Lecture Mollusks
Phylum Mollusca Classes 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 2/6/2017 2
Mollusk Terms Phora = Bearing Mono = One Placo = Plate Cephalo = Head Scapho = Sword Pelecy = Hatchet Poda = Foot LATIN LIVES 2/6/2017 3
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.
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 5
Mollusk Body Plan 6
Haemocoel Affinity of blood with oxygen enhanced by haemocyanin. Blood receives oxygen by diffusion from water stream into central vessel. 7
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 10
Excretion Waste collected from haemocoel filters into the pericardial coelom. Waste then discharged into mantle cavity through a duck 11
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 12
Gastropods Photo Credit for Florida Fighting Conch: LA Dawson, 2006, Wikimedia Commons
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 front 2. Coiling Spiral winding of the shell 14
Torsion : prosobranchs Happens during larval stage Torsion 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.
Untwisted : mantle cavity is back Feed on hydroids, anemones, and corals Immune to nematocysts Opisthobranchs 17
Proboscis of a predatory marine snail Mitra mitra. Kelletia kelletii are feeding on a dead fish using a long, prehensile proboscis.
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 19
Bivalves Bysuss 20
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. Feeding
Razor shell ( 맛조개 )
Gastropods and Bivalves Larval development http://oceanlink.island.net/abaloneproject/growthanddevelopment/growth%20and%20development.htm http://score.dnr.sc.gov/ktmlpro10/images/uploads/oysterlifecycle.jpg?0.40941442132799155 http://people.bu.edu/veliger/
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)
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 26
Cephalopods Anatomy http://cas.bellarmine.edu/tietjen/images/image32.gif http://scienceblogs.com/deepseanews/beak1.jpg
Centralized Nervous System Camouflage :change the color or chromatophores, pigmentcontaining and light-reflecting cells
Cephalopods Body evolved for active predation Use funnel for jet propulsion http://www.mbari.org/news/homepage/2004/loligo_close_350.jpg http://www.squidblog.net/uploads/squid_jet_diagram.gif
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, Flickr Photo Credit for Caribbean Reef Squids: Clark Anderson, 2006, Wikimedia Commons
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) 32
Mollusk Reproduction 33