10 Chap 16 mollusca

Mollusca
and
Introduction to Spiralia
Phylogeny of Protostomes
Spiralia
Ecdysozoa
Protostomia
Deuterostomia
Bilateria
Ancestry of Mollusca
Mollusca
Platyhelminthes,
Rotifera
Annelida
Eutrochozoa
Lophophorata
Lophotrochozoa
Spiralia
Protostomia
Ecdysozoa
Trochophore Larva
compare Hickman Fig. 16-6
• basis of the term Eutrochozoa
• present in many marine mollusks and annelids
Marine Mollusk Larvae
compare Hickman Fig.’s 16-6 and 16-7
Veliger
Phylum Mollusca
• Name means “soft-shelled nut”
• 2nd largest phylum in number of species
• Most are free-living and marine
– but many clams and snails are freshwater or
terrestrial
• Feeding habits:
– Scrapers and suspension feeders (rarely,
carnivores)
acoelomate
pseudocoelomate
(muscles, not
peritoneum)
eucoelomate
peritoneum
Eucoelomate
Body Design
ectoderm
mesoderm
endoderm
Coelom: fluid-filled cavity
between gut and body wall
that is lined with mesodermal
cells (peritoneum).
Important Mollusk Features
• coelom - just the pericardium, a sac around the
heart
• muscular foot - posterior, ventral, locomotory
• mantle - dorsal epidermis that makes the shell
– also encloses the body in a mantle cavity
– ciliated mantle cavity helps with respiration and
sometimes feeding
• radula - tongue-like scraper used for feeding
Molluscan Anatomy
(chiton; Hickman Fig. 16-9)
Mollusk Body Designs
Hickman Fig.’s 16-9, 16-18, 16-31, 16-38
motion while feeding
Radula
Hickman
Fig. 16-2
• not present
in Bivalvia
Mollusca Classes
required in ZO 110
•
•
•
•
Bivalvia - clams, mussels, oysters, etc.
Polyplacophora - chitons
Gastropoda - snails and slugs
Cephalopoda - squid, octopus, nautilus
Bivalvia
clams and mussels
• shell of two "valves”
• lateral, ciliated gills for respiration and
filter-feeding
• narrow foot for burrowing
• head just mouth and labial palps - no radula
Clam Filter-Feeding Flow
Hickman Fig. 16-30, 16-31
Dor.
Ant.
Pos.
Ven.
Valuable Bivalvia
• many are edible
– oysters, scallops, blue mussels, clams
• river mussels
– harvested for making seed pearls
– symbol of freshwater biodiversity
• popular with collectors
Bivalve Pest
Hickman Pg 343
Dreissena, the zebra mussel
Polyplacophora
chitons
• eight dorsal shell plates
• slow-moving - foot has strong suction
• grazer-scrapers with radula
– eat algae from rocks between or below
the tides
Gastropoda
snails and slugs
also conchs, limpets, abalones, and sea hares
• terrestrial, freshwater, or marine
• single shell, or none
• scrape up food or attack prey with radula
• most diverse mollusk class
– > 40,000 named species
Gastropod Body Design
Campbell Fig. 16.18
Snail Anatomy
Hickman Fig. 16-18
Shell-less Gastropods
Hickman Fig. 16-22, 16-23
Conus Eats a Fish
Hickman Fig. 16-16
Class Cephalopoda
nautilus, squid, octopus
• modification of foot, addition of a beak for
carnivory
• reduced shell or flotation for swimming
• improved respiration, circulation, and
neural/behavioral complexity support high
activity levels
Nautilus
Hickman Fig. 16-36
• many tentacles, without suckers
• large shell, floated by chambers of gas
Squid Features
Compare Hickman Fig. 16-38
•
•
•
•
streamlined shape
undulating lateral fins
funnel
arms & tentacles with
suckers, sometimes poison
Usual direction of
movement - dorsal
Giant Squid!
Artituthus can be 30 ft+
Complex Squid Behavior
Hickman Fig. 16-39
• shell reduced to pen
• mood and camouflage colors
• ink for concealment
Octopus
Hickman 16-40
• 8 arms with suckers
• shell lost, body soft
• ink sac
Pop Quiz 4
1. Term for the hard structure used by
cephalopods in feeding: _______
2. Term for the molluscan coelom that
is restricted to the area around the
heart: __________
3. Class name for the chitons: ______