Slide 1

-Determinate cleavage-Indeterminate cleavage Slide 2 PoriferaCnidaria Ctenophora Phoronida Ectoprocta Brachiopoda Echinodermata Chordata Platyhelminthes Mollusca Annelida Arthropoda Rotifera Nemertea Nematoda Radiata Deuterostomia Protostomia Bilateria Eumetazoa Metazoa Ancestral colonial flagellate Phylum: Mollusca Slide 3 ancestral protostome coelomate Annelids ancestral Mollusk chiton-like body plan squid/octopu s-like snail/slu g-like 3 main Mollusk body plans evolved clam-like Slide 4 Gastropoda (snails,slugs) Phylum: Mollusks- 4 Classes Polyplacophora (chitons) Bivalva (clams,oysters) Cephalopoda (squid,octopi) Slide 5 Phylum: Mollusca One of most successful of all phyla (over 150,000 known species) Occupy marine, freshwater and land habitats Surpassed only by arthropods in number of species Named for Latin molluscus (soft) for their soft bodies Possess durable shells Terrestrial forms occur in seasonally moist places (slugs, snails) Economic importance sources of human food (ex. clams, oysters, scallops, escargot) production of pearls and shell material negative impact of zebra mussels (native to Russia), an invasive species destroying American freshwater ecosystems extensive crop, flower damage caused by snails and slugs intermediate hosts for some serious parasitic diseases Largest of invertebrates- giant squid estimated at 30-50 feet long Slide 6 zebra mussels- invasive species economic impact, biological impact Slide 7 Phylum: Mollusks distinct bilateral symmetry, coelomate, protostome 3 main body areas (1) head-foot sensory structures at head muscular foot adapted for locomotion foot in cephalopods (ex. squid) divided into tentacles foot of free-swimming (pelagic) forms (ex. scallop) modified as fins or winglike projections (2) visceral mass fleshy body contains excretory, digestive, circulatory structures (3) mantle cavity formed from folds of dorsal body wall, surrounds visceral mass gills are specialized portion of mantle in mantle cavity filamentous projections rich in blood vessels large surface area, efficient, can extract 50% of oxygen from water cilia maintain constant stream of water over gills some forms withdraw into mantle for protection outer surface of mantle may secrete shell Body Plan Slide 8 Most have durable shell secreted by mantle bivalves may produce pearls of shell material around foreign objects The Radula is a rasping, tongue-like structure all mollusks except bivalves have this covered with row of backward-curving, sharp teeth gastropods (snails) use to scrape algae of surfaces so they can eat algae some use to puncture prey and extract food Phylum: Mollusks Slide 9 Circulatory system consists of heart and open flowing system 3-chambered heart 2 chambers (atria) collect aerated blood from gills third chamber (ventricle) pumps blood to body heart surrounded by pericardial cavity this is the coelom cephalopods (ex. octopus) are more complex with a closed system of vessels and auxiliary hearts Slide 10 Phylum: Mollusks Excretory system more efficient that that of lower invertebrates nitrogenous wastes removed by tubular nephridia funnel-shaped, cilia-lined nephrostome collects waste from coelom coiled tube from nephrostome connects to bladder bladder connected to excretory pore waste discharged into mantle cavity where nutrients and salts (maintain osmotic balance) are reabsorbed Slide 11 Phylum: Mollusks Reproduction most have separate sexes, some hermaphrodite forms cross-fertilization is the rule, even in hermaphrodites some change sexes within one season larva is trochophore ciliated for movement trochophore larva Slide 12 Phylum: Mollusks Class: Polyplacophora (chitons) considered most evolutionarily primitive mollusk entirely marine body is oval in shape overlapping calcareous plates on dorsal side broad flat foot (contains mucus glands) on ventral side used in locomotion Slide 13 Phylum: Mollusks Class: Gastropoda (snails, slugs) primarily marine; also freshwater and terrestrial shell of marine ones closed by a plate (operculum)- can pull into place head has paired sensory tentacles that may have terminal eyes visceral mass asymmetrical because of torsion during development results in rearrangement of body one side of larva grows faster giving rise to a right-handed coil 180 turn with respect to head and foot nervous system twisted digestive, excretory and reproductive system on top of head less room on right leads to loss of right gill, right auricle of heart and nephridium Slide 14 Phylum: Mollusks Class: Gastropoda (snails, slugs) varied feeding habits- heterotrophs examples- (just FYI) terrestrial are herbivores- serious garden pests whelks bore into other mollusk shells, sucking out their insides cone shells are predators with harpoon-like radula, inject poison into prey nudibranches can store and use nematocysts from Cnidarians that they eat- for protection have rudimentary lungs terrestrial forms evolved lung under mantle some water forms have lung and come to surface to breath whelk nudibranch cone shell Slide 15 Phylum: Mollusks Class: Bivalva (clams, scallops, mussels, oysters) 2 shells hinged together dorsally (left and right sides) by a ligament shells close with contraction of pair of adductor muscles mantle forms shells which start as umbo on larva and then grow with animal, resulting in concentric growth rings ligament holds shells together mantle envelops the internal organs incurrent/excurrent siphons maintain stream of water coming into/out of clam; aids respiration, feeding, excretion pair of gills on each side of visceral mass under folds of the mantle circulatory system - heart with open circulatory system lack distinct heads, radulas and tentacles large foot adapted for locomotion and anchoring sessile filter feeders with palps (folds with cilia on either side of the mouth) that aid in the handling of food particles reproduction- separate sexes, fertilization usually external scallops are mobile forms, abundant in marine and freshwater habitats, part of scallop eaten is adductor muscle Slide 16 Phylum: Mollusks Class: Bivalva (clams, scallops, mussels, oysters) Slide 17 Phylum: Mollusks Class: Cephalopoda (octopus, squid, nautilus) most intelligent predators that compete successfully with fish can learn complex tasks feeding eat fish, mollusks, crustaceans, worms foot evolved into a series of tentacles with suction cups or hooks to seize prey have paired jaws and radula Slide 18 Phylum: Mollusks Class: Cephalopoda (octopus, squid, nautilus) nervous system highly developed with brain rapid responses result from giant nerve fibers attached to mantle eyes are elaborate with retina similar to that in vertebrates circulatory system is closed with auxiliary hearts shells lack external shells except for a few nautilus species squids, cuttlefish- internal remnant of shell that provides stiffening support locomotion-very quick moving take water into mantle, expel it through siphon for propulsion (and also for gas exchange via gills) when threatened eject water violently tentacles for locomotion, also reproduction- sexes are separate Slide 19 The Table for Mollusca Symmetry: bilateral; all have 3 main body parts (head-foot, visceral mass, mantle); most secrete hard protective shell; gastropods show torsion in adult Segmentation: no Mesoderm present: yes, triploblastic Type of body cavity: coelomate; the coelom is the pericardial cavity in the adult Ciliated larva: yes, trocophore larva Protostome: yes Cleavage/cells: determinate Slide 20 The Table for Mollusca Nervous system: ganglia and sensory structures in head region, nerve ring around esophagus, nerve cords; Cephalopods are more advanced with highly developed brain and complex eyes Respiratory system: gills for gas exchange, rudimentary lungs in some gastropods Digestive system: complete, one-way; digestive tract in visceral mass; heterotrophs Excretory system: nephridia remove wastes Reproductive system: most have separate sexes, some snails are hermaphrodites, gonads in visceral mass, most go through free-swimming larval stage (trochophore) but in terrestrial slugs and snails this stage is completed inside egg Slide 21 The Table for Mollusca Circulatory system: most have heart with open circulatory system that pumps the fluid hemolymph around the body; cephalopods are more complex with a closed circulatory system and multiple hearts Members: Chitons, Bivalves (clams, scallops, mussels), Cephalopods (octopi, squid), Gastropods (snails, slugs) Habitat: mostly marine, some freshwater, some snails and slugs are terrestrial Relationship to other phyla: N/A