18IntestineFecal compactionAnus opens into mantle cavity
198. Nitrogenous waste Pair of coelomoducts Open to pericardial cavityDischarge into mantle cavity via nephridioporesProbably not homologous to annelid metanephridia (annelid origin = mesoderm; mollusk origin = ectoderm)
20Waste product? Ammonia in aquatic molluscs Uric acid in terrestrial molluscs
219. Nervous system - varied Polyplacophora (chitons) - decentralized, no gangliaCephalopods - as developed as in vert’sPrimitive gastropods:Nerve ring around esophagus, 2 pair of major nerve cords
22Reproduction and development Pair of gonads in coelomEggs + sperm into pericardial cavity, outside via coelomoductsFert external in sea waterMolluscs mostly dioecious, some gastropods hermaphroditic
23Most gastropods, all cephalopods: Sperm transferred to female’s mantle cavityInternal fertilizationHermaphroditic gastropods do reciprocal cross-fertilization
25Trochophore larvae Archaeogastropoda Polyplacophora Aplacophora Most marine bivalvesDevelops into veliger larvaeFoot, shell, other structures appear
26Phylogenetic significance of trochophore larvae Hatschik (1878)Present in molluscs, annelids, other phylaPromotes ctenophora - trochophore theory of bilateral animals from radial ancestorsbody shape, apical sense organs, statocysts, nervous systems
27Problem with ctenophora-trochophore connection Flatworms don’t fitDegenerate annelids?
29Class PolyplacophoraChitons and oval-flattened beasts - mostly in rocky intertidal zonesAll marine, ~ 800 spp.Mostly cmLargest (30 cm)is Cryptochiton stelleri from N. Pacific coast of N. America = Pacific gumshoe chiton
30Chiton characteristics: Most feed on algae and micro-organisms on rock surfacesFew are predators on small inverts1. Rudimentary headNo tentacles or eyes
31Characters 2. Mantle covers dorsal surface 3. Broad, ventral foot Secretes 8-piece shell3. Broad, ventral foot4. Many paired gills in mantle cavity5. Anterior mouth with radula
32Repro: 6. Dioecious trochophore larvae, no veliger external fert. in sea watermouthGills in mantle cavitymantlefoot
33Classification of Polyplacophora - 2 orders Order Lepidopleurida: few genera, Hanleya NE coastOrder Chitonida - most chitonsChaetopleura (New England - Fl)Chiton (gulf coast)Katherina (N. Pacific coast)Cryptochiton (N. Pacific coast)MopaliaIshnochiton
34Class AplacophoraSolenogasters are worm-like molluscs cm longLargest is Epimenia verrucova; 30 cmAll marineMostly deep waters, mSome crawl and feed on hydroids and coralsPoorly known, seldom seen, ~ 250 spp.
35Characteristics: 1. Worm-like body shape 2. No shell, mantle, or foot 3. Cuticle w/layers of imbedded calcareous spicules4. Ventral surface has longitudinal pedal groove5. Hermaphroditic6. Radula well-developed