Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Mollusca 2010 - The Bronx High School of Science
Document related concepts
Transcript
-Determinate cleavage -Indeterminate cleavage “Radiata” Metazoa Ancestral colonial flagellate Deuterostomia Eumetazoa Protostomia Bilateria Phylum: Mollusca Nematoda Nemertea Rotifera Arthropoda Annelida Mollusca Platyhelminthes Chordata Echinodermata Brachiopoda Ectoprocta Phoronida Ctenophora Cnidaria Porifera clam-like squid/octopu s-like snail/slu g-like 3 main Mollusk body plans evolved Annelids ancestral Mollusk chiton-like body plan ancestral protostome coelomate Phylum: Mollusks- 4 Classes Polyplacophora (chitons) Bivalva (clams,oysters) Cephalopoda (squid,octopi) Gastropoda (snails,slugs) 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 zebra mussels- invasive species economic impact, biological impact Phylum: Mollusks Body Plan •bilateral symmetry, coelomate, protostome •3 main body areas •(1) head-foot •sensory structures at head •muscular foot adapted for locomotion •cephalopod foot divided into tentacles (ex. squid) •free-swimming (pelagic) animal foot modified as fins or winglike projections (ex. scallop) •(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 animals withdraw into mantle for protection •in shelled animals mantle secretes shell Phylum: Mollusks • Most have durable shell •secreted by mantle •bivalves may produce pearls of shell material around foreign objects •Radula = rasping, tongue-like structure •in all mollusks except bivalves •covered w/ row of backward-curving, sharp teeth •gastropods (snails) use to scrape algae of surfaces for food •some use to puncture prey and extract food Phylum: Mollusks • Circulatory system consists of heart and open flowing system • 3-chambered heart • 2 chambers (atria) collect oxygenated blood from gills • third chamber (ventricle) pumps blood to body • heart surrounded by pericardial cavity (= coelem) • cephalopods (ex. octopus) more complex w/ closed system of vessels & auxiliary hearts Phylum: Mollusks • Excretory system more efficient than in 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 Phylum: Mollusks •Reproduction •most have separate sexes, some hermaphrodites •cross-fertilization is rule, even in hermaphrodites •some change sexes within one season •larva is trochophore •ciliated for movement trochophore larva Phylum: Mollusks Class: Polyplacophora (chitons) • most evolutionarily primitive mollusk • marine • body is oval shape • overlapping calcareous plates on dorsal side • broad flat foot (contains mucus glands) on ventral side for locomotion Phylum: Mollusks Class: Gastropoda (snails, slugs) •primarily marine, some freshwater & terrestrial •some have an operculum- “trap door” shell can pull into place for protection •head has paired sensory tentacles, may have terminal eyes Phylum: Mollusks Class: Gastropoda (snails, slugs) • visceral mass asymmetrical b/c torsion during development • one side of larva grows faster giving rise to a right-handed coil • 180˚ turn with respect to head & 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 Phylum: Mollusks Class: Gastropoda (snails, slugs) • varied feeding habits- heterotrophs • examples- (just FYI) • terrestrial ones herbivores- serious garden pests • whelks use radula to bore into other mollusk shells and suck out contents • cone shells are predators with harpoon-like radula, inject poison into prey • nudibranches can store/use nematocysts from Cnidarians eaten • have rudimentary lungs • terrestrial forms evolved lung under mantle • some water forms have lung and come to surface to breath cone shell whelk nudibranch Phylum: Mollusks Class: Bivalva (clams, scallops, mussels, oysters) • bivalve = 2 shells (L/R) • shells hinged together dorsally by a ligament • paired adductor muscles contract to close shells • we eat scallop adductor muscles! • mantle secretes shell • shell begins as umbo on larva • grows with animal • concentric growth rings • mantle • membrane that envelops internal organs (visceral mass) Phylum: Mollusks Class: Bivalva (clams, scallops, mussels, oysters) •pair of siphons •incurrent and excurrent •maintain stream of water moving in/out of animal •aids in respiration, feeding, excretion •respiratory system •paired gills •one on each side of visceral mass •circulatory system •heart with open circulatory system Phylum: Mollusks Class: Bivalva (clams, scallops, mussels, oysters) •lack distinct heads, radulas and tentacles •locomotion •large foot adapted for locomotion and anchoring •most are sessile •scallops are motile •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 Phylum: Class: Bivalva (clams, scallops, mussels, Mollusks oysters) Phylum: Mollusks Class: Cephalopoda (octopus, squid, nautilus) • most intelligent of mollusks • predators that compete successfully with fish • can learn complex tasks • feeding • eat fish, mollusks, crustaceans, worms • foot evolved into series of tentacles w/ suction cups/hooks to seize prey • paired jaws, radula Phylum: Mollusks Class: Cephalopoda (octopus, squid, nautilus) •nervous system •highly developed w/ brain •rapid responses via giant nerve fibers attached to mantle •elaborate eyes w/ retina similar to vertebrate •circulatory system •closed with auxiliary hearts •shells •no external shells (except for a few nautilus species) •squids, cuttlefish- internal remnant of shell that provides stiffening support Phylum: Mollusks Class: Cephalopoda (octopus, squid, nautilus) •locomotion •quick moving •take water into mantle, expel it through siphon for propulsion •also for gas exchange via gills •eject water violently if threatened •tentacles •reproduction •sexes separate The Table for Mollusca Symmetry: bilateral; 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; coelom = pericardial cavity in adult Ciliated larva: yes, trocophore Protostome: yes Cleavage/cells: determinate The Table for Mollusca Nervous system: ganglia & sensory structures in head region, nerve cords; Cephalopods more advanced w/ highly developed brain & 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 > nephrostome > bladder > excretory pore Reproductive system: most have separate sexes, some snails hermaphrodites, gonads in visceral mass, most go through freeswimming larval stage (trochophore) but in terrestrial mollusks this stage completed inside egg The Table for Mollusca Circulatory system: most have heart with open circulatory system that pumps the fluid hemolymph around the body; cephalopods more complex w/ a closed circulatory system and multiple hearts Members: Chitons, Bivalves (clams, scallops, mussels), Cephalopods (octopi, squid), Gastropods (snails, slugs) Habitat: most marine, some freshwater, some snails and slugs are terrestrial Relationship to other phyla: N/A
