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Life History of Aquatic Organisms (AFI-31306)
Lecture: Adaptive radiation in molluscs Martin Lankheet, EZO
THEME Lectures Tutorials Practicals Introduction to Life History theory
• Introduction to Life History theory
• Life histories of marine mammals and relevance for population zooplankton ecology
• Life history trade-offs • Density (in) dependent
regulation of population numbers
• Life-history trade-offs in zooplankton
Niche differentiation and feeding
• Food & food webs • Niche adaptation & eco-
morphology • Adaptive radiation in Lake
molluscs • Adaptive radiation in fishes • Eco-morphological
methodology
• Food & food webs assignment
• Mollusks: adaptation in bivalves and squids
• Reflection on cyprinid fish adaptations
• Feeding ecology of seals • Diversity of North Sea
fishes • Functioning and life history
of gastropods, bivalves and cephalopods
• Cyprinid fish: adaptive radiation
Migration, habitat choice and swimming
• Fish swimming • Swimming in 'non-fish' • Fish migration
• Analysis of larval swimming • Migration
• Larval swimming
Reproductive strategies
• Reproductive and life history strategies in aquatic organisms
• Reproduction in fishes • Physiology of reproduction
• Size of maturity & reproduction
• Physiology of reproduction
Position in the course
Phylum Mollusca
l Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses, cuttlefish and squids.
Phylum Mollusca
l Molluscs evolved in the sea and most molluscs are still marine. l Some gastropods and bivalves inhabit
freshwater. l A few gastropods (slugs & snails) are
terrestrial.
Humans & Molluscs
l Humans use molluscs in a variety of ways: l As food – mussels, clams, oysters, abalone,
calamari (squid), octopus, escargot (snails), etc.
l Pearls – formed in oysters and clams. l Shiny inner layer of some shells used to
make buttons.
Humans & Molluscs
l A few are pests or introduced nuisances: l Shipworms – burrow through wood,
including docks & ships. l Terrestrial snails and slugs damage garden
plants. l Molluscs serve as an intermediate host for
many parasites. l Zebra mussels – accidentally introduced
into the Great Lakes and reeking havoc with the ecosystem.
Outline
l General body plan l Adaptive radiation l Program:
l Tomorrow: l Dissect and study Helix aspersa (garden snail) l Biologists: Study Bivalves or Cephalopods
l Wednesday: l Video l Presentations/ demonstrations on Bivalves and
Cephalopods
Molluscs Phylogenetic Position and Development
Phylum Mollusca
l Molluscs have a mesoderm lined body cavity – a coelom.
l They are protostomes l Spiral, determinate cleavage l Schizocoelous coelom development
Mollusc Body Plan
l All molluscs have a similar body plan with three main parts: l A muscular foot l A visceral mass – containing digestive,
circulatory, respiratory and reproductive organs.
l A mantle – houses the gills and in some secretes a protective shell over the visceral mass.
Mollusc Body Plan
l Most molluscs have separate sexes with gonads located in the visceral mass.
Head-Foot Region
l Most molluscs have well developed head ends with sensory structures including photosensory receptors that may be simple light detectors or complex eyes (cephalopods).
Head-Foot Region
l The radula is a rasping, protrusible feeding structure found in most molluscs (not bivalves). l Ribbon-like
membrane with rows of tiny teeth.
Head-Foot Region
l The foot of a mollusc may be adapted for locomotion, attachment, or both.
l Pelagic forms may have a foot modified into wing-like parapodia.
Shells l When present, the calcareous shell is secreted by the
mantle and is lined by it. It has 3 layers: l Periostracum – outer organic layer helps to protect inner layers
from boring organisms. l Prismatic layer – densely packed prisms of calcium carbonate. l Nacreous layer – iridescent lining secreted continuously by the
mantle – surrounds foreign objects to form pearls in some.
Mantle Cavity
l The space between the mantle and the visceral mass is called the mantle cavity. l The respiratory organs (gills or lungs) are
generally housed here.
Internal Structure & Function
l Many molluscs have an open circulatory system with a pumping heart, blood vessels and blood sinuses.
l Most cephalopods have a closed circulatory system with a heart, blood vessels and capillaries.
Mollusc Life Cycle
l Most molluscs are dioecious, some are hermaphroditic.
l The life cycle of many molluscs includes a free swimming, ciliated larval stage called a trochophore. l Similar to annelid
larvae.
Mollusc Life Cycle
l The trochophore larval stage is followed by a free-swimming veliger larva in most species.
Major Mollusc Classes
l Four major classes of molluscs: l Class Polyplacophora
– the chitons l Class Gastropoda –
snails & slugs l Class Bivalvia – clams,
mussels, oysters l Class Cephalopoda –
octopus & squid
Class Polyplacophora
l Class Polyplacophora includes the chitons. l Eight articulated plates
or valves. l Can roll up.
l Live mostly in the rocky intertidal.
l Use radula to scrape algae off rocks.
l Gills are suspended from roof of mantle cavity.
Class Gastropoda
l Gastropoda is the largest of the molluscan classes. l 70,000 named species. l Include snails, slugs,
sea hares, sea slugs, sea butterflies.
l Marine, freshwater, terrestrial. l Benthic or pelagic
Class Gastropoda
l Gastropods show bilateral symmetry, but due to a twisting process called torsion that occurs during the veliger larval stage, the visceral mass is asymmetrical.
Class Gastropoda, coiling
l Coiling is not the same as torsion.
l Early gastropods had a planospiral shell where each whorl lies outside the others. l Bulky
l Conispiral shells have each whorl to the side of the preceding one. l Unbalanced
l Shell shifts over for better weight distribution.
Gastropod Feeding Habits
l Most gastropods are herbivores and feed by scraping algae off hard surfaces using the radula.
l Some are scavengers of dead organisms, again tearing off pieces with radular teeth.
Gastropod Feeding Habits l Some are carnivores, radula + chemicals to
bore through the shells of other molluscs. l Snails in the genus Conus feed on fish,
worms, and molluscs. l Highly modified radula used for prey capture. l They secrete a toxin that paralyzes their prey.
l Some are painful, even lethal, to humans.
Reproduction
l Monoecious and dioecious species. l Young may emerge as veliger larvae or
pass this stage inside the egg.
Internal Form and Function l Pulmonates lack gills.
l Have a highly vascular area in mantle that serves as lung.
l Lung opens to outside by small opening, the pneumostome.
l Aquatic pulmonates surface to expel a gas bubble and inhale by curling, thus forming a siphon.
Internal Form and Function
l Most have a single nephridium and well-developed circulatory and nervous systems.
l Sense organs include eyes, statocysts, tactile organs, and chemoreceptors.
l Eyes vary from simple cups holding photoreceptors to a complex eye with a lens and cornea
Major Groups of Gastropods l Pulmonata includes land and most freshwater snails
and slugs. l Ancestral ctenidia have been lost and the
vascularized mantle wall is now a lung. l Air fills lung by contraction of mantle floor.
l Anus and nephridiopore open near the pneumostome.
l Waste is forcibly expelled. l Monoecious
Class Bivalvia
l Bivalved molluscs have two shells (valves).
l Mussels, clams, oysters, scallops, shipworms.
l Mostly sessile filter feeders.
l No head or radula.
Class Bivalvia
l Part of the mantle is modified to form incurrent and excurrent siphons. l Used to pump water
through the organism for gas exchange and filter feeding.
l Sometimes used for jet propulsion.
Class Bivalvia - Locomotion
l Bivalves move around by extending the muscular foot between the shells.
l Scallops swim by clapping their shells together to create jet propulsion.
http://www.youtube.com/watch?v=u_RfgvIETEY&feature=related http://www.youtube.com/watch?v=vmi_I8QW5eo
Class Bivalvia
l Like other molluscs, bivalves have a coelom and an open circulatory system.
l The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange.
l Pair of kidneys is ventral and posterior to heart.
l Nervous system has three pairs of widely separated ganglia connected together.
l Sense organs are poorly developed.
Class Bivalvia - Feeding l Suspended organic matter enters incurrent siphon. l Gland cells on gills and labial palps secrete mucus to entangle
particles. l Food in mucous masses slides to food grooves at lower edge of
gills. l Cilia and grooves on the labial palps direct the mucous mass into
mouth. l Some bivalves feed on deposits in sand.
Class Bivalvia - Reproduction
l Bivalves usually have separate sexes.
l Zygotes develop into trochophore, veliger, and spat (tiny bivalve) stages.
Class Bivalvia - Reproduction
l In freshwater clams, fertilized eggs develop into glochidium larvae which is a specialized veliger. l Glochidia live as
parasites on fish and then drop off to complete their development.
Glochidium Larvae
http://www.youtube.com/watch?v=I0YTBj0WHkU&feature=related
Class Cephalopoda
l Cephalopods include octopuses, squid, nautiluses and cuttlefish.
l Marine carnivores with beak-like jaws surrounded by tentacles of their modified foot. l Modified foot is a funnel for expelling water from the
mantle cavity.
Class Cephalopoda - Shells
l Shells of Nautilus and early nautiloid and ammonoid cephalopods were made buoyant by a series of gas chambers.
Class Cephalopoda - Shells
l Cuttlefishes have a small curved shell, completely enclosed by the mantle.
Class Cephalopoda - Shells
l In squid, the shell has been reduced to a small strip called the pen, which is enclosed in the mantle.
Class Cephalopoda
l Cephalopods have a closed circulatory system.
l Nervous and sensory systems are more elaborate in cephalopods than in other molluscs. l The brain is the largest of any invertebrate.
Class Cephalopoda
l Most cephalopods have complex eyes with cornea, lens, chambers, and retina.
Class Cephalopoda – Communication l Visual signals allow cephalopods
to communicate. l Movement of body and arms l Color changes effected by
chromatophores (cells in the skin containing pigment granules).
l Chromatophores can change shape alternately dispersing and concentrating pigment.
Class Cephalopoda - Reproduction
l Sexes are separate in cephalopods.
l Juveniles hatch directly from eggs – no free-swimming larvae.
l One arm of male is modified as an intromittent organ, the hectocotylus. l Removes a
spermatophore from mantle cavity and inserts it into female.