11/30/18 Evolu4onary Perspec4ve • Triploblas4c • Coelomate Chapter 11 • Very successful – 100,000 living species Molluscan Success • Relaonships to other animals – Lophotrochozoans Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.1 Evolu4onary Relaonships of Molluscs to Other Animals. Table 11.1. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Molluscan Characteris4cs Body Organizaon • Head-foot – Elongate 1. Body of two parts: head-foot and visceral mass – Mouth 2. Mantle that secretes a calcareous shell and covers the visceral mass – Foot for aachment and locomo4on 3. Mantle cavity func4ons in excre4on, gas exchange, eliminaon of diges4ve wastes, and release of reproduc4ve products. • Visceral mass 4. Bilateral symmetry – Dorsal to head-foot 5. Trochophore larvae, spiral cleavage, and schizocoelous coelom formaon – Organs of diges4on, circulaon, reproduc4on, excre4on 6. Coelom reduced • Mantle 7. Open circulatory system (except Cephalopoda) – Enfolds body 8. Radula usually present – Secretes shell • Mantle cavity – Gas exchange, excre4on, eliminaon of diges4ve wastes and reproduc4ve products • Radula – Supported by odontophore – Rasping food Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. 1 11/30/18 Figure 11.2 Molluscan body organizaon. Figure 11.3 Molluscan shell and mantle. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.4 Radular structure. Class Gastropoda • Snails, limpets and slugs • 35,000 living species • Torsion – 180o counterclockwise twis4ng of visceral mass, mantle, and mantle cavity during development – Possible adap4ve significance • Head enters shell first. • Clean water enters anteriorly oriented mantle cavity opening. • Mantle sensory organs move to head region. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.5 Torsion in Gastropods. (a) A pretorsion gastropod larva. (b) A\er torsion the diges4ve tract is looped and mantle opens near head. (c) Hypothe4cal adult ancestor prior to torsion. (d) Modern adult gastropod aer torsion. Class Gastropoda • Shell coiling – Earliest fossils, one plane – Modern, asymmetrical • More compact • Internal organs asymmetrical and some4mes no longer paired • Locomoon – Flaened foot – Cilia propel over mucous trail – Muscular waves Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. 2 11/30/18 Class Gastropoda Figure 11.6 Gastropod structure. • Feeding and diges4on – Most scrape algae and aached organisms – Herbivores, predators, scavengers – Diges4ve tract • Ciliated • Food incorporated into mucous mass called protostyle. • Gas exchange – One or two gills in mantle cavity – Land snails (pulmonates) • Mantle cavity richly vascular for gas exchange with air Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Other Maintenance Func4ons Other Maintenance Func4ons • Open circulatory system – Blood bathes 4ssues in sinuses. • Excreon – Heart • Single ventricle and single auricle – Single nephridium – Funcons • Result of shell coiling • Transports nutrients, wastes and gases – Discharges into mantle cavity or adjacent to • Hydraulic skeleton mantle cavity (pulmonates) • Nervous system – Six ganglia plus nerve cords – Ammonia (aquac species) • Sensory structures – Uric acid (pulmonates) – Eyes at base or end of tentacles – Statocysts in foot – Osphradia in mantle cavity Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Reproduc4on • Dioecious Gastropod Diversity – External fer4lizaon • Eggs shed singly or in masses • Subclasses – Prosobranchia • Some dioecious marine species • 20,000 species • Monoecious • Mostly marine – Opisthobranchia – Copulaon for internal fer4lizaon • 2,000 species • Sperm transfer may be mutual or one-way. • Mostly marine • Eggs shed in strings or in masses • Sea hares, sea slugs • Shell, mantle cavity, and gills reduced or lost – Larval stages – Pulmonata • Trochophore • 17,000 species • Veliger – foot, eyes, tentacles, shell • Freshwater or terrestrial • Vascular mantle cavity serves as lung Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. 3 11/30/18 Figure 11.7 Variaons in the Gastropod Body Form. Class Bivalvia • Clams, oysters, mussels, scallops • 30,000 species • Shell and associated structures – Single shell consis4ng of two hinged valves (figure 11.8) – Mantle sheetlike and covers laterally compressed body. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.8 Inside View of a Bivalve Shell. Gas Exchange, Filter Feeding, and Digeson • Sedentary filter feeders – Loss of head and radula – Expansion of cilia-covered gills into folded sheets (lamellae) • Cilia create water currents into and through mantle cavity. – Gas exchange in water tubes (figure 11.9) – Food trapped along gill surface and transported to food grooves and labial palps (figure 11.10). – Digeson (figure 11.11) • Crystaline style and gastric shield Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.10 Bivalve feeding. Solid purple arrows show path of food par4cles. Dashed purple arrows show path of par4cles being rejected. Figure 11.9 Lamellibranch gill of a bivalve. Blue arrows show water movement. Red arrows show blood movement. Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. 4 11/30/18 Figure 11.11 Bivalve structure. Other Maintenance Func4ons • Open circulatory system – Mantle and gills oxygenate blood • Nephridia – Below pericardial cavity – Open to suprabranchial chamber • Nervous system – Three pairs of interconnected ganglia – Sensory receptors at mantle margin Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.12 Reproduc4on and Development Bivalve Circulaon. • Mostly dioecious • Gonads within visceral mass • Mostly external fer4lizaon • Trochophore and veliger larval stages (figure 11.13a, b) • Freshwater in family Unionidae – Parasi4c larval stage – Glochidium (figures 11.13c and 11.14) Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written Copyright © 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. consent of McGraw-Hill Education. Figure 11.13 Trochophore (a) and veliger (b) larval stages. Glochidia of an unionid bivalve. Figure 11.14 Mantle lure of a freshwater bivalve (Lampsilis reeviana). Copyright