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An Introduction to Invertebrates
Chapter 33 An Introduction to Invertebrates
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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.
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Figure 33.1 Figure 33.1 What function do the red whorls of this organism have?
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Porifera ANCESTRAL PROTIST Cnidaria Eumetazoa Common Lophotrochozoa
Figure 33.2 Porifera ANCESTRAL PROTIST Cnidaria Common ancestor of all animals Lophotrochozoa Eumetazoa Ecdysozoa Bilateria Figure 33.2 Review of animal phylogeny. Deuterostomia
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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
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Lophotrochozoa Platyhelminthes (20,000 species) Ectoprocta
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
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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)
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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
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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.
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Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia
Figure 33.UN01 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Figure 33.UN01 In-text figure, p. 670
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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.
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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
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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.
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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.
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Porifera Cnidaria Eumetazoa Lophotrochozoa Ecdysozoa Deuterostomia
Figure 33.UN02 Porifera Cnidaria Lophotrochozoa Eumetazoa Ecdysozoa Deuterostomia Figure 33.UN02 In-text figure, p. 671
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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.
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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.
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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
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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.
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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
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Phylum Cnidaria is divided into four major classes
Hydrozoa Scyphozoa Cubozoa Anthozoa © 2011 Pearson Education, Inc.
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(b) Scyphozoa (c) Cubozoa (d) Anthozoa (a) Hydrozoa Figure 33.7
Figure 33.7 Cnidarians. (a) Hydrozoa
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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.
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Portion of a colony of polyps
Figure Reproductive polyp Feeding polyp Medusa bud Gonad Medusa Portion of a colony of polyps Figure 33.8 The life cycle of the hydrozoan Obelia. Key 1 mm Haploid (n) Diploid (2n)
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Portion of a colony of polyps
Figure Reproductive polyp Feeding polyp Medusa bud MEIOSIS Gonad Medusa Sperm Egg SEXUAL REPRODUCTION Portion of a colony of polyps FERTILIZATION Zygote Figure 33.8 The life cycle of the hydrozoan Obelia. Key 1 mm Haploid (n) Diploid (2n)
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Portion of a colony of polyps
Figure 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)
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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.
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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.
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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.
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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.
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Porifera Cnidaria Lophotrochozoa Bilateria Ecdysozoa Deuterostomia
Figure 33.UN03 Porifera Cnidaria Lophotrochozoa Ecdysozoa Bilateria Deuterostomia Figure 33.UN03 In-text figure, p. 674
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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.
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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.
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Figure 33.9 Figure 33.9 A free-living marine flatworm. 5 mm
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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.
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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.
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Gastrovascular cavity Pharynx
Figure 33.10 Gastrovascular cavity Pharynx Gastrovascular cavity Mouth Eyespots Figure Anatomy of a planarian. Ventral nerve cords Ganglia
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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.
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Male Human host Female 1 mm Mature flukes Motile Ciliated larva larva
Figure 33.11 Male Human host Female 1 mm Mature flukes Figure The life cycle of a blood fluke (Schistosoma mansoni), a trematode. Motile larva Ciliated larva Snail host
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Tapeworms Tapeworms are parasites of vertebrates and lack a digestive system Tapeworms absorb nutrients from the host’s intestine © 2011 Pearson Education, Inc.
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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.
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100 m Hooks Sucker Proglottids with reproductive structures Scolex
Figure 33.12 100 m Hooks Sucker Proglottids with reproductive structures Figure Anatomy of a tapeworm. Scolex
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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.
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Jaws Crown of cilia Anus Stomach 0.1 mm Figure 33.13
Figure A rotifer. Anus Stomach 0.1 mm
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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.
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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.
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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.
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(a) Ectoprocts, colonial lophophorates
Figure 33.14a Figure Lophophorates. Lophophore (a) Ectoprocts, colonial lophophorates
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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.
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Lophophore (b) Lampshell, a brachiopod Figure 33.14b
Figure Lophophorates. (b) Lampshell, a brachiopod
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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.
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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.
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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 The basic body plan of a mollusc. Radula Mouth Nerve cords Foot Esophagus
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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.
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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.
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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.
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Figure 33.16 Figure A chiton.
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Gastropods About three-quarters of all living species of molluscs are gastropods Video: Nudibranchs © 2011 Pearson Education, Inc.
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(b) A sea slug (nudibranch)
Figure 33.17 (a) A land snail Figure Gastropods. (b) A sea slug (nudibranch)
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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.
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Mantle cavity Stomach Intestine Anus Mouth Figure 33.18
Figure The results of torsion in a gastropod.
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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.
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Figure 33.19 Figure A bivalve.
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The mantle cavity of a bivalve contains gills that are used for feeding as well as gas exchange
© 2011 Pearson Education, Inc.
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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 Anatomy of a clam. Shell Palp Water flow Foot Mantle cavity Incurrent siphon Gonad Gill
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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.
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Squid Octopus Chambered nautilus Figure 33.21
Figure Cephalopods. Chambered nautilus
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Squids use their siphon to fire a jet of water, which allows them to swim very quickly
© 2011 Pearson Education, Inc.
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One small group of shelled cephalopods, the nautiluses, survives today
© 2011 Pearson Education, Inc.
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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.
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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.
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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 Impact: Molluscs: The Silent Extinction Workers on a mound of pearl mussels killed to make buttons (ca. 1919)
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