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Chapter 9 Higher Invertebrates Phylum Mollusca • One of the most successful groups of animals in the ocean • Have soft bodies, usually covered by a calcium carbonate shell • Wide range of sizes, lifestyles and relationships to humans (i.e., some are food, others cause commercial damage) Molluscan Body • 2 major parts: – head-foot: region containing the head with its mouth and sensory organs and the foot, which is the animal’s organ of locomotion – visceral mass: dorsal body region containing the other organ systems, including: • circulatory (heart and vessels) • digestive (stomach, digestive glands, intestine and anus) • respiratory (gill) • excretory reproductive systems Molluscan Body • Mantle – protective tissue covering soft parts, extends from the visceral mass and hangs down on each side of the body, secretes the shell • mantle cavity: space between the mantle and the body • Radula – a ribbon of tissue containing teeth (found in all except bivalves) used for scraping, piercing, tearing or cutting pieces of food Chitin Molluscs • Class Polyplacophora - Chitons • Have flattened bodies often covered by 8 shell plates • Attach tightly to rocks, usually in intertidal zone • Most scrape algae and other organisms off the rocks with radulae for food Gastropod Molluscs • Class Gastropoda • May have no shell (nudibranchs), or a univalve (one-piece) shell – as the animal grows, whorls of the shell increase in size around a central axis • Feeding and nutrition for gastropods – exhibit wide variety of feeding styles – herbivores – using their radula, most feed on fine algae; some on large algae like kelps – carnivores – usually locate prey using its chemical trail; have evolved various behaviors for capturing/subduing prey – scavengers and deposit feeders – filter feeders Bivalve Molluscs • Class Bivalvia • Have shells divided into 2 jointed halves (valves) • Includes: – clams – oysters – mussels – scallops • Bivalve anatomy – no head or radula – laterally compressed bodies – shell halves attached dorsally at a hinge by ligaments – mantle often forms inhalant and exhalant openings to facilitate filter feeding • Bivalve adaptations to different habitats – soft-bottom burrowers (infauna) • siphons: structures formed when the mantle is fused around inhalant and exhalant openings, which project above the surface of sediments • siphons facilitate filter feeding while remaining buried in sand Cephalopod Molluscs • Class Cephalopoda • Squid • Octopus • nautilus • Named after the foot, which is modified into a head-like structure • Ring of tentacles projects from the anterior edge of the head, for use in prey capture, defense, reproduction and sometimes locomotion • Except for nautiloids, they lack shells or – Nautiloid cephalopods • produce large, coiled shells composed of chambers separated by septa (partitions) – gas-filled chambers aid with buoyancy – siphuncle: cord of tissue connecting the nautiloid to uninhabited chambers (it inhabits the last chamber) which removes seawater from each chamber as it forms • head has 60-90 tentacles coated with a sticky substance function in sensation or bringing food to the mouth – nautiloids (continued) • move using jet propulsion • usually dwell on the bottom during the day and migrate to the surface at night • eat hermit crabs and scavenge for other food on the bottom • squids have: – large cylindrical bodies with a pair of fins derived from mantle tissue – 10 appendages (8 arms + 2 tentacles) arranged in 5 pairs around the head and embellished with cup-shaped suckers which are attached by a short stalk and surrounded by toothed structures – the pen (a degenerate shell; an internal strip of hard protein) helps support the mantle – Octopus • octopods have 8 arms (no tentacles) with suckers without stalks or teeth, and sac-like bodies without fins • coleoids cloud water with a dark fluid called sepia containing melanin (a brown-black pigment) when disturbed • swim by jet propulsion by forcing water through a ventrallylocated siphon or by fin undulation (in squids) • octopods – better adapted to crawling over bottom • have the most advanced, complex nervous system among invertebrates • Color and shape in cephalopods – arm/body movements and color changes are used in communication – chromatophores: special skin cells containing pigment granules which are concentrated or dispersed to change color – cephalopods can produce general body color changes or stripes and other patterns • Feeding and nutrition – carnivores – prey is located with highly developed eyes and captured by tentacles or arms – a pair of powerful, beak-like jaws in the oral cavity is used to bite or tear tissues; octopods use radula to drill holes in shells – diet depends on and varies with habitat • squids are pelagic: fish, crustaceans, squid • cuttlefish find invertebrates on the bottom • octopods forage or lie in wait near the entrances to their dens Fun octopus links • https://www.youtube.com/watch?v=PmDTt kZlMwM • https://www.youtube.com/watch?v=IvvjcQI JnLg • https://www.youtube.com/watch?v=5MHJb xWO6OM Ecological Roles of Molluscs • Food for humans and other animals – snail shells are a calcium source for some marine birds – sperm whales consume masses of squid • Some snails are intermediate hosts to parasites • A few bivalves have commensal relationships (attaching to other animals) • Now we will talk about Annelids (segmented worms) Annelids: The Segmented Worms • Annelids—worms whose bodies are divided internally and externally into segments – segments increase mobility by enhancing leverage – hydrostatic skeleton – compartment contained fluid providing support to worm body – setae—small bristles used for locomotion, digging, anchorage and protection • Types of marine annelids – polychaetes – echiurans – Pogonophorans – tube worms Polychaetes • Polychaetes (class Polychaeta) are the most common marine annelids Polychaetes • Feeding and digestion – some errant species have mouth equipped with jaws and teeth and are active predators; tube dwellers may partially or completely leave the tube to feed – many sedentary species are filter or suspension feeders – digestive tract is usually a straight tube from the mouth to the posterior anus • food enters the mouth, nutrients are absorbed in the intestine, and wastes are excreted through the anus • Pogonophoran Annelids – deepsea worms near hydrothermal vents • Now we will talk about Nematodes Nematodes • Class Nematoda (Roundworms) • Round, slender, elongated bodies, tapering at both ends • Critical role as scavengers • Some are parasitic • Mast are hermaphroditic, some have separate sexes Ecological Role of Marine Worms • Nutrient cycling – through burrowing in sediment, release nutrients buried in the ocean bottom back to the surface for use by producers • Predator-prey relationships – Important links in food chains – consume organic matter unavailable to larger consumers, and then become food for largaer consumers themselves Ecological Role of Marine Worms – nematodes are the most abundant members of meiofauna – echiurans may be significant in the diet of some fishes – polychaetes are a major food source for invertebrates and vertebrates • Symbiotic relationships – tubes and burrows of non-carnivorous polychaetes provide protected and ventilated retreat for many commensals, e.g., scale worms, bivalves, small crabs • Now we will talk about the Arthropods • Arthropods include insects and crustaceans • Most numerous animals on Earth • Very successful Arthropods: Animals with Jointed Appendages • Phylum Arthropoda = 75% of identified species (include insects) • Have exoskeleton—a hard, protective exterior skeleton composed of protein and chitin • Molting—shedding and replacement of exoskeleton to permit animal’s growth • Body is divided into segments • Usually, each segment has a pair of jointed appendages, for locomotion, mouthparts, sensation, ornamentation Arthropods: Animals with Jointed Appendages • Have highly developed nervous systems – sophisticated sense organs – capacity for learning • 2 major groups of marine arthropods: – chelicerates – have a pair chelicerae (oral appendages) and lack mouthparts for chewing food – crustaceans – have appendages called mandibles that can be used to chew food Arthropod Chelicerates • Primitive group include spiders, ticks, scorpions, horseshoe crabs and sea spiders • 6 pairs of appendages; 1 pair are chelicerae for feeding • Horseshoe crabs – 3 body regions • cephalothorax – largest region with the most obvious appendages • abdomen – contains the gills • telson – a long spike used for steering and defense – body is covered by a carapace—a hard outer covering Arthropod Chelicerates • Horseshoe crabs (continued) – locomotion by walking or swimming by flexing the abdomen – mostly nocturnal scavengers – smaller males attach to females to mate, and eggs are laid in a depression on the beach; larvae return to the sea to grow Arthropod Chelicerates • Sea spiders – have small, thin bodies with 4 or more pairs of walking legs – feed on juices from cnidarians and other softbodied invertebrates, using a long sucking proboscis Arthropod Crustaceans • Crustaceans—marine mandibulates • Crustacean anatomy – 3 main body regions: • head • thorax • abdomen – appendages: • 2 pairs of sensory antennae • mandibles and maxillae used for feeding • walking legs, swimmerets (swimming legs), legs modified for reproduction, chelipeds (legs modified for defense) Arthropod Crustaceans – gas exchange • small crustaceans exchange gases through their body surface • larger crustaceans have gills • Molting – Crucial part of the life cycle – Frequency of molting decreases with age – Controlled by specific hormones produced in a gland in the head, initiated by environmental conditions, e.g., temperature, photoperiod Decapod Crustaceans • Order Decapoda – Crustacean animals with 5 pairs of walking legs: – crabs – lobsters – true shrimp • 1st pair of walking legs are chelipeds— pincers used for capturing prey and for defense • Wide range in size Decapod Crustaceans • Nutrition and digestion – chelipeds are used for prey capture – appendages are used for scavenging – predation and scavenging are usually combined – some decapods are deposit or filter feeders Arthropod Crustaceans • Order Stomatopoda – mantis shrimp • Highly specialized predators of fishes, crabs, shrimp and molluscs • 2nd pair of thoracic appendages – enlarged – has a movable finger that can be extended rapidly for prey capture/defense – can either spear or smash prey Arthropod Crustaceans • Order Euphausiacea - Krill • Pelagic, shrimp-like, 3-6 cm long • Important part of plankton - filter feeders that eat zooplankton • Most are bioluminescent – photophore: specialized light organ – swarms: large masses of individuals; bioluminescent is thought to signal swarming behavior • Food source for some whales, seals, penguins, and many fishes Arthropod Crustaceans • Order Amphipoda - amphipods • Shrimp-like, laterally compressed, with posterior 3 pairs of appendages directed backward • Many are burrowers; some construct tubes which they inhabit • Most are detritus feeders or scavengers, some are herbivores Arthropod Crustaceans • Class Copepoda – the largest group of small crustaceans • Usually the most abundant member of the zooplankton • Mostly suspension feeders; some rely on detritus, some are predators Arthropod crustaceans • Class Cirripedia (barnacles)– the only sessile crustaceans • Most have calcium carbonate shell • Attach directly to a hard surface, or have a stalk for attachment • Filter feed using cirripeds—feathery appendages which extend into the water when the shell is open Ecological Roles of Arthropods • Arthropods as food – important food sources for marine animals and humans – copepods form link in marine food chain between phytoplankton they eat and many animals that use copepods as a major food source – krill are consumed in large quantities by whales and other organisms Ecological Roles of Arthropods • Arthropods as symbionts – cleaning shrimps remove ectoparasites and other materials from reef fish – some copepods are ectoparasites for fish – barnacles are commensal with a wide diversity of hosts Ecological Roles of Arthropods • Role of arthropods in recycling and fouling – grass shrimp feed on detrital cellulose material, helps to break down algae and grasses in tidal marsh ecosystems – barnacles are a serious fouling problem on ship bottoms • attached barnacles can reduce ship speed by 30% • Economic significance – boat hulls require special paints and other anti-fouling measures • Now we will talk about Echinoderms Echinoderms: Animals with Spiny Skins • Phylum Echinodermata • Include sea stars, sea urchins and sea cucumbers • Larval forms exhibit bilateral symmetry but most adults exhibit a modified form of radial symmetry • Mostly benthic, and found at nearly all depths • Sea cucumbers and brittle stars are commonly found in deep-sea samples Echinoderm Structure • Endoskeleton: internal skeleton that lies just beneath the epidermis – ossicles: plates of calcium carbonate Echinoderm Structure • Water vascular system: unique hydraulic system that functions in locomotion, feeding, gas exchange and excretion – passes through a system of canals – attached to some canals are tube feet Echinoderm Sea Stars • Class Asteroidea – sea stars • Typically composed of a central disk + 5 arms or rays • On underside, ambulacral grooves with tube feet radiate from the mouth along each ray • Aboral surface: the side opposite the mouth, which is frequently rough or spiny Sea Stars • Feeding in sea stars – most are carnivores or scavengers of invertebrates and sometimes fish – prey are located by sensing of substances they release into the water – sea stars envelope and open bivalves, evert a portion of the stomach, and insert it into the bivalves to digest them Echinoderm Ophiuroids • Class Ophiuroidea – e.g. brittle, basket and serpent stars • Benthic with 5 slender, distinct arms, frequently covered with many spines • Lack pedicellariae and have closed abulacral grooves • Tube feet lack suckers and are used in locomotion and feeding • Brittle stars shed arms if disturbed Echinoderm Sea Urchins • Class Echinoidea Body enclosed by test—a hard exoskeleton • Benthic on solid surfaces (sea urchins) or in sand (heart urchins, sand dollars) • Regular (radial) echinoids: sea urchins; spheroid body with long, moveable spines • Irregular (bilateral) echinoids: heart urchins and sand dollars; have short spines on their tests Echinoderm Sea Cucumbers • Class Holothuroidea • Have elongated bodies, and usually lie on 1 side • Respiratory trees: a system of tubules located in the body cavity which accomplish gas exchange • Sexes are generally separate Echinoderm Crinoids • Class Crinoidea–sea lilies and feather stars • Primitive, flower-like echinoderms • Most are feather stars, which seldom move and cling to the bottom with grasping cirri • Suspension feeders • Can regenerate lost arms Ecological Roles of Echinoderms • Spiny skins deter most predators • Predators of molluscs, other echinoderms, cnidarians, crustaceans – crown-of-thorns sea star eats coral – sea urchins destroy kelp forests • Black sea urchins (Diadema antillarum) control algal growth on coral reefs • Sea cucumber poison, holothurin, has potential as a medicine • Now we will talk about hemichordates Hemichordates • Acorn worms (phylum Hemichordata) • Sessile bottom dwellers that burrow in sediments of intertidal mud or sand flats or under stones • Collects food with a large proboscis • Some species use their proboscis to dig burrows; the head protrudes from one end of the burrow, while the anus deposits fecal material near the other Invertebrate Chordates • Phylum Chordata • Have 4 key anatomical characteristics at some point in their life cycle: 1) notochord 2) pharyngeal gill slits 3) postanal tail 4) dorsal, hollow nerve tube Invertebrate chordates -Tunicates • Subphylum Urochordata • Mostly sessile, widely distributed • Named for their body covering – tunic: body covering, largely composed of a substance similar to cellulose • Types: – sea squirts – salps – larvaceans Sea Squirts • Lifestyles: solitary, colonial, compound – compound: organisms composed of several individuals (zooids) that share a common tunic • Filter feed on plankton in the water passing through their pharynx – some have symbiotic algae or bacteria • Can regenerate lost body parts Invertebrate Chordates - Cephalochordates • Subphylum Cephalochordata- lancelets • Fish-like chordates; slender, laterally compressed and eel-like in form and behavior • Benthic; burrow in coarse sands • Suspension feed by projecting their heads above the sand • Separate sexes practice internal fertilization