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Invertebrates II: Mollusca, Arthropoda, Echinodermata, Chordata (non-vertebrate chordates) ©2004 Amanda Demopoulos I. Phylum Mollusca More species (200,000+) than any other animal phylum except Arthropoda Soft body – often protected by CaCO3 shell Unsegmented, typically bilaterally symmetrical 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 Fig. 7.19 Radula – Ribbon of small chitin teeth used in feeding I. Phylum Mollusca • Exceptions to basic plan • • • • Bivalves lack radulas Squids have internal shells Octopuses have no shells Reproduction (for some gastropods and bivalves) • 2 larval forms • Trocophore – looks similar to annelid larva • Veliger – ciliated, wing-like, with shell Trocophore Veliger ©2004 Amanda Demopoulos I. Phylum Mollusca 4 classes A. Class Gastropoda (=stomach foot) • Largest, most common, most diverse group (40K-75K sp) Coiled mass of vital organs=visceral mass enclosed by a shell • • • • • • • Snails Limpets Abalones Nudibranchs – lose shell in larval stage Ventral creeping foot Diet • Many vegetarian (scrape algae off rocks with radula) Some predatory • • Prey on bivalves, worms, fishes, sponges I. Phylum Mollusca A. Class Gastropoda – Torsion : during late veliger stage, twisting of visceral mass 180º, counter-clockwise, resulting in coiled shell – Operculum : leathery, trap door – *Drawing: radula slide, live lettuce slugs-order Sacoglossa, marine snails* Abalones Snails Snails Snails Nudibranchs Giant clam I. Phylum Mollusca B. Class Bivalvia (=2 valved) • Laterally compressed • Hinged, 2-valved shell – (oysters, clams, mussels, scallops) muscles keep closed • No head , no radula • Sedentary lifestyle • Some have muscular foot for burrowing (e.g., clams) • Gills used for suspension feeding (active) & respiration • Water enters and leaves through siphons (incurrent and excurrent) • Some anchor to substrate with byssal threads (e.g., mussels) Scallops – Swim! (repeated clapping of valves) • *Drawing-Scallop shell, live flame scallop • Anterior adductor muscle Posterior adductor muscle Valves Mantle Foot I. Phylum Mollusca C. Class Cephalopoda (=head footed) 1. 2. 3. 4. Octopuses (5 cm – 9 m)– no shell; Cryptic, bite prey with beak-like jaw Squid (giant ~ 1000 kg, 18 m) – Shell reduced to pen made of chitin Cuttlefish – Carbonate shell=cuttlebone, aid in buoyancy Nautilus – Shell with chambers (septa) filled with gas, buoyancy organ • Exclusively marine • Fast moving, highly mobile predators • • • • • • • Large eyes Shell reduced or absent Foot modified as arms and tentacles bearing suckers Siphon – Directs water released from mantle cavity Move by jet propulsion-move in any direction Ink sac for defense-distraction http://www.pbs.org/wnet/nature/octopus/ I.Phylum Mollusca **Drawing-squid and 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 non-retractable w/suckers and hooks Cuttlefish 8 arms + 2 tentacles, retractable w/ suckers, no hooks eye 2 –extensible tentacle stalks fin mantle funnel arm tentacle clubs I. Phylum Mollusca C. Class Polyplacophora (Many-platebearing=Chitons, 800 species) • • • • Mostly graze algae on rocky shorelines Exclusively marine 8 overlapping plates *drawing-chiton* D. Class Scaphopoda (=spade foot, Tusk shells) • • © Charlotte M. Lloyd Predators on foraminifera and juvenile bivalves Most common in deep water, buried in sediment II. Phylum Arthropoda • Most species of any phylum (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 Subphylum Trilobitomorpha Class Trilobita • Marine • Extinct since 250 mya • Rich fossil history because of exoskeleton • Dorso-ventrally flattened • *drawing-trilobite fossil* 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 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 *Drawing-sea spider* PHOTO: Bill Rudman Subphylum Crustacea (40K species) • • • Contains majority of marine arthropod species Gills + two pairs of antennae (sensory) Larval forms – nauplius and zoea A. Class Copepoda (=oar foot, Copepods) • • • • • • 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 Subphylum Crustacea B. Cirripedia(= hairy foot, Barnacles) • Active suspension feeders (filter feeders) • Use feathery cirri (modified swimming appendages) • Sessile (attached to surfaces-whales, piers) • Fouling organisms (boats, whales) • Resemble mollusks superficially – calcareous plates Subphylum Crustacea C. Class Malacostraca (=soft shell, 75% crustacean species) 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 • ©2004 Amanda Demopoulos • *drawing-Gammarus slide, Daphnia slide* 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 Subphylum Crustacea C. Class Malacostraca 3. Order Euphausiacea (Krill) - holoplankton • Laterally compressed • • Head and anterior segments fused to form distinct carapace Widespread distribution • • • • • Up to 10 cm long (usually smaller) 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) Subphylum Crustacea C. Class Malacostraca 4. Order Decapoda (=10 legs, Crabs, Lobsters, Shrimps) Most species in Crustacea (~10,000) • • • • Largest crustaceans Five pairs of walking legs (deca=10) • • First pair usually modified as claws for feeding/defense Well-developed carapace = cephalothorax • • • Scavengers/Predators/Both Rest of body = abdomen, tail Laterally compressed, except crabs – abdomen under cephalothorax *drawing-crab zoea slide, lobster Fig. 7.30 Phylum Arthropoda Subphylum-Uniramia 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) • *Drawing-insect leg types a) walking legs b) swimming legs III.Phylum Echinodermata – spiny skin • • • • 6000 species Sea lilies, feather stars, brittle stars, sea stars, sand dollars, sea urchins, sea biscuits, sea cucumbers Radial symmetry Pentaradial symmetry in adults • Oral/aboral Endoskeleton = hard plates, ~95% calcium carbonate, covered by skin Complete digestive, nervous systems, and reproductive organs Regeneration Water vascular system = internal hydraulic system • • • • • • • • Unique to echinoderms Tube feet (podia) extended by pressure from ampullae (muscular sacs) Tube feet used for locomotion, feeding, sensory functions Connected to exterior through madreporite (porous plate) III.Phylum Echinodermata Class Stelleroidea = a star A. Subclass Asteroidea (=star like, Sea stars) • • Most species have five arms (some more), Tube feet on oral surface in ambulacral grooves Endoskeleton composed of CaCO3 plates • • • Flexible skeleton – permits movement Aboral surface often covered with pedicellariae • • Small claws used for grooming surface Predators • • Feed on bivalves, snails, barnacles Pry shells of bivalve apart and insert stomach Crown of Thorns Acanthaster planci III. Phylum Echinodermata Class Stelleroidea B. Subclass Ophiuroidea (Brittle stars, Serpent stars) • Arms long and very flexible • • • • • • May resemble writhing snakes Tube feet lack suckers (used for feeding) Central disk distinct 1 Mouth, no anus Cryptic – Usually not in open areas Scavengers/Detritivores • Particles collected by tube feet and passed to mouth III. Phylum Echinodermata C. Class Echinoidea (=spine like, Sea urchins, sea biscuits, sand dollars), (Echinus = Gr. Hedgehog) • Round, rigid test with movable spines and pedicellariae Spines and tube feet used for locomotion • • Tube feet in shallow ambulacral grooves (5 rows) along outside of test Complete digestive system • Mouth on bottom, anus on top • • Herbivores Feed on seaweeds and seagrasses (especially drifting) plus attached encrusting organisms • • Mouth includes Aristotle’s lantern (system of jaws and muscles used to bite off algae, other food from bottom)