1. Soft-bodied Animals More than 112,000 species
Phylum Mollusca
Soft-bodied Animals
More than 112,000 species

2. 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

3. 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)

4. 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

5. General Characteristics
True coelomates:
Reduced main body cavity – the hemocoel
Protostomes
Mouth develops first in the embryo

6. Four classes Amphineura (polyplacophora) Bivalvia Gastropoda
Cephalopoda

7. Class Amphineura (Polyplacophora) – the chitons
Marine organisms
Shell is made up of 8 articulating plates
Have a muscular foot for locomotion (crawling)
Reduced head

9. 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

10. 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

11. 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

13. 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

14. 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

15. 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
Giant Clam

16. 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

17. Separate sex – external fertilization
Burrow in sand or rock or attach to substrate by secreting byssal threads
Many leap with a foot
Separate sex – external fertilization
Geoduck

18. Mmmm oysters!

19. 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

20. 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

21. 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

22. Squid External Anatomy http://www. youtube. com/watch

23. Squid Internal Anatomy