november 3-4, 2014 phylum mollusca. conch squid nudibranch chiton clams, oysters octopus
TRANSCRIPT
November 3-4, 2014
Phylum Mollusca
Conch
Squid
Nudibranch
Chiton
Clams, Oysters
Octopus
General Characteristics
Soft-bodied invertebratesUnsegmented body, typically bilateral symmetry Internal or external calcium carbonate shell
(usually)Second largest animal phylum
~ 200,000 species Show Cephalization
Sensory organs towards one end of body “head” formation
Habitat/Lifestyle Sessile-mobile Benthic-pelagic Predators-Herbivores-deposit feeders-filter feeders
Typical Body Plan of Mollusks
Three main parts: Foot Mantle Shell
Foot: On ventral side muscular; used for crawling,
burrowing, or capturing prey Can be flat (snails) spade-shaped (clams) or modified into tentacles
(squid and octopus)
Abalone
Body Plan of Mollusks
Body covered with protective mantle: Thin layer of tissue that
covers most of the mollusk’s body
May or may not produce a shell
Shell: made by glands in mantle
that secrete calcium carbonate
Feeding with Radula
Diverse: herbivores, carnivores, filter feeders, detritivores.
Some use Radula for feeding Radula: flexible, tongue-shaped structure covered
with tiny teeth
Herbivores use radula to scrape or cut algae; carnivores use radula to drill through shells or flesh.
Radula
Filter Feeding
Clams, oysters, and scallops filter feed using feathery gills
Mucus produced by gills traps plankton as water comes in through siphons
Mollusc Reproduction & Development
Sexual reproduction, external In tentacled species, fertilization is internal and female
lays fertilized eggs Most have separate sexes that cross-fertilize eggs Some hermaphrodites-both sexesLarval stages Trochophore larva
Free swimming, ciliated, shell formation begins Veliger larva
Free swimming
Zygote
Trochophore
Veliger
Spat
Juvenile
Adult
Respiration
Aquatic species use gills inside mantle to exchange gases
Incurrent and excurrent siphon brings water in
Siphon: Tube-like structure
through which water enters and leaves
Circulation
Can be open or closed circulatory system Open system: blood is pumped by simple
heart into sinuses (large saclike space) then to gills, then back to heart; slower system; found in snails and clams
Closed system: blood is pumped by heart through blood vessels; faster system; found in faster-moving mollusks
6 Classes in Phylum Mollusca
1)Monoplacophora-simple hat shaped shells
2)Polyplacophora----chitons, 8 overlapping shells
3)Scaphopoda-tusk shells
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4) Gastropoda-snails, slugs, nudibranchs, and conchs, limpets, abalone
4) Bilvalvia - clams, oysters, scallops, and mussels
5) Cephalopoda squid, octopus, and nautilus
Class Gastropoda
“Stomach footed” molluscs
Have a single shell (snails) or no shell (slugs)
Class Gastropoda
NUDIBRANCHS Marine slug Lacks shell
Class Gastropoda
NUDIBRANCHS Feed on sponges Cnidaria,
algae Exposed feathery gills Can be toxic
Retain undigested nematocysts from Cnidaria=Kleptoplasty
Class Bivalvia, Bi-valve = two shells
two-part, hinged shellEx: clams, oysters, scallopsmussels Most sessile, benthicMost are filter feedersNo head or radulaBurrow
Sand, wood, rocks A few can use muscular foot that extends from shell for
movement
Scallops clap valves together to move
Class Bivalvia
Shell secreted by mantle
Oldest, raised part of shell called umbo
Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen
Have heart & open circulatory system
Class Cephalopoda
Octopus, squid, cuttlefish, & chambered nautilus Move by using mantle cavity as jet propulsion
Sucks water into mantle cavity, pushes water out of muscular siphon that can change size (speed) and direction.
Most intelligent mollusk Well developed head –centralized brainLarge eyes, visual predatorsLack outer shell, very flexibleActive, free swimming predatorsFoot divided into tentacles with suckers
Class Cephalopoda
Chromatophores: can change color, used for camoflauge and social signaling. 1st group with social signaling-reguires
more complex brain to interpret signals
Use their radula & beak to feed Closed circulatory system Highly developed nervous system
with vertebrate-like eyes Sexual reproduction
Separate sexes with internal fertilization
Class Cephalopoda
SQUID Largest invertebrate is the Giant Squid Large, complex brain 8 tentacles 2 arms- longer pair to catch prey Use jet propulsion Chromatophores Have internal shell called pen
Class Cephalopoda
Can squirt an inky substance into water to temporarily blind predators
Class Cephalopoda
OCTOPUS Eight tentacles Similar to squid Sit & wait predators = ambush Female dies after tending to eggs. Beak like jaws, radula
Importance of Mollusks
Filter water, healthy watersKeep algae growth doneFood for top predators and
economically important species.
Used by humans for food Pearls from oysters Shells used for jewelry