Polyplacophora: Tonicia
lebruni). b, c Magnified views
of ocelli on the anterior shell
plate. d Highly repetitive pallial
eyes along the mantle edge
of the scallop (Bivalvia:
Argopecten irradians).
e Cephalic eyes (Gastropoda:
Strombus). f Camera-type eyes
in the squid (Cephalopoda:
Loligo). g Cuttlefish
(Cephalopoda: Sepia). Images
are copyrighted and used with
permission by the following:
a–c A. Draeger and D. Eernisse,
d W. Capman, e H. Chaney, and
f–g L. J. Friesen
1.  Armor - protect when flat or
rolled up
a
Evo Edu Outreach (2008) 1:439–447
b
2.  Permit flexibility (shape of
rock) - Eight overlapping plates
c
3.  Light sensing organs
(thousands) in plates
•  No cephalic (head) eyes
d
e
© H. Chaney
© W. Capman
f
g
3
© L. J. Friesen
(Barber and Land 1967) to thousands (Wilkens 1986) per
individual. Structurally, pallial eyes in bivalves are more
diverse than cephalic eyes in other taxa. Pallial eyes can be
either open pit or closed lens eyes (Fig. 1a,b), and some
species may have several eye types along the mantle edge
(e.g., Barbatia cancellaria). Some pallial eyes can have
© L. J. Friesen
accessory organs that connect to the optic nerve and are
adjacent to each eye (e.g., Cerastoderma edule, Tridacna
maxima). Others may have single or double layers of
photoreceptor cells, each composed of a different photoreceptor cell type (ciliary vs. rhabdomeric; e.g., Pectinidae,
Laternulidae). In the giant clam, Tridacna maxima, pallial
Polyplacophora
Polyplacophora
What benefit might a chiton gain from the light
sensing organs in the plates?
Gumboot chiton - Cryptochiton stelleri
Up to 33 cm length!
Katharina
Diet
Diet
•  Mainly herbivorous –
algae, diatoms, as well
as bacteria, sponges,
bryozoans, and
incidental small
crustaceans
Tonicella lineata
Bird Rock Chitons
Nuttalina fluxa
Stenoplax conspicua
Placiphorella spp.
•  Traps and eats small crustaceans and worms under
its girdle.
Anyone going to U.C. Santa Cruz?
Lepidozona sp.
Go banana slugs!
4
Class:
Gastropoda
Gastropoda
Diet
•  Grazing
•  Suspension feeders
•  Snails, nudibranchs, limpets, abalone
•  Detritivores
•  Largest and most diverse mollusk class
•  Carnivores
•  40,000 - 100,000 species
•  Marine, fresh water, and terrestrial
•  Mainly benthic, but some pelagic
Gastropoda
Class: Gastropoda
Moon snail - burrowing
Foot
Changes from HAM
1. Crawling
Pteropod - swimming
1. Nervous system centralized in head
2. Burrowing
•  1 or 2 sensory tentacles
3. Leaping
•  Pair of eyes
4. Swimming
2.  Shell converted from shield to protective retreat
5. Clamping
Conch - leaping
Chestnut cowry Cypraea spadicea
Abalone - Haliotis spp.
5
Moon snail Euspira spp.
Syrinx aruanus
•  largest snail in the world
•  80 cm long; almost 40 lbs
Use radula to drill into
bivalves (enzyme helps
soften shell)
Sea Hare Aplysia spp.
Nudibranchs
Nudibranchs
Nudibranchs
6