PHYLUM MOLLUSCA
Mollusks Mollusks (Mollusca) –extremely diverse –characterized by a coelom great economic significance –pearls –mother of pearl economic / environmental costs –zebra mussel invasion –intermediate hosts for parasites
Body Plan of the Mollusks Distinct bilateral symmetry Digestive, excretory, and reproductive organs are all concentrated in a visceral mass and a muscular foot. May have differentiated head Folds constituting a mantle –gills - increased surface area for gas exchange Shells serve primarily for protection Radula - rasping tongue-like organ used for feeding Circulatory system (except cephalopods) consists of a heart and an open circulatory system. Nitrogenous wasted removed by nephridia
Mollusk Body Plans
Reproduction in mollusks –most have distinct male and female individuals –most engage in external fertilization –many have free-swimming larvae (trochophores) which closely resemble larval stage of many marine annelids
Mollusks & Movement Foot –Muscular organ to move, dig, slide… Radula –Rasping tongue to obtain food or drill holes in other shells Photo credit: USGS
Function of the Radula A layer of flexible skin, with hundred of sandpapery teeth, used to scrape algae off of rocks In full-on carnivore mode, the radula acts like a drill to pierce shells. These things even have poison glands to make things nastier Octopi and certain sea slugs do this.
Class Gastropoda snails, slugs, sea slugs
Incredible diversity of shell form
Gastropods The largest class…. Snails, slugs, and sea slugs Sometimes called the univalves (one shell) Live in water or on land Herbivores that use a radula to scrape food from surface. Visceral mass- Body found within the shell. Moves by a muscular foot
Open circulatory - blood flows through vessels, open spaces within body. Aquatic gastropods-gills for respiration; land gastropods -mantle for gas exchange. Nephridia - Filter wastes from the blood. Most land univalves are hermaphroditic…aquatic univalves - separate sexes with external fertilization. The abalone and conch are examples of marine univalves. Gastropods
Naked gastropods…the slugs Thick layer of mucus coating bodies-no shell Nudibranchs – Sea slugs that feed on jellyfish and incorporate the nematocysts into their own tissues. Some sea slugs secrete a poisonous mucus for protection.
Class Bivalvia clams, cockles, mussels, oysters, scallops
Freshwater mussels in Iowa!
Life cycle of the unionid bivalve +
Bivalvia: bivalves –clams, scallops, mussels and oysters –two lateral shells hinged together dorsally –mantle secretes shell and ligaments –most are sessile filter-feeders
BIVALVES Clams, Scallops, and Oysters Most are marine invertebrates. Open circulatory system Large muscular foot for digging. No distinct head Filter feeders. Gills are coated with mucus which trap food particles and oxygen. Mantle -Secretes the shell. Any particle caught in between the shell and mantle is coated to stop irritation (pearl)
pearls Mother-of-pearl inner smooth part of bivlave shell. Made primarily by oysters when a foreign object gets lodged inside between mantle and shell. Come in many colors
Class Cephalopoda squids, octopus, cuttlefish, nautilus
Cephalopoda: octopuses, squids, nautilus –most intelligent of the invertebrates –active marine predators –foot evolved into a series of tentacles equipped with structures to capture prey –highly developed nervous systems
Cephalopods Head-footed mollusks Octopus, Squid, and Chambered nautilus Most intelligent (Well developed nervous system) Only mollusk group which are all predators Free swimming Tentacles with suckers surrounding the head are used for moving and capturing prey. A sharp beak-like radula for ripping apart prey. Closed circulatory system (blood moves through blood vessels and is most efficient)
Adaptations to predatory life style Active and very mobile –Close circulatory systems Camouflage –Chromatophores in skin – CgtYWUybIEhttp:// CgtYWUybIE Exceptional vision Beak to tear prey Arms (tentacles) to grip prey
Bioluminescence! Complicated Chemical Reactions!