Transcript PHYLUM MOLLUSCA (Molle= soft body)

PHYLUM MOLLUSCA
(Molle= soft body)
PHYLUM MOLLUSCA
• OVER 100,OOO LIVING SPECIES; MANY 1000’S
OF FOSSIL SPECIES
• FOUND IN ALMOST ALL ENVIRONMENTS:
MARINE, FRESHWATER, TERRESTRIAL
• INCLUDES SNAILS, SLUGS, CLAMS, SQUIDS,
OCTOPUSES,
CHARACTERISTICS
• Body Plan: three main parts- head, foot, visceral mass
• body is unsegmented
CHARACTERISTICS
• Mantle - specialized tissue, secretes shell, may
be involved in feeding, reproduction and
respiration
• Radula – for rasping; in all but one class
Radula closeup
ALL ORGAN SYSTEMS ARE
PRESENT
• Circulation - Open
(Hemocoel) Hemocyanin
• Respiratory System gills (Ctenidia), lungs,
mantle, epidermis
• Osmoregulation Metanephridia also
excretion
ALL ORGAN SYSTEMS ARE
PRESENT
• Feeding - Radula
(scraping)
– Bivalves - Filter
feed
• Nervous System Complex system
of Ganglia
ALL ORGAN SYSTEMS ARE
PRESENT
• Reproductive System - usually
dioecious, monoecious in some
– Marine forms have free living
trochophore larva
– Other larval stages may be present
MOLLUSCAN CLASSES
Class Monoplacophora
“one plate”
• all known
from deep
marine waters
(>12,000 feet)
• have a single
circular shell
• with radula
Class Polyplacophora
“many plates”- (chitons)
•
have 8
overlapping
plates or shells
– reduced
head, no eyes
or tentacles
– all marine;
usually live on
rocky shores
– have radula,
gills
– external
fertilization
– scrape algae
Polyplacophora
• Respiration - Gills in pallial groove
• Circulation - Heart at posterior end
- single Aorta
• Excretion - Nephridia
• Nervous System and sense organs
- Ganglia and nerves
– Sub Radular organ - Feeding
– Esthetes - light sensing
– Osphradia - Sampling water
Polyplacophora
• Reproduction - Sexes Separate
–Usually external fertilization
–Trochophore larva
Class Aplacophora
“without plates”
• Rare; lack shell; wormlike
• deep marine; burrowing species;
predators
• About 320 species, not much is known
of them
• Your book separates them into two
separate classes:
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–
!
!
Caudofoveata
Solenogastres
Class Gastropoda
• Largest class of Molluscs
• Most important feature is Torsion
Torsion
• Twisting of body into loop
• Perhaps adaptation of veliger larva
• Disadvantages:
– Reduction of organs on right side
– Excretion - Mouth moves near anus
• Adavntages
– Allows water to be drawn from the
front
Gastropod - Locomotion
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Foot
Ciliary action below the foot
Operculum
Swimming
Gastropod - Nutrition
• Herbivores - Radula
• Carnivores
• Filter feeders
• NERVOUS SYSTEM
– Similar to Chiton - but in the shape of
“8”
Class - Bivalvia
• Includes Calms, Oysters, Mussels
• Has two Shells (Valves)
• Shell held together by Adductor
muscle
• Head is lost
• Filter feeders
• Mantle secretes the shell
MOLLUSCAN SHELL STRUCTURE
• Periostracum
; outer layer
• Prismatic;
middle layer
• Nacre; inside
layer- mother
of pearl
BIVALVIA
• Locomotion
–Foot (burrowers)
–Active swimmers (Scallops)
• Circulation
–Open system
• Excretion
–Nephridia
BIVALVIA
• Nervous System
– 2 pairs of ganglia
– Sense organs (statocysts, ocelli,
ospharidia)
• Reproduction
– Sexes separate
– Internal fertilization
– Larva - Glochidium
Class - Cephalopoda
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Includes Squid, octopus, Nautilus
Most advanced of Molluscs
Well developed head and eyes
Head has tentacles with suckers
Squids are largest of invertebrates
Locomotion by jet propulsion
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Class Scaphopoda
(tusk shells)
slender, tubular shells open at both ends
all marine
have tentacles around mouth
no defined head
no gills, respiration across mantle