1 -Determinate cleavage-Indeterminate cleavage

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

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

4 Gastropoda (snails,slugs) Phylum: Mollusks- 4 Classes Polyplacophora (chitons) Bivalva (clams,oysters) Cephalopoda (squid,octopi)

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

6 zebra mussels- invasive species economic impact, biological impact

7 Phylum: Mollusks 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 Body Plan

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 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 whelk nudibranch cone shell

16 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)

17 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

18 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

19 Phylum: Mollusks Class: Bivalva (clams, scallops, mussels, oysters)

20 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

21 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

22 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

23 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

24 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 free- swimming larval stage (trochophore) but in terrestrial mollusks this stage completed inside egg

25 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