Week 9, lec 1 - week 9 lecture 1 notes PDF

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week 9 lecture 1 notes...

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Gastropods, bivalves, psychic octopus, and giant squid Animal Phylogeny

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Traits Triploblastic, bilateral symmetry (most) Coelomate  body cavity

Outline  8 classes within the Phylum Mollusca - Gastropoda  snails, slugs, limpets - Bivalvia  clams, oysters - Cephalopoda  squid, octopus, cuttlefish - Polyplacophora  chitons - Caudofoveata - Aplacophora - Monoplacophora - Scaphopoda Phylum Mollusca  Extremely diverse  more than 100,000 species Gastropods  Abalone, snail, nudibranch, limpets, slug Cephalopods  Octopus, squid Bivalves  Clams, oysters Characteristics  Mostly marine of molluscs - Intertidal, shallow, deep  Some freshwater and terrestrial  Bilateral symmetry - Lost in gastropods  Triploblastic - Mesoderm and organs  Coelomate - Highly reduced and replaced with haemocoel (blood cavity) in some  Complete digestive tract  mouth and anus

Mollis = soft

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General body plan

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Mantle Cavity

Respiratory system

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Mollusca have a soft unsegmented body Most secrete a calcium carbonate shell Others have reduced internal shells, or no shells Microscopic to several meters - Giant squid  250kg Mantle = tissue secretes shell, creates mantle cavity Visceral mass = digestive, excretory and reproductive organs Muscular foot

Formed by mantle (tissue over visceral mass) Houses gills or ctenidia Excretory pores, anus, reproductive openings Gills = ctenidia Contact water in mantle cavity Filamentous/feathery with blood vessels - Increases surface area for gas exchange Some have blue blood  cooper containing compound called haemocyanin

Circulatory system

Open circulatory system (except cephalopods)

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Blood filled space (haemocoel) replaces coelom  blood not contained to blood vessels Blood (hemolymph) circulates within haemocoel Returns to gills, pumped to

heart, then to body

Complete Digestive tract

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Excretory system

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Nervous system

Shell

External shells

Reduced and internal shells No shell

Radula

Radula as a drill

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Radula darts Reproduction

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Mouth  esophagus  stomach  intestine  anus (mantle cavity) Radula + digestive enzymes Radula  tongue that can be specialised depending on what the mollusc is eating Nephridia - Remove metabolic and nitrogenous wastes from body cavity through the mantle cavity Osmotic balance - Water reabsorbed Waste excreted into mantle cavity Complex nervous systems Nerve ring around the esophagus Nerve cords extend from nerve ring Well developed eyes and brain in cephalopds Secreted by mantle Calcium carbonate – protection, support External Reduced and internal No shell Snails Chitons Bivalves Cuttlefish Squid Chitinous ‘pen’ Slug - Lost shell during evolution Octopus Rasping tongue-like organ  feeding Rows of chitinous teeth In all molluscs, except bivalves Scrape algae off substrate  e.g. slugs, snails Shred food inside mouth  e.g. squid Modified into a drill - E.g. moon snails sandy subtrates - Drill into bivalve shells Predatory whelks - Species of cabestana - Australian rocky shores 500 different species of cone shells Several of the most venomous live in australia Mostly gonochoristic (separate sexes) Some gastropods and bivavles are hermaphrodic External fertilisation  aquatic Internal fertilisation  terrestrial, some aquatic

Trochophore Larva

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Spiral cleavage (protosomes) Free-swimming larva in marine molluscs - Ciliated - Dispersal

Polyplacophora – Chitons Marine  mostly shallow or intertidal Oval body  8 dorsal calcareous plates Broad flat foot  creep, suction cup Grazing herbivores  radula

Class Gastropoda – Snails, Slugs, Limpets  Mostly marine, some freshwater and terrestrial  Spiralled shell  lost in slugs, flattened in limpets  Radula  scrape, drill, darts  Tentacles - Eyes, chemo- or mechano- sensors  Crawl, swim, burrow Gastropoda are Not Bilaterally Symmetrical  Torsion  180O rotation during development, moves anus and mantle cavity to anterior end  Coiling  spiral winding of shell Gastropoda – Terrestrial Snails and Slugs  No gills  mantle cavity has blood vessels (lung)  Pneumostome in mantle (breathing pore)  Allowed them to colonise land - Efficient excretory system (conserve water) - Internal fertilisation Hermaphrodites – Banana slugs  Size matters  Mate with similar sized slugs  Bite off each other’s’ penis Gastropoda – Nudibranchs  Sea slugs - Marine - No shell Nudibranchs  Rhinophores = sensory tentacles  Primarily chemosensory  Oral tentacles = identify food by taste or touch

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Gills or cerata for gas exchange Phyllodesmium sp. Found on coral – Xenia sp. Cryptic species which ingests and maintains symbiotic algae from coral

Pelagic and Venomous – Nudibranchs  Genus Glaucus  Preys on Physalia physalis (blue bottle)  Stores namatocytes  Used to subdue other prey and for defence Bivalvia – Clams, Oysters, Mussels, Scallops  Mostly marine, some freshwater  Two lateral shells + adductor muscles  Mantle folds  incurrent and excurrent siphons  Bivalves DO NOT have a radula - Filter feeders  Use gills to feed, mucous traps food particles  Cilia move food to mouth Bivalves and Byssal Threads  Mostly sessile  Attach using byssal threads  Clams  use foot as anchor to bury into sand  Scallops flap shells  the only motile bivalves Cephalopoda – Octopus, Squid, Nautilus  Marine predators  Most evolutionary advanced invertebrates  Well-developed eyes and brains  Foot modified into tentacles with suckers and siphon for jet propulsion  Shell reduced and internal or missing Cephalopods have a beak  Tentacles grab prey - Suckers - Secretes neurotoxin  Chitinous beak  shearing and tearing  Radula grinds food Nautilus  From Greek word for “sailor”  Often called “living fossils”  have been around for 500 MYA  Only (living) cephalopods with external shell  Camouflage - Darker, stripped surface - White underside  Many tentacles  no suckers - Detect predators and prey  Jet propulsion

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Can reach ~ 3ocm in diameter Gas chambers to control buoyancy - Limited to upper 300 m

The Kraken  13th Century monster  1800’s attacked boat off Angola  Norwegian fisherman reported good catches when Kraken was nearby Colossal Squid  Captured off a prolific fishing ground in Antarctica  Filmed in wild in 2013 off coast of Japan Cephalopod Venom – Blue-ringed Octopus  Venom causes motor paralysis and respiratory arrest within minutes  Toxin is created by bacteria in the salivatory glands of the octopus  The blue rings have evolved a symbiotic relationship - Bacteria given protection - Octopus used toxin for defence Cephalopods – Quick Escape  Siphon for jet propulsion  steer by orienting siphon  Ink sac  release ink when threatened and escape Cephalopods – Change colour  Chromatophores  Pigmented cells change size, change colour of skin  Match colour and texture of surroundings  Camouflage  Mating  Defence Cephalopods – organ systems  Closed circulatory system  Can get big: giant squid 18m  Well-developed sensory organs and brain  Ability to learn and behave  octopuses are considered most intelligent invertebrate Pharmaceuticals  Non-addictive pain killer from Magician cone, Conus magus - 1000 times more powerful than morphine  US approved painkiller Ziconotide derived from cone toxins in 2004 - Blocks pain signals from nerves to the brain  Toxin can treat Alzheimer’s disease, Parkinson’s disease and epilepsy...