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Slide 2 Phylum Mollusca Ex: Chitons, Snails, Clams, Octopods, and Squid Slide 3 General Characteristics It is believed that the molluscs evolved from annelids, but some scientists argue that they may have evolved from flatworms. 50% of the species are marine. Slide 4 General Characteristics Body Plan Soft bodied (term Mollusca is Latin for soft) invertebrates with bilateral symmetry. Usually protected by a calcareous shell. Slide 5 General Characteristics Body Plan Unsegmented body with a reduced coelum. The soft body parts are protected by a protective tissue called the mantle. Slide 6 General Characteristics Body Plan They possess a mantle cavity where the gills are located, into which the anus and kidneys release excretia, and into which eggs and sperm are released. Slide 7 General Characteristics Body Plan Two major parts: Head-foot: contains head, mouth, sensory organs, and muscular foot. Slide 8 General Characteristics Body Plan Visceral Mass: contains other organ systems, including circulatory, digestive, respiratory, excretory, and reproductive systems. (#4 is visceral mass) Slide 9 General Characteristics Most possess a radula. A ribbon of tissue that contains teeth. The radula is used for scraping, tearing, piercing, or cutting food. Slide 10 General Characteristics The shell is secreted (made) by the mantle. The shell consists of 3 layers: Periostracum: outer Prismatic: middle Nacreous: inner Slide 11 Class Polyplacophora Many plates Chitons Live in the rocky intertidal zone. Retain the greatest number of ancestral characteristics. Slide 12 Class Polyplacophora Shell: 8 overlapping plates held together by a tough girdle formed from the mantle. Foot used for attaching tightly to rocks. Slide 13 Class Polyplacophora They possess a radula with teeth that are mineralized with magnetite. Magnetite may become magnetized and the chitons may use the magnetic field of the earth to navigate (like a compass). Slide 14 Class Scaphopoda Sheath foot Tusk shells: shell resembles an elephant tusk with 2 openings. Foot protrudes from one end and is used for burrowing Slide 15 Class Scaphopoda Water enters and exits small end to exchange gases and remove waste. The foot or special tentacles emerge from the other end to feed on foramniferans. Slide 16 Class Gastropoda Stomach foot 75% of Mollusc species are Gastropods Great diversity Most are found on the benthos both on rocky and soft bottoms. Slide 17 Class Gastropoda The Shell Typically a pointed tube or cone into which the animal can contract. The opening can be closed with a cover called the operculum. Operculum---- Slide 18 Class Gastropoda Nudibranchs A subgroup of Molluscs that have lost all traces of a shell. Slide 19 Class Gastropoda The Foot Broad and mucus covered. May function as an adhesive gland that works like a suction cup. Slide 20 Class Pelecypoda or Bivalvia Hatchet foot Ex: Clams, Oysters, Mussels, Scallops. Typically sessile, living burrowed in sandy or muddy sediments. Slide 21 Class Pelecypoda The Shell Consists of 2 valves (plates) that generally completely cover the body, and are connected at a hinge by ligaments. They possess no head or radula. Filter feeders. Slide 22 Class Pelecypoda The Foot Used primarily for burrowing and anchoring. Slide 23 Class Pelecypoda Formation of Pearls An irritant (Usu. a grain of sand) comes between the shell and the mantle tissue. The response is to cover it with layers of nacreous material. If the irritant is spherical and embeds in the mantle tissue it becomes a pearl. Slide 24 Class Cephalopoda Ex: Squid, Octopus, Nautilus, Cuttlefish Slide 25 Class Cephalopoda Head foot Most advanced class of Molluscs. Have a highly developed brain and sense organs. Slide 26 Cephalopoda The eyes are very much like vertebrate eyes and are the dominant sense organ. Slide 27 Cephalopoda The Foot Modified into a head- like structure with a ring of tentacles surrounding the mouth. The tentacles are used for capturing prey, defense, reproduction, and in some cases locomotion. Slide 28 Cephalopoda The Foot Part of the foot is modified into a siphon used in jet propulsion. Ink can be expelled from the siphon to distract and confuse predators. Slide 29 Cephalopoda They are the largest of the invertebrates. Architeuthus: the giant squid can reach lengths of 60 ft. Slide 30 Cephalopoda The Shell With the exception of Nautilus they all have lost the heavy external shell. Squid have a small internal shell called the Pen, and octopi have no shell. Slide 31 Cephalopoda Color Change Cephalopods communicate through movements and color change. Color change involves specialized cells called chromatophores. Slide 32 Cephalopoda Feeding They are active carnivores. The radula is reduced. They have a pair of jaws shaped like the beak of a parrot. http://www.cephbase.u tmb.edu/viddb/vidsrch 2.cfmhttp://www.cephbase.u tmb.edu/viddb/vidsrch 2.cfm Slide 33 ****The End****