Chapter 28 Invertebrate Evolution. Animals are multicellular eukaryotes that are heterotrophs which ingest whole food and digest it internally They are

Chapter 28

Invertebrate Evolution

• Animals are multicellular eukaryotes that are heterotrophs which ingest whole food and digest it internally

• They are diploid and begin life as fertilized diploid eggs

• Animals are monophyetic and both invertebrates and vertebrates come from the same ancestor

• Colonial flagellate hypothesis states that animals are descended from an ancestor resembling a hollow spherical colony of flagellated cells

• This hypothesis suggests that radial symmetry preceded bilateral symmetry

• In a radial symmetrical animal, any longitudinal cut produces two identical halves

• In a bilaterally symmetrical animal, only one longitudinal cut yields two identical halves

Page 513

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

radial symmetry bilateral symmetry

anterior

posterior

dorsal

ventral

• Molecular data says the protists choanoflagellates are the closest living relatives to animals

• All of the different animal body plans were present by the Cambrian period

• As an animal develops, there are many possibilities reguarding the number, position, size, and patterns of its body parts

• Small shifts in Hox (homeotic) genes are responsible for major differences between animals that arise during development

• No adequate fossil record to trace early evolution of animals

• Phylogenetic tree of animals is based on molecular and morphological data

• When using molecular data, it is assumed that the more closely related two organisms, the more rRNA nucleotide sequences they will have in common

• Using molecular data has changed the earlier trees that were based on morphological characteristics only

Fig. 28.4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

multicellularity

molting ofcuticle

trochophore

lochophore

Chordates

Echinoderms

Arthropods

Roundworms

Annelids

Molluscs

Flatworms

Rotifers

Lophophores

Comb jellies

Cnidarians

Sponges

Ecd

yso

zoa

Lo

ph

otr

och

ozo

a

Pro

tost

om

iaD

eute

rost

om

ia

Bil

ater

iaR

adia

ta

common ancestor

bilateral symmetry3 tissue layers

body cavity

tissuelayers

choanoflagellateancestor

protostomedevelopment

radial symmetry2 tissue layers

deuterostomedevelopment

• Three types of symmetry exist in animals:

• 1) Asymmetrical symmetry is found in sponges that have no particular body shape

• 2) Radially symmetrical bodies of cnidarians and comb jellies that are organized circularly like a wheel where two identical halves result from any longitudinal cut

• 3) All other animals are bilaterally symmetrical as adults and only a longitudinal cut down the center will produce a definite left and right half

• Some radially symmetrical animals are sessile meaning they are non-motile staying attached to a substrate

• During the evolution of animals, bilateral symmetry is accompanied by cephalization, the localization of a brain and special sensory organs at anterior end

• Sponges are multicellular, but do not have true tissues so they have a cellular level of organization

• True tissues come about in other animals as they undergo embryogical development

• First three tissue layers are called germ layers because they give rise to organs and organ systems of the animal

• Cnidarians have only two tissue layers (ectoderm and endoderm) as embryos, and are diploblastic with a tissue level of organization

• Animals with three layers (ectoderm, mesoderm, and endoderm) as embryos are triblastic and have the organ level of organization

• Animals with three layers of tissue are either protostomes or deuterostomes

• Three major events differentiate the two:

• 1) Cleavage in protosomes is spiral and daughter cell fate is fixed and each cell becomes only one thing

• Cleavage in deuterosomes is radial and daughter cell fate is indeterminate and if separated each cell can become a complete organism

• 2) In protosomes, hollow ball of cells stage (blastula), a mouth forms near the blastopore

• In deuterosomes, anus appears near blastopore and later a mouth is formed

• 3) In protosomes, the mesoderm arises from cells located near embryonic blastopore and splitting occurs that produce the coelom

• In deuterosomes, the coelom arises as a pair of mesodermal pouches from the wall of the primitive gut. They enlarge, meet, and fuse


Protostomes

Cle

avag

e

Deuterostomes

Protostomes

Fat

e o

f b

last

op

ore

Deuterostomes

Protostomes

Co

elo

m f

orm

atio

n

Deuterostomes

top view side view top view side view

blastopore blastoporemouth

mouthprimitive gut primitive gutanus

anus

mesoderm mesoderm

Blastopore becomes mouth. Blastopore becomes the anus.

gut gut

Cleavage is radial anddeterminate.

Cleavage is spiral anddeterminate.

Coelom forms by asplitting of the mesoderm.

Coelom forms by anoutpocketing of primitive gut.

• Deuterosomes include echinoderms and chordates

• Protosomes are divided into ecdysozoa and lophotrochozoa

• Ecdysozoa include roundworms and arthropods

• These groups molt, or shed their outer covering as they grow

• All lophophores have the same type of feeding apparatus

• Sponges have few cell types and no nerve or musles cells

• Sponges are aquatic, largely marine animals with a saclike body filled with pores

• Interior of canals lined with flagellated cells, resembling choanoflagellates, called colar cells or choanocytes

• Movement of flagella brings water into central cavity and out the osculum in upper part

• Sponge is a stationary filter feeder or suspension feeder

• Microscopic food particles are engulfed by the collar cells and digested in food vacuoles

• All sponges have fibers of spongin, a type of collagen that acts as a skeleton

• Endoskeleton of sponges also contains spicules, small needle-like structures

Fig. 28.6


b. Sponge organization

sponge wall

pore

spicule

amoebocyte

collar cell (choanocyte)

nucleus

flagellum

amoebocyte

osculum

H2O inthroughpores

a. Yellow tube sponge, Aplysina fistularis

centralcavity

epidermal cellcollar

H2O out

© Andrew J. Martinez/Photo Researchers, Inc.

• Comb jellies are warm water marine invertebrates• Largest animal propelled by cilia• Body is made of a transparent jellylike substance called

mesoglea• Cnidarians are tubular or bell-shaped animals• Name comes from specialized stinging cells called

nematocysts that when touched are discharged• Some trap prey and others have spines that pentrate and

inject paralyzing toxins• Gastrovascular cavity digests food and is a supportive

hydrostatic skeleton• Mouth of polyp is directed upward, mouth of medusa is

directed downward

Fig. 28.7Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a.

b.

rows of cilia

tentacle

tentacles

a: © Jeff Rotman; b: © J. McCollugh/Visuals Unlimited


a. Sea anemone, Corynactis b. Cup coral, Tubastrea

c. Portuguese man-of-war, Physalia d. Jellyfish, Crambionellaa: © Azure Computer & Photo Services/Animals Animals/Earth Scenes; b: © Ron Taylor/Bruce Coleman;

c: © Runk/Schoenberger/Grant Heilman Photography; d:© Under Watercolours

• Sea anemones are sessile polyps that live attached to submerged structures

• Corals resemble sea anemones encased in a calcium carbonate (limestone) house

• Slow accumulation of limestone can result in reefs like the Great Barrier Reef off the coast of Australia

• Hydrozoans like Hydra have a dominant polyp

• Portuguese man-of-war is actually a colony of polyps

• In true jellyfishes, the medusa is the primary stage and polyp remains small


tentacle

mouth

nerve net

tissue layers

flagella

sensory cellcnidocyte

nematocyst

gland cell

bud

gastrovascularcavity

mesoglea(packingmaterial)

gastrovascularcavity

© CABISCO/Visuals Unlimited

• Flatworms (Platyhelminthes) are trochozoans because they have an extremely flat body

• They have one body opening, so digestive tract is called incomplete

• When two openings are in digestive tract, it is complete

• Dugesia is a planarian that lives in freshwater

• They capture food and feed through a muscluar pharynx

• Planarians are hermaphroditic or monoecious which means they possess both male and female sex organs

• They cross-fertilize


5 mm

cilia

e. Micrograph

flame cell

eyespots

pharynx extended through mouth

gastrovascular cavity

flame cell

excretory pore

fluid

excretory canal

auricle

a. Digestive system

b. Excretory system

transverse nervebrain lateral nerve cord

d. Nervous system

ovary testis genital pore

c. Reproductive system

excretory canal

eyespots

auricle

penis ingenital chamber

seminalreceptacle

spermduct

yolkgland

e: © Tom E. Adams/Peter Arnold, Inc.

• Flukes (Trematodes) and Tapeworms (Cestodes) are parasitic flatworms

• They are covered by a protective tegument which is a specialized body covering that resists host digestive juices

• Sensory organs on head are replaced by hooks and/or suckers for attachment to host

• Flukes named for organ they inhabit (liver)

• At anterior end is an oral sucker plus at least one other sucker

• Schistosoma, a blood fluke kills 200,000 people a year in Middle East, Asia, and Africa

Fig. 28.11


a. b.

5. In the snail, a mother sporocyst encloses many developing daughter sporocysts; daughter sporocysts enclose many developing larvae (cercariae).

4. Ciliated larvae (miracidia) hatch in water and enter a snail, the secondary host.

6. Larvae (cercariae) break out of daughter sporocysts, escape snail, and enter water.

1. Larvae penetrate skin of a human, the primary host, and mature in the liver.

3. Eggs migrate into digestive tract and are passed in feces.

© SPL/Photo Researchers, Inc.

2. Adult worms live and copulate in blood vessels of human gut.

• Tapeworms vary in length from a few millimeters to nearly 20 meters

• Head region is called scolex that contains hooks for attachment to intestinal wall of host

• Behind scolex, a series of reproductive units called proglottids are found that contain a full set of male and female sex organs

• Most tapeworms have complicated life cycles that usually involve several hosts

Fig. 28.12


hooks

suckerscolexproglottid

1.0 mm

1. Primary host ingests meat containing bladder worms.

6. Rare or uncooked meat from secondary host contains many bladder worms.

5. Livestock may ingest the eggs, becoming a secondary host as each larva becomes a bladder worm encysted in muscle.

4. Eggs leave the primary host in feces, which may contaminate water or vegetation.

2. Bladder worm attaches to human intestine where it matures into a tapeworm.

250 m

3. As the tapeworm grows, proglottids mature, and eventually fill with eggs.

Fig. 28.13

• RotifersCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

mouth

brain

eyespot

foot

toe

flame bulb

corona

stomach

intestine

cloacaanus

gastricgland

salivaryglands

germo-vitellarium

• Molluscs, the second most numerous group of animals, inhabit a variety of environments

• Include: chitons, limpets, slugs, snails, abalone, conchs, scallops, squid, and octopuses

• Molluscs share a three-part body plan made up of visceral mass, mantle, and foot

• Visceral mass is internal organs

• Mantle is covering of visceral mass that in some secretes a shell

• Foot is a muscular organ that maybe adapted for locomotion, attachment, food capture, or combination

• Many have a rasping, tonguelike radula for feeding

Fig. 28.15


gonad

kidney

anterior aorta

pericardial cavity

heart

posterior retractor muscle

posterior adductor muscle

posterior aorta

anus

excurrent siphon

incurrent siphon

gill

posterior ganglion

intestine mantle

shell

foot ganglion

foot

labial palps

mouth

anterior ganglion

anterior adductor muscle

esophagus

stomach

digestive gland

a. Scallop, Pecten sp. b. Mussels, Mytilus edulis

shelleyes

umbo

growth linesof shell

tentacleson mantle

c. Clam, Anodontaa: Courtesy Larry S. Roberts; b: © Fred Whitehead/Animals/Animals/Earth Scenes

• Gastropods are the largest class of molluscs which include slugs and snails

• They have elongated, flattened foot and most have a one-piece coiled shell that protects the visceral mass

• Cephalopod means head-footed

• Both squids and octopi can squeeze their mantle cavity so that water is forced out through a funnel, propelling them by jet propulsion

• Tentacles and arms that circle the head capture prey by adhesive secretions or suckers

Fig. 28.16


e. Chambered nautilus, Nautilus belauensis f. Bigfin reef squid, Sepioteuthis lessoniana

eye

arm

suckers

shell

eye

fins

tentacles

eye

spotted mantle covers shell

foot

eye

siphon

footfoot

eyes

tentacle

gills

mantle

a. Flamingo tongue shell, Cyphoma gibbosum

b. Nudibranch, Glossodoris macfarlandi

c. Land snail, Helix aspersa

d. Two-spotted octopus, Octopus bimaculatus

growthline

spiralshell

arms andtentacles

with suckers

a: © M. Gibbs/OSF/Animals Animals/Earth Scenes; b: © Kenneth W. Fink/Bruce Coleman, Inc.; c: © Farley Bridges; d: © Ken Lucas/Visuals Unlimited;e: © Douglas Faulkner/Photo Researchers, Inc.; f: © Georgette Douwma/Photo Researchers, Inc.

• Annelids are one trochozoan with segmentation and a well-developed coelom

• Segmentation is the repetition of body parts along the length of the body

• Coelom is fluid-filled and serves as a supportive hydrostatic skeleton

• Setae are bristles that protrude from body wall and anchor the worm

• Oligochaetes have few setae and polychaetes have many setae

• Earthworms, Lumbricus terrestris are oligochaetes

• They are hermaphraditic with both testes and ovaries

• During mating, two worms lie parallel facing opposite directions

• The clitellum of each worm secretes muscus to prevent drying of sperm as it passes between the worms

• There is no larval stage

• About two-thirds of annelids are marine polychaetes

• Setae are bundles on parapodia or paddlelike appendages used for swimming and respiration

• Leeches are freshwater annelids without setae

• Some like medicinal leech can keep blood flowing by means of hirudin, a powerful anticoagulant in saliva


a.

c.

clitellum

b.

circular muscles

typhlosole

setaecoelom

ventral nerve cord

subneural blood vessel

dorsal blood vessel

nephridium

cuticle

esophagus

hearts (5 pairs)

pharynxbrain

mouth

ventral nerve cord

seminal vesicle

nephridium

gizzard

clitellum

ventral blood vessel

dorsal blood vessel

crop

anus

anterior end

anterior end

clitellum

longitudinalmuscles

coelomiclining

muscular wallof intestine

excretorypore

ventralblood vessel

c: © Roger K. Burnard/Biological Photo Service

• Roundworms (Nematoda) are nonsegmented worms

• They have a pseudocoelom meaning the mesoderm is inside body wall, but not around the digestive (gut) cavity

• Parasitic roundworms include:

• Ascaris infections of humans, cats, dogs, pigs, and other vertebrates

• Symptoms depend on the stage of infection

• In lungs, can cause pneumonia-like symptoms

• In intestine, causes malnutrition

• Trichinosis is caused when humans eat pork with encysted Trichinella larva

• Offspring encyst in skeletal muscles

• Filarial worms transmitted to dogs by mosquitoes cause heart worm

• Elephantiasis caused by filarian worm Wuchereria bancrofti that reside in lymphatic vessels and prevent fluid flow

• Pinworms are the most common nematode parasite in the United States

Fig. 28.19


cyst

SEM 400a. b. c.

a: © Lauritz Jensen/Visuals Unlimited; b: © James Solliday/Biological Photo Service; c: © Vanessa Vick/The New York Times/Redux

• Arthropods vary greatly and are the most successful group of all animals

• Important arthropod characteristics:

• 1) A rigid but jointed exoskeleton composed primarily of chitin, a strong, flexible, nitrogenous polysaccharide

• Exoskeleton is hard and nonexpandable so must be molted to grow

• Before molting, body secretes a new, larger exoskeleton under the old one

• Enzymes partially dissolve the old one, animal wriggles out, and new exoskeleton expands and hardens

• 2) Segmentation is apparent because each segment has a pair of jointed appendages even though some are fused into a head, thorax, and abdomenAppentages are highly adapted to a particular function

• 3) Well-developed nervous system with a brain and nerve cord

• Head has sense organs including eyes-simple and compound

• Many have well-developed touch, small, taste, balance, and hearing

• 4) Variety of respiratory organs:

• Marine forms with gills; terrestrial forms have book lungs or air tubes called tracheae

• 5) Reduced competition through metamorphosis in which arthropods undergo drastic change in form and physiology from immature larva to adult

• Among arthropods, larva eat different foods and live in different environments than adult

Fig. 28.20


ommatidium

photoreceptors

rhabdom

cornea

optic nerve

d. Compound eyec. Molting

joint

a. Joint movement

seta

epicuticle

exocuticle

endocuticle

epidermis

b. Exoskeleton composition

Dragonfly

compoundeye

opening totegumental

gland

flexormuscle

extensormuscle

basementmembrane

tegumentalgland

pigmentcell

c: © OSF/London Scientific Films/Animals Animals/Earth Scenes

• Crustaceans have calcium carbonate in addition to chitin

• Decapods include lobsters, crabs, crayfish, hermit crabs, and shrimp

• Thorax bears five pairs of walking appendages

• Copepods and krill feed on algae and serve as food for fishes and whales

• Barnacles have thick, heavy shell and live on wharf pilings, ship hulls, rocks, and bodies of whales

Fig. 28.21


a. Sally lightfoot crab, Grapsus grapsus

d. Gooseneck barnacles, Lepas anatiferab. Red-backed cleaning shrimp, Lysmata grasbhami c. Copepod, Diaptomus

single simple eye

legs

carapace

carapace

eye

eye

mouth

stalk

plates

antenna

antennae

legs (5 pairs)

walking legs(4 legs are visible)

swimming legs(5 pairs)

uropods(sides)

spinyappendages

a: © Michael Lustbader/Photo Researchers, Inc.; b: © Bruce Robinson/Corbis; c: © Kim Taylor/Bruce Coleman, Inc.; d: © Kjell Sandved/Butterfly Alphabet

telson(center)

Fig. 28.22


Cephalothorax

carapace

a. b.

compoundeye

stomach

mouthantennae

Abdomen

gills

brain

mouth

dorsal abdominal arteryheart

anus

testis

anus

telson

uropods

swimmerets

fifth walking leg

claspers

fourth walking leg

third walking leg

second walking leg

first walking leg (modifiedas a pincerlike claw)

opening ofsperm duct

digestivegland

spermduct

ventralnerve cord

greengland

• In centipedes, each body segment has a pair of walking legs

• Live in moist environments where they are active predators on worms, insects, and crustaceans

• In millipedes, each of four thoracic segments bears one pair of legs and abdominal segments have two pairs of legs

• Millipeds live under stones or burrow in soil where they feed on leaf litter

Fig. 28.23


a. b.a: © Larry Miller/Photo Researchers, Inc.; b: © David Aubrey/Corbis

• Insect body is divided into head, thorax, and abdomen

• Head bears sense organs and mouthparts

• Thorax bears three pairs of legs and possibly one or two pairs of wings

• Abdomen contains most of the internal organs

• Excretory system consists of Malpighian tubules which extend into hemocoel and collect nitrogenous wastes that are concentrated and excreted into the digestive tract

• Insects like grasshoppers, undergo incomplete metamorphorsis, a gradual change- egg, nymph, adult

• Insects like butterflies, undergo complete metamorphosis- egg, larva, pupa, adult

Fig. 28.24


elongate, membranous forewing

piercing-sucking mouthpartsantenna

Mealybug, order Homoptera Beetle, order Coleoptera Leafhoppe r, order Homoptera Head louse, order Anoplura

antenna

narrow, membranous forewing

constrictedwaist

stinger

ovipositor slenderabdomen

white, granularsecretion

piercing-suckingmouthparts

Hard forewingscover membranoushindwings andabdomen.

chewingmouthparts

thickenedforewing (2)

membranoushindwings (2)

piercing-suckingmouthparts

wingless,flat body

chewingmouthparts

Dragonfl y , order OdonataW asp, order Hymenoptera (Mealybug, leafhopper, dragonfly): © Farley Bridges; (Beetle): © Wolfgang Kaehler/Corbis; (Louse): © Darlyne A. Murawski/Peter Arnold, Inc.; (Wasp): © Johnathan Smith; Cordaiy Photo Library/Corbis

chewingmouthparts

• Chelicerates have a cephalothorax and an abdomen

• Ticks, mites, scorpions, spiders, and harvestmen are all arachnids

• Ticks are ectoparasities on vertebrates and can carry diseases such as Rocky Mountain spotted fever and Lyme disease

Fig. 28.26


a. Horseshoe crab, Limulus b. Kenyan giant scorpion, Pandinus

abdomen

compound eye

carapace

telson

stinger pedipalp

chelicera

walking legs

abdomen cephalothorax

c. Black widow spide r , Latrodectusa: © Jana R. Jirak/Visuals Unlimited; b: © Tom McHugh/Photo Researchers, Inc.; c: © Ken Lucas

• Echinoderms are primarily bottom-dwelling marine animals

• Although echinoderms are radially symmetrical as adults, their larva are free-swimming filter feeders with bilateral symmetry

• They have a unique water-vascular system consisting of canals and appendages that function in locomotion, feeding, gas exchange, and sensory reception

• Asteroidea contain the sea stars and holothurians include sea cucumbers

Fig. 28.27ab


arm

anus

endoskeletal plates

spine

gonads

ampullatube feetradial canal

skin gill

eyespot

tube feet

central disk

b. Red sea star, Mediastara.

aboral side

arm

bivalve mollusc

aboral side

pyloricstomachcardiac

stomach

sieve plate(madreporite)

coelomiccavity

digestivegland

b: © Randy Morse, GoldenStateImages.com

Fig. 28.27cd


d. Purple sea urchin, Strongylocentrotusc. Sea cucumber, Pseudocolochirus

spinesfeeding tentacles

c: © Alex Kerstitch/Visuals Unlimited; d: © Randy Morse/Animals Animals/Earth Scenes

Documents

Chapter 28 Invertebrate Evolution. Animals are multicellular eukaryotes that are heterotrophs which ingest whole food and digest it internally They are