Chapter 33

Invertebrates

Let’s meet the … Invertebrates

Life Without a Backbone

InvertebratesAre animals that lack a backboneAccount for 95% of known animal species

Xmas Tree Worm

A review of animal phylogeny

Ancestral colonialchoanoflagellate

Eumetazoa

Bilateria

Deuterostomia

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Invertebrate diversity

PORIFERA (5,500 species)

A sponge

CNIDARIA (10,000 species)

A jelly

PLACOZOA (1 species) KINORHYNCHA (150 species)0.5 mm

A placozoan (LM) A kinorhynch (LM)250 µm

PLATYHELMINTHES (20,000 species) ROTIFERA (1,800 species)

A marine flatworm A rotifer (LM)

ECTOPROCTA (4,500 species) PHORONIDA (20 species)

Ectoprocts Phoronids

BRACHIOPODA (335 species) NEMERTEA (900 species)

A brachiopod A ribbon wormACANTHOCEPHALA (1,100 species) CTENOPHORA (100 species)

An acanthocephalan A ctenophore, or comb jelly

MOLLUSCA (93,000 species) ANNELIDA (16,500 species)

An octopus A marine annelidLORICIFERA (10 species) PRIAPULA (16 species)

5 mm

50 µm

A loriciferan (LM) A priapulan

Invertebrate Diversity

Invertebrate DiversityNEMATODA (25,000 species) ARTHROPODA (1,000,000 + species)

A roundworm A scorpion (an arachnid)

CYCLIOPHORA (1 species) TARDIGRADA (800 species)100 µm

100 µm

A cycliophoran (colorized SEM) Tardigrades (colorized SEM)

ONYCHOPHORA (110 species) HEMICHORDATA (85 species)

An onychophoran An acorn worm

ECHINODERMATA (7,000 species) CHORDATA (52,000 species)

A sea urchin 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

Azure vase sponge (Callyspongia plicifera)

Osculum

Spicules

Waterflow

Flagellum

CollarFood particlesin mucus

Choanocyte

Phagocytosis offood particles Amoebocyte

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.

Spongocoel. Water passing through porocytes

enters a cavity called the spongocoel.

Porocytes. Water enters the epidermis through

channels formed by porocytes, doughnut-shaped cells that span the body wall.

Epidermis. The outer layer consists of tightly

packed epidermal cells.

Mesohyl. The wall of this simple sponge consists of

two layers of cells separatedby a gelatinous matrix, themesohyl (“middle matter”).

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.

Amoebocyte. Amoebocytes transport nutrients to other cells ofthe sponge body and also produce materials for skeletal fibers (spicules).

5

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1

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

Mouth/anus

TentacleGastrovascularcavity

Gastrodermis

Mesoglea

Epidermis

Tentacle

Bodystalk

Mouth/anus

MedusaPolyp

Tentacle

“Trigger”

Nematocyst

Coiled thread

DischargeOf thread

Cnidocyte

Prey

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

Threads can inject poison into the prey, or stick to or entangle the target

Classes of Phylum Cnidaria

Hydrozoan Life Cycle

Feeding polyp

Reproductivepolyp

Medusabud

ASEXUALREPRODUCTION(BUDDING)

GonadMedusa

MEIOSIS

FERTILIZATION

SEXUALREPRODUCTION Egg Sperm

Developingpolyp

Portion ofa colonyof polyps

Maturepolyp

Planula(larva) Key

Haploid (n)Diploid (2n)1 mm

Zygote

A colony ofinterconnected

polyps (inset,LM) results

from asexualreproductionby budding.

1

Some of the colony’s polyps, equipped with tentacles, are specialized for feeding.

2 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding.

3

The medusae swim off, grow, and reproduce sexually.

4

The zygote develops into a solid ciliated larva called a planula.5 The planula eventually settles

and develops into a new polyp.6

Classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa

(a) These colonial polyps are members of

class Hydrozoa.

(b) Many species of jellies (class

Scyphozoa), including thespecies pictured here, are bioluminescent. The largest scyphozoans have tentaclesmore 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 andother large prey, is more potent than cobra venom.

(d) Sea anemones and other

members of class Anthozoaexist 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 Hydra

Purple coral

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 BilateriaWhich consists of animals with bilateral

symmetry and triploblastic development

Flatworms

Members of phylum PlatyhelminthesLive in marine, freshwater, and damp terrestrial

habitats. Some are parasitic.Are flattened dorsoventrally and have bilateral

symmetryUndergo triploblastic developmentAre 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 thetip of a muscular pharynx thatextends from the animal’sventral side. Digestive juicesare spilled onto prey, and thepharynx sucks small pieces offood into the gastrovascularcavity, where digestion continues.

Digestion is completed withinthe cells lining the gastro-vascular cavity, which hasthree branches, each withfine subbranches that pro-vide an extensive surface area.

Undigested wastesare egestedthrough the mouth.

Ganglia. Located at the anterior endof the worm, near the main sourcesof sensory input, is a pair of ganglia,dense clusters of nerve cells.

Ventral nerve cords. Fromthe ganglia, a pair ofventral nerve cords runsthe length of the body.

Gastrovascularcavity

Eyespots

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

These larvae penetratethe skin and blood vessels of humans working in irrigated fields contaminated with infected human feces.

Asexual reproduction within a snail results in another type of motilelarva, which escapes from the snail host.

Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces.

The eggs develop in water into ciliated larvae. These larvaeinfect snails, the intermediate hosts.

Snail host

1 mm

Female

Male

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2

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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.

1

Tapeworms (Class Cestoda)Are also parasitic and lack a digestive system

Proglottids withreproductive structures

200 µm

HooksSucker

Scolex

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 Rotifers have an alimentary canal

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 lophophoreA horseshoe-shaped, suspension-feeding

organ bearing ciliated tentacles that trap suspended food particles

EctoproctsAre colonial animals that superficially resemble

plantsLophophore

Ectoprocts, such as this sea mat (Membraniporamembranacea), are colonial lophophorates.

(a)

Phoronids

Are tube-dwelling marine worms ranging from 1 mm to 50 cm in length

Lophophore

In phoronids such as Phoronis hippocrepia, the lophophore and mouth are at one end of an elongated trunk.

(b)

Brachipods 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

Lophophore

Brachiopods have a hinged shell. The two parts of the shell are dorsal and ventral.

(c)

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

Visceral mass

Mantle

Foot

Coelom Intestine

Gonads

Mantlecavity

Anus

Gill

Nervecords Esophagus

Stomach

ShellRadula

Mouth

Mouth

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.

Radula. The mouth region in many mollusc species contains a rasp-like feeding organ called a radula. This belt of backward-curved teeth slides back and forth, scraping and scooping like a backhoe.

The nervous system consists

of a nerve ring around the

esophagus, from which nerve

cords extend.

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 land snail (a)

A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution.

(b)

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

Anus

Mantlecavity

StomachIntestine

Mouth

Bivalves (Molluscs of class Bivalvia) Include many species of clams, oysters,

mussels, and scallopsHave 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 areaGut Coelom

Heart

Adductormuscle

AnusExcurrentsiphon

Waterflow

IncurrentsiphonGill

Mantlecavity

Foot

Palp

Mouth

Shell

Mantle

Clam locomotion

Cephalopods

Class Cephalopoda includes squids and octopusesCarnivores 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 cephalopodsThe nautiluses, survives today

(c) Chambered nautiluses are the only living cephalopods with an external shell.

Annelids

AnnelidsSegmented wormsHave bodies composed of a series of fused

rings3 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

MouthSubpharyngealganglion

Pharynx EsophagusCrop

Gizzard

Intestine

Metanephridium

Ventralvessel

Nervecords

Nephrostome

Intestine

Dorsalvessel

Longitudinalmuscle

Circularmuscle

Epidermis Cuticle

Septum(partitionbetweensegments)

Anus

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.

Coelom. The coelom of the earthworm is partitioned by septa.

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.

Tiny blood vessels are abundant in the earthworm’s skin, which functions as its respiratory organ. The blood contains oxygen-carryinghemoglobin.

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.

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.

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.

Chaetae. Each segment has four pairs of

chaetae, bristles that provide traction for

burrowing.

Many of the internal structures are repeated within each segment of

the earthworm.

Giant Australian earthworm

Clitellum

Earthworm anatomy

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 animals50 µmEncysted juveniles Muscle tissue

Trichinella spiralis encysted in human muscle tissue

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 ArthropodaAre 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

Antennae(sensoryreception)

Head Thorax

Swimmingappendages

Walking legs

Mouthparts (feeding)Pincer (defense)

AbdomenCephalothorax

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

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

(a) Dust mites are ubiquitous scavengers in human dwellings but are harmless except to those people who are allergic to them (colorized SEM).

(b) Web-building spiders are generally most active during the daytime.

(c)

50 µm

Cheliceriforms Most modern cheliceriforms are

arachnids A group that includes spiders,

scorpions, ticks, and mites

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)

Digestivegland

Intestine

HeartStomach

Brain

Eyes

Poisongland

PedipalpChelicera

Book lung

Spermreceptacle

Gonopore(exit for eggs)Silk gland

Spinnerets

Anus

Ovary

Myriapods

Subphylum Myriapoda Includes millipedes and

centipedes Millipedes, class Diplopoda

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

relativesAre more species-rich than all other forms of

life combinedLive in almost every terrestrial habitat and in

fresh waterThe internal anatomy of an insect includes

several complex organ systems

Insect anatomy

Compound eye

Antennae

Anus

Vagina

OvaryDorsalartery Crop

Abdomen Thorax Head

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.

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.

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.

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.

Malpighian tubules. Metabolic wastes are

removed from the hemolymph by excretory organs called Malpighian

tubules, which are out-pocketings of the

digestive tract.

Insects Flight is one key to the great success of

insectsAn 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

Larva (caterpillar)(a)(b) Pupa

(c) Pupa(d) Emerging adult

(e) Adult

movie

26 Orders of InsectsORDER

Blattodea 4,000 Cockroaches have a dorsoventrally flattened body, with legs modified for rapid running. Forewings, when present, areleathery, whereas hind wings are fanlike. Fewer than 40 cock-roach species live in houses; the rest exploit habitats ranging from tropical forest floors to caves and deserts.

Beetles comprise the most species-rich order of insects. They have two pairs of wings, one of which is thick and leathery, theother membranous. They have an armored exoskeleton andmouthparts adapted for biting and chewing. Beetles undergocomplete metamorphosis.

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. Earwigshave biting mouthparts and large posterior pincers. They un-dergo incomplete metamorphosis.

Dipterans have one pair of wings; the second pair has become modified into balancing organs called halteres. Their head islarge and mobile; their mouthparts are adapted for sucking,piercing, or lapping. Dipterans undergo complete metamorpho-sis. 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 aresometimes erroneously called bugs.) Hemipterans have two pairs of wings, one pair partly leathery, the other membranous.They have piercing or sucking mouthparts and undergoincomplete metamorphosis.

Ants, bees, and wasps are generally highly social insects. Theyhave 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 com-plete metamorphosis.

Termites are widespread social insects that produce enormous colonies. It has been estimated that there are 700 kg oftermites for every person on Earth! Some termites have twopairs of membranous wings, while others are wingless. They feed on wood with the aid of microbial symbionts carried in specialized chambers in their hindgut.

Coleoptera 350,000

Dermaptera 1,200

Diptera 151,000

Hemiptera 85,000

Hymenoptera 125,000

Isoptera 2,000

APPROXIMATENUMBER OF

SPECIESMAIN CHARACTERISTICS EXAMPLES

Germancockroach

Japanesebeetle

Earwig

Horsefly

Leaf-Footedbug

Cicada-killer wasp

Termite

26 Orders of InsectsLepidoptera 120,000 Butterflies and moths are among the best-known insects. They

have two pairs of wings covered with tiny scales. To feed, theyuncoil a long proboscis. Most feed on nectar, but some species feed on other substances, including animal blood or tears.

Odonata5,000 Dragonflies and damselflies have two pairs of large, membran-

ous wings. They have an elongated abdomen, large, compound eyes, and chewing mouthparts. They undergo incomplete meta-morphosis and are active predators.

Orthoptera 13,000 Grasshoppers, crickets, and their relatives are mostly herbi-vorous. They have large hind legs adapted for jumping, twopairs 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.

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.

Phthiraptera 2,400 Commonly called sucking lice, these insects spend their entire life as an ectoparasite feeding on the hair or feathers of a singlehost. Their legs, equipped with clawlike tarsi, are adapted forclinging to their hosts. They lack wings and have reduced eyes.Sucking lice undergo incomplete metamorphosis.

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.

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.

Trichoptera 7,100 The larvae of caddisflies live in streams, where they make houses from sand grains, wood fragments, or other material held to-gether by silk. Adults have two pairs of hairy wings and chewingor lapping mouthparts. They undergo complete metamorphosis.

Swallowtailbutterfly

Dragonfly

Katydid

Stick insect

HumanBodylouse

Flea

Silverfish

Caddisfly

ORDERAPPROXIMATE

NUMBER OFSPECIES

MAIN CHARACTERISTICS EXAMPLE

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 shellsof these barnacles capture organisms and organic particles suspended inthe water.

Deuterostomes

Echinoderms and chordates are deuterostomes

Chordates and echinoderms share the characteristics of deuterostomesRadial cleavageFormation of the mouth at the end of the

embryo opposite the blastopore

Echinoderms

Echinoderm characteristics 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

network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange

Echinoderm movie

Echinoderm anatomy

StomachAnus

Ringcanal

Gonads

AmpullaPodium

Radialnerve

Tubefeet

Spine

Gills

A short digestive tract runs from the mouth on the bottom of the central disk to the anus on top of the disk.

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.

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 podiumcontract, they force water back into the ampulla, making the podium shorten and bend.

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.

Digestive glands secrete digestive juices and aid in

the absorption and storage of nutrients.

Central disk. The central disk has a nerve ring and

nerve cords radiating from the ring into the arms.

Echinoderm classes

Sea Stars

Sea stars, class AsteroideaHave multiple arms radiating from a central diskThe 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

Sea Urchin

Sand Dollar

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 echinodermsThey 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