Figure 33.0 Ochre sea stars, Pisaster ochraceus

ANCESTRAL PROTIST Common ancestor of all animals Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Eumetazoa 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) Curved hooks 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 brachiopod 0.1 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 urchin Deuterostomia

Figure 33.UN01 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia

Figure 33.UN02 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Eumetazoa

(a) These colonial polyps are members of class Hydrozoa. (b) Many species of jellies (class Scyphozoa), including the species pictured here, are bioluminescent. The largest scyphozoans have tentacles more 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 and other large prey, is more potent than cobra venom. (d) Sea anemones and other members of class Anthozoa exist only as polyps.

Anatomy of a planarian

A rotifer

Lophophore Ectoprocts, such as this sea mat (Membranipora membranacea), 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 colonial choanoflagellate Eumetazoa Bilateria Deuterostomia Porifera Cnidaria Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida) Echinodermata Chordata

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)