Mollusks and Annelids

Mollusks Head/Foot Visceral Mass Mantle Sense organs, locomotion, mouth Visceral Mass Organ systems Mantle Secretes shell Gaseous exchange (gills or lungs)

Basic Anatomy

Class Gastropoda Snails, abalone, slugs, nudibranchs, limpets Slow moving predators or herbivores Gills in most, some have lungs Coiling and torsion of visceral mass Open circulatory system

Gastropoda Body Plan

Gastropoda Torsion

Gastropoda Coiling

Class Bivalvia Clams, muscles, scallops Open circulatory system Laterally compressed Shell in two halves, hinged Suspension feeders Open circulatory system

Bivalvia Feeding

Bivalvia Body Plan

Class Cephalopoda Octopus, squid, nautilus Foot developed into tentacles Very mobile predators Highly advanced brain and eyes Closed circulatory system

Nautilus Anatomy

Squid Anatomy

Cephalopod Eye Develops from ectoderm Convergent evolution

Taningia danae Largest light producing squid - ~2 meters (7 ft)

Taningia danae Grips prey with rows of hooks – not suckers Eats fish and other squid

Architeuthis dux Largest invertebrate - ~18 meters (60 feet)

Architeuthis dux Catches prey with double row of spiny suckers Eats fish and other squid

Annelids Segmented (metamers) Septa separate coelem at each segment Longitudinal and circular muscles Peristaltic movement Closed circulatory system Advanced nephridia

Body Plan

Class Polychaeta Very diverse methods of feeding Parapodia Movement Gas exchange

Class Oligochaeta Examples Earthworms Tubifex worms

Longitudinal Anatomy

Circulatory System Closed – capillary network for exchange Dorsal and ventral blood vessels Five aortic arches for pumping (heart)

Cross Sectional Anatomy

Nephridia Found in each segment

Reproduction Hermaphroditic – exchange sperm Clitellum Attach during mating Secretes cocoon

Class Hirudinea Leeches Anterior and posterior sucker No septa Coelom filled with muscle and connective tissue Many lack enzymes for digestion – rely on bacteria