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INVERTEBRATES Mollusca, Annelida, Arthropoda, Echinodermata Animals that lack vertebrae (classed by a characteristic they don’t have.) 97% of all species on Earth are invertebrates. Phylum Mollusca ©2004 Amanda Demopoulos Phylum Mollusca • • • More species (200,000+) than any other animal phylum except Arthropoda Soft body – often protected by CaCO3 shell Unsegmented, typically bilaterally symmetrical Mollusca: Major Characteristics 1.Cephalization have a distinct head with sense organs & brain (mostly) 2.Bilaterally symmetrical (mostly) SNAIL, CLAM, CHITON, & SQUID Basic Mollusk Body Plan Head (eyes/sensory), visceral mass (organs), muscular foot Mantle – covers visceral mass, secretes shell Radula – Ribbon of small chitin teeth used in feeding Gills (ctenidia-comb like) for gas exchange in mantle cavity Radula – Ribbon of small chitin teeth used in feeding 4 Classes of Mollusca 1. Class Polyplacophora Many-plate-bearing = Chitons 800 species • Mostly graze algae on rocky shorelines • Exclusively marine • 8 overlapping plates 2. Gastropoda snails, slugs, nudibranchs, conchs & abalone Class Gastropoda Most gastropods are herbivores Stomach-Foot Stomach-Foot (class Gastropoda) contains about 70% of all mollusk species. A few stomach-foots are found on land. The stomach-foot include: snails, limpets and abalones, which have shells. Slugs and nudibranchs are also stomachfoots, but do not have shells. Abalones Snails Snails Snails Nudibranchs 3. Pelecypoda or Bivalvia clams, oysters, & mussels No head and no radula Class Bivalvia Most bivalves are suspension feeders Bivalvia Anatomy Class Bivalvia Hinged, 2-valved shell (oysters, clams, mussels, scallops) muscles keep closed No head , no radula Sedentary lifestyle Some have muscular foot for burrowing (clams) Gills used for suspension feeding & respiration Water enters and leaves through siphons Some anchor to substrate (mussels) Scallops – Swim! (repeated clapping of valves) 4. Cephalopoda squid, octopus, & nautilus Class Cephalopoda - Octopus and squid have beak-like jaws - Mouth is central among tentacles Octopus 8 arms, non-retractable w/ 2 rows of suckers Nautilus 60-90 suckerless tentacles Squid 8 arms + 2 tentacles nonretractable w/suckers and hooks Cuttlefish 8 arms + 2 tentacles, retractable w/ suckers, no hooks Cephalopods Octopuses are considered among the most intelligent invertebrates. Chambered nautiluses are the only living cephalopods with an external shell. (b) (a) (c) Squids are speedy carnivores with beaklike jaws and well-developed eyes. Note the different shells in cephalopods external in Nautilus, internal in squids, and missing in octopuses. PHYLUM Annelida Earthworms Leeches Tubeworms Annelids: Major Characteristics Segmented worms (1mm-3m) •Body composed of repeated segments 1. Cephalization 2. Bilateral symmetry 3. Coelom well developed and divided by septa (except in leeches); coelomic fluid supplies turgidity and acts as a hydrostatic skeleton Annelids: Major Characteristics •Body wall •Outer circular and inner longitudinal muscle layers •Protective elastic outer transparent moist cuticle secreted by epithelium •Closed circulatory system •Respiratory gas exchange through skin, gills or parapodia •Digestive system of many has 2 openings, mouth and anus (some have no gut) •Excretory system •Nervous systems 1. Polychaeta Three Classes Tubeworms, feather dusters, bristle worms, mainly marine •Free-living predators •Burrowing •Tube building Body segments have pairs of parapodia • locomotion • feeding • gas exchange • protection tipped with setae (bristles), often 4 pairs • Three Classes 2. Oligochaeta • Earthworms, mainly terrestrial and freshwater • Few marine species • Benthic – mud and sand (deposit feeders) • No parapodia • Locomotion – expansion and contraction Earthworm Anatomy Annelid Movement 3. Hirudinea Three Classes •Leeches •Hirudin – anticoagulating chemical so blood does not clot •mainly freshwater but with marine and terrestrial species •No parapodia •One anterior/one posterior sucker Phylum Arthropoda The vast majority of known animal species, including insects, crustaceans, and arachnids, are arthropods. All arthropods have segmented exoskeleton and jointed appendages. Phylum Arthropoda • Most species of any phylum – over 1 million - 75% of all animals species described • Insects, spiders, centipedes, crabs, lobsters, shrimp, barnacles, etc. • Segmented, bilaterally symmetrical body •Jointed appendages •Exoskeleton made of chitin •Growth requires molting - defenseless • Body segments •Head, thorax, abdomen •Some groups have head and thorax fused = cephalothorax • Discuss 3 subphyla and representative classes 1. Subphylum Chelicerata A. Class Merostomata (=legs attached to mouth) • Horseshoe crabs-Not true crabs • Named for feeding appendages – chelicerae • Distinctive, horseshoe-shaped carapace • No antennae • Benthic predators/scavengers on clams and small invertebrates • No jaws - Grind food with bristles on walking legs (must be walking to “chew”) • Much of what we know understand about vision based on horseshoe crab eyes • Blood is used to test injectable pharmaceutical solutions for bacterial contamination 2. Subphylum Chelicerata B. Class Pycnogonida (= thick knees, Sea spiders) • All marine • Superficially resemble spiders • Mouth at end of large proboscis • Carnivores •Feed on sea anemones, hydrozoans, •other soft inverts • Legs much longer than body, more than 8 2. Subphylum Chelicerata C. Arachnida spiders, scorpions, mites • Largest class in Chelicerata • Cephalothorax and abdomen • Mouth called chelicerae (first appendage •Pinchers or fangs • Pedipalps •Second pair of appendages •Handle prey, sensory • Four pair of walking legs 2. Subphylum Chelicerata Arachnids Chelicerae are feeding appendages PHOTO: Bill Rudman Cheliceriform Anatomy Class Trilobita •Marine •Extinct since 250 mya •Rich fossil history because of exoskeleton •Dorso-ventrally flattened 3. Subphylum Crustacea (40K species) • • • Contains majority of marine arthropod species Gills + two pairs of antennae (sensory) Larval forms – nauplius and zoea • • • • • • Extremely abundant holoplankton (always plankton) Some live on/in substrates (benthos) **Among most abundant animals on earth** Important primary consumers of phytoplankton Small << 1-2 mm Some parasitic forms A. Class Copepoda (=oar foot, Copepods) 3. Subphylum Crustacea B. Class Cirripedia (= hairy foot, Barnacles) •Active suspension feeders (filter feeders) •Use feathery cirri (modified swimming appendages) •Sessile (attached to surfaceswhales, piers) •Fouling organisms (boats, whales) •Resemble mollusks superficially – calcareous plates 3. Subphylum Crustacea C. Class Malacostraca (=soft shell, 75% crustacean species-Discuss 4 Orders) 1. Order Amphipoda (Amphipods) beach hoppers, sand fleas, whale lice • Laterally compressed •Generally small (< 2 cm), but larger in deep ocean •Head and tail downward • Widespread distribution •Generally free living •Important scavengers 3. Subphylum Crustacea C. Class Malacostraca 2. Order Isopoda (Isopods-rock lice, fish lice) • Dorsoventrally compressed • Generally small (< 2 cm), but larger in deep ocean • • • • • Related to terrestrial pill bugs Widespread distribution Generally free living Important scavengers Some parasites 3. Subphylum Crustacea C. Class Malacostraca 3. Order Euphausiacea (Krill) holoplankton •Laterally compressed •Up to 10 cm long (usually smaller) •Head and anterior segments fused to form distinct carapace •Widespread distribution •Important primary consumers and predators •Important prey for larger consumers (whales, penguins, fish) •Keystone species in some ecosystems (Polar, Southern Ocean) •Aggregate in schools (billions of individuals) 3. Subphylum Crustacea C. Class Malacostraca 4. Order Decapoda (=10 legs, Crabs, Lobsters, Shrimps) • Most species in Crustacea (~10,000) • Scavengers/Predators/Both • Largest crustaceans • Five pairs of walking legs (deca=10) • First pair usually modified as claws for feeding/defense • Well-developed carapace = cephalothorax • Rest of body = abdomen, tail • Laterally compressed, except crabs – abdomen under cephalothorax Fig. 7.30 4. Subphylum-Uniramia A. Class Insecta = Hexapoda (6 footed) • 1 million species described to date • Found in every known terrestrial + freshwater habitat, some marine except deep sea • Diversity attributable to • Feeding specialization • Dispersal capabilities • Predator-avoidance possibilities (flight) 4. Subphylum-Uniramia A. Class Insecta = Hexapoda (6 footed) Tracheal tubes are used in gas exchange Insect wings are modified cuticle, not appendages “Insects are more species rich than all other forms of life combined.” Insect Anatomy Complete Metamorphosis In incomplete metamorphosis (not shown), the juvenile looks like the adult 4. Subphylum-Uniramia A. Class Diplopoda = 2 pair of legs per segment = millipedes B. Class Chilopoda = 1 pair of legs per segment = centipedes Millipedes, herbivores, were perhaps the first land animals Centipedes are carnivores Phylum Echinodermata Echinoderms, such as sand dollars, sea stars, and sea urchins, are aquatic animals that display radial symmetry as adults. They move and feed by using a network of internal cannals to pump water to different pars of the body. Phylum Echinodermata “Spiny skin” 6000 species Sea lilies, feather stars, brittle stars, sea stars, sand dollars, sea urchins, sea biscuits, sea cucumbers Radial symmetry Endoskeleton = hard plates, ~95% calcium carbonate, covered by skin Complete digestive, nervous systems, and reproductive organs Regeneration Water vascular system = internal hydraulic system Sea Stars Sea stars posses multiple arms, upon which are numerous tube feet, and a calciferous endoskeleton Phylum Echinodermata Tube feet (podia) extended by pressure from ampullae (muscular sacs) Tube feet used for locomotion, feeding, sensory functions Phylum Echinodermata Crown of Thorns Acanthaster planci Echinoderm Anatomy The End