1 Molluscs Zoology Chapter 10

2 Phylum: Mollusca Classes include: Classes include: –1) Gastropoda (snails, slugs) –2) Bivalvia (clams, oysters, scallops) –3) Cephalopoda (squid, octopus, chambered nautilus) –4) Polyplacophora (chitons) –5) Monoplacophora –6) Scaphopoda –7) Caudofoveata –8) Solenogastres We will focus on the first 3 listed We will focus on the first 3 listed Read Chapter 10; Do: Q 3-15 page 201; Due: 11/8 Read Chapter 10; Do: Q 3-15 page 201; Due: 11/8

3 Phylum: Mollusca Characteristics 1. Body bilaterally symmetrical, unsegmented, definite head 1. Body bilaterally symmetrical, unsegmented, definite head 2. Muscular foot (ventral body wall), adapted for locomotion 2. Muscular foot (ventral body wall), adapted for locomotion 3. Dorsal body wall forms mantle enclosing mantle cavity; may contain gills or lungs, secretes shell 3. Dorsal body wall forms mantle enclosing mantle cavity; may contain gills or lungs, secretes shell 4. Epithelium ciliated with mucous glands & sensory nerve endings 4. Epithelium ciliated with mucous glands & sensory nerve endings 5. Coelom limited to small cavity surrounding heart (pericardial cavity) 5. Coelom limited to small cavity surrounding heart (pericardial cavity)

4 Mollusc Characteristics, cont. 6. Digestive system complex, radula (rasping organ) present, anus usually empties into mantle cavity 6. Digestive system complex, radula (rasping organ) present, anus usually empties into mantle cavity 7. Circulatory system – open, heart is 3-chambered (2-chambered in gastropods), blood vessels & sinuses present, respiratory pigments in blood 7. Circulatory system – open, heart is 3-chambered (2-chambered in gastropods), blood vessels & sinuses present, respiratory pigments in blood 8. Gas exchange – gills, lung, mantle, or body surface 8. Gas exchange – gills, lung, mantle, or body surface 9. Metanephridia (kidneys, 1 or 2) open into pericardial cavity & empty metabolic waste into mantle cavity 9. Metanephridia (kidneys, 1 or 2) open into pericardial cavity & empty metabolic waste into mantle cavity 10. Nervous system – paired cerebral, pleural, pedal & visceral ganglia; ganglia centralized in nerve ring 10. Nervous system – paired cerebral, pleural, pedal & visceral ganglia; ganglia centralized in nerve ring 11. Sensory organs of touch, smell, taste, equilibrium, & vision (some have eyes) are highly developed 11. Sensory organs of touch, smell, taste, equilibrium, & vision (some have eyes) are highly developed

5 Mollusc FYI 2 nd largest phyla (Arthropoda largest) 2 nd largest phyla (Arthropoda largest) 75,000 named living species; 35,000 fossil species 75,000 named living species; 35,000 fossil species Diversity vast Diversity vast –Size: Giant squid 18m long & 454kg Giant squid 18m long & 454kg Giant clam 1.5m long & 225kg Giant clam 1.5m long & 225kg 80% 5cm or less 80% 5cm or less –Niche/lifestyle: Aquatic & terrestrial Aquatic & terrestrial Bottom feeders, borers, pelagic forms, burrowers Bottom feeders, borers, pelagic forms, burrowers Herbivorous grazers, predaceous carnivores, ciliary filter feeders Herbivorous grazers, predaceous carnivores, ciliary filter feeders Economic Importance Economic Importance –Food (to humans & other organisms), jewelry (pearls), shipworms & some snails (burrowers), crop/garden pest, intermediate host to many trematodes

6 Mollusc Body Plan Consists of head-foot portion & visceral mass portion Consists of head-foot portion & visceral mass portion –Head-foot – contains feeding, cephalic, sensory, & locomotor organs –Visceral mass – contains digestive, circulatory, respiratory, & reproductive organs Mantle surrounds head-foot & visceral mass, a mantle cavity between mantle and body mass, mantle cavity contains gills or lung, mantle secretes shell Mantle surrounds head-foot & visceral mass, a mantle cavity between mantle and body mass, mantle cavity contains gills or lung, mantle secretes shell

7 Head-Foot Mouth w/ sense organs Mouth w/ sense organs –radula – rasping tongue may contain up to 250,000 teeth, not in bivalves or some gastropods – Photosensory receptors, include eyes Photosensory receptors, include eyes – eyes-pop-out-on-stalks-realtime.html eyes-pop-out-on-stalks-realtime.htmlhttp:// eyes-pop-out-on-stalks-realtime.html Tentacles often present Tentacles often present – Foot portion for locomotion – muscular contraction for creeping movements (have mucous glands for gliding) Foot portion for locomotion – muscular contraction for creeping movements (have mucous glands for gliding) –Some modified for attachment, compressed as in bivalves, or modified into funnel-shape for jet propulsion – – – source=vgc&hl=en&aq=f#q=jet+propulsion+in+squid&hl=en&tbs=vid: 1&ei=vFrPTLC2IYSclgf8_cjnCA&start=10&sa=N&fp=35970b3192b2a18 source=vgc&hl=en&aq=f#q=jet+propulsion+in+squid&hl=en&tbs=vid: 1&ei=vFrPTLC2IYSclgf8_cjnCA&start=10&sa=N&fp=35970b3192b2a18http:// source=vgc&hl=en&aq=f#q=jet+propulsion+in+squid&hl=en&tbs=vid: 1&ei=vFrPTLC2IYSclgf8_cjnCA&start=10&sa=N&fp=35970b3192b2a18 –

8 Mantle & Mantle Cavity Covering visceral mass is the mantle & mantle cavity Covering visceral mass is the mantle & mantle cavity –Mantle is sheath of skin surrounding visceral mass with a space between (mantle cavity) –Mantle outer surface secretes shell Houses respiratory organs (lungs or gills); surface also serves in gas exhange Houses respiratory organs (lungs or gills); surface also serves in gas exhange Products of digestive, excretory, reproductive systems empty into mantle cavity Products of digestive, excretory, reproductive systems empty into mantle cavity Shell – composed of 3 layers Shell – composed of 3 layers –Periostracum is outer layer (very resistant) –Prismatic layer is middle layer (dense CaCO 3 layers) –Nacreous layer is inner layer (protein & CaCO 3, continuously laid and very smooth, “mother-of-pearl”)

9 Visceral Mass Open circulatory system contains a pumping heart Open circulatory system contains a pumping heart Digestive system specialized to feeding habits of various molluscs Digestive system specialized to feeding habits of various molluscs Paired kidneys, ducts do double duty as discharge duct of sperm/ova Paired kidneys, ducts do double duty as discharge duct of sperm/ova Nerve ganglia paired, connected by nerve cords, sensory organs Nerve ganglia paired, connected by nerve cords, sensory organs Reproduction – most are dioecious, some gastropods are hermaphroditic Reproduction – most are dioecious, some gastropods are hermaphroditic

10 Class: Gastropoda These include snails, slugs, nudibranchs, conchs, whelks, periwinkles, sea slugs, sea hares, & sea butterflies These include snails, slugs, nudibranchs, conchs, whelks, periwinkles, sea slugs, sea hares, & sea butterflies 40,000 living species & 15,000 fossil species 40,000 living species & 15,000 fossil species SNAIL Univalve

11 Torsion – a rotation of the mantle cavity to the front of the body Occurs during veliger larval stage; 2 stages of 90  rotation Occurs during veliger larval stage; 2 stages of 90  rotation After torsion, anus & mantle cavity are located anterior and open above mouth; the left gill, kidney, & heart auricle now located on right side but right gill, kidney, & heart auricle now on left; nerve cords twisted in figure “8”. After torsion, anus & mantle cavity are located anterior and open above mouth; the left gill, kidney, & heart auricle now located on right side but right gill, kidney, & heart auricle now on left; nerve cords twisted in figure “8”. –This allows space inside shell, so sensitive head can be withdrawn into shell for protection –Problem: “fouling”, which can occur since anus is above mouth; still do not understand what evolutionary pressure would have favored such a strange adaptation Coiling is the twisting or spiral winding of the shell; not same as torsion Coiling is the twisting or spiral winding of the shell; not same as torsion

12 Shell-less Gastropods Terrestrial Slug Marine Nudibranch Marine Nudibranchs

13 Website for nudibranchs 06/nudibranchs/doubilet-photography 06/nudibranchs/doubilet-photography 06/nudibranchs/doubilet-photography 06/nudibranchs/doubilet-photography

14 Class: Bivalvia Class includes: scallops, oysters, clams, mussels, shipworms

15 e=related e=related e=related e=related Most bivalves are sedentary suspension feeders; no head or radula & little cephalization (but some have eyes – scallops) Most bivalves are sedentary suspension feeders; no head or radula & little cephalization (but some have eyes – scallops) Umbo – olders part of the shell Umbo – olders part of the shell 3-chambered heart 3-chambered heart Crystalline style – gelatinous rod in stomach which rotates and releases digestive enzymes to digest food Crystalline style – gelatinous rod in stomach which rotates and releases digestive enzymes to digest food Dioecious, fertilization external, development usually from trochophore to veliger larvae to spat to adult in marine forms Dioecious, fertilization external, development usually from trochophore to veliger larvae to spat to adult in marine forms –Some freshwater clams have a larval form called glochidia which brood in gill tubes of adult and when a fish passes by the clam disperses them at fish; the glochidia attach to gills and live parasitically for days.

16 Cephalopoda These include squid, octopus, chambered nautilus, & cuttlefish These include squid, octopus, chambered nautilus, & cuttlefish –All are marine, all are active predators –Feed on small invertebrates, fish, crustaceans, worms –Arms adapted to quickly snatch prey and delicately manipulate it –Salivary glands of cuttlefish/octopus have poison glands which secrete venom –All have a strong beak with radula capable of tearing food During embryonic development, the head & foot become indistinguishable; ring around mouth bearing tentacles & arms derived from head but actual tentacles & arms derived from foot; part of foot tissue develops into funnels within mantle cavity During embryonic development, the head & foot become indistinguishable; ring around mouth bearing tentacles & arms derived from head but actual tentacles & arms derived from foot; part of foot tissue develops into funnels within mantle cavity

17 Class: Cephalopoda Chambered Nautilus  Cuttlefish Cuttlefish shell - internal Chambered nautilus shell external and unique; gas filled chambers increase as animal grows

18 Squid Squid shell much reduced; thin flexible strip (pen)

19 Octopus Octopus – shell is absent

20 Cool Cephalopod Stuff Eyes Eyes –Good example of convergent evolution (eye of human & eye of cephalopod) –Eye contains cornea, lens, chambers, retina Human Eye

21 Ink Production Ink Production –Cephalopod ink is a dark pigment released into water by most species of cephalopod, usually as an escape mechanism. All cephalopods, with the exception of the Nautilus and the species of octopus belonging to the suborder Cirrina are able to release ink. –Consists mainly of melanin & mucous & assorted amino acids; manufactured in ink gland; stored in ink sac and emptied into rectum –Some other molluscs, like sea hares, are able to make and eject ink; example of convergent evolution. –Ink used in foods for coloring; it is tasteless; some new studies indicate squid ink may be toxic to some cells esp cancer cells –Also used as ink; sepia is name of ink mainly from cuttlefish – Squid-Ink/ Squid-Ink/ Squid-Ink/

22 Color Change Color Change Color change in cephalopods due to cells called chromatophores Color change in cephalopods due to cells called chromatophores These cells are located in skin and are quite complex; under nervous system & hormonal control These cells are located in skin and are quite complex; under nervous system & hormonal control Cause skin color and texture to change quickly Cause skin color and texture to change quickly Some deep sea squids are bioluminescent Some deep sea squids are bioluminescent # # # # 01_ _ _ _041

23 Locomotion Locomotion Mantle cavity modified into funnel shaped siphon which is used to aid in jet propulsion; siphon direction can be controlled so that direction of movement is controlled Mantle cavity modified into funnel shaped siphon which is used to aid in jet propulsion; siphon direction can be controlled so that direction of movement is controlled Squid & cuttlefish have lateral fins serving as stabilizers; squid built for speed while cuttlefish are a bit slower swimmers Squid & cuttlefish have lateral fins serving as stabilizers; squid built for speed while cuttlefish are a bit slower swimmers Octopus better suited for slower swimming or crawling across substrate Octopus better suited for slower swimming or crawling across substrate Q Q Q Q

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