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Chapter 33 Invertebrates Let’s meet the … Invertebrates Life Without a Backbone Invertebrates Are animals that lack a backbone Account for 95% of known animal species Xmas Tree Worm Eumetazoa Ancestral colonial choanoflagellate Chordata Echinodermata Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida) Cnidaria Porifera A review of animal phylogeny Deuterostomia Bilateria Invertebrate diversity PORIFERA (5,500 species) A sponge PLACOZOA (1 species) CNIDARIA (10,000 species) A jelly KINORHYNCHA (150 species) 0.5 mm 250 µm A placozoan (LM) A kinorhynch (LM) ROTIFERA (1,800 species) PLATYHELMINTHES (20,000 species) A marine flatworm ECTOPROCTA (4,500 species) A rotifer (LM) PHORONIDA (20 species) Ectoprocts Phoronids Invertebrate Diversity BRACHIOPODA (335 species) A brachiopod ACANTHOCEPHALA (1,100 species) NEMERTEA (900 species) A ribbon worm CTENOPHORA (100 species) 5 mm An acanthocephalan MOLLUSCA (93,000 species) A ctenophore, or comb jelly ANNELIDA (16,500 species) An octopus LORICIFERA (10 species) A marine annelid PRIAPULA (16 species) 50 µm A loriciferan (LM) A priapulan Invertebrate Diversity ARTHROPODA (1,000,000 + species) NEMATODA (25,000 species) A roundworm A scorpion (an arachnid) CYCLIOPHORA (1 species) TARDIGRADA (800 species) 100 µm 100 µm A cycliophoran (colorized SEM) Tardigrades (colorized SEM) HEMICHORDATA (85 species) ONYCHOPHORA (110 species) An onychophoran An acorn worm ECHINODERMATA (7,000 species) A sea urchin CHORDATA (52,000 species) A tunicate Sponges (Phylum Porifera) Sponge characteristics Sessile Porous body Choanocytes: flagellated collar cells generate a water current through the sponge and ingest suspended food by phagocytosis Live in both fresh and marine waters Lack true tissues (groups of similar cells that form a functional unit). All animals except sponges belong to the clade Eumetazoa, the animals with true tissues Most sponges are hermaphrodites (each individual functions as both male and female) Sponges Sponges are suspension feeders Capturing food particles suspended in the water that passes through their body 5 Choanocytes. The spongocoel is lined with feeding cells called choanocytes. By beating flagella, the choanocytes create a current that draws water in through the porocytes. Azure vase sponge (Callyspongia plicifera) 4 Spongocoel. Water passing through porocytes enters a cavity called the spongocoel. 3 Porocytes. Water enters the epidermis through channels formed by porocytes, doughnut-shaped cells that span the body wall. 2 Epidermis. The outer layer consists of tightly packed epidermal cells. 1 Mesohyl. The wall of this simple sponge consists of two layers of cells separated by a gelatinous matrix, the mesohyl (“middle matter”). Flagellum Collar Food particles in mucus Choanocyte Osculum Phagocytosis of food particles Spicules Water flow Amoebocyte 6 The movement of the choanocyte flagella also draws water through its collar of fingerlike projections. Food particles are trapped in the mucus coating the projections, engulfed by phagocytosis, and either digested or transferred to amoebocytes. 7 Amoebocyte. Amoebocytes transport nutrients to other cells of the sponge body and also produce materials for skeletal fibers (spicules). Cnidarians (Phylum Cnidaria) A diverse range of both sessile and floating organisms including hydras, jellies, sea anemones, and corals Cnidarian characteristics radial symmetry gastrovascular cavity (digestive compartment) Cnidocytes movie Cnidarian Body Plan Relatively simple diploblastic (two germ layers), radial body plan Basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity A single opening functions as both mouth and anus There are two variations on this body plan The sessile polyp and the floating medusa Polyp Medusa Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Body stalk Epidermis Tentacle Mouth/anus Cnidarian Feeding Cnidarians are carnivores That use tentacles to capture prey The tentacles are armed with cnidocytes Unique cells that function in defense and the capture of prey Tentacle Threads can inject poison into the prey, or stick to or entangle the target “Trigger” Discharge Of thread Nematocyst Coiled thread Cnidocyte Prey Classes of Phylum Cnidaria Hydrozoan Life Cycle 2 Some of the colony’s polyps, equipped with tentacles, are specialized for feeding. 3 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding. 4 The medusae swim off, grow, and reproduce sexually. Reproductive polyp 1 A colony of interconnected polyps (inset, LM) results from asexual reproduction by budding. Feeding polyp Medusa bud MEIOSIS Gonad Medusa SEXUAL REPRODUCTION Sperm Egg ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps FERTILIZATION Zygote Developing polyp Mature polyp Planula (larva) 1 mm 6 The planula eventually settles and develops into a new polyp. 5 The zygote develops into a solid ciliated larva called a planula. Key Haploid (n) Diploid (2n) Classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa (b) Many species of jellies (class Scyphozoa), including the (a) These colonial polyps are members of class Hydrozoa. species pictured here, are bioluminescent. The largest scyphozoans have tentacles more than 100 m long dangling from a bell-shaped body up to 2 m in diameter. (c) The sea wasp (Chironex fleckeri) is a member of class Cubozoa. Its poison, which can subdue fish and other large prey, is more potent than cobra venom. (d) Sea anemones and other members of class Anthozoa exist only as polyps. Cnidarian Classes In the class Hydrozoa Most hydrozoans alternate between polyp and medusa forms. Freshwater Hydras exist only in the polyp form. In the class Scyphozoa Jellies (medusae) are the prevalent form of the life cycle In the class Cubozoa, which includes box jellies and sea wasps The medusa is box-shaped and has complex eyes Class Anthozoa includes the corals and sea anemones Which occur only as polyps Purple coral Hydra Hydra movie 1 Hydra movie 2 Coral reproduction Jellyfish movie Bilateria Most animals have bilateral symmetry The vast majority of animal species belong to the clade Bilateria Which consists of animals with bilateral symmetry and triploblastic development Flatworms Members of phylum Platyhelminthes Live in marine, freshwater, and damp terrestrial habitats. Some are parasitic. Are flattened dorsoventrally and have bilateral symmetry Undergo triploblastic development Are acoelomates (lack a coelom) with gastrovascular cavities. Lack a digestive system entirely and absorb nutrients across their body surface. Flatworm Classes Turbellarians Are nearly all free-living and mostly marine Turbellarians Planarians are common examples of turbellarians They have light-sensitive eyespots and centralized nerve nets Pharynx. The mouth is at the tip of a muscular pharynx that extends from the animal’s ventral side. Digestive juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastrovascular cavity, where digestion continues. Digestion is completed within the cells lining the gastrovascular cavity, which has three branches, each with fine subbranches that provide an extensive surface area. Undigested wastes are egested through the mouth. Gastrovascular cavity Eyespots Ganglia. Located at the anterior end of the worm, near the main sources of sensory input, is a pair of ganglia, dense clusters of nerve cells. Ventral nerve cords. From the ganglia, a pair of ventral nerve cords runs the length of the body. Monogeneans and Trematodes Live as parasites in or on other animals They parasitize a wide range of hosts Most monogeneans are parasites of fish Trematodes (Flukes) that parasitize humans spend part of their lives in snail hosts 1 Mature flukes live in the blood vessels of the human intestine. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right. Male Female 1 mm 5 These larvae penetrate the skin and blood vessels of humans working in irrigated fields contaminated with infected human feces. 2 Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces. 3 The eggs develop in water into ciliated larvae. These larvae infect snails, the intermediate hosts. 4 Asexual reproduction within a snail results in another type of motile larva, which escapes from the snail host. Snail host Tapeworms (Class Cestoda) Are also parasitic and lack a digestive system Proglottids with reproductive structures 200 µm Scolex Hooks Sucker Rotifers (Phylum Rotifera) Are tiny animals that inhabit fresh water, the ocean, and damp soil Rotifers are smaller than many protists Rotifers have an alimentary canal But are truly multicellular and have specialized organ systems A digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelom Some species of rotifers reproduce by parthenogenesis In which females produce more females from unfertilized eggs 0.1 mm Rotifers (Phylum Rotifera) Rotifer movie 2 Three Phyla of Lophophorates: Ectoprocts, Phoronids, and Brachiopods Lophophorates have a lophophore A horseshoe-shaped, suspension-feeding organ bearing ciliated tentacles that trap suspended food particles Ectoprocts Are colonial animals that superficially resemble plants Lophophore (a) Ectoprocts, such as this sea mat (Membranipora membranacea), are colonial lophophorates. Phoronids Are tube-dwelling marine worms ranging from 1 mm to 50 cm in length Lophophore (b) In phoronids such as Phoronis hippocrepia, the lophophore and mouth are at one end of an elongated trunk. Brachipods Superficially resemble clams and other hingeshelled molluscs But the two halves of the shell are dorsal and ventral rather than lateral, as in clams Lophophore (c) Brachiopods have a hinged shell. The two parts of the shell are dorsal and ventral. Nemerteans (Phylum Nemertea) Commonly called proboscis worms or ribbon worms The nemerteans unique proboscis Is used for defense and prey capture Is extended by a fluid-filled sac Nemerteans also have a closed circulatory system In which the blood is contained in vessels distinct from fluid in the body cavity Molluscs (Phylum Mollusca) Phylum Mollusca: Includes snails and slugs, oysters and clams, and octopuses and squids Mollusc characteristics Body plan: muscular foot, visceral mass, and a mantle Mantle is a fold of tissue that drapes over the visceral mass and secretes the shell. Most molluscs are marine, though some inhabit fresh water and some are terrestrial Molluscs are soft-bodied animals, but most are protected by a hard shell Most molluscs have separate sexes with gonads located in the visceral mass The life cycle of many molluscs includes a ciliated larval stage called a trochophore Mollusc anatomy Nephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph. Heart. Most molluscs have an open circulatory system. The dorsally located heart pumps circulatory fluid called hemolymph through arteries into sinuses (body spaces). The organs of the mollusc are thus continually bathed in hemolymph. The long digestive tract is coiled in the visceral mass. Visceral mass Coelom Mantle Mantle cavity Intestine Gonads Stomach Shell Radula Anus The nervous system consists of a nerve ring around the esophagus, from which nerve cords extend. Gill Foot Nerve cords Esophagus Mouth Mouth Radula. The mouth region in many mollusc species contains a rasp-like feeding organ called a radula. This belt of backwardcurved teeth slides back and forth, scraping and scooping like a backhoe. Classes of molluscs Chitons Class Polyplacophora is composed of the chitons (Oval-shaped marine animals encased in an armor of eight dorsal plates) Gastropods About three-quarters of all living species of molluscs belong to class Gastropoda (a) A land snail (b) A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution. Gastropods Gastropod characteristics Most are marine, but there are also many freshwater and terrestrial species Possess a single, spiraled shell Slugs lack a shell or have a reduced shell The most distinctive characteristic of this class is a developmental process known as torsion, which causes the animal’s anus and mantle to end up above its head Mantle cavity Anus Mouth Stomach Intestine Bivalves (Molluscs of class Bivalvia) Include many species of clams, oysters, mussels, and scallops Have a shell divided into two halves Bivalves The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange Hinge area Mantle Gut Coelom Heart Shell Adductor muscle Mouth Anus Excurrent siphon Palp Water flow Foot Mantle cavity Gill Incurrent siphon Clam locomotion Cephalopods Class Cephalopoda includes squids and octopuses Carnivores with beak-like jaws surrounded by tentacles of their modified foot Octopus Most octopuses creep along the sea floor in search of prey (a) Octopuses are considered among the most intelligent invertebrates. Squid Squids use their siphon to fire a jet of water, which allows them to swim very quickly (b) Squids are speedy carnivores with beaklike jaws and well-developed eyes. `One small group of shelled cephalopods The nautiluses, survives today (c) Chambered nautiluses are the only living cephalopods with an external shell. Annelids Annelids Segmented worms Have bodies composed of a series of fused rings 3 Classes Oligochaeta, Polychaeta, Hirudinea Classes of Annelida Oligochaetes Oligochaetes (class Oligochaeta) Are named for their relatively sparse chaetae (bristles made of chitin) Include the earthworms and a variety of aquatic species Earthworms eat their way through the soil, extracting nutrients as the soil moves through the alimentary canal Which helps till the earth, making earthworms valuable to farmers Earthworm anatomy Coelom. The coelom of the earthworm is partitioned by septa. Each segment is surrounded by longitudinal muscle, which in turn is surrounded by circular muscle. Earthworms coordinate the contraction of these two sets of muscles to move (see Figure 49.25). These muscles work against the noncompressible coelomic fluid, which acts as a hydrostatic skeleton. Epidermis Septum (partition between segments) Circular muscle Many of the internal structures are repeated within each segment of the earthworm. Chaetae. Each segment has four pairs of chaetae, bristles that provide traction for burrowing. Longitudinal muscle Dorsal vessel Anus Intestine Nerve cords Cerebral ganglia. The earthworm nervous system features a brain-like pair of cerebral ganglia above and in front of the pharynx. A ring of nerves around the pharynx connects to a subpharyngeal ganglion, from which a fused pair of nerve cords runs posteriorly. Cuticle Metanephridium. Each segment of the worm contains a pair of excretory tubes, called metanephridia, with ciliated funnels, called nephrostomes. The metanephridia remove wastes from the blood and coelomic fluid through exterior pores. Nephrostome Pharynx Tiny blood vessels are abundant in the earthworm’s skin, which functions as its respiratory organ. The blood contains oxygen-carrying hemoglobin. Ventral vessel Clitellum Esophagus Metanephridium Crop Giant Australian earthworm Intestine Gizzard Mouth Subpharyngeal ganglion The circulatory system, a network of vessels, is closed. The dorsal and ventral vessels are linked by segmental pairs of vessels. The dorsal vessel and five pairs of vessels that circle the esophagus of an earthworm are muscular and pump blood through the circulatory system. Ventral nerve cords with segmental ganglia. The nerve cords penetrate the septa and run the length of the animal, as do the digestive tract and longitudinal blood vessels. Polychaetes Members of class Polychaeta possess paddlelike parapodia that function as gills and aid in locomotion Parapodia Leeches Members of class Hirudinea are blood-sucking parasites, such as leeches Nematodes (roundworms) Nematodes are nonsegmented pseudocoelomates covered by a tough cuticle Among the most widespread of all animals, nematodes, or roundworms Are found in most aquatic habitats, in the soil, in moist tissues of plants, and in the body fluids and tissues of animals Nematode movie Nematodes The cylindrical bodies of nematodes are covered by a tough coat called a cuticle 25 µm Nematodes Some species of nematodes are important parasites of plants and animals Encysted juveniles Trichinella spiralis encysted in human muscle tissue Muscle tissue 50 µm Arthropods Arthropods are segmented coelomates that have an exoskeleton and jointed appendages Two out of every three known species of animals are arthropods Members of the phylum Arthropoda Are found in nearly all habitats of the biosphere Arthropod Characteristics The diversity and success of arthropods Are largely related to their segmentation, hard exoskeleton, and jointed appendages Arthropods have an open circulatory system In which fluid called hemolymph is circulated into the spaces surrounding the tissues and organs A variety of organs specialized for gas exchange have evolved in arthropods The body of an arthropod is completely covered by the cuticle, an exoskeleton made of chitin When an arthropod grows it molts its exoskeleton in a process called ecdysis Segmentation Early arthropods, such as trilobites showed little variation from segment to segment As arthropods evolved the segments fused, and the appendages became more specialized The appendages of some living arthropods are modified for many different functions Cephalothorax Abdomen Antennae (sensory reception) Head Thorax Swimming appendages Walking legs Pincer (defense) Mouthparts (feeding) Subphyla of Arthropoda Cheliceriforms Named for clawlike feeding appendages called chelicerae Includes spiders, ticks, mites, scorpions, and horseshoe crabs Most of the marine cheliceriforms are extinct But some species survive today, including the horseshoe crabs Cheliceriforms Most modern cheliceriforms are arachnids A group that includes spiders, scorpions, ticks, and mites 50 µm (a) Scorpions have pedipalps that are pincers (b) Dust mites are ubiquitous scavengers in (c) Web-building spiders are generally specialized for defense and the capture of human dwellings but are harmless except most active during the daytime. food. The tip of the tail bears a poisonous to those people who are allergic to them stinger. (colorized SEM). Arachnids Arachnids have an abdomen and a cephalothorax Which has six pairs of appendages, the most anterior of which are the chelicerae. (4 pairs of walking legs) Intestine Digestive gland Stomach Heart Brain Eyes Poison gland Ovary Anus Book lung Spinnerets Silk gland Sperm Gonopore (exit for eggs) receptacle Chelicera Pedipalp Myriapods Subphylum Myriapoda Millipedes, class Diplopoda Includes millipedes and centipedes Have a large number of legs Each trunk segment has two pairs of legs Centipedes, class Chilopoda Are carnivores with jaw-like mandibles Have one pair of legs per trunk segment Insects Subphylum Hexapoda, insects and their relatives Are more species-rich than all other forms of life combined Live in almost every terrestrial habitat and in fresh water The internal anatomy of an insect includes several complex organ systems Insect anatomy The insect body has three regions: head, thorax, and abdomen. The segmentation of the thorax and abdomen are obvious, but the segments that form the head are fused. Abdomen Thorax Head Compound eye Heart. The insect heart drives hemolymph through an open circulatory system. Cerebral ganglion. The two nerve cords meet in the head, where the ganglia of several anterior segments are fused into a cerebral ganglion (brain). The antennae, eyes, and other sense organs are concentrated on the head. Antennae Ovary Malpighian tubules. Anus Metabolic wastes are removed from the Vagina hemolymph by excretory organs called Malpighian tubules, which are outpocketings of the digestive tract. Tracheal tubes. Gas exchange in insects is accomplished by a tracheal system of branched, chitin-lined tubes that infiltrate the body and carry oxygen directly to cells. The tracheal system opens to the outside of the body through spiracles, pores that can control air flow and water loss by opening or closing. Nerve cords. The insect nervous system consists of a pair of ventral nerve cords with several segmental ganglia. Dorsal artery Crop Insect mouthparts are formed from several pairs of modified appendages. The mouthparts include mandibles, which grasshoppers use for chewing. In other insects, mouthparts are specialized for lapping, piercing, or sucking. Insects Flight is one key to the great success of insects An animal that can fly can escape predators, find food, and disperse to new habitats much faster than organisms that can only crawl Metamorphosis Many insects undergo metamorphosis during their development In incomplete metamorphosis, the young, called nymphs Resemble adults but are smaller and go through a series of molts until they reach full size (example: grasshoppers) Insects with complete metamorphosis have larval stages specialized for eating and growing that are known by such names as maggot, grub, or caterpillar The larval stage looks entirely different from the adult stage Metamorphosis from the larval stage to the adult stage occurs during a pupal stage Metamorphosis movie (a) Larva (caterpillar) (b) Pupa (c) Pupa (d) Emerging adult (e) Adult 26 Orders of Insects ORDER Blattodea Coleoptera Dermaptera Diptera Hemiptera Hymenoptera Isoptera APPROXIMATE NUMBER OF SPECIES 4,000 350,000 1,200 151,000 85,000 125,000 2,000 MAIN CHARACTERISTICS EXAMPLES Cockroaches have a dorsoventrally flattened body, with legs modified for rapid running. Forewings, when present, are leathery, whereas hind wings are fanlike. Fewer than 40 cockroach species live in houses; the rest exploit habitats ranging from tropical forest floors to caves and deserts. German cockroach Beetles comprise the most species-rich order of insects. They have two pairs of wings, one of which is thick and leathery, the other membranous. They have an armored exoskeleton and mouthparts adapted for biting and chewing. Beetles undergo complete metamorphosis. Japanese beetle Earwigs are generally nocturnal scavengers. While some species are wingless, others have two pairs of wings, one of which is thick and leathery, the other membranous. Earwigs have biting mouthparts and large posterior pincers. They undergo incomplete metamorphosis. Dipterans have one pair of wings; the second pair has become modified into balancing organs called halteres. Their head is large and mobile; their mouthparts are adapted for sucking, piercing, or lapping. Dipterans undergo complete metamorphosis. Flies and mosquitoes are among the best-known dipterans, which live as scavengers, predators, and parasites. Hemipterans are so-called “true bugs,” including bed bugs, assassin bugs, and chinch bugs. (Insects in other orders are sometimes erroneously called bugs.) Hemipterans have two pairs of wings, one pair partly leathery, the other membranous. They have piercing or sucking mouthparts and undergo incomplete metamorphosis. Ants, bees, and wasps are generally highly social insects. They have two pairs of membranous wings, a mobile head, and chewing or sucking mouthparts. The females of many species have a posterior stinging organ. Hymenopterans undergo complete metamorphosis. Termites are widespread social insects that produce enormous colonies. It has been estimated that there are 700 kg of termites for every person on Earth! Some termites have two pairs of membranous wings, while others are wingless. They feed on wood with the aid of microbial symbionts carried in specialized chambers in their hindgut. Earwig Horsefly LeafFooted bug Cicada-killer wasp Termite 26 Orders of Insects ORDER Lepidoptera Odonata APPROXIMATE NUMBER OF SPECIES 120,000 5,000 EXAMPLE MAIN CHARACTERISTICS Butterflies and moths are among the best-known insects. They have two pairs of wings covered with tiny scales. To feed, they uncoil a long proboscis. Most feed on nectar, but some species feed on other substances, including animal blood or tears. Swallowtail butterfly Dragonflies and damselflies have two pairs of large, membranous wings. They have an elongated abdomen, large, compound eyes, and chewing mouthparts. They undergo incomplete metamorphosis and are active predators. Dragonfly Orthoptera 13,000 Grasshoppers, crickets, and their relatives are mostly herbivorous. They have large hind legs adapted for jumping, two pairs of wings (one leathery, one membranous), and biting or chewing mouthparts. Males commonly make courtship sounds by rubbing together body parts, such as a ridge on their hind leg. Orthopterans undergo incomplete metamorphosis. Katydid Phasmida Phthiraptera Siphonaptera Thysanura 2,600 2,400 2,400 450 Stick insects and leaf insects are exquisite mimics of plants. The eggs of some species even mimic seeds of the plants on which the Insects live. Their body is cylindrical or flattened dorsoventrally. They lack forewings but have fanlike hind wings. Their mouthparts are adapted for biting or chewing. Commonly called sucking lice, these insects spend their entire life as an ectoparasite feeding on the hair or feathers of a single host. Their legs, equipped with clawlike tarsi, are adapted for clinging to their hosts. They lack wings and have reduced eyes. Sucking lice undergo incomplete metamorphosis. Fleas are bloodsucking ectoparasites on birds and mammals. Their body is wingless and laterally compressed. Their legs are modified for clinging to their hosts and for long-distance jumping. They undergo complete metamorphosis. Stick insect Human Body louse Flea Silverfish are small, wingless insects with a flattened body and reduced eyes. They live in leaf litter or under bark. They can also infest buildings, where they can become pests. Silverfish Trichoptera 7,100 The larvae of caddisflies live in streams, where they make houses from sand grains, wood fragments, or other material held together by silk. Adults have two pairs of hairy wings and chewing or lapping mouthparts. They undergo complete metamorphosis. Caddisfly Crustaceans While arachnids and insects thrive on land Crustaceans, for the most part, have remained in marine and freshwater environments Crustaceans, subphylum Crustacea Typically have biramous (branched) appendages that are extensively specialized for feeding and locomotion Decapods Decapods are all relatively large crustaceans And include lobsters, crabs, crayfish, and shrimp Ghost crabs (genus Ocypode) live on sandy ocean beaches worldwide. Primarily nocturnal, they take shelter in burrows during the day. Decapod movie Planktonic crustaceans Planktonic crustaceans include many species of copepods Which are among the most numerous of all animals Planktonic crustaceans known as krill are consumed in vast quantities by whales. Barnacles Barnacles are a group of mostly sessile crustaceans whose cuticle is hardened into a shell The jointed appendages projecting from the shells of these barnacles capture organisms and organic particles suspended in the water. Deuterostomes Echinoderms and chordates are deuterostomes Chordates and echinoderms share the characteristics of deuterostomes Radial cleavage Formation of the mouth at the end of the embryo opposite the blastopore Echinoderms Echinoderm characteristics Sea stars and most other echinoderms are slowmoving or sessile marine animals A thin, bumpy or spiny skin covers an endoskeleton of hard calcareous plates Unique to echinoderms is a water vascular system network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange Echinoderm movie Echinoderm anatomy A short digestive tract runs from the mouth on the bottom of the central disk to the anus on top of the disk. Central disk. The central disk has a nerve ring and nerve cords radiating from the ring into the arms. Digestive glands secrete digestive juices and aid in the absorption and storage of nutrients. Radial canal. The water vascular system consists of a ring canal in the central disk and five radial canals, each running in a groove down the entire length of an arm. Stomach Anus Spine Gills Ring canal Gonads Radial nerve The surface of a sea star is covered by spines that help defend against predators, as well as by small gills that provide gas exchange. Madreporite. Water can flow in or out of the water vascular system into the surrounding water through the madreporite. Ampulla Podium Tube feet Branching from each radial canal are hundreds of hollow, muscular tube feet filled with fluid. Each tube foot consists of a bulb-like ampulla and suckered podium (foot portion). When the ampulla squeezes, it forces water into the podium and makes it expand. The podium then contacts the substrate. When the muscles in the wall of the podium contract, they force water back into the ampulla, making the podium shorten and bend. Echinoderm classes Sea Stars Sea stars, class Asteroidea Have multiple arms radiating from a central disk The undersurfaces of the arms bear tube feet, each of which can act like a suction disk (a) A sea star (class Asteroidea) Brittle Stars Brittle stars have a distinct central disk and long, flexible arms (b) A brittle star (class Ophiuroidea) Sea Urchins and Sand Dollars Sea urchins and sand dollars have no arms, but they do have five rows of tube feet that function in movement Sand Dollar Sea Urchin Sea Lilies and Feather Stars Sea lilies live attached to the substrate by a stalk Feather stars Crawl about using their long, flexible arms (d) A feather star (class Crinoidea) Sea Cucumbers Sea cucumbers do not look much like other echinoderms They lack spines, and their endoskeleton is much reduced (e) A sea cucumber (class Holothuroidea) Sea Daisies Sea daisies were discovered in 1986 And only two species are known (f) A sea daisy (class Concentricycloidea) Chordates (Phylum Chordata) Chordates Two subphyla of invertebrates as well as the hagfishes and the vertebrates Share many features of embryonic development with echinoderms Review of Animal Phyla