Download Phylum Annelida - MR. Hill`s class

Phylum Mollusca
• Soft-bodied Animals
• More than 112,000 species
General Characteristics
• Bilateral Symmetry
– Reduced segmentation
• Three body parts
– Head (contains mouth)muscular foot:
• Locomotion, digging, supports internal organs
• May be modified in squid and octopus
– Visceral Hump (above the head)
• Contains the internal organs (heart, organs of digestion, reproduction
and excretion)
– Mantle
• Thin body covering (contains calcium carbonate)
• Secretes shell
• Reduce surface area for gas exchange  evolved gills
General Characteristics
• Respiration
– Gills(protected in mantle cavity), lungs, mantle or
body surface
• Nitrogenous wastes are excreted through
nephridia
• Open circulatory system with dorsal heart and
vessels, hemocoel for return of circulatory fluid
• Complete digestive system with mouth, radula=
flexible tongue like strip of tissue covered with
tough abarsive teeth that point backward
– Radula is used to graze, drill, or function as a poisonous
dart (or beak i.e. octopus)
General Characteristics
• Nervous system with dorsal
brain, nerve ring, pair of
solid ventral nerve cords
• Reproduction:
– Sexual with the development
of the trochophore larvae
(nearly identical to annelids)
– Trochophore larvae becomes
the veliger larvae
• swimming
• Has a shell
Trochophore Larvae
Veliger Larvae
General Characteristics
• True coelomates:
– Reduced main
body cavity – the
hemocoel
• Protostomes
– Mouth develops
first in the embryo
Four classes
•
•
•
•
Amphineura (polyplacophora)
Bivalvia
Gastropoda
Cephalopoda
Class Amphineura (Polyplacophora)
– the chitons
• Marine organisms
• Shell is made up of 8
articulating plates
• Have a muscular foot for
locomotion (crawling)
• Reduced head
Chitons cont’d
• About 650 species of
these organisms
• Cling to rocks in the
intertidal zone and use a
tooth-like radula to
scrape food off of rocks
(herbivores)
• Breathe through gills
Gumboot Chiton
Class Gastropoda (Stomach-foot)
• Largest molluscan class
• Snails and Slugs, Sea slugs
• Characterized by a single shell
with characteristic cone shape
• Breathe through gills (ctenidia) or
the mantle cavity acts as a
primitive lung (gas diffusion)
• Muscular foot extends along the
ventral surface of the organism
Class Gastropoda
• Gastropods undergo a process called
torsion during larval development
• The visceral mass twists 180 degrees in
relation to the head
• Results in the mantle cavity, gills and anus
being brought to the front of the animal
• Because of torsion the gastropod is able to
retract its head into its mantle cavity
when threatened
Gastropods cont’d
• Head contains a pair of
antennae and a pair of eyes
• Scraping radula to pick up food
• Slug does not have a shell
– Usually becomes active during
the cool moist part of the day
• Only molluscan class to become
terrestrial
• Open circulatory system
– Circulatory fluid = hemolymph
• Herbivorous or carnivorous
Nudibranchs (Sea Slugs)
• Marine gastropods that lack
shells
• Nudibranch means “naked gill”
• refers to the fact that gas
exchange happens across the
entire surface of these animals
Class Bivalvia (2 shells connected
by hinge)
• Clam, Oysters, Mussels, Scallops
(most are sessile)
• Mainly marine – living in intertidal
zone
• Large visceral hump and a muscular
foot with a reduced head covered
with a thin mantle
• The mantle produces a cavity where
the gills and 2 siphons (incurrent and
excurrent) are found
• http://www.youtube.com/watch?v=Z
BfviWg7kKM&feature=related
Giant Clam
Bivalvia cont’d
• Filter feeders:
– Take water containing food into the mantle cavity and pass it over
the mouth
– Excess water is forced out through the excurrent siphon
• Oldest part of the shell is the area surrounding the hinge (called
the umbo)
• Exclusively marine
• No radula
Swimming
Scallop
• Burrow in sand or rock or
attach to substrate by
secreting byssal threads
• Many leap with a foot
• Separate sex – external
fertilization
Geoduck
Mmmm oysters!
Class Cephalopoda (Head-foot)
• Squids, octopuses, cuttlefish,
and nautilus
• All members of this class are
marine
• Squid and octopus are among
the most intelligent of the
invertebrates
• All carnivorous
• Have tentacles and a central
mouth containing a sharp beak
Cephalopods cont’d
• Many of these organisms
contain a large ink sac that is
used when trying to escape
from potential predators
• They have well developed eyes
and brains
• They contain special pigment
cells called chromatophores
which enable them to change
color
Squid Candles
Cephalopods cont’d
• They have gills in the mantle
cavity
• Their circulatory system is a
closed one
• Jet propulsion: Can force
water out siphon
• Catch prey with arms injecting
poison with radula
• Internal fertilization – lay eggs
Squid External Anatomy
http://www.youtube.com/watch?v=e8RfE0mPsRc
http://www.youtube.com/watch?v=O5hEmZCuX0Y
Squid Internal Anatomy