1. CHAPTER 12 MOLLUSCAN SUCCESS

3. The amazing characteristics of the mollusca phylum had been preserved from generations to generations it was noted that Arthropodas, one of the Molluscan are the most successful of the animal phyla in terms of numbers of species of about 110,000. These great molluscan species comprise the vast majority of habitats in both aquatic and terrestrial location. These vast diverse species spans from the arctic seas to the tropics and from rivers, streams, valleys to the forest and mountainsides and where ever they are the poses the same characteristics of the mollusca phylum that is distinct from the rest. Wherever they are characteristics of the mollusca phylum that are adaptable to the current or new location is admirable. The can easily adapt to live in deserts and they can become preys or predators to other animals and they know how to defend themselves from the invaders.

4. The uniqueness of the characteristics of the mollusca phylum is impressive and because of their basic body type these animals had evolved into a variety of different forms adapted to specific environments and their hard shell is amazingly protecting them and their shelter as well. In the vast seas the characteristics of the mollusca phylum that have no shells such as squids and octopuses are amazing. They can swim fast and can defend themselves against their attackers through their powerful muscles, tentacles, and the technique they used to hide from the enemy using the ink in their body. Many people love to see these amazing creatures and because of these uniqueness and characteristics of the mollusca phylum they appear in a wide range of sizes, colors, forms. They are considered to be one of the most very successful group in the animal kingdom. They had increased their population and they have more than 100,000 species since their existence began.

5. Class Gastropoda gastropods, slugs, and snails

12. Class Bivalvia bivalves and clams

14. The body is laterally compressed. The only external structures are the labial palps ; in some groups, there are sensory tentacles and photoreceptors at the edge of the mantle . Bivalves also possess two ctenida (in most cases) and a muscular foot. The edges of the mantle are fused in some taxa and prolonged to form tube-like siphons . One siphon carries water to the mantle cavity (the inhalent siphon) and one from it (the exhalent siphon); in many taxa they are fused but the water streams remain separate. A bivalve uses its muscular foot either to attach itself to a substrate or to burrow. Scallops propel themselves through the water by jet propulsion: rapid closing of the valves squirts water out of the mantle cavity, and the animal "swims" in the opposite direction.

16. The evolutionary relationships of bivalve lineages are not currently well understood. There appear to be many parallel lines of evolution that obscure relationships between taxa. However, there is some consensus that Protobranchia (Palaeotaxodonta), Pteriomorpha, Heterodonata, and Anomalodesmata are legitimate taxonomic groups. Pteriomorphans, characterized by reduced or absent siphons, usually have filibranch ctenida. Heterodontans are typified by possessing large siphons and have lamellibranch gill structure. Lastly, anomalodesmatans are the septibranch bivalves. Many bivalves (such as clams or oysters) are used as food in places all over the world. Pearl oysters are used for commercial production of pearls. Bivalves can also cause economic damage. The glochidia larvae of some freshwater mussels can be serious parasites of fish, and some marine bivalves bore through wood, causing damage to wooden ships, pilings, and other wood structures.

18. Class Cephalopoda octopuses and squids

21. Cephalopods are gonochoric. A female typically possesses a single oviduct. A male produces spermatophores that it transfers to the female's genital pore by means of a specialized arm or tentacle. In some species, the specialized arm tip may be pinched off and left in the female's mantle cavity: this is known as the hectocotylus arm. Mating in some cephalopods includes courtship rituals that may consist of color changes, body movements, or combinations of both. Cephalopods exhibit spiral cleavage and are protostomous, but they have no larval stage: their development is direct. Octopods typically tend their eggs until hatching. Most cephalopods are semelparous. With the exception of Nautilus, cephalopods contain pigment-rich cells in the epidermis surrounded by cells containing contractile fibers. These cells, called chromatophores, are responsible for the ability of the cephalopods to change color and patterns accurately and rapidly in response to danger or emotion. Chromatophores may also be under hormonal control. When the contractile fibers are stimulated, they contract and expose a larger amount of color.

22. Cephalopods possess well-developed nervous systems and complex sensory organs. The ganglia are large and close to each other, forming a large brain. Certain upper lobes within the brain serve as controls for memory and learning. Cephalopods also possess ganglia elsewhere within the mantle cavity linked to the brain by giant axons that are involved with muscular contraction. The eyes in Nautilus are primitive, but in other cephalopods are highly developed and resemble vertebrate eyes with a cornea, lens, retina, and iris. These eyes are capable of forming images and distinguishing colors. Cephalopods are of considerable economic importance to humans. Many species of squid and octopus are eaten. Nautilus shells are often used decoratively, and the internal shell of a cuttlefish, or cuttle bone, is sold in the pet trade as a calcium source for birds. Giant cephalopods such as squid and octopuses are also a great source of sea-monster folklore.

23. Class Polyplacophora

27. Class Scaphopoda tusk shells

31. Class Monoplacophora

33. Neopilina galatheae , top (dorsal) view. Neopilina is peculiar because of the replication of various of its organs and organ systems, reminiscent of metameric animals. The class Monoplacophora is well known as fossils, and until 1952 all of its members were believed to have been extinct since the Devonian period, about 350 million years ago. [This shell, relatively thin, was damaged while being dredged.]

34. Neopilina galatheae , bottom (ventral) view. The oval, flat foot is characteristic of the classes Monoplacophora, Polyplacophora and Gastropoda . The foot is bordered on each (left and right) sides by five gills.

35. Neopilina galatheae , side (lateral) view. The anterior end, denoted by the slightly coiled apex, is on the right.

36. Class Aplacophora

46. Gadila aberrans occidental tuskshell Antalis entale