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Chapter 33 Invertebrates.

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1 Chapter 33 Invertebrates

2 Overview: Life Without a Backbone
Invertebrates are animals that lack a backbone They account for 95% of known animal species


4 LE 33-2 Porifera Cnidaria Echinodermata Chordata
Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida) Deuterostomia Bilateria Eumetazoa Ancestral colonial choanoflagellate

5 LE 33-3a A sponge A jelly 0.5 mm 250 µm A placozoan (LM)
A kinorhynch (LM) A marine flatworm A rotifer (LM) Ectoprocts Phoronids

6 LE 33-3b A brachiopod A ribbon worm 5 mm An acanthocephalan
A ctenophore, or comb jelly An octopus A marine annelid 50 µm A loriciferan (LM) A priapulan

7 LE 33-3c A roundworm A scorpion (an arachid) 100 µm 100 µm
A cycliophoran (colorized SEM) Tardigrades (colorized SEM) An onychophoran An acorn worm A sea urchin A tunicate

8 Concept 33.1: Sponges are sessile and have a porous body and choanocytes
Sponges, phylum Porifera, live in both fresh and marine waters Sponges lack true tissues and organs

9 Sponges are suspension feeders, capturing food particles suspended in the water that passes through their body

10 LE 33-4 Flagellum Food particles in mucus Choanocyte Choanocytes
Collar Osculum Azure vase sponge (Callyspongia plicifera) Spongocoel Phagocytosis of food particles Amoebocyte Porocytes Spicules Epidermis Water flow Amoebocyte Mesohyl

11 Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food Most sponges are hermaphrodites: Each individual functions as both male and female

12 Concept 33.2: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes
All animals except sponges belong to the clade Eumetazoa, animals with true tissues Phylum Cnidaria is one of the oldest groups in this clade

13 Cnidarians have diversified into a wide range of both sessile and floating forms including jellies, corals, and hydras They exhibit a relatively simple diploblastic, radial body plan

14 Video: Hydra Eating Daphnia (time lapse)
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 floating medusa Video: Hydra Eating Daphnia (time lapse)

15 Mouth/anus Tentacle Polyp Medusa Gastrovascular cavity Gastrodermis
Mesoglea Body stalk Epidermis Tentacle Mouth/anus

16 Video: Hydra Releasing Sperm
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 Video: Hydra Budding Video: Hydra Releasing Sperm

17 Prey Tentacle “Trigger” Discharge of thread Nematocyst Coiled thread

18 Phylum Cnidaria is divided into four major classes:
Hydrozoa Scyphozoa Cubozoa Anthozoa


20 LE 33-7 Scyphozoans (jellies) Cubozoan (sea wasp) Anthozoan
(sea anemone) Hydrozoans

21 Video: Thimble Jellies Video: Clownfish and Anemone
Video: Jelly Swimming Video: Thimble Jellies Video: Clownfish and Anemone Video: Coral Reef

22 Hydrozoans Most hydrozoans alternate between polyp and medusa forms

23 LE 33-8–3 Reproductive polyp Feeding polyp Medusa bud MEIOSIS Gonad
SEXUAL REPRODUCTION Egg Sperm ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps FERTILIZATION Zygote Developing polyp Mature polyp Planula (larva) Key Haploid (n) 1 mm Diploid (2n)

24 Scyphozoans In the class Scyphozoa, jellies (medusae) are the prevalent form of the life cycle

25 Cubozoans In the class Cubozoa, which includes box jellies and sea wasps, the medusa is box-shaped and has complex eyes

26 Anthozoans Class Anthozoa includes the corals and sea anemones, which occur only as polyps

27 Concept 33.3: 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

28 Flatworms Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats They are flattened dorsoventrally and have a gastrovascular cavity Although flatworms undergo triploblastic development, they are acoelomates

29 Flatworms are divided into four classes:
Turbellaria (mostly free-living flatworms) Monogenea (monogeneans) Trematoda (trematodes, or flukes) Cestoda (tapworms)


31 Turbellarians Turbellarians are nearly all free-living and mostly marine The best-known turbellarians are commonly called planarians


33 Planarians have light-sensitive eyespots and centralized nerve nets
The planarian nervous system is more complex and centralized than the nerve nets of cnidarians

34 Pharynx Gastrovascular cavity Eyespots Ganglia Ventral nerve cords
LE 33-10 Pharynx Gastrovascular cavity Eyespots Ganglia Ventral nerve cords

35 Monogeneans and Trematodes
Monogeneans and trematodes live as parasites in or on other animals They parasitize a wide range of hosts Trematodes that parasitize humans spend part of their lives in snail hosts

36 LE 33-11 Mature flukes live in the blood vessels
of the human intestine Male Female 1 mm Larvae penetrate skin and blood vessels of humans. Blood flukes reproduce sexually in the human host. Fertilized eggs exit host in feces. Eggs develop in water into ciliated larvae. Larvae infect snails. Asexual reproduction within snail results in another type of motile larva. Snail host

37 Most monogeneans are parasites of fish

38 Tapeworms Tapeworms are also parasitic and lack a digestive system

39 reproductive structures
LE 33-12 Proglottids with reproductive structures 200 µm Scolex Hooks Sucker

40 Rotifers Rotifers, phylum Rotifera, are tiny animals that inhabit fresh water, the ocean, and damp soil Rotifers are smaller than many protists but are truly multicellular and have specialized organ systems Video: Rotifer

41 LE 33-13 0.1 mm

42 Rotifers have an alimentary canal: a digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelom Rotifers reproduce by parthenogenesis, in which females produce offspring from unfertilized eggs

43 Lophophorates: Ectoprocts, Phoronids, and Brachiopods
Lophophorates have a lophophore, a horseshoe-shaped, suspension-feeding organ with ciliated tentacles

44 Ectoprocts are colonial animals that superficially resemble plants

45 LE 33-14 Lophophore Lophophore Ectoprocts Phoronids Brachiopods

46 Phoronids are tube-dwelling marine worms ranging from 1 mm to 50 cm in length

47 Brachiopods superficially resemble clams and other hinge-shelled molluscs, but the two halves of the shell are dorsal and ventral rather than lateral, as in clams

48 Nemerteans Members of phylum Nemertea are commonly called proboscis worms or ribbon worms


50 The nemerteans’ unique proboscis is used for defense and prey capture and 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

51 Concept 33.4: Molluscs have a muscular foot, a visceral mass, and a mantle
Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids 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

52 All molluscs have a similar body plan with three main parts:
Muscular foot Visceral mass Mantle

53 Visceral mass Coelom Heart Intestine Nephridium Gonads Mantle Stomach
Radula Mantle cavity Shell Mouth Radula Anus Gill Mouth Nerve cords Foot Esophagus

54 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

55 There are four major classes of molluscs:
Polyplacophora (chitons) Gastropoda (snails and slugs) Bivalvia (clams, oysters, and other bivalves) Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses)

56 Chitons Class Polyplacophora consists of the chitons, oval-shaped marine animals encased in an armor of eight dorsal plates


58 Gastropods About three-quarters of all living species of molluscs belong to class Gastropoda Video: Nudibranchs

59 A sea slug. Nudibranchs, or sea slugs,
LE 33-18 A land snail A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution.

60 Most gastropods are marine, but many are freshwater and terrestrial species
Most have a single, spiraled shell Slugs lack a shell or have a reduced shell The most distinctive characteristic of gastropods is torsion, which causes the animal’s anus and mantle to end up above its head

61 LE 33-19 Stomach Intestine Mantle cavity Anus Mouth

62 Bivalves Molluscs of class Bivalvia include many species of clams, oysters, mussels, and scallops They have a shell divided into two halves


64 The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange

65 LE 33-21 Coelom Hinge area Mantle Gut Heart Adductor muscle Shell Anus
Mouth Excurrent siphon Palp Water flow Foot Mantle cavity Incurrent siphon Gill

66 Cephalopods Class Cephalopoda includes squids and octopuses, carnivores with beak-like jaws surrounded by tentacles of their modified foot

67 Most octopuses creep along the sea floor in search of prey

68 Octopuses are considered among the most intelligent invertebrates.
LE 33-22a Octopuses are considered among the most intelligent invertebrates.

69 Squids use their siphon to fire a jet of water, which allows them to swim very quickly

70 LE 33-22b Squids are speedy carnivores with beaklike jaws and well-developed eyes.

71 One small group of shelled cephalopods, the nautiluses, survives today

72 LE 33-22c Chambered nautiluses are the only living cephalopods with an external shell.

73 Concept 33.5: Annelids are segmented worms
Annelids have bodies composed of a series of fused rings The phylum Annelida is divided into three classes: Oligochaeta (earthworms and their relatives) Polychaeta (polychaetes) Hirudinea (leeches)


75 Video: Earthworm Locomotion
Oligochaetes Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin They include the earthworms and a variety of aquatic species Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal Video: Earthworm Locomotion

76 Giant Australian earthworm Cerebral ganglia Gizzard Mouth
LE 33-23 Cuticle Epidermis Coelom Septum (partition between segments) Circular muscle Longitudinal muscle Metanephridium Anus Dorsal vessel Chaetae Intestine Ventral vessel Nerve cords Nephrostome Metanephridium Clitellum Esophagus Crop Pharynx Intestine Giant Australian earthworm Cerebral ganglia Gizzard Mouth Ventral nerve cords with segmental ganglia Subpharyngeal ganglion Circulatory system

77 Polychaetes Members of class Polychaetes have paddlelike parapodia that work as gills and aid in locomotion Video: Tubeworms

78 LE 33-24 Parapodia

79 Leeches Members of class Hirudinea are blood-sucking parasites, such as leeches


81 Concept 33.6: Nematodes are nonsegmented pseudocoelomates covered by a tough cuticle
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 The cylindrical bodies of nematodes (phylum Nematoda) are covered by a tough coat called a cuticle Video: C. elegans Crawling Video: C. elegans Embryo Development (time lapse)

82 LE 33-26 25 µm

83 Some species of nematodes are important parasites of plants and animals

84 Encysted juveniles Muscle tissue 50 µm

85 Concept 33.7: 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

86 General Characteristics of Arthropods
The diversity and success of arthropods are largely related to their segmentation, hard exoskeleton, and jointed appendages

87 Early arthropods, such as trilobites, showed little variation from segment to segment


89 Video: Lobster Mouth Parts
As arthropods evolved, the segments fused, and the appendages became more specialized The appendages of some living arthropods are modified for many different functions Video: Lobster Mouth Parts

90 LE 33-29 Cephalothorax Abdomen Thorax Head Antennae (sensory reception) Swimming appendages (two sets located under abdomen Walking legs Pincer (defense) Mouthparts (feeding)

91 The body of an arthropod is completely covered by the cuticle, an exoskeleton made of chitin
When an arthropod grow, it molts its exoskeleton in a process called ecdysis

92 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

93 Molecular evidence suggests that living arthropods consist of four major lineages that diverged early in the phylum’s evolution: Cheliceriforms (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) Myriapods (centipedes and millipedes) Hexapods (insects and relatives) Crustaceans (crabs, lobsters, shrimps, barnacles, and many others)


95 Cheliceriforms Cheliceriforms, subphylum Cheliceriformes, are named for clawlike feeding appendages called chelicerae Most marine cheliceriforms are extinct, but some species survive today, including horseshoe crabs


97 Most modern cheliceriforms are arachnids, which include spiders, scorpions, ticks, and mites

98 LE 33-31a Scorpions have pedipalps that are pincers specialized for defense and the capture of food. The tip of the tail bears a poisonous stinger.

99 LE 33-31b 50 µm Dust mites are ubiquitous scavengers in human dwellings but are harmless except to those people who are allergic to them (colorized SEM).

100 Web-building spiders are generally most active during the daytime.
LE 33-31c Web-building spiders are generally most active during the daytime.

101 Arachnids have an abdomen and a cephalothorax, which has six pairs of appendages, the most anterior of which are the chelicerae

102 Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland
LE 33-32 Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland Anus Book lung Spinnerets Gonopore (exit for eggs) Chelicera Pedipalp Sperm receptacle Silk gland

103 Myriapods Subphylum Myriapoda includes millipedes and centipedes
Millipedes, class Diplopoda, have many legs Each trunk segment has two pairs of legs


105 Centipedes, class Chilopoda, are carnivores with jaw-like mandibles
They have one pair of legs per trunk segment


107 Insects Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined They live in almost every terrestrial habitat and in fresh water The internal anatomy of an insect includes several complex organ systems

108 LE 33-35 Abdomen Thorax Head Compound eye Antennae Dorsal artery Crop
Cerebral ganglion Anus Heart Vagina Malpighian tubules Ovary Tracheal tubes Mouthparts Nerve cords

109 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

110 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

111 Video: Butterfly Emerging
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 Video: Butterfly Emerging

112 LE 33-36 Larva (caterpillar) Pupa Pupa Emerging adult Adult

113 Video: Bee Pollinating
Insects are classified into about 26 orders Video: Bee Pollinating

EXAMPLES Blattodea 4,000 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

EXAMPLES Coleoptera 350,000 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

EXAMPLES Dermaptera 1,200 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. Earwig

EXAMPLES Diptera 151,000 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, predetors, and parasites. Horsefly

EXAMPLES Hemiptera 85,000 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. Leaf- footed bug

EXAMPLES Hymenoptera 125,000 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. Cicada-killer wasp

EXAMPLES Isoptera 2,000 Termites are widespread social insects that produce enormous colonies. It had 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. Termite

EXAMPLES Lepidoptera 120,000 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

EXAMPLES Odonata 5,000 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

EXAMPLES 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 of their hind leg. Orthopterans undergo incomplete metamorphosis. Katydid

EXAMPLES Phasmida 2,600 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. Stick insect

EXAMPLES Phthiraptera 2,400 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. Human body louse

EXAMPLES Siphonaptera 2,400 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. Flea

EXAMPLES Thysanura 450 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

EXAMPLES 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

129 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 branched appendages that are extensively specialized for feeding and locomotion

130 Decapods are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp


132 Planktonic crustaceans include many species of copepods, which are among the most numerous of all animals


134 Barnacles are a group of mostly sessile crustaceans
They have a cuticle that is hardened into a shell


136 Concept 33.8: Echinoderms and chordates are deuterostomes
Sea stars and other echinoderms, phylum Echinodermata, may seem to have little in common with phylum Chordata, which includes the vertebrates

137 Chordates and echinoderms share characteristics of deuterostomes:
Radial cleavage Development of the coelom from the archenteron Formation of the mouth at the end of the embryo opposite the blastopore

138 Video: Echinoderm Tube Feet
Echinoderms Sea stars and most other echinoderms are slow-moving 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, a network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange Video: Echinoderm Tube Feet

139 Spine Stomach Anus Radial canal
LE 33-39 Spine Stomach Anus Gills Central disk Madreporite Digestive glands Radial nerve Ring canal Gonads Ampulla Radial canal Podium Tube feet

140 Radial anatomy of many echinoderms evolved from the bilateral symmetry of ancestors
Living echinoderms are divided into six classes: Asteroidia (sea stars) Ophiuroidea (brittle stars) Echinoidea (sea urchins and sand dollars) Crinoidea (sea lilies and feather stars) Holothuroidea (sea cucumbers) Concentricycloidea (sea daisies)


142 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

143 A sea star (class Asteroidea)
LE 33-40a A sea star (class Asteroidea)

144 Brittle Stars Brittle stars have a distinct central disk and long, flexible arms

145 A brittle star (class Ophiuroidea)
LE 33-40b A brittle star (class Ophiuroidea)

146 Sea Urchins and Sand Dollars
Sea urchins and sand dollars have no arms but have five rows of tube feet

147 A sea urchin (class Echinoidea)
LE 33-40c A sea urchin (class Echinoidea)

148 Sea Lilies and Feather Stars
Sea lilies live attached to the substrate by a stalk Feather stars crawl using long, flexible arms

149 A feather star (class Crinoidea)
LE 33-40d A feather star (class Crinoidea)

150 Sea Cucumbers Sea cucumbers do not look much like other echinoderms
They lack spines, and their endoskeleton is much reduced

151 A sea cucumber (class Holothuroidea)
LE 33-40e A sea cucumber (class Holothuroidea)

152 Sea Daisies Sea daisies were discovered in 1986, and only two species are known

153 A sea daisy (class Concentricycloidea)
LE 33-40f A sea daisy (class Concentricycloidea)

154 Chordates Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates Chordates share many features of embryonic development with echinoderms


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