marine invertebrates

Marine Invertebrates• Overview: Life Without a Backbone• Invertebrates– Are animals that lack a backbone– Account for 95% of known animal species

• A review of animal phylogeny

Ancestral colonialchoanoflagellate

Eumetazoa

Bilateria

Deuterostomia

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• Exploring invertebrate diversity

PORIFERA (5,500 species)

A sponge

CNIDARIA (10,000 species)

A jellyPLACOZOA (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

• Exploring invertebrate diversityBRACHIOPODA (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

• Exploring 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 are sessile and have a porous body and choanocytes

• Sponges, phylum Porifera– Live in both fresh and marine waters– Lack true tissues and organs

• Phylum- Poriferia “pore bearers”• Aggregation of specialized cells• Cells are independent from each other & do not

form true tissues & organs• Simplest multicellular animals

• Nearly all are marine• Sessile• Variety of color, shape, and sizes• Ostia (tiny pores) allow water to enter and circulate

through series of canals where plankton and organic particles are filtered & eaten

• Flexible skeletal frame gives the spongy texture• If cells separated can even regroup and form new sponge• Outer surface covered with flat cells called pinacocytes &

pore cells (porocytes) which allows water to enter• Water pumped into larger feeding chamber lined with

collar cells (choanocytes)• Each choanocytes has flagellum the creates currents and

a thin collar that traps food particles, which is ingested by body of cell

• Water leaves through osculum, large opening at top of sponge

• Type of suspension feeders that actively filter food particles (filter feeders)

• Marine sponges show more complex arrangement with collar cells are restricted to chambers connected to outer pores by a network of channels

• Marine sponges have single osculum but have several oscula which serves as exit from many canals

• Helps meet higher demands for water flow for larger sponges

• Large sponges have spicules that are transparent made of siliceous or calcareous supporting structures of different shapes and sizes

• Skeleton made of protein spongin• Some may spicules, spongin, or both• Wandering cells, amebocytes, secret spicules

and sponging, transport and store food particles, and transform into other types if cells to quickly repair damage to the sponge

• Reproduce asexually• If piece breaks off, it can form new sponge• Reproduce sexually• Specialized collar cells or amebocytes can turn into gametes• Large nutrient rich egg and smaller sperm cell with flagellum• Most are hermaphrodites• Some have separate male and female organisms• Typically broadcast spawning• Egg retained inside of body until fertilization• Early development takes place inside• Flagellated sphere of cells (larva) is called parenchymula

larva is planktonic & drifts with currents• Settles & metamorphosis into juvenile

• 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, the

mesohyl (“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

6

7

4

3

2

1

• Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes

• All animals except sponges– Belong to the clade Eumetazoa, the animals with

true tissues• Phylum Cnidaria– Is one of the oldest groups in this clade

Cnidaria/Coelenterata

• Next evolutionary jump• Have tissues that perform specific functions• Sometimes called coelenterates include sea

anemones, jellyfishes, and• corals• Radial symmetry• If cut like pizza all resulting slices would be similar• Look the same from all sides• No head, front, or back• Oral surface and aboral surface• Central mouth with tentacles• Mouth open into a gut (only one opening)

• Capture prey with nematocycts (stinging structures) found within tentacles

• Two basic forms: Polyp and medusa• Some life history includes both others are either polyp or

medusa• Larva is called planula, ciliated stage with two cell layers• Settles and metamorphoses into a polyp or develops into

medusa• Two layer of cells form body wall-one the epidermis and

other gastrodermis• Gelatinous middle layer is mesoglea- does not contain

cells• In medusae this layer expands to form gelatinous domed

bell

• 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

• 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

• The phylum Cnidaria is divided into four major classes

– Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa

(a) These colonial polyps are members of class Hydrozoa.

(b) Many species of jellies (classScyphozoa), 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 othermembers of class Anthozoaexist only as polyps.

Hydrozoans• Most hydrozoans– Alternate between polyp and medusa forms

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 asexualreproduction

by 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

Hydrozoans (class Hydrozoa)• Feathery or bushy colonies of tiny polyps attached to

pilings, shells, seaweeds, and other surfaces• Polyps may be specialized for feeding, defense, or

reproduction• Reproductive polyps produce minute, plantonic medusae• Medusae release gametes & fertilized eggs develop into

free swimming planula larvae• Each planula larvae settles and develops into a polyp• The poylp divides repeatedly and develops into a colony• Some lack poylp stage and develop into a medusae• Few lack medusae stage and develop into gamete

producing polyps

Scyphozoans• In the class Scyphozoa– Jellies (medusae) are the prevalent form of the life cycle

Scyphozoans (class Scyphozoa)

• Larger jellyfish• Large medusae are dominate stage in life cycle• Polyps small & release juvenile medusae• Few lack polyp stage• Bell reach diameter of 2 m (6.6 ft)• Bell diameter in deep water is 3 m (10 ft)• Swim with rhythmic contractions of bell but easily carried

by currents• Some species stings range from a rash to fatalities• Cubomedusae once classified as scyphozoa now own

class Cubozoa• Sea wasp (box jelly)

Cubozoans• In the class Cubozoa, which includes box jellies and sea wasps

– The medusa is box-shaped and has complex eyes

Anthozoans• Class Anthozoa includes the corals and sea anemones– Which occur only as polyps

Anthozoans (class Anthozoa)

• Solitary or colonial polyps that lack medusae stage

• Largest number of species• Polyps more complex• Gut contain septa increasing surface area for

digestion of large prey• Septa provide support for larger species• Sea anemones have large polyps

• 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

Feeding and digestion

• Carnivores• Use nematocysts to capture prey• Each nematocyst contains fluid-filled capsule

containing thread that is ejected• Thread my be spines or long tube that wrap

around prey• Toxic• Extracellular digestion-out side the cells• Intracellular digestion within cells lining gut

Behavior

• Lack brain & true nerves• Nerve cells interconnect forming nerve net

that transmits impulses in all directions• Sea anemones can tell if other member is

from same clone• Known to attack even kill anemones from

other clones• Some medusae have primitive eyes• Medusae have statocysts to help with balance

Comb Jellies: Radial Symmetry Revisited

• Comb jellies, ctenophores (phylum Ctenophora)• All marine about 100 species• Gelatinous body with 8 rows of ciliary combs that beat in

waves• Beating of combs refracts light creating multicolor effect• Body length few millimeters to 2 m• Found in warm and cold waters• Carnivores• Swarms consume large numbers of fish larvae and other

plankton• Capture prey with long tentacles with colloblasts (sticky

cells)• Few have nematocysts

Flatworms

• Members of phylum Platyhelminthes– Live in marine, freshwater, and damp terrestrial

habitats– Are flattened dorsoventrally and have a

gastrovascular cavity• Although flatworms undergo triploblastic

development– They are acoelomates

• Simplest flatworms• Have central nervous system• Simple brain- aggregation of nerve cells• Have several nerve cord running from brain

through the length of body• Nervous system coordinates movement of

well-developed muscular system• Gut has one opening

• Have middle layer of tissues, in developing embryos it is called mesoderm

• Mesoderm gives rise to muscles, reproductive system and other organs

• 20,000 known species• Turbellarians most common have striking

color patters• Live in or on oysters, crabs, & other

invertebrates

• Flatworms are divided into four classes

Turbellarian• Turbellarians– Are nearly all free-living and mostly marine

Monogeneans and Trematode• Monogeneans and trematodes– Live as parasites in or on other animals– Parasitize a wide range of hosts

• Flukes (trematodes)• Largest group 6,000 species• All parasites• Feed on tissues, blood, or intestinal contents• Adult flukes live in vertebrates

• Larvae may inhabit like snails and clams or vertebrates like fish

• Larva must be eaten by a vertebrate• Common in fish, seabirds, and whales• Most monogeneans– Are parasites of fish

Tapeworm• Tapeworms– Are also parasitic and lack a digestive system

Proglottids withreproductive structures

200 µm

HooksSucker

Scolex

Tapeworms (cestodes)

• Parasitic• Have long body with repeating units• Live in intestine of most species of vertebrates• Head attaches to walls of gut by suckers and

hooks• Lack gut or mouth• Absorb nutrients from host across body wall• Found in invertebrates and vertebrates• Longest recorded in sperm whale was 50 ft

Ribbon Worms (phylum Nemertea)

• Ribbon or nemertean worms• More complex than flatworms• Complete digestive tract (mouth, gut, anus)• Have circulatory system• Proboscis-long flesh tube to capture prey• Inverted in cavity above mouth

Nemerteans• Members of phylum Nemertea– Are commonly called proboscis worms or ribbon worms

• Feed of worms and crustaceans• 900 species mostly marine• Found in all oceans most common in shallow

temperate waters• Some nocturnal, some brightly colored found

under rocks at low tides• Elastic, and proboscis may extend to a meter or

more beyond body length• Longest invertebrate reaches 100 ft

• 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 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

• All molluscs have a similar body plan with three main parts– A muscular foot– A visceral mass– A mantle

Visceral mass

Mantle

Foot

Coelom IntestineGonads

Mantlecavity

Anus

Gill

Nervecords Esophagus

StomachShellRadula

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.

• 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

• There are four major 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)

• Most gastropods– 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

scallops– Have a shell divided into two halves

• The mantle cavity of a bivalve– Contains gills that are used for feeding as well as gas

exchangeHinge area

Gut Coelom

Heart

Adductormuscle

AnusExcurrentsiphon

Waterflow

IncurrentsiphonGill

Mantlecavity

Foot

Palp

Mouth

Shell

Mantle

Cephalopods

• Class Cephalopoda includes squids and octopuses– Carnivores with beak-like jaws surrounded by

tentacles of their modified foot

• Most octopuses– Creep along the sea floor in search of prey

(a) Octopuses are considered among the most intelligent invertebrates.

• 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 are segmented worms• Annelids– Have bodies composed of a series of fused rings

• 20,000 species• Series of similar compartments• (segmented)• Gut through all segments and lies in cavity known as

coelom• Coelom fluid filled & divided by partitions• Segments acts as hydrostatic skeleton contracting in

sequence by muscles in body wall• Efficient crawlers & burrowers

• The phylum Annelida is divided into three classes

Polychaetes• Members of class Polychaeta– Possess paddlelike parapodia that function as gills

and aid in locomotion

Parapodia

Polychaetes (class Polychaeta)

• Body segments of most have a pair of flattened extensions or parapodia

• Parapoda have stiff sharp bristles (setae)• Have closed circulatory system• Muscular contractions help circulation of blood• Small organisms oxygen in water can easily move

across body wall to all tissues• Large organisms have gills on parapodia• Gills thin wall extensions of body that have

capillaries where gas exchange takes place

• Have plantonic larval stage-trochophore• Biologist compare larvae stage of polychaetes with

other invertebrates to examine evolutionary relationships

• Typical length is 5 to 10 cm• Many crawl hiding under rocks• Nereis (sandworms) carnivores• Have several pairs of eyes & other sensory organs• Use proboscis with jaws to capture prey• Others are deposit feeder• Many live in temporary or permanent tubes made

from mucus, proteins, bits of seaweed, cemented mud particles, sand grains, or tiny fragments of shells

Oligochaetes

• Oligochaetes (class Oligochaeta)– Are named for their relatively sparse chaetae, or

bristles made of chitin– Include the earthworms and a variety of aquatic

species

Leeches• Members of class Hirudinea– Are blood-sucking parasites, such as leeches

• 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• Round worms, hardly ever seen• Found in large numbers in rich organic sediments• Many are parasitic found in most marine organisms• Adapted to live in sediment or tissues of other organisms• Typically pointed at both ends• Feed mostly on bacteria and organic matter• Anus lies within body cavity filled with fluid that

transports nutrients

• The cylindrical bodies of nematodes (phylum Nematoda)– Are covered by a tough coat called a cuticle

25 µm

• 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

• Layer of muscle in the tough but flexible body pushes and squeezes against the fluid which acts as hydrostatic skeleton that provides support and aids in locomotion

• 10,000 to 25,000 species and estimates that half a million still undiscovered

• Anisakis and few related inhabit seals and dolphins• Larvae found on flesh of many types of fish and may

infect humans who eat raw or poorly cooked fish• Often larvae are vomited or coughed up without

further complications• Sometimes penetrate into walls of stomach or

intestine causing symptoms similar to ulcers• A risk all sashimi and cerviche lovers take

Cerviche

Sashimi

Kinilaw

General Characteristics of Arthropods• The diversity and success of arthropods– Are largely related to their segmentation, hard

exoskeleton, and jointed appendages

• Early arthropods, such as trilobites– Showed little variation from segment to segment

Figure 33.28

• 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

Figure 33.29

• 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

• 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

• Molecular evidence now suggests– That living arthropods consist of four major lineages

that diverged early in the evolution of the phylum

Table 33.5

Cheliceriforms• Cheliceriforms, subphylum Cheliceriformes– Are named for clawlike feeding appendages called

chelicerae– Include spiders, ticks, mites, scorpions, and

horseshoe crabs

• Most of the marine cheliceriforms are extinct– But some species survive today, including the

horseshoe crabs

Figure 33.30

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

Figure 33.31a–c

• Most modern cheliceriforms are arachnids– A group that includes spiders, scorpions, ticks, and

mites

• Arachnids have an abdomen and a cephalothorax– Which has six pairs of appendages, the most

anterior of which are the chelicerae

Digestivegland

Intestine

HeartStomach

Brain

Eyes

Poisongland

PedipalpChelicera

Book lung

Spermreceptacle

Gonopore(exit for eggs)Silk gland

Spinnerets

Anus

Ovary

Figure 33.32

Myriapods• Subphylum Myriapoda– Includes millipedes and centipedes

• Millipedes, class Diplopoda– Have a large number of legs

• Each trunk segment– Has two pairs of legs

Figure 33.33

• Centipedes, class Chilopoda– Are carnivores with jaw-like mandibles– Have one pair of legs per trunk segment

Figure 33.34

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

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.

Figure 33.35

• Flight is obviously 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

• 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

• 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

Larva (caterpillar)(a)(b) Pupa

(c) Pupa(d) Emerging adult

(e) AdultFigure 33.6a–e

• Insects are classified into about 26 ordersORDER

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

Figure 33.37

• Insects are classified into about 26 ordersLepidoptera 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

ORDERAPPROXIMATENUMBER OF

SPECIES

MAIN CHARACTERISTICS EXAMPLE

Figure 33.37

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 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.

(a)

Figure 33.38a

• 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.

(b)

Figure 33.38b

• 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.

(c)

Figure 33.38c

• Concept 33.8: Echinoderms and chordates are deuterostomes

• At first glance, sea stars and other echinoderms, phylum Echinodermata– May seem to have little in common with phylum

Chordata, which includes the vertebrates

• 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

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

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.

Figure 33.39

• The radial anatomy of many echinoderms– Evolved secondarily from the bilateral symmetry of

ancestors

• Living echinoderms are divided into six classes

Table 33.6

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)Figure 33.40a

Brittle Stars• Brittle stars have a distinct central disk– And long, flexible arms

(b) A brittle star (class Ophiuroidea)Figure 33.40b

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

(c) A sea urchin (class Echinoidea)Figure 33.40c

Sea Lilies and Feather Stars• Sea lilies – Live attached to the substrate by a stalk

Sea Cucumbers• Feather stars– Crawl about using their long, flexible arms

(d) A feather star (class Crinoidea)Figure 33.40d

Sea Cucumbers• Sea cucumbers– Upon first inspection do not look much like other

echinoderms– Lack spines, and their endoskeleton is much reduced

(e) A sea cucumber (class Holothuroidea)Figure 33.40e

Sea Daisies• Sea daisies were discovered in 1986– And only two species are known

(f) A sea daisy (class Concentricycloidea)Figure 33.40f

Chordates• Chordates– Phylum Chordata– Consists of two subphyla of invertebrates as well as

the hagfishes and the vertebrates– Shares many features of embryonic development

with echinoderms

• A summary of animal phyla

Table 33.7