Figure 33.0 Ochre sea stars, Pisaster ochraceus

ANCESTRALPROTIST

Commonancestor ofall animals

Porifera

Cnidaria

Lophotrochozoa

Ecdysozoa

Deuterostomia

Eum

etazoa Bilateria

Porifera (5,500 species)

A sponge

Cnidaria (10,000 species)

A jelly

Acoela (400 species)

Acoel flatworms (LM)

1.5 mm

Placozoa (1 species)

0.5 mm

A placozoan (LM)

Ctenophora (100 species)

A ctenophore, or comb jelly

Platyhelminthes(20,000 species)

A marine flatworm

Acanthocephala(1,100 species)

Curvedhooks

An acanthocephalan (LM)

Mollusca(93,000 species)

An octopus

A ribbon worm

A cycliophoran(colorized SEM) A marine annelid

100 m

Lophotrochozoa

Nemertea(900 species)

Cycliophora(1 species)

Ectoprocts A rotifer (LM)

A brachiopod0.1

mm

Annelida(16,500 species)

Ectoprocta(4,500 species)

Rotifera(1,800 species)

Brachiopoda(335 species)

Loricifera (10 species)

50 m

Ecdysozoa

A loriciferan (LM)

Priapula (16 species) Onychophora (110 species)

A priapulan

Nematoda(25,000 species)

Tardigrada(800 species)

Arthropoda(1,000,000 species)

An onychophoran

A roundworm(colored SEM)

Tardigrades(colorized SEM)

A scorpion (an arachnid)

100 m

Hemichordata(85 species)

Chordata(52,000 species)

A tunicate

Echinodermata (7,000 species)

An acorn worm

A sea urchinDeuterostomia

Figure 33.UN01

PoriferaCnidaria

LophotrochozoaEcdysozoaDeuterostomia

Figure 33.UN02

Porifera

Cnidaria

Lophotrochozoa

Ecdysozoa

Deuterostomia

Eu

me

tazo

a

(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.

Anatomy of a planarian

A rotifer

Lophophore

Lophophore

Lophophore

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

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

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

(a) (b) (c)

Table 33.3 Major Classes of Phylum Mollusca

A chiton

The results of torsion in a gastropod

A bivalve: Scallop

Anatomy of a clam

Cephalopods: Squid (top left and bottom left), nautilus (top right), octopus (bottom right)

Anatomy of an earthworm

Classes of Phylum Annelida

Parapodia

Free-living nematode

External anatomy of an arthropod

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

Class Dipolopoda (millipedes)

Anatomy of a grasshopper, an insect

Metamorphosis of a butterfly

Crustaceans: Lobster (top left), banded coral shrimp (bottom left), barnacles (right)

Ancestral colonialchoanoflagellate

Eumetazoa

Bilateria

Deuterostomia

Po

rife

ra

Cn

ida

ria

Oth

er b

ila

teri

an

s (i

ncl

ud

ing

Nem

ato

da

, A

rth

rop

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a,M

oll

usc

a, a

nd

An

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Ech

ino

de

rmat

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Ch

ord

ata

Anatomy of a sea star

(a) A sea star (class Asteroidea) (b) A brittle star (class Ophiuroidea)

(c) A sea urchin (class Echinoidea) (d) A feather star (class Crinoidea)

(e) A sea cucumber (class Holothuroidea) (f) A sea daisy (class Concentricycloidea)