Lecture Mollusks

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Aculifera – with spicules Aplacophora - mollusks without shells Polyplacophora ( Amphineura) – chiton, eight plates, intertidal

Conchifera – with shells Monoplacophora - mollusks with one shell, ancient Gastropoda ( Univalve) – snails, slugs, abalones, whelks, periwinkles, giant

conch, most species

Pelecypoda ( Bivalve) - clams, oysters, mussels, second largest species.

Scaphopoda - a tubular shell - tusk shells Cephalopoda – squid, octopus, chambered nautilus

Phylum Mollusca Classes

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Mollusk TermsLATIN LIVES

• Phora = Bearing• Mono = One• Placo = Plate• Cephalo = Head• Scapho = Sword• Pelecy = Hatchet• Poda = Foot

• Head = Eyes, Mouth ( Radula –rasping sucking tongue) and Tentacles • Visceral Mass = Mantle which secretes the shell, and the gills,

intestines, kidneys, heart.• Foot = large muscular organ to move the body.

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Mollusk Body Plan• Mantle : A thick epidermis that covers the dorsal side of

the body- the epidermis of the mantle secretes calcium carbonate and conchiolin (protein), and creates a shell.

• Mantle cavity - space between mantle and visceral mass- houses the respiratory organs (ctenidia, or gills) and the openings of excretory, reproductive & digestive organs

• The muscular foot is adapted for locomotion, attachment, food capture-Or a combination of the above

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Mollusk Body Plan

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Haemocoel

• Affinity of blood with oxygen enhanced by haemocyanin.

• Blood receives oxygen by diffusion from water stream into central vessel.

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Shell

• Shield protecting soft-bodied mollusks against predators, mechanical damage and desiccation

• Evolutionary loss of shell : loss of protection balanced by gain in mobility and lightness

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Excretion

• Waste collected from haemocoel filters into the pericardial coelom.

• Waste then discharged into mantle cavity through a duck

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Class Polyplacophora (Chitons)

-Marine mollusks that have oval bodies with eight overlapping dorsal calcareous plates

-Body is not segmented under the plates-Most chitons are grazing herbivores

Photo Credit for Lined Chiton: Kirt L. Onthank, 2007, Wikimedia Commons

Gastropods

Photo Credit for Florida Fighting Conch: LA Dawson, 2006, Wikimedia Commons

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Class Gastropoda (Snails and slugs)

-A primarily marine group-Heads typically have pairs of tentacles with eyes at the ends-During embryological development, gastropods undergo

1. Torsion – Mantle cavity and anus are moved from the posterior to the front2. Coiling – Spiral winding of the shell

Torsion : prosobranchsHappens during larval stageTorsion may have benefits - increased water current - allowing the animal to

withdraw more deeply into the shell

Disadvantage- could result in fouling of the mouth and sense organs.

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Opisthobranchs

• Untwisted : mantle cavity is back

• Feed on hydroids, anemones, and corals

• Immune to nematocysts

Proboscis of a predatory marine snail Mitra mitra.

Kelletia kelletii are feeding on a dead fish using a long, prehensile proboscis.

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Class Bivalvia (Bivalves)• Includes clams, scallops, mussels, oysters and

others• Have two lateral (right and left) shells (valves)

hinged together dorsally• Head and sensory organs lost, Radula lost • Most are sessile filter-feeders

-Water circulation is mediated by siphons and rhythmic beating of cilia on gills- Feeding assisted by ciliated labial palps

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Bivalves

Bysuss

Feeding

The labial palps secrete a mucus that entangles suspended food and nutrient particles within the water to produce a ball of food and mucus called a bolus. Afterwards, cilia on the palps direct the bolus into the mouth.

Razor shell (맛조개)

Gastropods and Bivalves

http://people.bu.edu/veliger/http://oceanlink.island.net/abaloneproject/growthanddevelopment/growth%20and%20development.htmhttp://score.dnr.sc.gov/ktmlpro10/images/uploads/oysterlifecycle.jpg?0.40941442132799155

Larval development

Manila clam culture• sexual maturity is generally attained when the

clams about 20 mm. • Males and females : Eggs and sperm are

released into the water where fertilization occurs

• The fertilized eggs develop into straight-hinge, free swimming larvae within 24 hours. This 90µm shelled larva is called a veliger larva

• The microscopic clam feeds on phytoplankton of a size range of 2 to 20µm. This veliger stage lasts for about two weeks, during which it grows to approximately 200µm.

• a pediveliger crawls with its foot and swims with its velum looking for a suitable habitat

• preferred higher in the intertidal zone than most clams, in shallow depth of sand-gravel substrate. http://innovativeaqua.com/Publication/clam.pdf

Scaphopoda (Tusk shells)

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Class Cephalopoda• Expanded along the dorsoventral axis, and

ventral side becomes anterior.• Foot has evolved into a series of arms equipped

with suction cups -Squids have 10; octopuses, 8; and nautiluses, 80 to 90

• Have highly developed nervous systems• Exhibit complex patterns of behavior and a high

level of intelligence• Closed circulatory system

Cephalopods

http://cas.bellarmine.edu/tietjen/images/Image32.gif

Anatomyhttp://scienceblogs.com/deepseanews/beak1.jpg

Centralized Nervous System

Camouflage :change the color or chromatophores, pigment-containing and light-reflecting cells

Cephalopods

Body evolved for active predation Use funnel for jet propulsion

http://www.squidblog.net/uploads/squid_jet_diagram.gifhttp://www.mbari.org/news/homepage/2004/loligo_close_350.jpg

Cephalopods

Video with Octopus and Cuttlefish: Start at 1:20 minutes http://www.youtube.com/watch?v=zC0zOLqYnRg&feature=related

Chambered Nautilus Photo Credit for Octopus: Albert Kok, 2007, Wikimedia Commons

Cephalopods

Photo Credit for Flamboyant Cuttlefish: Jenny Huang, 2006, FlickrPhoto Credit for Caribbean Reef Squids: Clark Anderson, 2006, Wikimedia Commons

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Mollusk Reproduction• Most mollusks have distinct

male and female individuals• Most engage in external

fertilization• In marine mollusks, embryos

develop through spiral cleavage-Trochophores: Free-swimming larval stage-Veliger: Second free-swimming larval stage (Only in bivalves and snails)

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Mollusk Reproduction