PROTOSTOMES II MOLLUSKSARTHROPODS

MOLLUSKS Clams, snails, slugs, chitons, octopuses Clams, snails, slugs, chitons, octopuses Probably evolved early—after evolution of coelom but before segmented body Probably evolved early—after evolution of coelom but before segmented body 2 nd only to arthropods in # of species 2 nd only to arthropods in # of species

Main characteristics of Mollusks Soft body usu. covered by calcium carbonate shell Soft body usu. covered by calcium carbonate shell Broad, flat, muscular foot Broad, flat, muscular foot Body organs concentrated in visceral mass above foot Body organs concentrated in visceral mass above foot Mantle Mantle

Radula (except in filter feeders) Radula (except in filter feeders) Reduced coelom Reduced coelom Main body cavity is hemocoel Main body cavity is hemocoel Most have open circulatory system Most have open circulatory system –Blood bathes tissues directly –Heart  aorta  smaller bld vessels  sinuses (hemocoel)  blood vessels  gills  heart

Development of mollusks Pass through one or more larval stages: Pass through one or more larval stages: Trocophore larva Trocophore larva In many molusks, trocopohore larva develops into veliger larva (**unique to mollusks) In many molusks, trocopohore larva develops into veliger larva (**unique to mollusks)

Gastropods: “Stomach-footed” mollusks Marine gastropods have gills; in land gastropods, mantle functions as lung Marine gastropods have gills; in land gastropods, mantle functions as lung Torsion Torsion Head with tentacles Head with tentacles 2 simple eyes 2 simple eyes

SNAILS

WHELK

CONCH

Class Bivalvia Clams, oysters, scallops, mussels Clams, oysters, scallops, mussels Have 2-part shell Have 2-part shell Suspension feeders Suspension feeders –Incurrent siphon brings in water –Mucus of gills catches food particles –Excurrent siphon brings waste water out

Class Cephalopoda: “Head-footed” Mollusks Fast-swimming predatory animals Fast-swimming predatory animals Mouth surrounded by tentacles or arms Mouth surrounded by tentacles or arms Mantle is thick and muscular Mantle is thick and muscular Well-developed eye sees images Well-developed eye sees images Intelligent Intelligent Ink sac Ink sac Chromatophores Chromatophores

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ARTHROPODS Segmented bodies Segmented bodies Exoskeleton of chitin and protein Exoskeleton of chitin and protein Paired, jointed appendages Paired, jointed appendages –Swimming –Walking –Sensory structures –Manipulation of food

Nervous system Nervous system –Cerebral ganglia (brain) –Ventral nerve cord –Antennae –Many have compound eyes Open circulatory System Open circulatory System Specialized respiratory structures Specialized respiratory structures –Gills –Tracheae –Book lungs

A survey of Arthropods A survey of Arthropods

Subphylum Myriapoda Centipedes (Chilopoda) Centipedes (Chilopoda) 1 pair legs/segment 1 pair legs/segment Carnivorous Carnivorous Long legs – run rapidly Long legs – run rapidly Poison claws on 1 st segment behind head Poison claws on 1 st segment behind head Millipedes (Diplopoda) Millipedes (Diplopoda) 2 pairs legs/segment 2 pairs legs/segment Herbivores Herbivores Crawl slowly Crawl slowly

Arachnids Cephalothorax and abdomen Cephalothorax and abdomen 6 pairs of jointed appendages 6 pairs of jointed appendages Gas exchange by tracheae, book lungs, or both Gas exchange by tracheae, book lungs, or both

Crustaceans Primarily aquatic – gills Primarily aquatic – gills Hard mandibles for biting and grinding Hard mandibles for biting and grinding Maxillae- manipulate and hold food Maxillae- manipulate and hold food Decapods – 5 pairs of walking legs Decapods – 5 pairs of walking legs Chelipeds – large claws Chelipeds – large claws

Insects Most numerous and diverse group on the planet Most numerous and diverse group on the planet 6 legs 6 legs 3 distinct body regions: head, thorax, and abdomen 3 distinct body regions: head, thorax, and abdomen 1 pair of antennae, simple and comound eyes 1 pair of antennae, simple and comound eyes e-function/index.html e-function/index.html e-function/index.html e-function/index.html

Respiration Respiration –Air enters tracheal tubes through spiracles in body wall –Allows for high metabolic rate Excretion through Malpighian tubules Excretion through Malpighian tubules –Discharged into intestine Separate sexes Separate sexes –Fertilization is internal Several molts occur during development Several molts occur during development

Metamorphosis Incomplete or complete Incomplete or complete Incomplete : Incomplete : egg  larva (w/o functional wings)  adult Complete: Complete: Egg  larva  pupa  adult

Some insects are social: bees, ants Some insects are social: bees, ants Pheromones Pheromones

Success of Insects Exoskeleton – protects from predators and dessication Exoskeleton – protects from predators and dessication Segmentation – mobility, flexibility Segmentation – mobility, flexibility Jointed appendages – adaptable for many different things – movement, feeding Jointed appendages – adaptable for many different things – movement, feeding Flying – distribution, ability to move to more suitable environment Flying – distribution, ability to move to more suitable environment Reproductive capability – many eggs, protected by thick membrane Reproductive capability – many eggs, protected by thick membrane Defensive and offensive capability Defensive and offensive capability