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

Class Aplacophora  No shell, worm-like Photo: Woods Hole Oceanographic Institute

Class Scaphopoda  Tusk shells

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 ]

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?