1. Billman, Bonin, & Olson Per. 5
Mollusca
Billman, Bonin, & Olson
Per. 5

2. General Characteristics
1)Bilaterally symmetrical. 2)Body has more than two cell layers, tissues and organs. 3)Body without cavity. 4)Body possesses a through gut with mouth and anus. 5)Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. 6)Has a nervous system with a circum-oesophagal ring, ganglia and paired nerve chords. 7)Has an open circulatory system with a heart and an aorta.
8)Has gaseous exchange organs called ctenidial gills. 9)Has a pair of kidneys. 10)Reproduction normally sexual and gonochoristic. 11)Feed a wide range of material. 12)Live in most environments.

3. General Characteristics
After the Arthropods the Mollusks are the most successful of the animal phyla in terms of numbers of species. There are about 110,000 species known to science most of which are marine.
They also exhibit an enormous range in size, from species which are almost microscopic to the largest of all invertebrates the giant squid which can weighs 270 kg and measures up to 12 meters long in the body, with tentacles as much as another 50 meters in length.

4. Classes of Mollusca

5. Amphineura

6. Monoplacophora

7. Gastropoda

8. Scaphopoda

9. Bivalvia

10. Cephalopoda

11. Body Plan

12. Body Plan Head-foot Visceral Lump
The body is divided into two functional regions, the head-foot and the visceral lump.
Head-foot
It is mostly a muscular organ covered in cilia and rich in mucous cells
includes a mouth, eyes and tentacles, the last two may be much reduced or even absent.
species with shells the head-foot can be drawn into the shell
Visceral Lump
entirely nonmuscular and contains the organs of digestion and reproduction
it includes the gonads, the kidney, the heart and the digestive diverticulum.

13. Feeding Digestion can occur in a ciliated tract or intracellularly
Pelecypods are mainly filter feeders
Cephalopods are active predators
Gastropods have a sharp radula for drilling through shells
some species have a single radula tooth while others may have several hundred thousand. In some the teeth are hollow and poison containing and are used as weapons

14. Respiration Use external gills for respiration
Diffusion also occurs through the moist skin
Respiration is through gills called ctenidia.

15. Circulation
Have an open circulatory system, meaning blood does not circulate entirely within vessels but is collected from gills, pumped through heart, and released directly into spaces in tissues from which it returns to gills and then to heart.
Such a blood-filled space is known as a hemocoel ("blood cavity").
hemocoel has largely replaced coelom, which is reduced to a small area around the heart and to the cavities of the organs of reproduction and excretion

16. Excretion Carried out by a pair of nephridia
Tubular structures that collect fluids from coelom and exchange salts and other substances with body tissues as the fluid passes along tubules for excretion.
Nephridia empty into the mantle cavity
Excretion of wastes is through structures called metanephridia and through the body and gill surfaces.

17. Response Cephalization is present
complexity of the nervous system varies with each species
Neurons are arranged in a ganglial pattern with two longitudinal nerve chords and a circum-oesophagal ring
cephalopods have eyes capable of image formation
Bivalves don’t have eyes, but they have cells that are tactile and photosensitive

18. Movement
the head-foot is the muscular organ with cilia and many mucous cells
Herbivorous forms glide by way of waves from muscular contraction
Carnivorous forms such as cephalopods use jet propulsion (water sprayed from the mantle cavity by a siphon)
Sea Hares and Cuttlefish use lateral fins
Bivalves use the foot to burrow into the sand

19. Reproduction
visceral mass contains the organs of reproduction (gonads)
usually sexual and gonochoristic
Fertilization is external
Mostly dioecious but Gastropods are monoecious
Egg becomes juvenile (cephalopods, snails, and some bivalves) or the egg becomes a trochophora larva (Chitons, monoplacophorans, scaphopods)

20. Bibliography
"The Molluscs (Phylum Mollusca) ." The Earth Life Web. N.p., n.d. Web. 15 Apr <
"The Mollusca." UCMP - University of California Museum of Paleontology. N.p., n.d. Web. 15 Apr < php>.
"Phylum Mollusca." Infusion. N.p., n.d. Web. 15 Apr <
“Phylum Mollusca Lecture Outline.” N.p., n.d. Web. 15 Apr <