Download Phylum Mollusca (molluscus

Phylum Mollusca
(molluscus - “soft bodied”)
Bilateral, triploblastic, Eucoelomates
VERY successful, believed to have
150,000 species… 4.5 million years of
evolutionary success…
Found in most environments, exploiting
most habitats (terrestrial & aquatic)
3 body regions: head/foot, visceral
mass, mantle
Success due to: Mantle
Highly muscular tissue that surrounds
the visceral mass (guts!)
Many mollusks can extract calcium
from water/food, secrete a shell from
this tissue
Mantle cavity – space between mantle
and “foot” (gas exchange, excretion,
release of gametes, locomotion)
Success due to: Shell
Ability to extract calcium from
water/food, cement together
Secreted by mantle
Protection from predators & weather
1 piece – conch, helmit shells, whelks,
nautilus
2 piece – clams, oysters, scallops
Reduced internal or no shell – slug,
squid, cuttlefish, octopus
Success due to: Muscular
Foot
Modified mass of muscle, based on
evolutionary use…
Digging (clams)
Swimming (scallops)
Crawling (snails & slugs…mucous gland for
land varieties!)
Grabbing (squid, octopus, cuttlefish)
Communication (squid, octopus, cuttlefish)
Success due to: Radula
Most have a “rasping tongue”
that is used to scrape food off
of substrates…
Reproduction, Respiraton,
Nervous
Mostly dioecious (males and females), a
few are monoecious (cross fertilization is
the rule)…
Gills - located between the mantle and the
visceral mass (in the mantle cavity)
From simple ganglia to most advanced
invertebrate brains (great muscle control,
incredible sensory control…)
Digestion, Excretion,
Circulation
Great variation, due to habitat
Complete digestive tract, with anus
Open circulatory system, except
cephalopods
Class Polyplacophora
most primitive;
entirely marine; oval
bodies with 8 dorsal
plates.
Broad, flat foot for
locomotion
Chitons
Class Gastropoda
“Stomach footed” mollusks
most numerous! mostly
marine, some freshwater &
terrestrial;
Visceral bodies enclosed in
coiled shell during early
development (most retain the
shell)
Broad, flat foot for
locomotion (terrestrial
species secrete slime!)
Slugs & Snails
Class Bivalvia
Shell consisting of 2 valves
or halves
Wedge shaped, muscular
foot for digging and
locomotion
Filter feeders! Sedentary
lifestyle – loss of
head/radula…
Siphons draw in water –
passes over gills for
respiration & for feeding
Clams, oysters, mussels,
scallops
Class Cephalopoda
Marine predators (fast swimmers)
“Head footed” mollusks (most
advanced!)
Reduced, internal shell (or
absent!)
CLOSED circulatory system
Highly developed visual system
Tentacles/arms w/suction cups
Jet propulsion for movement
Squid, octopus, cuttlefish,
nautilus
Several other smaller,
less studied classes