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Figure 33.21b Chapter 33 Octopus An Introduction to Invertebrates Invertebrates are animals that lack a backbone. (Trivia: they account for more than 95% of known animal species.) © 2014 Pearson Education, Inc. Figure 33.3a Porifera (5,500 species) Acoela (400 species) Ctenophora (100 species) 1.5 mm A sponge Cnidaria (10,000 species) Acoel flatworms (LM) Placozoa (1 species) 0.5 mm A ctenophore, or comb jelly A jelly A placozoan (LM) © 2014 Pearson Education, Inc. Figure 33.3ba Lophotrochozoa A marine flatworm Ectoprocta (4,500 species) Ectoprocts © 2014 Pearson Education, Inc. Rotifera (1,800 species) 100 µm Platyhelminthes (20,000 species) A rotifer (LM) Brachiopoda (335 species) A brachiopod Figure 33.3bb Lophotrochozoa Acanthocephala (1,100 species) Mollusca (100,000 species) Annelida (16,500 species) Curved hooks A marine annelid An octopus An acanthocephalan (LM) Nemertea (900 species) Cycliophora (1 species) 100 µm A cycliophoran (colorized SEM) © 2014 Pearson Education, Inc. A ribbon worm Figure 33.3c Ecdysozoa Loricifera (10 species) Priapula (16 species) Tardigrada (800 species) 100 µm 50 µm A loriciferan (LM) A priapulan Onychophora (110 species) Nematoda (25,000 species) Tardigrades (colorized SEM) Arthropoda (1,000,000 species) A roundworm A scorpion (an arachnid) An onychophoran © 2014 Pearson Education, Inc. Figure 33.3d Deuterostomia Hemichordata (85 species) An acorn worm Chordata (56,000 species) A tunicate © 2014 Pearson Education, Inc. Echinodermata (7,000 species) A sea urchin Sponges are animals that lack true tissues • Animals in the phylum Porifera are known informally as sponges • They are sedentary and live in marine waters or fresh water • Sponges are filter feeders, capturing food particles suspended in the water that passes through their body • Water is drawn through pores into a cavity called the spongocoel and out through an opening called the osculum • Sponges lack true tissues and organs although they do have different cell types • Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food • Sponges consist of a gelatinous noncellular mesohyl layer between two cell layers • Wandering though the mesohyl are amoebocytes. They take up food from water and from choanocytes, digest it, and carry nutrients to other cells. © 2014 Pearson Education, Inc. ● ● ● ● Most sponges are hermaphrodites: Each individual functions as both male and female producing gametes that are released After fertilization, flagellated larva swim until they find a suitable location, when they will attach and develop into a sessile adult Amoebocytes also secrete tough skeletal fibers within the mesohyl. In some groups of sponges, these fibers are sharp spicules of calcium carbonate or silica. Other sponges produce more flexible fibers from a collagen protein called spongin. ● (We use these pliant, protein honeycombed skeletons as bath sponges.) Sponges are classified by their type of skeleton/spicules: silica (glass sponges), calcium carbonate (chalk sponges) , or spongin (bath sponges). © 2014 Pearson Education, Inc. Figure 33.4 Choanocytes Collar Food particles in mucus Choanocyte Osculum Spongocoel Flagellum Phagocytosis Amoebocyte of food particles Pores Spicules Epidermis Water flow Amoebocytes Mesohyl Azure vase sponge (Callyspongia plicifera) © 2014 Pearson Education, Inc. Concept 33.2: Cnidarians are an ancient phylum of eumetazoans All animals except sponges and a few other groups belong to the clade Eumetazoa, animals with true tissues © 2014 Pearson Education, Inc. Cnidarians • Cnidarians have diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras • They exhibit a relatively simple diploblastic, radial body plan • The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity • A single opening functions as mouth and anus • There are two variations on the body plan: the sessile polyp and motile medusa • A polyp adheres to the substrate by the aboral end of its body • A medusa has a bell-shaped body with its mouth on the underside and do not attach to the substate but move freely • Cnidarians are carnivores that use tentacles to capture prey • The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey. Nematocysts are specialized organelles within cnidocytes that eject a stinging thread • Movements of contractile cells are controlled by a noncentralized nerve net associated with simple sensory receptors that are distributed radially around the body. © 2014 Pearson Education, Inc. Figure 33.5 Mouth/anus Polyp Tentacle Medusa Gastrovascular cavity Gastrodermis Body stalk Mesoglea Epidermis Tentacle Mouth/anus © 2014 Pearson Education, Inc. Figure 33.6 Tentacle Cuticle of prey Thread Nematocyst “Trigger” Thread discharges Cnidocyte © 2014 Pearson Education, Inc. Thread (coiled) Figure 33.7 The four classes of Phylum Cnidaria (b) Scyphozoa (a) Hydrozoa © 2014 Pearson Education, Inc. (c) Cubozoa (d) Anthozoa Phylum Cnidaria is divided into four major classes • In the class Scyphozoa, jellies (medusae) are the prevalent form of the life cycle Jellies • The class Cubozoa, which includes box jellies, the medusa is box-shaped and has complex eyes in the fringe of the medusa. Cubozoans often have highly toxic cnidocytes • Class Anthozoa includes the corals and sea anemones, and these cnidarians occur only as polyps •Corals secrete a hard external skeleton. Each polyp generation builds on the skeletons of earlier generations to form the structures we call coral © 2014 Pearson Education, Inc. Sea anemones Video: Clownfish and Anemone © 2014 Pearson Education, Inc. Figure 33.8-3 Most hydrozoans alternate between polyp and medusa forms Feeding polyp Reproductive polyp Medusa bud MEIOSIS Gonad Medusa Egg ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps 1 mm SEXUAL REPRODUCTION FERTILIZATION Developing polyp © 2014 Pearson Education, Inc. Sperm Zygote Planula (larva) Mature polyp Hydra, a freshwater cnidarian, exists only in polyp form and reproduces asexually by budding Key Haploid (n) Diploid (2n) Lophotrochozoans • Bilaterian animals have bilateral symmetry and triploblastic development. Most have a coelom and a digestive tract with two openings • The clade Bilateria contains Lophotrochozoa, Ecdysozoa, and Deuterostomia • Lophotrochozoa includes the flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids © 2014 Pearson Education, Inc. Flatworms Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats Although flatworms undergo triploblastic development, they are acoelomates Flatworms have a gastrovascular cavity with one opening Gas exchange takes place across the surface, and protonephridia regulate the osmotic balance Their dorsoventrally flattened shape maximizes surface area for gas exchange © 2014 Pearson Education, Inc. The best-known free-living flatworms are planarians Planarians live in fresh water and prey on smaller animals Planarians have light-sensitive eyespots centralized nerve nets Pharynx Gastrovascular cavity Mouth Eyespots Ventral nerve cords Ganglia Their nervous system is more complex and centralized than the nerve nets of cnidarians Planarians are hermaphrodites and can reproduce sexually, or © 2014 Pearson Education, Inc. Parasitic Species Parasitic flatworms live in or on other animals Two important groups of parasitic flatworms are the trematodes and the tapeworms Trematodes parasitize a wide range of hosts, and most have complex life cycles with alternating sexual and asexual stages © 2014 Pearson Education, Inc. Figure 33.11 Trematodes that parasitize humans spend part of their lives in snail Hosts. They produce surface proteins that mimic their host and release molecules that manipulate the host’s immune System. Human host Female 1 mm Mature flukes Motile larva Ciliated larva Snail host © 2014 Pearson Education, Inc. Male • Tapeworms are parasites of vertebrates and lack a digestive system. (Tapeworms absorb nutrients from the host’s intestine.) • Suckers and hooks on the head, or scolex, anchor the worm in the digestive tract of the host. • A long series of segments or proglottids, sacs of sex organs, lie posterior to the scolex. • Mature proglottids, loaded with thousands of eggs, are released from the posterior end of the tapeworm and leave with the host’s feces. • Hermaphroditic and self-fertilizing, the proglottids near the head are male and produce sperm. Hooks As more segments are added from the head end, Sucker the existing segments become Proglottids with female and produce eggs which reproductive structures are fertilized by the sperm from the anterior end. Scolex © 2014 Pearson Education, Inc. Molluscs Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids Most molluscs are marine, though some inhabit fresh water and some snails and slugs are terrestrial Molluscs are soft-bodied animals, but most are protected by a hard shell All molluscs have a similar body plan with three main parts Muscular foot Visceral mass Mantle Many molluscs also have a water-filled mantle cavity and feed using a rasplike radula © 2014 Pearson Education, Inc. Figure 33.15 Metanephridium Visceral mass Coelom Heart Intestine Gonads Mantle Digestive tract Stomach Shell Mantle cavity Mouth Radula Anus Gill Foot © 2014 Pearson Education, Inc. Nerve cords Esophagus Mouth Radula Most molluscs have separate sexes with gonads located in the visceral mass, but many snails are hermaphrodites The life cycle of many molluscs includes a ciliated larval stage called a trochophore Four of the major classes of molluscs are Polyplacophora (chitons) Gastropoda (snails and slugs) Bivalvia (clams, oysters, and other bivalves) Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses) © 2014 Pearson Education, Inc. Figure 33.16 Chitons are oval-shaped marine animals encased in an armor of eight dorsal plates They use their foot like a suction cup to grip rock, and their radula to scrape algae off the rock surface © 2014 Pearson Education, Inc. Figure 33.17 Gastropods: Snails and Slugs About three-quarters of all living species of molluscs are gastropods (a) A land snail (b) A sea slug (nudibranch) Most gastropods are marine, but many are freshwater and terrestrial Gastropods move slowly by a rippling motion of the foot or by cilia Most have a single, spiraled shell that functions in protection from injury, dehydration, and predation. Slugs lack a shell or have a reduced shell. © 2014 Pearson Education, Inc. • A characteristic of gastropods is torsion, which causes the animal’s anus and mantle to end up above its head. This occurs during embryonic development, when the visceral mass is rotated up to 180 degrees, so the anus and mantle cavity are above the head in adults. • After torsion, some of the organs that were bilateral are reduced or lost on one side of the body. • Torsion is different from the coiling of a shell. • Many gastropods have distinct heads with eyes at the tips of tentacles. • Most gastropods use their scraping radula to graze on algae or plant material. • In place of the gills found in most aquatic gastropods, the lining of the mantle cavity of terrestrial snails functions as a lung. © 2014 Pearson Education, Inc. Bivalves • Bivalves are marine and include many species of clams, oysters, mussels, and scallops • They have a shell divided into two halves drawn together by adductor muscles • Some bivalves have eyes and sensory tentacles along the edge of their mantle • The mantle cavity of a bivalve contains gills that are used for feeding (they are suspension feeders)as well as gas exchange • Bivalves have no distinct head and the radula has been lost. • Motility varies-- sessile mussels attach themselves to rocks by threads they secrete; clams can slowly pull themselves into sand or mud using their muscular foot; scallops can “swim” in short bursts by flapping their shells and jetting water out of their mantle cavity © 2014 Pearson Education, Inc. Figure 33.19 Mantle Hinge area Coelom Gut Heart Adductor muscle (one of two) Digestive gland Anus Mouth Excurrent siphon Shell Palp Foot © 2014 Pearson Education, Inc. Mantle cavity Gonad Gill Water flow Incurrent siphon Cephalopods Cephalopods are carnivores with beak-like jaws surrounded by tentacles (formed from the modified foot which also forms the siphon) They are able to immobilize prey with a poison present in their saliva Most octopuses creep along the sea floor in search of prey • Cephalopods have a closed circulatory system, welldeveloped sense organs, and a complex brain • The shell is reduced and internal in squids// lost in octopi • Squids use their siphon to fire a jet of water, which allows them to swim very quickly • One small group of shelled cephalopods, the nautiluses, survives today © 2014 Pearson Education, Inc. Figure 33.20 Squid Octopus Chambered nautilus © 2014 Pearson Education, Inc. Figure 33.21 Molluscs are the animal group with the largest number of recent extinctions Other invertebrates Molluscs An endangered Pacific island land snail, Partula suturalis Amphibians Insects Fishes Birds Mammals Reptiles (excluding birds) Recorded extinctions of animal species © 2014 Pearson Education, Inc. Workers on a mound of pearl mussels killed to make buttons (ca. 1919) Annelids Annelids are coelomates with bodies composed of a series of fused rings Recent molecular analyses indicate that the annelids can be divided into two major clades, the Errantia and the Sedentaria. Most members of clade Errantia are mobile, marine organisms Many errantians have a pair of paddle-like or ridge-like structures called parapodia on each body segment. Each parapodium has numerous chaetae, bristles made of chitin © 2014 Pearson Education, Inc. Sedentarians Sedentarians tend to be less mobile than errantians. Some species burrow into the substrate, while others live in protective tubes Tube-dwelling sedentarians often have elaborate gills or tentacles used for filter feeding This clade also contains the leeches and the earthworms © 2014 Pearson Education, Inc. Leeches Leeches include predators of invertebrates, and parasites that suck blood Leeches secrete a chemical called hirudin to prevent blood from coagulating Most species of leeches live in fresh water; some are marine or terrestrial Earthworms Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal Earthworms are hermaphrodites but cross-fertilize © 2014 Pearson Education, Inc. Video: Earthworm Locomotion Anus Skin Metanephridium Clitellum Esophagus Crop Pharynx Intestine Cerebral ganglia Gizzard Mouth Subpharyngeal ganglion Circulatory system vessels © 2014 Pearson Education, Inc. Ventral nerve cords Concept 33.4: Ecdysozoans are the most species-rich animal group Ecdysozoans are covered by a tough coat called a cuticle The cuticle is shed or molted through a process called ecdysis The two largest phyla are nematodes and arthropods © 2014 Pearson Education, Inc. Nematodes Nematodes, or roundworms, are found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals They have an alimentary canal, but lack a circulatory system Body wall muscles are all longitudinal, and their contraction produces a thrashing motion Caenorhabditis elegans is a model organism in research Some species of nematodes are important parasites of plants and animals. Trichinella spiralis can be acquired by humans from undercooked pork © 2014 Pearson Education, Inc. Figure 33.27 Encysted juveniles © 2014 Pearson Education, Inc. Muscle tissue 50 µm Arthropods Two out of every three known species of animals are arthropods and they are found in nearly all habitats of the biosphere The arthropod body plan consists of a segmented body, hard exoskeleton called the cuticle made of layers of protein and the polysaccharide chitin, and jointed appendages • The exoskeleton protects and provides an attachment site for muscles. When an arthropod grows, it molts its exoskeleton. The appendages of some living arthropods are modified for functions such as walking, feeding, sensory reception, reproduction, and defense. These modified appendages are jointed and come in pairs © 2014 Pearson Education, Inc. Arthropods show extensive cephalization with the number of sense organs in the head, having eyes, olfactory receptors, and antennae that function in touch and smell Arthropods have an open circulatory system in which hemolymph is circulated into the spaces surrounding the tissues and organs A variety of organs specialized for gas exchange have evolved in arthropods Morphological and molecular evidence suggests that living arthropods consist of three major lineages: Chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) Myriapods (centipedes and millipedes) Pancrustaceans (lobsters and other crustaceans, as well as insects and their relatives) © 2014 Pearson Education, Inc. Chelicerates • Chelicerates, subphylum Chelicerata, are named for clawlike feeding appendages called chelicerae which serve as pincers or fangs • Two body parts- the cephalothorax and abdomen • Lack sensory antennae and most have simple eyes • Most marine cheliceriforms are extinct, but some species survive today, including horseshoe crabs © 2014 Pearson Education, Inc. Figure 33.32 Most modern chelicerates are arachnids, which include spiders, scorpions, ticks, and mites 50 µm Scorpion Dust mite Web-building spider © 2014 Pearson Education, Inc. Arachnids: • Arachnids have an abdomen and a cephalothorax, which has six pairs of appendages: the chelicerae, the pedipalps (which function in sensing or feeding), and four pairs of walking legs • Gas exchange in spiders occurs in respiratory organs called book lungs • Many spiders produce silk, a liquid protein, from specialized abdominal glands • The liquid is spun by spinnerets into fibers that solidify • Web designs are characteristic of each species • Silk is also used to wrap eggs or as “drop lines” for rapid escapes © 2014 Pearson Education, Inc. Figure 33.33 Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland Anus Book lung Spinnerets Silk gland © 2014 Pearson Education, Inc. Gonopore (exit for eggs) Sperm receptacle Chelicera Pedipalp Myriapods: millipedes and centipedes All living myriapods are terrestrial They have a pair of antennae and three pairs of appendages modified as mouthparts Millipedes eat decaying leaves and plant matter. Millipedes have many legs, with two pairs per trunk segment (a) Millipede (b) Centipede © 2014 Pearson Education, Inc. Centipedes are carnivores. Centipedes have one pair of legs per trunk segment. Poison claws on the foremost trunk segment paralyze prey and aid in defense Crustaceans Crustaceans live in marine and freshwater environments Many crustaceans have highly specialized appendages Small crustaceans exchange gases through the cuticle; larger crustaceans have gills Most crustaceans have separate males and females Isopods include terrestrial, freshwater, and marine species Pill bugs are a well-known group of terrestrial isopods Decapods are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp Planktonic crustaceans include many species of copepods, which are among the most numerous of all animals They are rivaled in abundance by shrimplike krill © 2014 Pearson Education, Inc. Figure 33.35 Brine shrimp A ghost crab, an example of a decapod Pill bugs © 2014 Pearson Education, Inc. Barnacles Insects Hexapoda is an enormous clade including insects and their relatives Insects live in almost every terrestrial habitat and in fresh water. Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops The internal anatomy of an insect includes several complex organ systems The insect nervous system consists of a pair of ventral nerve cords with several segmental ganglia. The two cords meet in the head, where the ganglia are fused into a cerebral ganglion (brain). In the complete digestive system, there are regionally specialized organs with discrete functions. Most insects have separate males and females and reproduce sexually © 2014 Pearson Education, Inc. Figure 33.38 Abdomen Thorax Head Compound eye Antennae Heart Dorsal artery Crop Cerebral ganglion Anus Vagina Malpighian tubules Ovary Tracheal tubes © 2014 Pearson Education, Inc. Nerve cords Mouthparts • Individuals find and recognize members of their own species by bright colors, sound, or odors Flight is one key to the great success of insects One or two pairs of wings emerge from the dorsal side of the thorax. Wings are extensions of the cuticle and are not true appendages. Insect wings are very diverse: Dragonflies have two similar pairs of wings. The wings of bees and wasps are hooked together and move as a single pair. Butterfly wings work together as the anterior wings overlap the posterior wings. In beetles, the posterior wings function in flight, while the anterior wings act as covers. © 2014 Pearson Education, Inc. 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 Some nymphs like grasshoppers look similar to the adult while others like mayflies, look totally different © 2014 Pearson Education, Inc. Figure 33.40 Insects with complete metamorphosis have larval stages known by such names as maggot, grub, or caterpillar The larval stage looks entirely different from the adult stage (a) Larva (caterpillar) (b) Pupa (c) Later stage (d) Emerging pupa adult (e) Adult © 2014 Pearson Education, Inc. Concept 33.5: Echinoderms and chordates are deuterostomes Echinoderms (phylum Echinodermata) include sea stars and sea urchins Echinoderms and chordates constitute the clade Deuterostomia Deuterostomes are defined primarily by DNA similarities Phylum Chordata consists of two basal groups of invertebrates as well as vertebrates Chordates are bilaterally symmetrical coelomates with segmented bodies Chordates did not evolve from echinoderms, but have evolved separately from them for at least 500 million years © 2014 Pearson Education, Inc. Echinoderms Sea stars and most other echinoderms are slow-moving or sessile marine animals A thin epidermis covers an endoskeleton of hard calcareous plates Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion and feeding Males and females are usually separate, and sexual reproduction is external • Most adult echinoderms have radial symmetry with multiples of five • Echinoderm larvae have bilateral symmetry • Living echinoderms are divided into five classes: Asteroidea (sea stars and sea daisies), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies and feather stars), and Holothuroidea (sea cucumbers) © 2014 Pearson Education, Inc. Asteroidea: Sea Stars Commonly known as starfish, Sea stars have multiple arms radiating from a central disk The undersurface of each arm bears tube feet, which grip substrate with adhesive chemicals Sea stars feed on bivalves by prying them open with their tube feet, everting their stomach, and digesting their prey externally with digestive enzymes Sea stars can regrow lost arms © 2014 Pearson Education, Inc. Digestive tract Stomach Anus Spine Gills Madreporite Central disk Radial nerve Digestive glands Ring canal Gonads Ampulla Podium Tube feet Radial canal © 2014 Pearson Education, Inc. Ophiuroidea: Brittle Stars Brittle stars have a distinct central disk and long, flexible arms, which they use for movement Some species are suspension feeders, while others are predators or scavengers © 2014 Pearson Education, Inc. Echinoidea: Sea Urchins and Sand Dollars Sea urchins and sand dollars have no arms but have five rows of tube feet Their spines are used for locomotion and protection Sea urchins feed on seaweed using a jaw-like structure on their underside © 2014 Pearson Education, Inc. Crinoidea: Sea Lilies and Feather Stars Sea lilies live attached to the substrate by a stalk Feather stars can crawl using long, flexible arms Both are suspension feeders Crinoidea have changed little over the course of evolution © 2014 Pearson Education, Inc. Holothuroidea: Sea Cucumbers Sea cucumbers lack spines, have a very reduced endoskeleton, and do not look much like other echinoderms Sea cucumbers have five rows of tube feet; some of these are developed as feeding tentacles © 2014 Pearson Education, Inc. Figure 33.UN08 Phylum Porifera (sponges) Description Lack true tissues; have choanocytes (collar cells—flagellated cells that ingest bacteria and tiny food particles) Cnidaria (hydras, jellies, sea anemones, corals) Unique stinging structures (nematocytes) housed in specialized cells (cnidocytes); diploblastic; radially symmetrical; gastrovascular cavity (digestive compartment with a single opening) Dorsoventrally flattened acoelomates; gastrovascular cavity or no digestive tract Pseudocoelomates with alimentary canal (digestive tube with mouth and anus); jaws (trophi); head with ciliated crown Coelomates with lophophores (feeding structures bearing ciliated tentacles) Platyhelminthes (flatworms) Lophotrochozoa Deuterostomia Ecdysozoa Bilateria Eumetazoa Metazoa Rotifera (rotifers) Lophophorates: Ectoprocta, Brachiopoda Mollusca (clams, snails, squids) Annelida (segmented worms) Coelomates with three main body parts (muscular foot, visceral mass, mantle); coelom reduced; most have hard shell made of calcium carbonate Coelomates with segmented body wall and internal organs (except digestive tract, which is unsegmented) Nematoda (roundworms) Cylindrical pseudocoelomates with tapered ends; no circulatory system; undergo ecdysis Arthropoda (spiders, centipedes, crustaceans, and insects) Coelomates with segmented body, jointed appendages, and exoskeleton made of protein and chitin Echinodermata (sea stars, sea urchins) Coelomates with bilaterally symmetrical larvae and five-part body organization as adults; unique water vascular system; endoskeleton Coelomates with notochord; dorsal, hollow nerve cord; pharyngeal slits; post-anal tail (see Chapter 34) Chordata (lancelets, tunicates, vertebrates) © 2014 Pearson Education, Inc.