Chapter 15 Glossary, Summary, and Practice Questions

KEY TERMS

acoelomate without a body cavity

Actinopterygii ray-finned fishes

amniote a clade of animals that possesses an amniotic egg; includes reptiles (including birds) and mammals amoebocyte an amoeba-like cell of sponges whose functions include distribution of nutrients to other cells in the sponge Amphibia frogs, salamanders, and caecilians

ampulla of Lorenzini a sensory organ that allows sharks to detect electromagnetic fields produced by living things

Annelida a phylum of worm-like animals with metamerism anthropoids a clade consisting of monkeys, apes, and humans Anura frogs

Apoda caecilians

Arthropoda a phylum of Ecdysozoa with jointed appendages and segmented bodies

asymmetrical having no plane of symmetry

bilateral symmetry a type of symmetry in which there is only one plane of symmetry that creates two mirror-image sides

body plan the shape and symmetry of an organism

brachiation swinging through trees

budding a form of asexual reproduction that occurs through the growth of a new organism as a branch on an adult organism that breaks off and becomes independent; found in plants, sponges, cnidarians, and some other invertebrates

caecilian a legless amphibian that belongs to clade Apoda

Cephalochordata a chordate clade whose members possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage

cephalothorax a fused head and thorax

chaeta a chitinous projection from the cuticle found in annelids

chelicerae a modified first pair of appendages in subphylum Chelicerata

chitin a tough nitrogen-containing polysaccharide found in the cuticles of arthropods and the cell walls of fungi

choanocyte a cell type unique to sponges with a flagellum surrounded by a collar used to maintain water flow through the sponge, and capture and digest food particles

Chondrichthyes jawed fishes with paired fins and a skeleton made of cartilage

Chordata a phylum of animals distinguished by their possession of a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some point during their development

clitellum a specialized band of fused segments in some annelids, which aids in reproduction Cnidaria a phylum of animals that are diploblastic and have radial symmetry and stinging cells cnidocyte a specialized stinging cell found in Cnidaria

coelom a lined body cavity derived from mesodermal embryonic tissue

complete digestive system a digestive system that opens at one end, the mouth, and exits at the other end, the anus, and through which food normally moves in one direction

craniate a proposed clade of chordates that includes all groups except the tunicates and lancelets

Crocodilia crocodiles and alligators

ctenidia specialized gills in mollusks

cutaneous respiration gas exchange through the skin

deuterostome describing an animal in which the blastopore develops into the anus, with the second opening developing into the mouth

dioecious having separate male and female sexes

diphyodont refers to the possession of two sets of teeth in a lifetime

diploblast an animal that develops from two embryonic germ layers

dorsal hollow nerve cord

chordates

a hollow, tubular structure derived from ectoderm, which is located dorsal to the notochord in

down feather feather specialized for insulation

Echinodermata a phylum of deuterostomes with spiny skin; exclusively marine organisms

epidermis the layer of cells that lines the outer surface of an animal

eucoelomate describing animals with a body cavity completely lined with mesodermal tissue

eutherian mammal a mammal with a complex placenta, which connects a fetus to the mother; sometimes called placental mammals

extracellular digestion a form of digestion, the breakdown of food, which occurs outside of cells with the aid of enzymes released by cells

fragmentation a form of asexual reproduction in which a portion of the body of an organism breaks off and develops into a living independent organism; found in plants, sponges, and some other invertebrates

frog a tail-less amphibian that belongs to clade Anura

gastrodermis the layer of cells that lines the gastrovascular cavity of cnidarians

gastrovascular cavity the central cavity bounded by the gastrodermis in cnidarians

gemmule a structure produced by asexual reproduction in freshwater sponges that is able to survive harsh conditions germ layer a collection of cells formed during embryogenesis that will give rise to future body tissues gnathostome a jawed fish

hagfish an eel-like jawless fish that lives on the ocean floor and is a scavenger

hemocoel the internal body cavity seen in arthropods

heterodont teeth different types of teeth modified by different purposes

intracellular digestion the digestion of matter brought into a cell by phagocytosis

lamprey a jawless fish characterized by a toothed, funnel-like, sucking mouth

lancelet a member of Cephalochordata; named for its blade-like shape

lateral line the sense organ that runs the length of a fish’s body, used to detect vibration in the water Lophotrochozoa a clade of invertebrate organisms that is a sister group to the Ecdysozoa madreporite a pore for regulating entry and exit of water into the water vascular system

mammal one of the groups of endothermic vertebrates that possess hair and mammary glands

mammary gland in female mammals, a gland that produces milk for newborns

mantle a specialized epidermis that encloses all visceral organs and secretes shells in mollusks

marsupial one of the groups of mammals that includes the kangaroo, koala, bandicoot, Tasmanian devil, and several other species; young develop within a pouch

medusa a free-floating cnidarian body plan with a mouth on the underside and tentacles hanging down from a bell

mesoglea the non-living, gel-like matrix present in between ectoderm and endoderm in cnidarians mesohyl the collagen-like gel containing suspended cells that perform various functions in sponges metamerism having a series of body structures that are similar internally and externally, such as segments Mollusca a phylum of protostomes with soft bodies and no segmentation

monoecious having both sexes in one body, hermaphroditic

monotreme an egg-laying mammal

Myxini hagfishes

nacre a calcareous secretion produced by bivalve mollusks to line the inner side of shells as well as to coat foreign particulate matter

nematocyst the harpoon-like organelle within a cnidocyte with a pointed projectile and poison to stun and entangle prey

Nematoda a phylum of worms in Ecdysozoa commonly called roundworms containing both free-living and parasitic forms

notochord a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and in the adult stage of some chordates

osculum the large opening in a sponge body through which water leaves

Osteichthyes bony fishes

ostracoderm one of the earliest jawless fishes covered in bone

Petromyzontidae the clade of lampreys pharyngeal slit an opening in the pharynx pneumatic bone an air-filled bone

polyp the stalk-like, sessile life form of a cnidarians with mouth and tentacles facing upward, usually sessile but may be able to glide along a surface

Porifera a phylum of animals with no true tissues, but a porous body with a rudimentary endoskeleton post-anal tail a muscular, posterior elongation of the body extending beyond the anus in chordates Primates includes lemurs, tarsiers, monkeys, apes, and humans

prosimians a group of primates that includes bush babies of Africa, lemurs of Madagascar, and lorises, pottos, and tarsiers of southeast Asia

protostome describing an animal in which the mouth develops first during embryogenesis and a second opening developing into the anus

pseudocoelomate an animal with a coelom that is not completely lined with tissues derived from the mesoderm as in eucoelomate animals

radial symmetry a type of symmetry with multiple planes of symmetry all cross at an axis through the center of the organism

radula a tongue-like scraping organ with chitinous ornamentation found in most mollusks

salamander a tailed amphibian that belongs to the clade Urodela

Sarcopterygii lobe-finned fishes

sebaceous gland in mammals, a skin gland that produce a lipid mixture called sebum

Sphenodontia the reptilian clade that includes the tuataras

spicule a short sliver or spike-like structure, in sponges, they are formed of silicon dioxide, calcium carbonate, or protein, and are found in the mesohyl

spiracle a respiratory openings in insects that allow air into the tracheae spongocoel the central cavity within the body of some sponges Squamata the reptilian clade of lizards and snakes

stereoscopic vision two overlapping fields of vision from the eyes that produces depth perception

sudoriferous gland a gland in mammals that produces sweat and scent molecules swim bladder in fishes, a gas filled organ that helps to control the buoyancy of the fish tadpole the larval stage of a frog

Testudines turtles

tetrapod a four-footed animal; includes amphibians, reptiles, birds, and mammals

trachea in some arthropods, such as insects, a respiratory tube that conducts air from the spiracles to the tissues

triploblast an animal that develops from three germ layers tunicate a sessile chordate that is a member of Urochordata Urochordata the clade composed of the tunicates Urodela salamanders

vertebral column a series of separate bones that surround the spinal cord in vertebrates

water vascular system a system in echinoderms in which water is the circulatory fluid

CHAPTER SUMMARY

Features of the Animal Kingdom

Animals constitute a diverse kingdom of organisms. Although animals range in complexity from simple sea sponges to human beings, most members share certain features. Animals are eukaryotic, multicellular, heterotrophic organisms that

ingest their food and usually develop into motile creatures with a fixed body plan. Most members of the animal kingdom have differentiated tissues of four main classes—nervous, muscular, connective, and epithelial—that are specialized to perform different functions. Most animals reproduce sexually, leading to a developmental sequence that is relatively similar across the animal kingdom.

Organisms in the animal kingdom are classified based on their body morphology and development. True animals are divided into those with radial versus bilateral symmetry. Animals with three germ layers, called triploblasts, are further characterized by the presence or absence of an internal body cavity called a coelom. Animals with a body cavity may be either coelomates or pseudocoelomates, depending on which tissue gives rise to the coelom. Coelomates are further divided into two groups called protostomes and deuterostomes, based on a number of developmental characteristics.

Sponges and Cnidarians

Animals included in phylum Porifera are parazoans and do not possess true tissues. These organisms show a simple organization. Sponges have multiple cell types that are geared toward executing various metabolic functions.

Cnidarians have outer and inner tissue layers sandwiching a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion. The cnidocyte is a specialized cell for delivering toxins to prey and predators. Cnidarians have separate sexes. They have a life cycle that involves morphologically distinct forms—medusoid and polypoid—at various stages in their life cycle.

Flatworms, Nematodes, and Arthropods

Flatworms are acoelomate, triploblastic animals. They lack circulatory and respiratory systems, and have a rudimentary excretory system. The digestive system is incomplete in most species. There are four traditional classes of flatworms, the largely free-living turbellarians, the ectoparasitic monogeneans, and the endoparasitic trematodes and cestodes.

Trematodes have complex life cycles involving a secondary mollusk host and a primary host in which sexual reproduction takes place. Cestodes, or tapeworms, infect the digestive systems of primary vertebrate hosts.

Nematodes are pseudocoelomate members of the clade Ecdysozoa. They have a complete digestive system and a pseudocoelomic body cavity. This phylum includes free-living as well as parasitic organisms. They include dioecious and hermaphroditic species. Nematodes have a poorly developed excretory system. Embryonic development is external and proceeds through larval stages separated by molts.

Arthropods represent the most successful phylum of animals on Earth, in terms of number of species as well as the number of individuals. They are characterized by a segmented body and jointed appendages. In the basic body plan, a pair of appendages is present per body segment. Within the phylum, classification is based on mouthparts, number of appendages, and modifications of appendages. Arthropods bear a chitinous exoskeleton. Gills, tracheae, and book lungs facilitate respiration. Embryonic development may include multiple larval stages.

Mollusks and Annelids

The phylum Mollusca is a large, mainly marine group of invertebrates. Mollusks show a variety of morphologies. Many mollusks secrete a calcareous shell for protection, but in other species, the shell is reduced or absent. Mollusks are protostomes. The dorsal epidermis in mollusks is modified to form the mantle, which encloses the mantle cavity and visceral organs. This cavity is distinct from the coelomic cavity, which the adult animal retains, surrounding the heart. Respiration is facilitated by gills known as ctenidia. A chitinous scraper called the radula is present in most mollusks.

Mollusks are mostly dioecious and are divided into seven classes.

The phylum Annelida includes worm-like, segmented animals. Segmentation is both external and internal, which is called metamerism. Annelids are protostomes. The presence of chitinous hairs called chaetae is characteristic of most members. These animals have well-developed nervous and digestive systems. Polychaete annelids have parapodia that participate in locomotion and respiration. Suckers are seen in the order Hirudinea. Breeding systems include separate sexes and hermaphroditism.

Echinoderms and Chordates

Echinoderms are deuterostome marine organisms. This phylum of animals bear a calcareous endoskeleton composed of ossicles covered by a spiny skin. Echinoderms possess a water-based circulatory system. The madreporite is the point of entry and exit for water for the water vascular system.

The characteristic features of Chordata are a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets), together with the

vertebrates. Most tunicates live on the ocean floor and are suspension feeders. Lancelets are suspension feeders that feed on phytoplankton and other microorganisms.

Vertebrates

The earliest vertebrates that diverged from the invertebrate chordates were the jawless fishes. Hagfishes are eel-like scavengers that feed on dead invertebrates and other fishes. Lampreys are characterized by a toothed, funnel-like sucking mouth, and some species are parasitic on other fishes. Gnathostomes include the jawed fishes (cartilaginous and bony fishes) as well as all other tetrapods. Cartilaginous fishes include sharks, rays, skates, and ghost sharks. Bony fishes can be further divided into ray-finned and lobe-finned fishes.

As tetrapods, most amphibians are characterized by four well-developed limbs, although some species of salamanders and all caecilians are limbless. Amphibians have a moist, permeable skin used for cutaneous respiration. Amphibia can be divided into three clades: salamanders (Urodela), frogs (Anura), and caecilians (Apoda). The life cycle of amphibians consists of two distinct stages: the larval stage and metamorphosis to an adult stage.

The amniotes are distinguished from amphibians by the presence of a terrestrially adapted egg protected by amniotic membranes. The amniotes include reptiles, birds, and mammals. A key adaptation that permitted reptiles to live on land was the development of scaly skin. Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles).

Birds are endothermic amniotes. Feathers act as insulation and allow for flight. Birds have pneumatic bones that are hollow rather than tissue-filled. Airflow through bird lungs travels in one direction. Birds evolved from dinosaurs.

Mammals have hair and mammary glands. Mammalian skin includes various secretory glands. Mammals are endothermic, like birds. There are three groups of mammals living today: monotremes, marsupials, and eutherians. Monotremes are unique among mammals as they lay eggs, rather than giving birth to live young. Eutherian mammals have a complex placenta.

There are 16 extant (living) orders of eutherian mammals. Humans are most closely related to Primates, all of which have adaptations for climbing trees, although not all species are arboreal. Other characteristics of primates are brains that are larger than those of other mammals, claws that have been modified into flattened nails, and typically one young per pregnancy, stereoscopic vision, and a trend toward holding the body upright. Primates are divided into two groups: prosimians and anthropoids.

ART CONNECTION QUESTIONS

• Figure 15.3 Which of the following statements is false?

• Eumetazoa have specialized tissues and Parazoa do not.
• Both acoelomates and pseudocoelomates have a body cavity.
• Chordates are more closely related to echinoderms than to rotifers according to the figure.
• Some animals have radial symmetry, and some animals have bilateral symmetry.
• Figure 15.24 Which of the following statements about the anatomy of a mollusk is false?
• Mollusks have a radula for scraping food.

REVIEW QUESTIONS

• Which of the following is not a feature common to most

animals?

• development into a fixed body plan
• asexual reproduction
• specialized tissues
• heterotrophic nutrient sourcing
• 
  Mollusks have ventral nerve cords.
• The tissue beneath the shell is called the mantle.
• The mantle cavity contains hemolymph.
• Figure 15.33 Which of the following statements about common features of chordates is true?
• The dorsal hollow nerve cord is part of the chordate central nervous system.
• In vertebrate fishes, the pharyngeal slits become the gills.
• Humans are not chordates because humans do not have a tail.
• Vertebrates do not have a notochord at any point in their development; instead, they have a vertebral column.

• Which of the following does not occur?
• radially symmetrical diploblast
• diploblastic eucoelomate
• protostomic coelomate
• bilaterally symmetrical deuterostome

• The large central opening in the poriferan body is called the .
• emmule
• picule
• stia
• osculum
• Cnidocytes are found in .
• phylum Porifera
• phylum Nemertea
• phylum Nematoda
• phylum Cnidaria
• Cubozoans are .
• polyps
• medusoids
• polymorphs
• sponges
• Which group of flatworms are primarily external parasites of fish?
• monogeneans
• trematodes
• cestodes
• turbellarians
• Crustaceans are .
• ecdysozoans
• nematodes
• arachnids
• parazoans
• A mantle and mantle cavity are present in .

• class Oligochaeta
• class Bivalvia
• class Polychaeta
• class Hirudinea
• Annelids have a .
• pseudocoelom
• a true coelom
• no coelom
• none of the above

CRITICAL THINKING QUESTIONS

• How are specialized tissues important for animal function and complexity?
• Using the following terms, explain what classifications and groups humans fall into, from the most general to the most specific: symmetry, germ layers, coelom, embryological development.
• Describe the feeding mechanism of sponges and identify how it is different from other animals.
• Compare the structural differences between Porifera and Cnidaria.
• Speculate as to what advantage(s) a complete digestive system has over an incomplete digestive system?
• 
  Echinoderms in their larval state have .

• triangular symmetry
• radial symmetry
• hexagonal symmetry
• bilateral symmetry
• The circulatory fluid in echinoderms is .

• blood
• mesohyl
• water
• saline
• Which of the following is not a member of the phylum Chordata?
• Cephalochordata
• Echinodermata
• Urochordata
• Vertebrata
• Members of Chondrichthyes differ from members of Osteichthyes by having a .
• jaw
• bony skeleton
• cartilaginous skeleton
• two sets of paired fins
• Squamata includes .
• crocodiles and alligators
• turtles
• tuataras
• lizards and snakes
• Sudoriferous glands produce .
• sweat
• lipids
• sebum
• milk
• Which of the following is a Monotreme?
• kangaroo
• koala
• bandicoot
• platypus

• Describe a potential advantage and disadvantage of the cuticle of ecdysozoans.
• Describe the morphology and anatomy of mollusks.
• Sessile adult tunicates lose the notochord; what does this suggest about one function of this structure?
• During embryonic development, what features do we share with tunicates or lancelets?
• What can be inferred about the evolution of the cranium and the vertebral column from examining hagfishes and lampreys?
• Explain why frogs are restricted to a moist environment.

• Describe three adaptations that allow for flight in birds.