BIOLOGY. An Introduction to Invertebrates CAMPBELL. Reece Urry Cain Wasserman Minorsky Jackson

CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson 33 An Introduction to Invertebrates Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick

Deuterostomia Metazoa Eumetazoa Bilateria Ecdysozoa Lophotrochozoa Figure 33.UN08 Phylum Porifera (sponges) Cnidaria (hydras, jellies, sea anemones, corals) Platyhelminthes (flatworms) Rotifera (rotifers) Lophophorates: Ectoprocta, Brachiopoda Mollusca (clams, snails, squids) Annelida (segmented worms) Nematoda (roundworms) Arthropoda (spiders, centipedes, crustaceans, and insects) Echinodermata (sea stars, sea urchins) Chordata (lancelets, tunicates, vertebrates) Description Lack true tissues; have choanocytes (collar cells flagellated cells that ingest bacteria and tiny food particles) Unique stinging structures (nematocytes) housed in specialized cells (cnidocytes); diploblastic; radially symmetrical; gastrovascular cavity (digestive compartment with a single opening) Dorsoventrally flattened acoelomates; gastrovascular cavity or no digestive tract Pseudocoelomates with alimentary canal (digestive tube with mouth and anus); jaws (trophi); head with ciliated crown Coelomates with lophophores (feeding structures bearing ciliated tentacles) Coelomates with three main body parts (muscular foot, visceral mass, mantle); coelom reduced; most have hard shell made of calcium carbonate Coelomates with segmented body wall and internal organs (except digestive tract, which is unsegmented) Cylindrical pseudocoelomates with tapered ends; no circulatory system; undergo ecdysis Coelomates with segmented body, jointed appendages, and exoskeleton made of protein and chitin Coelomates with bilaterally symmetrical larvae and five-part body organization as adults; unique water vascular system; endoskeleton Coelomates with notochord; dorsal, hollow nerve cord; pharyngeal slits; post-anal tail (see Chapter 34)

Figure 33.2 Porifera ANCESTRAL PROTIST Cnidaria Common ancestor of all animals Eumetazoa Bilateria Lophotrochozoa Ecdysozoa Deuterostomia

Figure 33.UN03 Porifera Cnidaria Lophotrochozoa Ecdysozoa Deuterostomia Bilateria Bilaterian animals have bilateral symmetry and triploblastic development Most have a coelom and a digestive tract with two openings

Concept 33.3: Lophotrochozoans, a clade identified by molecular data, have the widest range of animal body forms Some develop a lophophore for feeding, others pass through a trochophore larval stage, and a few have neither feature The clade Lophotrochozoa was identified by molecular data Lophotrochozoa includes the flatworms, rotifers, ectoprocts, brachiopods, molluscs, and annelids

Flatworms Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats Triploblastic, acoelomates Flatworms have a gastrovascular cavity with one opening Gas exchange takes place across the surface, and protonephridia regulate the osmotic balance Their dorsoventrally flattened shape maximizes surface area for gas exchange

Figure 33.9 MAKE CONNECTIONS: Maximizing Surface Area Folding Flattening SA: 6 (3 cm 3 cm) = 54 cm 2 V: 3 cm 3 cm 3 cm = 27 cm 3 1 µm Thylakoid SA: 2 (3 cm 1 cm) + 2 (9 cm 1 cm) + 2 (3 cm 9 cm) = 78 cm 2 V: 1 cm 3 cm 9 cm = 27 cm 3 Diagrams comparing surface area (SA) for two different shapes with the same volume (V) Branching Projections

Flatworms are divided into two lineages Rhabditophora (Planarian) Free-living Planarians live in fresh water and prey on smaller animals Planarians have light-sensitive eyespots and centralized nerve nets The planarian nervous system is more complex and centralized than the nerve nets of cnidarians

Parasitic rhabditophorans live in or on other animals Two important groups of parasitic rhabditophorans are the trematodes and the tapeworms parasites of vertebrates and lack a digestive system Tapeworms absorb nutrients from the host s intestine

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

Ectoprocts and Brachiopods Lophophorates have a lophophore, a crown of ciliated tentacles around their mouth Lophophorates have a true coelom

Molluscs Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids Mostly marine, soft-bodied animals but most are protected by a hard shell 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)

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

Gastropods About three-quarters of all living species of molluscs are gastropods Gastropods move slowly by a rippling motion of the foot or by cilia Most have a single, spiraled shell that functions in protection from injury, dehydration, and predation

Cephalopods Cephalopods are carnivores with beak-like jaws surrounded by tentacles of their modified foot Squids use their siphon to fire a jet of water, which allows them to swim very quickly

Annelids Annelids are coelomates with bodies composed of a series of fused rings The phylum Annelida was traditionally divided into three clades Polychaeta (polychaetes) Oligochaeta (oligochaetes) Hirundinea (leeches) two major clades - Errantia - Sedentaria

Sedentarians Sedentarians tend to be less mobile than errantians Some species burrow into the substrate, while others live in protective tubes

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

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 Caenorhabditis elegans is a model organism in research Trichinella spiralis can be acquired by humans from undercooked pork

Arthropod Two out of every three known species of animals are arthropods The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages trilobite

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

Figure 33.29 Experiment Origin of Ubx and abd-a Hox genes? Other ecdysozoans Arthropods Common ancestor Onychophorans Results 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 These modified appendages are jointed and come in pairs 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

Morphological and molecular evidence suggests that living arthropods consist of three major lineages that diverged early in the phylum s evolution Chelicerates (sea spiders, horseshoe crabs, scorpions, ticks, mites, and spiders) Myriapods (centipedes and millipedes) Pancrustaceans (lobsters and other crustaceans, as well as insects and their relatives)

Chelicerates Chelicerates, clade Chelicerata, are named for clawlike feeding appendages called chelicerae Most modern chelicerates are arachnids, which include spiders, scorpions, ticks, and mites

Myriapods The clade Myriapoda includes millipedes and centipedes All living myriapods are terrestrial They have a pair of antennae and three pairs of appendages modified as mouthparts

Pancrustaceans Together, insects and crustaceans form the clade Pancrustacea Crustaceans Crustaceans live in marine and freshwater environments, have highly specialized appendages Planktonic crustaceans copepod

Insects Hexapoda is an enormous clade including insects and their relatives, live in almost every terrestrial habitat and in fresh water The internal anatomy of an insect includes several complex organ systems

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

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 Insect wings are an extension of the cuticle

Figure 33.41 Archaeognatha (bristletails; 350 species) Zygentoma (silverfish; 450 species) Winged insects (many orders; six are shown below) Complete metamorphosis Incomplete metamorphosis Coleoptera (beetles; 350,000 species) Hemiptera (85,000 species) Diptera (151,000 species) Orthoptera (13,000 species) Hymenoptera (125,000 species) Proboscis Lepidoptera (120,000 species)

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 In incomplete metamorphosis, the young, called nymphs, resemble adults but are smaller and go through a series of molts until they reach full size