Mollusks

Zebra Mussels Invaded Great Lakes- came from Great Britain Reproduce quickly-one female releases 40,000 Cause problems-clog intake pipes- Competition for other organisms Clean water since filter feeders

Characteristics 1. Have a head/foot - elongated with an anterior head-contains mouth and sensory system-foot used for locomotion and attachment 2. Visceral Mass - contains the organs 3. Have a Mantle – outer covering and enfolds most of the body

Cont… Coelome - fluid filled body cavity Primary induction  one of the three primary tissues interacts with another (endo, meso, ecto)

Cont… No segmentation Bilateral symmetry Organs systems for circulation, respiration, digestion, and excretion Trochophore (stationary) or Veliger (free swimming found in gastropods and bivalves) larvae Veliger Trochophore

INFO Respiration - most mollusks breath with gills (ctenidium) located in their mantle cavity (space between mantle and visceral mass)- –visceral mass contain the organs –Mantle - heavy fold of tissue wrapped around the visceral mass Sexuality – Diecious, hermaprhoditic –Pulmonate snail – “cupets arrow”

Circulation - three chambered heart and Most have open circulatory system-(blood leaks out of vessels and bathes the body’s tissues directly, i.e. no capillaries, blood vessels connected to sinuses) Closed circulatory system - octopus and squid-blood never leaves vessels (capillary system).

Excretion  nephridia (cilia that beat) rid the mollusk of waste- Mantle secrets a calcareous shell that protects the visceral mass –In bivalves this process helps in the production of pearls.

History Cambrian time  570 MYA Brachiopods, cephalopods, and gastropods Cephalopods in shell

Three Major Classes BivalvesGastropodsCephalopods

Bivalves sessile (stationary) filter feeders. Two part hinged shell with a hinge keeping it together No distinct head region Siphons-used to filter sea water for food Reproduce sexually-male, female, hermaphrodite-external fertilization 2 nd stage of larvae is called veliger

Bivalve cont… Oysters, scallop, clam, mussel Oldest part of shell and bump is called umbo Adductor muscles hold shell together (also called a ligament) If a grain of sand or parasite become lodged between shell and mantle then the mantle secrets a layer of material around the particle forming a pearl Umbo

Gastropods Snails and slugs Marine, freshwater, terrestrial Head, foot, visceral mass, and mantle Foot used for locomotion Tentacles on head where eyes are located Single shell

Gastropods cont… Respiration either by gills, skin, or lungs Radula  rasping tongue that scraps food Undergo torsion or twisting of the shell 180° External & internal fertilization Have Trochophore and veliger (free swimming) larvae

Cephalopods Means head and foot Foot has evolved into tentacles Octopus, squid, nautilus, cuttlefish Use siphons for jet propulsion

Cephalopods Cont… Have beak for eating Closed circulatory system Large brain and eye- can learn Have pigment cells (chromatophores) in epidermis to camouflage

NautilusCuttlefish

Interesting Class  Polyplacophora Chiton  reduced head and flattened foot Shell is divided into 8 parts Feed on algae External fertilization but no veliger stage

Homework Why would you expect the blood pressure inside most mollusk’s blood vessels to be quite low? Contrast the feeding habits of cephalopods with those of gastropods. Squids are the fastest swimmers of all aquatic invertebrates. Name two structural adaptations in squids that may have enhanced their swimming ability.