An Introduction to Invertebrates Chapter 33 An Introduction to Invertebrates

Overview: Life Without a Backbone Invertebrates are animals that lack a backbone They account for 95% of known animal species They are morphologically diverse For example, the Christmas tree worm (Spirobranchus giganteus) has tentacles for gas exchange and feeding © 2011 Pearson Education, Inc.

Porifera (5,500 species) Placozoa (1 species) Figure 33.3a Porifera (5,500 species) Placozoa (1 species) 0.5 mm A sponge Cnidaria (10,000 species) A placozoan (LM) Ctenophora (100 species) A jelly Figure 33.3 Exploring: Invertebrate Diversity Acoela (400 species) 1.5 mm Acoel flatworms (LM) A ctenophore, or comb jelly

Lophotrochozoa Figure 33.3b Platyhelminthes (20,000 species) Ectoprocta (4,500 species) Rotifera (1,800 species) Brachiopoda (335 species) 0.1 mm A brachiopod Ectoprocts A marine flatworm A rotifer (LM) Acanthocephala (1,100 species) Nemertea (900 species) Cycliophora (1 species) Annelida (16,500 species) Curved hooks Figure 33.3 Exploring: Invertebrate Diversity 100 m An acanthocephalan (LM) A cycliophoran (colorized SEM) A marine annelid Mollusca (93,000 species) A ribbon worm Lophotrochozoa An octopus

Onychophora (110 species) Figure 33.3c Loricifera (10 species) Priapula (16 species) Onychophora (110 species) 50 m A loriciferan (LM) A priapulan An onychophoran Nematoda (25,000 species) Tardigrada (800 species) Arthropoda (1,000,000 species) 100 m Figure 33.3 Exploring: Invertebrate Diversity A roundworm (colored SEM) Tardigrades (colorized SEM) Ecdysozoa A scorpion (an arachnid)

Echinodermata (7,000 species) Figure 33.3d Hemichordata (85 species) Chordata (52,000 species) A tunicate Echinodermata (7,000 species) An acorn worm Figure 33.3 Exploring: Invertebrate Diversity Deuterostomia A sea urchin

Concept 33.1: Sponges are basal animals that lack true tissues Animals in the phylum Porifera are known informally as sponges They are sedentary and live in marine waters or fresh water © 2011 Pearson Education, Inc.

Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN01 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN01 In-text figure, p. 670

Sponges lack true tissues and organs Sponges are suspension feeders, capturing food particles suspended in the water that passes through their body Water is drawn through pores into a cavity called the spongocoel and out through an opening called the osculum Sponges lack true tissues and organs © 2011 Pearson Education, Inc.

Food particles in mucus Flagellum Choanocyte Collar Azure vase sponge Figure 33.4 Food particles in mucus Flagellum Choanocyte Collar Azure vase sponge (Callyspongia plicifera) Choanocyte Osculum Spongocoel Phagocytosis of food particles Amoebocyte Pore Figure 33.4 Anatomy of a sponge. Spicules Epidermis Water flow Amoebocytes Mesohyl

Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food Sponges consist of a gelatinous noncellular mesohyl layer between two cell layers Amoebocytes are found in the mesohyl and play roles in digestion and structure Most sponges are hermaphrodites: Each individual functions as both male and female © 2011 Pearson Education, Inc.

Concept 33.2: Cnidarians are an ancient phylum of eumetazoans All animals except sponges and a few other groups belong to the clade Eumetazoa, animals with true tissues Phylum Cnidaria is one of the oldest groups in this clade © 2011 Pearson Education, Inc.

They exhibit a relatively simple diploblastic, radial body plan Cnidarians have diversified into a wide range of both sessile and motile forms including jellies, corals, and hydras They exhibit a relatively simple diploblastic, radial body plan The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity A single opening functions as mouth and anus © 2011 Pearson Education, Inc.

A polyp adheres to the substrate by the aboral end of its body There are two variations on the body plan: the sessile polyp and motile medusa A polyp adheres to the substrate by the aboral end of its body A medusa has a bell-shaped body with its mouth on the underside Medusae do not attach to the substate but move freely © 2011 Pearson Education, Inc.

Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Body Figure 33.5 Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Body stalk Epidermis Figure 33.5 Polyp and medusa forms of cnidarians. Tentacle Mouth/anus Polyp Medusa

Cnidarians are carnivores that use tentacles to capture prey The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey Nematocysts are specialized organelles within cnidocytes that eject a stinging thread © 2011 Pearson Education, Inc.

Tentacle Cuticle of prey Thread Nematocyst “Trigger” Thread discharges Figure 33.6 Tentacle Cuticle of prey Thread Nematocyst “Trigger” Figure 33.6 A cnidocyte of a hydra. Thread discharges Thread (coiled) Cnidocyte

Phylum Cnidaria is divided into four major classes Hydrozoa Scyphozoa Cubozoa Anthozoa © 2011 Pearson Education, Inc.

(b) Scyphozoa (c) Cubozoa (d) Anthozoa (a) Hydrozoa Figure 33.7 Figure 33.7 Cnidarians. (a) Hydrozoa

Hydrozoans Most hydrozoans alternate between polyp and medusa forms Hydra, a freshwater cnidarian, exists only in polyp form and reproduces asexually by budding Video: Hydra Budding Video: Hydra Releasing Sperm Video: Hydra Eating Daphnia (time lapse) © 2011 Pearson Education, Inc.

Figure 33.8-3 Portion of a colony of polyps Reproductive polyp Feeding polyp Medusa bud MEIOSIS Gonad Medusa Sperm Egg SEXUAL REPRODUCTION ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps FERTILIZATION Zygote Developing polyp Figure 33.8 The life cycle of the hydrozoan Obelia. Planula (larva) Mature polyp Key 1 mm Haploid (n) Diploid (2n)

Scyphozoans In the class Scyphozoa, jellies (medusae) are the prevalent form of the life cycle Video: Jelly Swimming Video: Thimble Jellies © 2011 Pearson Education, Inc.

Cubozoans In the class Cubozoa, which includes box jellies and sea wasps, the medusa is box-shaped and has complex eyes Cubozoans often have highly toxic cnidocytes © 2011 Pearson Education, Inc.

Anthozoans Class Anthozoa includes the corals and sea anemones, and these cnidarians occur only as polyps Corals often form symbioses with algae and secrete a hard external skeleton Video: Clownfish and Anemone Video: Coral Reef © 2011 Pearson Education, Inc.

Concept 33.3: Lophotrochozoans, a clade identified by molecular data, have the widest range of animal body forms Bilaterian animals have bilateral symmetry and triploblastic development Most have a coelom and a digestive tract with two openings The clade Bilateria contains Lophotrochozoa, Ecdysozoa, and Deuterostomia © 2011 Pearson Education, Inc.

Porifera Cnidaria Lophotrochozoa Bilateria Ecdysozoa Deuterostomia Figure 33.UN03 Porifera Cnidaria Lophotrochozoa Ecdysozoa Bilateria Deuterostomia Figure 33.UN03 In-text figure, p. 674

The clade Lophotrochozoa was identified by molecular data Some develop a lophophore for feeding, others pass through a trochophore larval stage, and a few have neither feature Lophotrochozoa includes the flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids © 2011 Pearson Education, Inc.

Flatworms Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats Although flatworms undergo triploblastic development, they are acoelomates They are flattened dorsoventrally and have a gastrovascular cavity with one opening Gas exchange takes place across the surface, and protonephridia regulate the osmotic balance © 2011 Pearson Education, Inc.

Flatworms are divided into two lineages Catenulida, or “chain worms,” reproduce asexually by budding Rhabditophora are more diverse and include both free-living and parasitic species © 2011 Pearson Education, Inc.

Figure 33.9 Figure 33.9 A free-living marine flatworm. 5 mm

Free-Living Species The best-known rhabditophorans are planarians Planarians live in fresh water and prey on smaller animals Planarians have light-sensitive eyespots and centralized nerve nets © 2011 Pearson Education, Inc.

The planarian nervous system is more complex and centralized than the nerve nets of cnidarians Planarians are hermaphrodites and can reproduce sexually, or asexually through fission © 2011 Pearson Education, Inc.

Gastrovascular cavity Pharynx Figure 33.10 Gastrovascular cavity Pharynx Gastrovascular cavity Mouth Eyespots Figure 33.10 Anatomy of a planarian. Ventral nerve cords Ganglia

Parasitic Species Parasitic rhabditophorans live in or on other animals Two important groups of parasitic rhabditophorans are the trematodes and the tapeworms © 2011 Pearson Education, Inc.

Trematodes Trematodes parasitize a wide range of hosts, and most have complex life cycles with alternating sexual and asexual stages Trematodes that parasitize humans spend part of their lives in snail hosts They produce surface proteins that mimic their host and release molecules that manipulate the host’s immune system © 2011 Pearson Education, Inc.

Male Human host Female 1 mm Mature flukes Motile Ciliated larva larva Figure 33.11 Male Human host Female 1 mm Mature flukes Figure 33.11 The life cycle of a blood fluke (Schistosoma mansoni), a trematode. Motile larva Ciliated larva Snail host

Tapeworms Tapeworms are parasites of vertebrates and lack a digestive system Tapeworms absorb nutrients from the host’s intestine © 2011 Pearson Education, Inc.

The scolex contains suckers and hooks for attaching to the host Proglottids are units that contain sex organs and form a ribbon behind the scolex Fertilized eggs, produced by sexual reproduction, leave the host’s body in feces © 2011 Pearson Education, Inc.

100 m Hooks Sucker Proglottids with reproductive structures Scolex Figure 33.12 100 m Hooks Sucker Proglottids with reproductive structures Figure 33.12 Anatomy of a tapeworm. Scolex

Rotifers 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 Video: Rotifer © 2011 Pearson Education, Inc.

Jaws Crown of cilia Anus Stomach 0.1 mm Figure 33.13 Figure 33.13 A rotifer. Anus Stomach 0.1 mm

Some species are unusual in that they lack males entirely Rotifers have an alimentary canal, a digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelom Rotifers reproduce by parthenogenesis, in which females produce offspring from unfertilized eggs Some species are unusual in that they lack males entirely © 2011 Pearson Education, Inc.

Lophophorates: Ectoprocts and Brachiopods Lophophorates have a lophophore, a crown of ciliated tentacles around their mouth Lophophorates have a true coelom Lophophorates include two phyla: Ectoprocta and Brachiopoda © 2011 Pearson Education, Inc.

Ectoprocts (also called bryozoans) are sessile colonial animals that superficially resemble plants A hard exoskeleton encases the colony, and some species are reef builders © 2011 Pearson Education, Inc.

(a) Ectoprocts, colonial lophophorates Figure 33.14 Lophophore Lophophore Figure 33.14 Lophophorates. (b) Lampshell, a brachiopod (a) Ectoprocts, colonial lophophorates

Brachiopods are marine and attach to the seafloor by a stalk Brachiopods 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 Brachiopods are marine and attach to the seafloor by a stalk © 2011 Pearson Education, Inc.

Molluscs Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids Most molluscs are marine, though some inhabit fresh water and some snails and slugs are terrestrial Molluscs are soft-bodied animals, but most are protected by a hard shell © 2011 Pearson Education, Inc.

All molluscs have a similar body plan with three main parts Muscular foot Visceral mass Mantle Many molluscs also have a water-filled mantle cavity and feed using a rasplike radula © 2011 Pearson Education, Inc.

Nephridium Heart Heart Visceral mass Digestive tract Coelom Intestine Figure 33.15 Nephridium Heart Heart Visceral mass Digestive tract Coelom Intestine Gonads Mantle Stomach Mantle cavity Shell Mouth Radula Anus Gill Figure 33.15 The basic body plan of a mollusc. Radula Mouth Nerve cords Foot Esophagus

Most molluscs have separate sexes with gonads located in the visceral mass, but many snails are hermaphrodites The life cycle of many molluscs includes a ciliated larval stage called a trochophore © 2011 Pearson Education, Inc.

Four of the major classes of molluscs are Polyplacophora (chitons) Gastropoda (snails and slugs) Bivalvia (clams, oysters, and other bivalves) Cephalopoda (squids, octopuses, cuttlefish, and chambered nautiluses) © 2011 Pearson Education, Inc.

Chitons Chitons are oval-shaped marine animals encased in an armor of eight dorsal plates They use their foot like a suction cup to grip rock, and their radula to scrape algae off the rock surface © 2011 Pearson Education, Inc.

Figure 33.16 Figure 33.16 A chiton.

Gastropods About three-quarters of all living species of molluscs are gastropods Video: Nudibranchs © 2011 Pearson Education, Inc.

(b) A sea slug (nudibranch) Figure 33.17 (a) A land snail Figure 33.17 Gastropods. (b) A sea slug (nudibranch)

Most have a single, spiraled shell Most gastropods are marine, but many are freshwater and terrestrial species The most distinctive characteristic of gastropods is torsion, which causes the animal’s anus and mantle to end up above its head; torsion is different from the coiling of a shell Most have a single, spiraled shell Slugs lack a shell or have a reduced shell © 2011 Pearson Education, Inc.

Mantle cavity Stomach Intestine Anus Mouth Figure 33.18 Figure 33.18 The results of torsion in a gastropod.

Bivalves Bivalves are marine and include many species of clams, oysters, mussels, and scallops They have a shell divided into two halves drawn together by adductor muscles Some bivalves have eyes and sensory tentacles along the edge of their mantle © 2011 Pearson Education, Inc.

Figure 33.19 Figure 33.19 A bivalve.

The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange © 2011 Pearson Education, Inc.

Coelom Hinge area Mantle Gut Heart Adductor muscle (one or two) Figure 33.20 Coelom Hinge area Mantle Gut Heart Adductor muscle (one or two) Digestive gland Anus Mouth Excurrent siphon Figure 33.20 Anatomy of a clam. Shell Palp Water flow Foot Mantle cavity Incurrent siphon Gonad Gill

Cephalopods Cephalopods are carnivores with beak-like jaws surrounded by tentacles of their modified foot Most octopuses creep along the sea floor in search of prey © 2011 Pearson Education, Inc.

Squid Octopus Chambered nautilus Figure 33.21 Figure 33.21 Cephalopods. Chambered nautilus

Squids use their siphon to fire a jet of water, which allows them to swim very quickly © 2011 Pearson Education, Inc.

One small group of shelled cephalopods, the nautiluses, survives today © 2011 Pearson Education, Inc.

Cephalopods have a closed circulatory system, well-developed sense organs, and a complex brain Shelled cephalopods called ammonites were common but went extinct at the end of the Cretaceous 65.5 million years ago © 2011 Pearson Education, Inc.

Protecting Freshwater and Terrestrial Molluscs Molluscs are the animal group with the largest number of recent extinctions The most threatened groups are Freshwater bivalves, including pearl mussels Terrestrial gastropods, including Pacific island land snails These molluscs are threatened by habitat loss, pollution, and non-native species © 2011 Pearson Education, Inc.

Recorded extinctions of animal species (Data: International Union for Figure 33.22 Molluscs Other invertebrates Amphibians Insects Birds Fishes Mammals Reptiles (excluding birds) An endangered Pacific island land snail, Partula suturalis Recorded extinctions of animal species (Data: International Union for Conservation of Nature, 2008) Figure 33.22 Impact: Molluscs: The Silent Extinction Workers on a mound of pearl mussels killed to make buttons (ca. 1919)

Annelids Annelids have bodies composed of a series of fused rings Annelids are coelomates The phylum Annelida is divided into two groups Polychaeta (polychaetes) Oligochaeta (earthworms and their relatives, and leeches) © 2011 Pearson Education, Inc.

Polychaetes Members of class Polychaetes have paddle-like parapodia that work as gills and aid in locomotion Most polychaetes are marine Video: Tubeworms © 2011 Pearson Education, Inc.

Figure 33.23 Figure 33.23 A polychaete. Parapodia

Oligochaetes Oligochaetes (class Oligochaeta) are named for relatively sparse chaetae, bristles made of chitin Video: Earthworm Locomotion © 2011 Pearson Education, Inc.

Earthworms Earthworms eat through soil, extracting nutrients as the soil moves through the alimentary canal Earthworms are hermaphrodites but cross-fertilize Some reproduce asexually by fragmentation Video: Earthworm Locomotion © 2011 Pearson Education, Inc.

Figure 33.24 Cuticle Coelom Epidermis Septum (partition between segments) Circular muscle Metanephridium Longitudinal muscle Anus Dorsal vessel Chaetae Intestine Skin Ventral vessel Fused nerve cords Nephrostome Metanephridium Clitellum Figure 33.24 Anatomy of an earthworm, an oligochaete. Esophagus Crop Pharynx Intestine Giant Australian earthworm Cerebral ganglia Gizzard Ventral nerve cords with segmental ganglia Mouth Subpharyngeal ganglion Circulatory system vessels

Leeches Most species of leeches live in fresh water; some are marine or terrestrial Leeches include predators of invertebrates, and parasites that suck blood Leeches secrete a chemical called hirudin to prevent blood from coagulating © 2011 Pearson Education, Inc.

Figure 33.25 Figure 33.25 A leech.

Concept 33.4: Ecdysozoans are the most species-rich animal group Ecdysozoans are covered by a tough coat called a cuticle The cuticle is shed or molted through a process called ecdysis The two largest phyla are nematodes and arthropods © 2011 Pearson Education, Inc.

Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN04 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN04 In-text figure, p. 683

Nematodes Nematodes, or roundworms, are found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals They have an alimentary canal, but lack a circulatory system Reproduction in nematodes is usually sexual, by internal fertilization Video: C. elegans Crawling Video: C. elegans Embryo Development (Time Lapse) © 2011 Pearson Education, Inc.

Figure 33.26 Figure 33.26 A free-living nematode (colorized SEM). 25 m

Caenorhabditis elegans is a model organism in research Some species of nematodes are important parasites of plants and animals Thrichinella spiralis can be acquired by humans from undercooked pork © 2011 Pearson Education, Inc.

Encysted juveniles Muscle tissue 50 m Figure 33.27 Figure 33.27 Juveniles of the parasitic nematode Trichinella spiralis encysted in human muscle tissue (LM).

Arthropods 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 © 2011 Pearson Education, Inc.

Arthropod Origins The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages This body plan dates to the Cambrian explosion (535–525 million years ago) Early arthropods show little variation from segment to segment © 2011 Pearson Education, Inc.

Figure 33.28 Figure 33.28 A trilobite fossil.

Arthropod evolution is characterized by a decrease in the number of segments and an increase in appendage specialization These changes may have been caused by changes in Hox gene sequence or regulation © 2011 Pearson Education, Inc.

EXPERIMENT Other ecdysozoans Origin of Ubx and abd-A Hox genes? Figure 33.29 EXPERIMENT Other ecdysozoans Origin of Ubx and abd-A Hox genes? Arthropods Onychophorans Common ancestor RESULTS Figure 33.29 Inquiry: Did the arthropod body plan result from new Hox genes? Ant  antenna J  jaws L1–L15  body segments

General Characteristics of Arthropods The appendages of some living arthropods are modified for functions such as walking, feeding, sensory reception, reproduction, and defense Video: Lobster Mouth Parts © 2011 Pearson Education, Inc.

Pincer (defense) Mouthparts (feeding) Figure 33.30 Cephalothorax Abdomen Thorax Antennae (sensory reception) Head Swimming appen- dages (one pair per abdominal segment Figure 33.30 External anatomy of an arthropod. Walking legs Pincer (defense) Mouthparts (feeding)

When an arthropod grows, it molts its exoskeleton The body of an arthropod is completely covered by the cuticle, an exoskeleton made of layers of protein and the polysaccharide chitin When an arthropod grows, it molts its exoskeleton © 2011 Pearson Education, Inc.

Arthropods have eyes, olfactory receptors, and antennae that function in touch and smell Arthropods have an open circulatory system in which hemolymph is circulated into the spaces surrounding the tissues and organs A variety of organs specialized for gas exchange have evolved in arthropods © 2011 Pearson Education, Inc.

Molecular evidence suggests that living arthropods consist of four major lineages that diverged early in the phylum’s evolution Chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) Myriapods (centipedes and millipedes) Hexapods (insects and relatives) Crustaceans (crabs, lobsters, shrimps, barnacles, and many others) © 2011 Pearson Education, Inc.

Chelicerates Chelicerates, subphylum Chelicerata, are named for clawlike feeding appendages called chelicerae The earliest cheliceriforms were eurypterids (water scorpions) Most marine cheliceriforms (including eurypterids) are extinct, but some species survive today, including horseshoe crabs © 2011 Pearson Education, Inc.

Figure 33.31 Figure 33.31 Horseshoe crabs (Limulus polyphemus).

Most modern cheliceriforms are arachnids, which include spiders, scorpions, ticks, and mites © 2011 Pearson Education, Inc.

Scorpion Dust mite Web-building spider Figure 33.32 50 m Figure 33.32 Arachnids. Web-building spider

Gas exchange in spiders occurs in respiratory organs called book lungs Arachnids have an abdomen and a cephalothorax, which has six pairs of appendages: the chelicerae, the pedipalps, and four pairs of walking legs Gas exchange in spiders occurs in respiratory organs called book lungs Many spiders produce silk, a liquid protein, from specialized abdominal glands © 2011 Pearson Education, Inc.

Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland Figure 33.33 Stomach Intestine Heart Brain Digestive gland Eyes Ovary Poison gland Figure 33.33 Anatomy of a spider. Anus Book lung Spinnerets Gonopore (exit for eggs) Chelicera Pedipalp Sperm receptacle Silk gland

Myriapods Myriapods are terrestrial, and have jaw-like mandibles Subphylum Myriapoda includes millipedes and centipedes Myriapods are terrestrial, and have jaw-like mandibles Millipedes eat decaying leaves and plant matter Millipedes have many legs, with two pairs per trunk segment © 2011 Pearson Education, Inc.

Figure 33.34 (a) Millipede Figure 33.34 Myriapods. (b) Centipede

Centipedes are carnivores Centipedes have one pair of legs per trunk segment © 2011 Pearson Education, Inc.

Insects Subphylum Hexapoda, insects and relatives, has more species than all other forms of life combined They live in almost every terrestrial habitat and in fresh water The internal anatomy of an insect includes several complex organ systems © 2011 Pearson Education, Inc.

Abdomen Thorax Head Compound eye Antennae Heart Dorsal artery Crop Figure 33.35 Abdomen Thorax Head Compound eye Antennae Heart Dorsal artery Crop Cerebral ganglion Anus Vagina Figure 33.35 Anatomy of a grasshopper, an insect. Malpighian tubules Ovary Tracheal tubes Nerve cords Mouthparts

Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms Insect and plant diversity declined during the Cretaceous extinction, but has been increasing in the 65 million years since © 2011 Pearson Education, Inc.

Flight is 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 © 2011 Pearson Education, Inc.

Figure 33.36 Figure 33.36 Ladybird beetle in flight.

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 © 2011 Pearson Education, Inc.

The larval stage looks entirely different from the adult stage Insects with complete metamorphosis have larval stages known by such names as maggot, grub, or caterpillar The larval stage looks entirely different from the adult stage Video: Butterfly Emerging © 2011 Pearson Education, Inc.

(a) Larva (caterpillar) (b) Pupa (c) Later-stage pupa (d) Emerging Figure 33.37 (a) Larva (caterpillar) (b) Pupa (c) Later-stage pupa Figure 33.37 Complete metamorphosis of a butterfly. (d) Emerging adult (e) Adult

Most insects have separate males and females and reproduce sexually Individuals find and recognize members of their own species by bright colors, sound, or odors Some insects are beneficial as pollinators, while others are harmful as carriers of diseases, or pests of crops Insects are classified into more than 30 orders Video: Bee Pollinating © 2011 Pearson Education, Inc.

Figure 33.38 Archaeognatha (bristletails; 350 species) Thysanura (silverfish; 450 species) Winged insects (many orders) Complete metamorphosis Incomplete metamorphosis Coleoptera (beetles; 350,000 species) Hemiptera (85,000 species) Diptera (151,000 species) Orthoptera (13,000 species) Figure 33.38 Exploring: Insect Diversity Hymenoptera (125,000 species) Proboscis Lepidoptera (120,000 species)

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 branched appendages that are extensively specialized for feeding and locomotion Small crustaceans exchange gases through the cuticle; larger crustaceans have gills © 2011 Pearson Education, Inc.

Most crustaceans have separate males and females Isopods include terrestrial, freshwater, and marine species Pill bugs are a well known group of terrestrial isopods Decapods are all relatively large crustaceans and include lobsters, crabs, crayfish, and shrimp © 2011 Pearson Education, Inc.

(a) Ghost crab (b) Krill (c) Barnacles Figure 33.39 Figure 33.39 Crustaceans. (b) Krill (c) Barnacles

Planktonic crustaceans include many species of copepods, which are among the most numerous of all animals © 2011 Pearson Education, Inc.

Barnacles are a group of mostly sessile crustaceans They have a cuticle that is hardened into a shell © 2011 Pearson Education, Inc.

Concept 33.5: Echinoderms and chordates are deuterostomes Echinoderms (phylum Echinodermata) include sea stars and sea urchins Chordates (phylum Chordata) include the vertebrates Echinoderms and chordates constitute the clade Deuterostomia © 2011 Pearson Education, Inc.

Deuterostomes share developmental characteristics Radial cleavage Formation of the anus from the blastopore However, some other animals also share these developmental characteristics Deuterostomes are defined primarily by DNA similarities © 2011 Pearson Education, Inc.

Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN05 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN05 In-text figure, p. 692

Echinoderms Sea stars and most other echinoderms are slow-moving or sessile marine animals A thin epidermis covers an endoskeleton of hard calcareous plates Echinoderms have a unique water vascular system, a network of hydraulic canals branching into tube feet that function in locomotion and feeding Males and females are usually separate, and sexual reproduction is external © 2011 Pearson Education, Inc.

Figure 33.40 Short digestive tract Stomach Anus Spine Gills Central disk Madreporite Figure 33.40 Anatomy of a sea star, an echinoderm. Radial nerve Digestive glands Ring canal Gonads Ampulla Podium Tube feet Radial canal

Most adult echinoderms have radial symmetry with multiples of five Echinoderm larvae have bilateral symmetry Video: Echinoderm Tube Feet © 2011 Pearson Education, Inc.

Living echinoderms are divided into five classes Asteroidea (sea stars and sea daisies) Ophiuroidea (brittle stars) Echinoidea (sea urchins and sand dollars) Crinoidea (sea lilies and feather stars) Holothuroidea (sea cucumbers) © 2011 Pearson Education, Inc.

Asteroidea: Sea Stars and Sea Daisies Sea stars have multiple arms radiating from a central disk The undersurface of each arm bears tube feet, which grip substrate with adhesive chemicals Sea stars feed on bivalves by prying them open with their tube feet, everting their stomach, and digesting their prey externally with digestive enzymes Sea stars can regrow lost arms © 2011 Pearson Education, Inc.

Sea daisies were discovered in 1986, and only three species are known Sea daisies live on submerged wood and absorb nutrients through a membrane that surrounds their body © 2011 Pearson Education, Inc.

Figure 33.41 Figure 33.41 A sea daisy (clade Asteroidea).

Ophiuroidea: Brittle Stars Brittle stars have a distinct central disk and long, flexible arms, which they use for movement Some species are suspension feeders, while others are predators or scavengers © 2011 Pearson Education, Inc.

Figure 33.42 Figure 33.42 A brittle star (clade Ophiuroidea).

Echinoidea: Sea Urchins and Sand Dollars Sea urchins and sand dollars have no arms but have five rows of tube feet Their spines are used for locomotion and protection Sea urchins feed on seaweed using a jaw-like structure on their underside © 2011 Pearson Education, Inc.

Figure 33.43 Figure 33.43 A sea urchin (clade Echinoidea).

Crinoidea: Sea Lilies and Feather Stars Sea lilies live attached to the substrate by a stalk Feather stars can crawl using long, flexible arms Both are suspension feeders © 2011 Pearson Education, Inc.

Figure 33.44 Figure 33.44 A feather star (clade Crinoidea).

Holothuroidea: Sea Cucumbers Sea cucumbers lack spines, have a very reduced endoskeleton, and do not look much like other echinoderms Sea cucumbers have five rows of tube feet; some of these are developed as feeding tentacles © 2011 Pearson Education, Inc.

Figure 33.45 Figure 33.45 A sea cucumber (clade Holothuroidea).

Chordates Phylum Chordata consists of two subphyla of invertebrates as well as hagfishes and vertebrates Chordates are bilaterally symmetrical coelomates with segmented bodies Chordates share many features of embryonic development with echinoderms, but have evolved separately for at least 500 million years © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc.