Invertebrate Zoology Lecture 20: Phylum Mollusca General; Cephalopoda focus Lecture outline Phylum Mollusca Diversity Evolutionary relationships Bauplan Basics Body systems (briefly…) Feeding/digestion Circulation/gas exchange Osmoregulation/excretion Nervous system/sensory Reproduction Focus: Class Cephalopda Cephalopoda diversity Evolution of cephalopods Class Polyplacophora: “many plates” The chitons Class Gastropoda Snails, slugs, nudibranchs et al. Class Bivalvia: “two valves” Clams, mussels and scallops Class Cephalopoda: “Head-footed” Nautilus, cuttlefish, squid, octopus Class Monoplacophora Limpet-like shell Chiton-like segmentation Mostly deep sea www.mcz.harvard.edu Class Aplacophora No shell, worm-like Photo: Woods Hole Oceanographic Institute Class Scaphopoda Tusk shells www.paleos.com Phylogeny: Classic protostomes Hypothesis 1: Phylogeny: Based on molecular data, cuticle features Bauplan basics Sketch along with the professor! Shell Mantle Mantle cavity, contains Ctenidia Anus & Renal/genital pores Foot: wide, flat and muscular Note epipodial tentacles in some Head cephalic tentacles radula Visceral mass enclosed by mantle Contains main body systems Feeding/digestion Radula or filter feeding Structure used for filter-feeding in bivalves? Salivary glands with toxins, digestive enzymes Complete digestive system Anus empties into mantle cavity Circulation/gas exchange Ctenidium (sketch) Ctenidial axis & ctenidial filaments Hemolymph flow, water flow & countercurrent exchange Circulatory system Open (except Cephalopoda) Heart with two atria and a muscular ventricle Pericardial cavity is part of reduced coelom Note key aspects of circulation pattern! [Fig. 20.34] Circulation/gas exchange Osmoregulation/excretion Metanephridia (=kidneys) Also associated with reduced coelom Nephridiopore (renal pore) empties into? Nervous system “Primitive” forms: i.e. Polyplacophora Ganglia at head Four longitudinal cords Cross-connections Nervous system Gastropoda Ganglia at head Two longitudinal cords Additional ganglia Pre-torsion Post-torsion Reproduction Gonochoristic or hermaphroditic Gonads associated with reduced coelom Ancestral condition: spawning via genital pores (empty into mantle cavity) Sometimes linked with nephridiopore Some with elaborate structures & behaviors for internal fertilization Focus: Cephalopoda Diversity: living forms (slides) Nautilus Cuttlefish Squid Octopus Evolution of cephalopods Ancestral cephalopod: key features (handout) Three key lineages (handout) Ammonoids Nautiloids and Nautilus features (handout) Coleoids Ammonoidea Nautiloids See handouts for key features Extinct Coleoidea: Belemnoidea Focus: extant Coleoidea Predatory adaptations Previously… Streamlined shape Shell reduction Funnel/siphon jet propulsion Further arm development Further cephalic tentacle development Eye development Eye structure Classic example of convergent evolution Focus: extant Coleoidea Predatory adaptations Nervous system Further adaptations of the mantle Musculature Chromatophores (slides) Photophores Fins Ink sac Life history: Loligo opalescens Mating Egg laying Development Hatching Where have all the young squid gone?
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