BIOLOGY 2402GENERAL ZOOLOGY

LABORATORY TERMINOLOGYAND

ACCESSORY MATERIAL

A GUIDE TO WHAT IS REQUIRED FROM LAB MANUAL EXERCISESRevised August 2009

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EXERCISE 1 – THE MICROSCOPE

Exercise 1A – COMPOUND LIGHT MICROSCOPE

basein-base illuminatoriris diaphragm leverstagecoarse adjustment knobfine adjustment knobtransformer control knobobjectives:

scanning-power (4X)low-power (10X)high-power (40X) oil immersion (100X)

parfocal lensnosepieceocular (10X)interocular distance scale

*Note: Never use the coarse adjustment knob while looking at an object with a high-powered lens.

**Omit: “How to Use the Oil-Immersion Objective” & “How to Measure Size of Microscopic Objects.”

Exercise 1B – STEREOSCOPIC DISSECTING MICROSCOPE

basein-base illuminatorstagezoom objectivesubstage mirror controlreflected vs. transmitted lightreflected light mirrorocularfocus control knobtransformer

Exercise 1C – ELECTRON MICROSCOPE

Be able to distinguish between micrographs taken through a transmission electron microscope and a scanning electron microscope. How does an electron microscope relate (in terms of magnification) to the other two types of microscopes you have used today?

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EXERCISE 2 – CELL STRUCTURE AND DIVISION

Exercise 2A – THE CELL—UNIT OF PROTOPLASMIC ORGANIZATION

Squamous Epithelial Cell Egg Cell of Sea Starplasma membrane (or cell membrane) plasma membranecytoplasm cytoplasmnucleus nuclear envelope

nucleusnucleolus

Organelles Electron Micrograph Cell Model cytoplasmic organelles (cont.)

endoplasmic reticulum nucleus endoplasmic reticulum (ER)

ribosomes nuclear membrane rough ERmitochondria (look for the cristae) chromatin smooth ERGolgi complex nucleolus ribosomesnucleus cytoplasmic organelles centriolesnucleolus mitochondria cytosol

Golgi complex cell membraneExercise 2B – CELL DIVISION—MITOSIS AND CYTOKINESIS

Know the cell cycle:interphasemitosis (PMAT)

-prophaseasterspindle fiberscentromerechromosome

-metaphasemetaphase plate

-anaphasedaughter chromosome

-telophasecytokinesiscleavage furrow

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EXERCISE 3 – EMBRYOLOGY

Exercise 3B – CLEAVAGE PATTERNS—SPIRAL AND RADIAL CLEAVAGE [BEGINS ON PAGE 37]

Spiral Cleavage: Early Embryology of the Ribbon Worm, Cerebratulus

Protostomia (protostomes are animals in which the embryonic blastopore forms the mouth)

Cerebratulus (a ribbon worm)distinguish between unfertilized ovum vs. fertilized, undivided ovum (=zygote)morula stageblastula stage

-blastocoel

gastrula stage-archenteron-blastopore

In “Early embryology of Cerebratulus, a nemeterean worm,” (Fig. 3-8), omit figure J.

Radial Cleavage: Early Embryology of the Sea Star, Asterias

Deuterostomia (deuterostomes are animals in which a secondary embryonic opening forms the mouth.)

Asterias (the sea star) – on photos “Embryology of a sea star,” (Fig. 3-9), figures A-I only; omit J-L.distinguish between unfertilized ovum vs. fertilized, undivided ovum (figures A and B)morula stageblastula stage

-blastocoel

gastrula stage-archenteron-blastopore

-blastocoelExercise 3C – FROG DEVELOPMENT

fertilized egg (zygote)vegetal pole/hemisphereanimal pole/hemispheremorula stageblastula stage

-blastocoel

gastrula stage-blastopore-yolk plug-germ layers:

endoderm1

ectoderm2

mesoderm3

-archenteron4

-blastocoel-neural plate-notochord

“Early embryology of a frog to a tadpole stage”, (Fig. 3-10), figures A-H only; omit I-L.1All yellow on models represents endoderm.2All pink/orange to reddish color on models represents mesoderm.3Ectoderm is the dark brown to black layer on the outer surface of the models.4Space (or cavity) represented by the blue color on models is the archenteron.

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EXERCISE 4 – TISSUE STRUCTURE AND FUNCTION

*Read the introductory paragraphs. Know the terms in bold print.

General Description of Basic Tissue TypesEpithelial Tissue (simple):

simple squamous epitheliumsimple cuboidal epitheliumsimple columnar epitheliumpseudostratified epithelium

Epithelial Tissue (stratified):stratified squamous epithelium, keratinizedstratified squamous epithelium, nonkeratinized

Connective Tissue:areolar connective tissueadipose connective tissuehyaline cartilage (contains lacunae)bone

-osteocyte-osteon-osteon canal-lamellae-lacuna-canaliculi

blood -- (erythrocytes, leukocytes, platelets)

Muscle Tissue:smooth muscleskeletal muscle

-striationscardiac muscle

-striations-intercalated disk

Nervous Tissue:neuron

*Note: There are only four basic types of tissue—epithelial, connective, muscle, and nervous. All types within each of the four categories will be referred to as specific tissue types.

Exercise 4A – TISSUES COMBINED INTO ORGANS

Cross-section through the Trachea (pg. 63)hyaline cartilagepseudostratified epitheliumloose connective tissuesmooth muscle

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SOME IMPORTANT CONCEPTS IN ZOOLOGY

The purpose of this exercise is to demonstrate the concepts of homology and primitive vs. derived characters and the use of these concepts in the classification of organisms. These ideas provide an important framework for the study of relationships among organisms in that they demonstrate first, the similarity of structure among closely related organisms and second, the modifications of basic structural plans that distinguish specific organisms. Such studies of relationships among organisms are known as the subdiscipline in biology called systematics. In addition, you will examine the similarities and differences among serially homologous structures; that is, structures that are repeated within an individual organism.

Today's exercise uses mammalian structures to illustrate these principles.

HOMOLOGY AND CONVERGENCE

Homology is defined as equivalence of structure that results from inheritance from a common ancestor. That is, structures in different organisms are homologous if each has been derived (in evolutionary time) from the same structure in the common ancestor of those organisms.

Consider structure S in organism A. Suppose that two subpopulations of A become geographically isolated from one another for a long period of evolutionary time and are subjected to different selection pressures, mutation rates and/or genetic drift in isolation. Individuals of the descendent populations A' and A" may now possess the modified structures S' and S", respectively. These structures (S' and S") are homologous, no matter how similar or different they appear because they were both derived from the ancestral structure, S.

S'A' SA =Homologous Structures

S"A"

Similarity due to convergence occurs when the organisms B' and C' having similar structures S' and S", respectively, did not share a common ancestor with structure S that gave rise to both S' and S". Rather, structures of different origin, say Q (in B) and R (in C), became modified, presumably under similar selection pressures, to resemble one another in their respective descendents, B' and C'.

QB S'B'=Convergent Structures

RC S"C'

The problem arises: How do we distinguish homologous from convergent structures? We certainly have very little chance of discovering the common ancestor of divergent organisms, and even if we did, the processes that led to modification of structure took place over long periods of time and would be impossible to follow through all descendent populations. We therefore must look for some other types of evidence to distinguish homologous similarity from convergent similarity. One approach is to examine the structures in question in detail. Because homologous structures were (by definition) from the same ancestral structure and because the processes of replication of structure from generation to generation via DNA replication are basically conservative, then homologous structures should resemble one another in many details, such as shape, composition, relationships to other structures, and developmental processes. Convergent structures, on the other hand, may resemble one another in ways that only reflect functional similarity.

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The problem of distinguishing homologous from convergent structures can be quite complex, however. On the one hand, convergence can lead to remarkable similarities among distantly related organisms. Perhaps the most striking examples of convergence in the mammals are those between some of the marsupials and the placentals that exploit similar ecological habitats on different continents. Note the overall resemblance in the following placental/marsupial pairs:

Placentals Marsupials

LargePredators

Gliders

Large Rodent Habits

SmallRodentHabits

Despite the superficial resemblances, the differences in internal structure and reproductive biology between marsupials and placentals suggest very early divergence between these two subgroups and consequently, very distant relationships between members of these pairs.

Conversely, homologous structures may appear quite dissimilar at first glance due to major modifications of the ancestral structure in one or all lines of descendent. As a further complication, modifications may even be associated with functional changes. For example, the wing of a bat and the human hand are homologous structures because both were derived from the manus (hand or forefoot) of a primitive mammalian ancestor. The ancestral structure probably resembled the following diagram:

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Dorsal View: Right Manus

Careful inspection of the bat wing and the human hand will reveal the same arrangement of bones, although the relative sizes of bones are different. Examine skeletons of the bat wing, human hand, and forefoot of a cat. Identify the homologous bones among these structures (you do need to know the names of these bones). Note the modifications that have evolved in these different organisms. How are these modifications related to changes in function? (A diagram of the vertebrate forelimb is at the end of this section)

Now consider another type of wing: that of a bird. Note the arrangement of bones that contribute to the wing skeleton. Is it the same as that supporting the bat wing? In birds the number forelimb digits have been reduced and the carpals and metacarpals are fused as the carpometacarpus.

Wings of birds and bats are convergent structures. Each type of wing was derived independently; that is, birds and bats never shared a winged ancestor. If we examine these structures at another level however, we find that they are homologous. Wings of birds and bats, although not homologous as wings, are homologous as forelimbs. Birds and bats did share a common ancestor (one that we would probably classify as a reptile) that had an arrangement of bones in the forelimb that was probably very similar to that illustrated above for our primitive mammalian ancestor.

CLASSIFICATION

The goal of evolutionary classification is to construct groupings of organisms which reflect the phylogenetic relationships among them. For example, in the Linnaean hierarchy of classification (kingdom, phylum, class, order, family, genus, species), if two species are placed in the same genus, those two species are presumed to be more closely related to one another than either is to a third species placed in another genus. That is, those two congeneric species shared a more common ancestor with one another than either did with the third species. The following diagram illustrates the relationships among six taxa, A-F. (A taxon is any grouping of organisms in the hierarchical classification.) In this diagram we see that taxa B and C are more closely related to one another than either is to A or D, as indicated by their sharing a common ancestor (which shall remain nameless) at node I. Now consider taxon A. Taxon A is more closely related to the lineage containing taxa B and C than it is to taxon D, by virtue of the common ancestor which A and (B+C) share at node II. Taxon A is said to be the sister group of (B+C). (And, for that matter, at another level, B is the sister group of C.) Now consider taxon D. What is D's sister group? That is, with which taxon or taxa did it share the most recent common ancestor?

A B C D E F

I

II

III

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In theory, evolutionary classification is very straightforward, but in practice, the determination of phylogenetic relationships is not always easy. The characteristics one should use to construct an evolutionary classification are those which reflect the common ancestry of the organisms in question. Certainly this means that the characters for study should be homologous (by now you should have an appreciation for the potential difficulties in determining those homologies). Additionally, the characteristics chosen should reflect modifications of ancestral structure that are unique to lineages of organisms. The criterion for evolutionary classification, then, is the use of shared, derived (specialized) characteristics rather than primitive characteristics.

Consider the genealogy illustrated on the next page. Although it is contrived, it demonstrates some important concepts in evolutionary classification.

In this example, characteristics are listed for each of the taxa, A-F. 1, 2, 3, and 4 are the ancestral or primitive states of the characters in question. 1', 1", 2', 3', 3", and 4' represent derived character states.

A B C D E F (1', 2, 3', 4) (1', 2', 3', 4) (1', 2', 3', 4') (1, 2, 3', 4) (1, 2, 3", 4) (1", 2, 3", 4)

Which characteristics distinguish the following groups from one another?B from C _________________________________________________A from (B+C) ______________________________________________(A+B+C) from D ____________________________________________E from F _________________________________________________(E+F) from (A+B+C) _________________________________________

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Note that characteristic 4 is shared by most taxa in this diagram. Also notice that it carries almost no information as to the relationships among organisms except to distinguish B from C. Remember, 4 is a primitive characteristic; one that has not been modified in most lineages but has been inherited, unaltered, from the common ancestor shared by all the taxa in this example. Also note that each taxon has a unique mixture of primitive features retained from its ancestors and new, evolved or derived traits.

In the example above you were given information on the relationships of the taxa in question. In most instances, however, the true genealogy of a group of organisms is not known, and we infer relationships based on shared, derived characteristics. It becomes important to distinguish primitive from derived characteristics. This task is complicated by the fact that the ancestor of a lineage is very unlikely to be available for examination. What other characteristics might be used to decide if a characteristic is likely to be primitive? (By the way, this question has occupied many evolutionary biologists for a long time, and continues to do so.)

Now, try your hand at discovering characteristics that serve to define groups. On one of the tables, you will find a variety of mammal skulls. Your task is to examine these skulls and decide which characteristics serve to define groups (such as rabbits, rodents, carnivores, etc.) and distinguish them from other groups. Compare notes with the other students in the class. We will compile a list of distinguishing characteristics on the board.

SERIAL HOMOLOGY

The homology between structures in different organisms that we have just been discussing is phylogenetic homology: similarity due to common ancestry. In addition, there can be similarity among repetitive structures within the same organism due to common embryonic origin. Such similarity is called serial homology. For example, individual vertebrae along the human vertebral column are serially homologous.

Use the figure below to find the basic regions of a lumbar vertebra. Then examine the vertebrae along the length of the vertebral column and determine the serial homology (noting both similarities and differences) of the following parts:

spinous process

transverse process (rib, in the thoracic region) inferior articular process

superior articular process

body

Examine the vertebral column on the human skeleton. It is divided into five regions, as follows:Cervical--vertebrae 1-7Thoracic--vertebrae 8-19Lumbar--vertebrae 20-24Sacral--vertebrae 25-29 (fused)Coccygeal--vertebrae 30-34 (fused and variable in number in humans); vertebrae in the tail of other vertebrates are called Caudal vertebrae

Now, examine the vertebral columns on some other mammal skeletons in the lab and compare them to the disarticulated vertebrae and ribs from a giraffe. Arrange the giraffe vertebrae in order along the length of the table and notice the differences (some subtle, some quite obvious) between adjoining vertebrae.

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The more obvious structural differences between vertebrae of each group are characteristics useful in distinguishing regions. For example, note the number of foramina (=passages) in the cervical vertebrae.

Despite these variations, serial homologies can be established along the vertebral column. Embryologically, each vertebra is formed by a series of components that are essentially identical from one vertebra to the next in early development. The differences among vertebrae are due to variations in the relative growth and fusion of these elements. These elements include precursors to the spinous process, the body, and the transverse processes (which become ribs in the thoracic region of the column).

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Generalized Vertebra (amniote)

Generalized Vertebrate Forelimb

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EXERCISE 6 – PROTOZOAN GROUPS

Read the introductory paragraphs. For the classification, you are required to know only the taxa as listed below (**note: there are taxa in the lab manual that you are not required to identify). Note also that you must be able to (correctly) identify, name, and classify the genera (in italics) and informally named groups as given in the following list.

Kingdom Protista (the protozoa)“amebas” – (relationship unresolved) Amoeba, Difflugia, radiolarians,

foraminiferansPhylum Euglenozoa – Euglena, Trypanosoma, TrichonymphaPhylum Chlorophyta - VolvoxPhylum Apicomplexa – PlasmodiumPhylum Ciliophora – Paramecium, Stentor, Vorticella

As a beginning to this lab, you will receive a lab talk on scientific names and nomenclature. Students are expected to be able to use nomenclature correctly from this point on. Review the information on p. 67.

Exercise 6A —AMOEBA AND OTHERSRead carefully the introductory paragraph on “Where Found”.Study of Live Specimens—Examine living material of Pelomyxa (a naked ameba) and Difflugia (an ameba with a test, or shell).

General Features—For exam purposes, identify all genera examined (Amoeba, Pelomyxa, Chaos) as Amoeba.

plasmalemma food vacuoleectoplasm contractile vacuoleendoplasm nucleuspseudopodium

Other Sarcodines—Be able to identify on prepared slides. Know what a “test” is.Difflugiaforaminiferansradiolarians

Exercise 6B – PHYLUM EUGLENOZOA—EUGLENA, TRYPANOSOMA, TRICHONYMPHA; PHYLUM CHLOROPHYTA-VOLVOX; Read carefully the introductory paragraphs.

EuglenaRead “Where Found”.Study of Live Specimens – Examine living material of Euglena.

Stained Slide of Euglenaflagellum (there may be a specially labeled slide) pelliclechloroplasts contractile vacuole

TrypanosomaRead the introductory paragraphs. The trypanosomes in this lab will be found on a demonstration slide in which an oil immersion objective is used to magnify the blood sample sufficiently for you to identify the organism. The trypanosome shown is the cause of African Sleeping Sickness. The only feature you are to identify is the undulating membrane.

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Demonstration FlagellatesOn demonstration scopes are specimens of the following:

Trichonympha (from termite gut; “Termite Flagellates”)

PHYLUM CHLOROPHYTA-VOLVOX

VolvoxRead “Where Found”.If available, examine living colonies of Volvox.

General Featureszooidsflagelladaughter colonies

Exercise 6C – PHYLUM APICOMPLEXA—PLASMODIUMRead the introductory paragraphs. Examine the life cycle diagram in the lab manual. You are to examine a prepared slide of a blood sample infected with Plasmodium, the cause of the disease Malaria. The life stage of the organism seen in this slide should be the trophozoite stage (often called the signet-ring for its shape). Know trophozoite.

Exercise 6D – PHYLUM CILIOPHORA—PARAMECIUM AND OTHER CILIATESRead “Where Found”.Study of Live Specimens – Examine living Paramecium.

General Structure and Functionoral groovecytopharynxciliapelliclefood vacuolecontractile vacuolemacronucleusmicronucleusbinary fissionconjugation

Other CiliatesVorticella: be able to identify: stalk, body, cilia, and nucleus

Stentor: be able to identify: macronucleus and cilia

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EXERCISE 7 – THE SPONGES

Read the introductory paragraphs. You are required to know only the taxa given on this handout. (Note: there are taxa given in the lab manual that you are not required to identify.) Genus names are in italics. Those names not in italics are common names which you also are required to know. You must be able to place each organism examined within the correct classification scheme—i.e. kingdom, phylum, class (if given), genus, and common name. You also must know the general characteristics of each group (as given in the lab manual).

Kingdom AnimaliaPhylum Porifera – Grantia (=Sycon), glass sponge

Exercise 7A – GRANTIA

We will be using Grantia for this exercise. (Grantia is the same as Sycon, a syconoid sponge.) Read “Where Found” to become familiar with the typical habitat of these organisms. You may omit “Cellular Structure”, “Reproduction”, and “Skeleton”. Omit “Asconoid Type of Canal System” and “Projects and Demonstrations”.

Gross StructureSyconoid

External Structureosculumspiculesspongocoeldermal ostia

Prepared Slidespongocoelradial canalsincurrent canals

Examine a prepared slide of Commercial Spongespongin fiber

*Note: spicules may be a characteristic used in the classification of sponges.

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EXERCISE 8 – THE RADIATE ANIMALS

Read the introductory section. Be able to distinguish between a polyp and a medusa on sight. Classification (as you are to know it) is directly below. Under “Classification” in the lab manual, you need to be familiar with the general characters of each of the three classes—Hydrozoa, Scyphozoa, and Anthozoa. Know the meaning of the terms monoecious and dioecious.

Kingdom AnimaliaPhylum Cnidaria

Class Hydrozoa – Hydra, Obelia, Gonionemus, PhysaliaClass Scyphozoa – AureliaClass Anthozoa – Metridium, corals

Exercise 8A – CLASS HYDROZOA—HYDRA, OBELIA, AND GONIONEMUSRead the introductory paragraph and the section entitled “Where Found”. You may omit the section on “Feeding and Digestion” except for the last paragraph.

Hydra , a solitary hydroidLive specimens are for observation only. Find and identify all the following structures on the prepared slides.

basal disc epidermishypostome gastrodermismouth buds/buddingtentacles gonadsgastrovascular cavity cnidocytes nematocysts

Obelia, a colonial hydroidFind and identify all the following structures on the prepared slides.

hydranth perisarc coenosarc hydrotheca hypostome mouth tentacles

cnidocytesgonangiumblastostylemedusa buds/medusagonothecagonopore

Gonionemus, a hydromedusaexumbrellasubumbrellatentaclescnidocytesadhesive padvelummanubriummouth

gastrovascular cavityradial canalsring canalgonadsepidermisgastrodermismesoglea

Physalia (Portuguese man-of-war): understand “polymorphism”; know the “pneumatophore”Exercise 8B – CLASS SCYPHOZOA—AURELIA, A”TRUE” JELLYFISHRead the third paragraph under “Where Found”.

General Structurerhopaliumtentaclesoral armsmouthgastric pouches

gonadsnematocystsring canal

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Developmental Stages planula larvascyphistoma

strobilaephyra

Exercise 8C – CLASS ANTHOZOA—METRIDIUM, A SEA ANEMONE, AND ASTRANGIA, A STONY CORAL

External Structurebodyoral disctentaclesmouthcolumnbasal discsiphonoglyphperistomeepidermis

Internal Structurepharynxgastrovascular cavityradial chambersprimary septaseptal perforations incomplete septaacontiagonads

CoralsRead carefully the introduction under “Astrangia, a stony coral”.Examine various hard coral skeletons on display in the lab.

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EXERCISE 9 – THE FLATWORMS

Read carefully the introductory paragraphs. Be prepared to explain how acoelomates are advanced over the radiate animals. Under “Classification” in the lab manual, omit “Class Monogenea”, but know the general characters of the three remaining classes.

Kingdom AnimaliaPhylum Platyhelminthes

Class Trematoda – Clonorchis (liver fluke), Schistosoma (blood fluke)Class Cestoda – Taenia (tapeworm)

Class Turbellaria – Dugesia (planarian)

Exercise 9A – CLASS TURBELLARIA—THE PLANARIANSRead “Where Found”. Observe live planarians. Omit the regeneration experiment.

DugesiaPrepared Slide (whole mount and cross section)

auriclegastrovascular cavitypharynxeyespotepidermisdorsoventral muscle fibersparenchyma

Modelovaryovovitelline ducttestisvas deferenssperm ductpenis bulbcommon genital antrumseminal receptacleexcretory canalsprotonephridiumnerve cordcerebral ganglioneyespot

Exercise 9B – CLASS TREMATODA—THE DIGENETIC FLUKESRead “Where Found”. Read about Schistosoma, the human blood fluke. Omit “Observations of the Living Flukes”.

Clonorchis (prepared slide, whole mount)oral suckerventral sucker mouthpharynxintestineexcretory porebladder

testes genital poreseminal receptacle ovary yolk glands uterus

Exercise 9C – CLASS CESTODA—THE TAPEWORMSRead carefully the introductory section.

Taenia (model)

scolex suckers neckrostellum

proglottidgenital poreexcretory canaltestesvagina

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ovariesuteruseggsyolk gland (or vitelline gland)vas deferensnerve cord

(prepared slide)scolexsuckersrostellumneckproglottidgenital poretestesvaginaovariesuterusvas deferensnerve cordeggs

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EXERCISE 10 – FIVE SMALL PROTOSTOME PHYLA (PSEUDOCOELOMATES)

Read the introductory section. Understand the differences between acoelomate, pseudocoelomate, and eucoelomate animals.

Kingdom AnimaliaPhylum Nematoda - Ascaris, vinegar eel, hook worm, TrichinellaPhylum Rotifera - rotifersPhylum Nematomorpha - horsehair worms

Exercise 10A - ASCARIS, THE INTESTINAL ROUNDWORM.Read carefully the introductory paragraph concerning nematodes. Know the general characteristics of the group. Read "Where Found".

Preserved specimenspicules mouthlipsanuscuticlelateral linespseudocoelintestinevagina uterioviductsovariestestisvas deferensseminal vesicle

Prepared slide, x-sectioncuticleepidermispseudocoeluterusoviductsovariesintestinetestesseminal vesiclevas deferens

***TAKE CARE TO WASH YOUR HANDS THOROUGHLY AFTER HANDLING THE PRESERVED ASCARIS. IT IS POSSIBLE FOR THE EGGS TO REMAIN VIABLE EVEN AFTER SEVERAL YEARS OF BEING SUBMERGED IN PRESERVATIVES.

Other Nematodes: The following are to be seen on prepared slides. Identify and classify.vinegar eels (free-living)hook worms (parasitic)Trichinella (parasitic)

Exercise 10B - OTHER PSEUDOCOELOMATE

Phylum Rotifera (=rotifers)coronafoot

Phylum Nematomorpha (horsehair worm)

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EXERCISE 11 - THE MOLLUSCS

Read the introductory paragraphs. Under "Classification" in the lab manual, know the general characteristics of each group included in the classification section below. Note: omit the classes Monoplacophora, Caudofoveata, and Solenogastres.

Kingdom AnimaliaPhylum Mollusca

Class Scaphopoda - tusk shellClass Bivalvia - freshwater clam, GlochidiaClass Gastropoda - land snail, freshwater snail, slugClass Polyplacophora - chitonClass Cephalopoda - squid, octopus, Nautilus, ammonite

Exercise 11A - CLASS BIVALVIA—THE FRESHWATER CLAM.Read "Where Found".

External structure (The Shell)valves (left and right) hinge ligamentumbo/umboneslines of growthadductor muscle scarfoot retractor muscle scarfoot protractor scarpallial linepseudocardinal teethlateral teethnacreous layer

Internal structuresincurrent aperature (or siphon)excurrent aperature (or siphon)gills mantle cavityvisceral massfootlabial palpsmouth gill lamellaesuprabranchial chamberheartintestinecoelomic cavityopen system of circulation

SlidesGlochidia

Modelhinge ligament umbo/umbonesadductor muscle scarfoot retractor muscle scarfoot

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labial palpsheartintestinedigestive glandcoelomic cavitystomachanuskidneyincurrent aperature (or siphon)excurrent aperature (or siphon)gillsmantle cavity

Exercise 11B - CLASS GASTROPODA—THE PULMONATE LAND SNAILRead "Where Found".

foot head tentacles eyes radula (prepared slide)

Exercise 11C - CLASS POLYPLACOPHORA—THE CHITON.Read "Where Found".

headfootmantlemantle cavitygill

Exercise 11D - CLASS CEPHALOPODA—THE SQUID.Read "Where Found" and "Behavior". Note: examine the fossil ammonite on the side table.

headarmslateral finsmantlecollareyestentaclesmouthjawsfunnel (=siphon)mantle cavitypallial cartilages

funnel retractor musclesanusink sacgillsbranchial heartsystemic heartkidneyradulaliverstomachstellate gangliapenrectum

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EXERCISE 12 – THE ANNELIDS

Read the introductory paragraphs. Be sure to understand the concepts of segmentation and metamerism. Also understand the method of locomotion utilized by the annelids.

Kingdom AnimaliaPhylum Annelida

Class Polychaeta - clamwormClass Oligochaeta – Lumbricus (earthworm)Class Hirudinida – Hirudo (medicinal leech)

Exercise 12A – CLASS POLYCHAETA—THE CLAMWORMRead “Where Found” and “Behavior” (see living specimens if available.)External Features

headmetamereparapodiaanuscirri

prostomiumperistomial tentaclespharynxmouthjaws

notopodiumneuropodiumsetaeventral cirrusdorsal cirrus

Exercise 12B – CLASS OLIGOCHAETA—THE EARTHWORMSRead “Where Found” and “Behavior”. External Structure Internal Structure (Earthworm)

peristomiummouthprostomiummetamereanusclitellumsetaemale poresseminal groovesfemales poresdorsal pore

pharynxesophaguscropgizzardintestinecalciferous glandschloragogue cellstyphlosoledorsal vessel

aortic archesseminal vesiclesseminal receptaclesnephridiacerebral ganglionventral nerve cord

Pay particular attention to the paragraph on “Earthworm Copulation”.

Histology of Cross Section (see Fig. 12-5)cuticleepidermiscircular muscle layerlongitudinal muscle layer

parietal peritoneum visceral peritoneumchloragogue tissuelumen of intestine

typhlosoleventral nerve corddorsal vessel

Exercise 12C – CLASS HIRUDINIDA—THE LEECHRead “Where Found” and “Behavior” (although there are no live specimens for observation.)External Features

annulioral sucker mouth

caudal suckeranusmale genital porefemale pore

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EXERCISE 13 – THE CHELICERATE ARTHROPODS

Read the introductory paragraphs.

Kingdom AnimaliaPhylum Arthropoda

Subphylum TrilobitaSubphylum Chelicerata

Class Merostomata – Limulus (horseshoe crab)Class Arachnida – spiders, scorpions, ticks, mites,

Exercise 13A: THE CHELICERATE ARTHROPODS—HORSESHOE CRAB & GARDEN SPIDER

HORSESHOE CRAB Read “Where Found”. (See live specimen if available.) This and all other members of the

Arthropoda periodically shed their exoskeleton in a process called ecdysis

External Featuresexoskeleton

cephalothorax (=prosoma)carapacecompound eyessimple eyesmouthcheliceraepedipalpswalking legschelae

gnathobaseschilariaabdomengenital operculumgenital poresgills/book gillslamellaetelsonanus

Pay particular attention to the section on “Reproduction”.

Class Arachnida: Note the diversity demonstration of arachnids on the side table (ticks, mites, scorpion, and daddy-long-legs).

GARDEN SPIDERRead “Where Found” and “Behavior” (although we have no living specimens to observe.)

External Features (refer to Fig. 13-4)fang

exoskeleton abdomenlung slit cephalothoraxepigynum pedicelspinnerets walking legsanus chelicerae

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EXERCISE 14– THE CRUSTACEAN ARTHROPODS

Kingdom AnimaliaPhylum Arthropoda

Subphylum CrustaceaClass Malacostraca – Cambarus (crayfish), lobster, crab, isopodsClass Branchiopoda – DaphniaClass Maxillopoda – ostracods, copepods, barnacles

Exercise 14A – SUBPHYLUM CRUSTACEA – THE CRAYFISH & OTHER CRUSTACEANSRead the introductory paragraphs. Pay particular attention to the bold terms: mandibles, antennae (two pairs), maxillae (two pairs), gill-breathing arthropods, and biramous. Read “Where Found” and note that the lobster is a marine form whereas the crayfish is found in freshwater.

External Featuresexoskeletoncephalothoraxcarapacebranchiostegitesgill chambergillsrostrumcompound eyeantennaemaxillipedsabdomenswimmerets telsonanusuropodsseminal receptacle

Dissection of the Appendages

serial homologyuropodsswimmeretscopulatory organswalking legschelipedschelaebiramousuniramousoviduct openingmaxillipedsmaxillaemandiblesantennaerenal openingantennulesgills

Internal Structurehearthepatopancreas/livergastric musclesmandibular musclesextensor musclesflexor musclesostiagonadsstomach -cardiac chamber -pyloric chamberintestineesophagusgastric millantennal (or green) glandssupraesophageal ganglia

Other Crustaceans – Be able to Identify and Classify from Prepared Slides

CLASS BRANCHIOPODADaphnia

CLASS MAXILLOPODAostracodscopepodsbarnacles

EXERCISE 15 – THE ARTHROPODS: MYRIAPODS AND INSECTS

Read the introductory paragraph. Be able to distinguish uniramous and biramous.

Kingdom AnimaliaPhylum Arthropoda

Subphylum Myriapoda

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Class Chilopoda – centipedesClass Diplopoda – millipedes

Subphylum HexapodaClass Insecta – Romalea

Exercise 15A – THE MYRIAPODS – CENTIPEDES AND MILLIPEDESRead the introductory paragraph.

CLASS CHILOPODA – THE CENTIPEDES CLASS DIPLOPODA – THE MILLIPEDESocelliantennaelabrummandiblesfirst maxillae

second maxillaemaxillipedspoison fangsanusspiracles

ocelliantennaelabrummandibleslabiumspiracles

EXERCISE 15B – THE INSECTSRead the introductory paragraphs. The study of insects is entomology. Note the group’s chief characteristics: walking legs (three pairs), antennae (one pair), head, thorax, abdomen, tracheal tubes, and wings. The dissection is described on the following pages.

Class Insecta – RomaleaExternal Structureexoskeletoncompound eyesantennaeocellilabrummandibleslabiummaxillaeprothoraxmesothoraxmetathoraxspiracleswingsfemurtibiatarsusclawstympanumovipositor

Internal Structre (on handout) hemocoelovarian tubulesrectumhindgutMalpighian tubulesgastric caecaesophaguscropproventriculustracheaventral nerve cordsubesophageal ganglion

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ROMALEA

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The internal anatomy of grasshoppers is often poorly preserved because the exoskeleton prevents penetration of preservative. However, it is often possible to see the major features. Unlike crayfish, an insect’s viscera are distributed throughout the body.

Cut off the wings and legs. To open the grasshopper, insert a pair of fine scissors under the lateral pleural membrane of the ninth abdominal segment above the spiracle and cut forward to the thorax. Keep the tips of the scissors up against the inside of the exoskeleton, or you may destroy internal organs that lie close to the dorsal surface. Repeat the cut on the other side. Now extend the cuts forward through the exoskeleton of the thorax to just behind the head. Make a third cut to one side of the dorsal midline of the thorax, then carefully lift the exoskeleton and gently tease away any adhering tissue. Cut the large flight muscles that attach near the bases of the wings. Trim off large pieces of the cuticle as they are freed. Once the animal is opened, pin it down securely in the tray, and flood the tray with water to float the internal organs.

The organs of an insect sit in a large cavity, the hemocoel. It is not a true coelom because there are no mesenteries and it is not lined with peritoneum. If your animal was well-fed prior to preservation, large yellowish fat bodies may fill the cavity. If it was collected during the breeding season, the gonads will be large.

Reproductive System. The gonads are located in the abdomen beneath the heart. Gently probe the gonadal tissue to separate the organs. The paired ovaries of females are composed of many ovarian tubules that connect to oviducts passing posteriorly to the vagina. Dorsal to the vagina is a small diverticulum of the reproductive tract, the seminal receptacle, where sperm are stored following copulation. As each egg passes through the oviduct, a few sperm are released to fertilize the egg as it is laid. In the fall, grasshoppers deposit their eggs in the soil. In the spring, nymphs that look similar to adults hatch and begin to feed. They molt five times before reaching adult size.

In males, the testes lie dorsal to the intestine. Sperm ducts from each testis pass ventrally to unite into a single ejaculatory duct, which passes into a terminal copulatory organ.

Digestive and Excretory Systems. Once the gonads have been teased aside, you should see the hindgut of the digestive system in the abdomen. If you extend your cut posteriorly, you should reveal where the intestinal portion of the hindgut enlarges into the rectum. When water is scarce, the rectum reclaims moisture from the fecal material before it is voided.

Follow the hindgut forward to an area where serveral tubules branch from the digestive tract. This marks the junction of the midgut with the hindgut. The tubules are the Malpighian tubules of the insect’s excretory system. Hemolymph bathes the tubules as they extend out into the hemocoel. Small molecules in the hemolymph diffuse across the tubules. As fluids travel through the tubules toward the gut, nutrients and ions are reabsorbed, leaving waste materials and water that pass on to the rectum and are voided. Some insects reclaim so much fluid from the tubes and hindgut that the fecal pellets are often as dry as dust.

The anterior junction of the midgut with the foregut is marked by several fingerlike projections, the gastric caeca. Food passes into the caeca where it is digested and absorbed. The foregut is subdivided into two regions. An esophagus conveys food from the pharynx into the crop, a storage area. From the crop, food enters the proventriculus (gizzard), where it is ground into fine particles by hardened cuticular plates in the wall of the proventriculus.

Gas-Exchange System. On the sides of the abdominal segments, find spiracles, openings into the gas-exchange system. Connected to the inside of each spiracle is a trachea. Air enters through the spiracles in the body wall and diffuses through the tracheae that ramify throughout the body. In the tissues, the tracheae branch into small tracheoles that press into cells, supplying their oxygen needs and removing carbon dioxide. In large insects, such as the grasshopper, large balloon-like air sacs are located in the body cavity. Muscle movements compress them, promoting air flow.

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Nervous System. Remove the digestive and reproductive systems by cutting through the esophagus and stripping the posteriorly located organs. Look at the floor of the body cavity. You should see the ventral nerve cord beneath some covering membranes. Gently tease away the tissues to expose the nerve cord. Note the paired ganglia. Are they all the same size? If not, how would you explain the difference?

Follow the nerve cord forward to the esophageal region and find the supraesophageal ganglion above the esophagus and the subesophageal ganglion beneath. They are connected by the circumesophageal connectives that pass around the esophagus.

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EXERCISE 16 – THE ECHINODERMS

Read the introductory paragraphs. Be familiar with the distinguishing characters of the phylum: dermal endoskeleton, water-vascular system, pedicellariae, dermal branchiae, and pentaradiate symmetry.

Phylum EchinodermataClass Crinoidea – sea lilies, feather starsClass Asteroidea – Asterias (sea star)Class Ophiuroidea – brittle starsClass Echinoidea – sea urchins, sea biscuits, sand dollarsClass Holothuroidea – Cucumaria (sea cucumber)

Exercise 16A – CLASS ASTEROIDEA—THE SEA STARSRead “Where Found” and “Behavior”. Be prepared to define/describe the following: pentaradial symmetry, rays (or arms), oral-aboral flattening, ampullae, spines, dermal branchiae, pedicellariae, and eyespot.

External Structure ABORAL SURFACE

central discrays (bivium & trivium)madreporite plateanus

epidermisspinespedicellariaedermal branchiae (=skin gills)

ORAL SURFACEambulacral groovetube feet (=podia)

ambulacral spines

mouthperistomial membranestomach

Endoskeletonossiclesepidermisdermisperitoneum

ambulacral ossiclesampullaeambulacral poresambulacral ridge

Internal Structurecoelomic cavitypyloric stomachpyloric ductpyloric cecaintestinerectal ceca

cardiac stomachgastric ligamentsgonadsstone canalring canalradial canal

Exercise 16B – CLASS OPHIUROIDEA—THE BRITTLE STARSRead “Where Found”. Examine the brittle star on display on the side table. Also observe the live specimen (in the aquarium) if available.

Exercise 16C – CLASS ECHINOIDEA—THE SEA URCHINRead “Where Found”. Observe live sea urchins if available.

External Structurespinesambulacral regions

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mouthteethAristotle’s lanternambulacral platesanusanal plategenital plates

Exercise 16D – CLASS HOLOTHUROIDEA—THE SEA CUCUMBERRead “Where Found”. Observe the live specimen if available.

External Structuremouthtentaclesanuswater-vascular systempodia

Internal Structurecoelomic cavitypharynxstomachintestinecloacarespiratory treesretractile muscles

longitudinal muscle bandsring canalampullaegonadendoskeleton

Exercise 16E – CLASS CRINOIDEA—THE FEATHER STARS AND SEA LILIESAlthough extant, we have only fossil crinoids on display.

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EXERCISE 17 – PHYLUM CHORDATA: A DEUTEROSTOME GROUP

Read the introductory paragraphs. Be familiar with the distinguishing characters of the phylum: notochord, pharyngeal gill slits, dorsal tubular nerve cord, postanal tail, endostyle or thyroid gland.

Kingdom AnimaliaPhylum Chordata

Subphylum Urochordata – tunicates, sea squirtsSubphylum Cephalochordata – Branchiostoma, Amphioxus, lancelet

Exercise 17A—SUBPHYLUM UROCHORDATA (TUNICATES, SEA SQUIRTS)Read “Where Found”.

External Features (we will not learn internal features of the adult tunicate)Adult tunicate (whole specimen)

incurrent siphonexcurrent siphontunic or test

Tadpole larva (whole mount on prepared slide)adhesive papillaenotochordincurrent apertureexcurrent aperturebranchial basket

Exercise 17B—SUBPHYLUM CEPHALOCHORDATA (BRANCHIOSTOMA, AMPHIOXUS, LANCELET)Read “Where Found”.

External Structure—Adult Amphioxus (=Branchiostoma) (whole mount slide)dorsal fincaudal finventral finrostrumoral hoodatriopore atriumanus

gonadsmyotomesfin raysvelumpharynxwheel organintestinegill bars

gill slitshepatic cecumendostylenotochorddorsal nerve cordphotoreceptor cells

Cross-section Slidedorsal finfin raymetapleural foldsmyotomesnerve cordnotochordpharynx

gill barsgill slitsatriumendostylehepatic cecumintestine

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EXERCISE 18 - THE FISHES—LAMPREYS, SHARKS, AND BONY FISHES

Kingdom AnimaliaPhylum Chordata

Subphylum Vertebrata - vertebratesSuperclass Agnatha - jawless vertebrates; agnathans

Class Petromyzontida - lampreysClass Myxini - hagfishes, slime hags

Superclass GnathostomataClass Chondrichthyes - Squalus

EXERCISE 18A - CLASS PETROMYZONTIDA—THE LAMPREYSRead the introductory paragraphs.Ammocoete Larva (whole mount slide)

myotomesoral hoodoral papillaegill slitscloacal openingcaudal findorsal finnerve cordbrainnotochordvelum

pharynxgill pouchesgill barsendostyleesophagusintestineanusliverhearteyes

Adult Lamprey - external structuredorsal finscaudal finbuccal funnelmouthtonguenostril

pineal organeyesexternal gill slitslateral line systemurogenital sinus

Adult Lamprey - internal structure, longitudinal sectiondorsal aortanotochordspinal cordbrainolfactory sacnostriltonguecranial cartilagepapillaebuccal funnel

mouthhorny teethpharynxrespiratory tubeventral aortainternal gill slitsliverheartespophagus

Exercise 18B - The Cartilaginous Fishes—SqualusRead "Where Found".

Squalus - external structureheadtrunktailpectoral finspelvic fins

dorsal finscaudal fin (heterocercal)mouthteeth

nostrils

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eyesrostrumspiraclesgill slits

lateral linecloacal openingplacoid scales

Squalus - internal structurelivergallbladderbile ductstomachduodenumpancreasspleenileumspiral valverectal glandcolonrugaetestesepididymissperm ductkidneyscloacaseminal vesiclessperm sacs

urogenital papillaovariesoviduct yolk sac (if embryos are present)ostium tubaeatriumventricleconus arteriosusdorsal aortaexternal gill slitsinternal gill slitsgill chambersgill archesgill rakersgill raysprimary lamellaesecondary lamellaedemibranchsholobranch

claspers

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DIVERSITY LAB RULES

MAMMALS

DO NOT PICK UP ANY OF THE SKULLS.

BIRDS

DO NOT PICK UP ANY BIRD SPECIMENS EXCEPT SKULLS, WHICH YOU MAY CAREFULLY HANDLE.

HERPS (=AMPHIBIANS & REPTILES)

DO NOT SHAKE OR REMOVE SPECIMENS FROM JARS. DO NOT HANDLE THE SKULLS.

WHAT YOU NEED TO KNOW

I. BE ABLE TO PLACE EVERY ORGANISM INTO THE CORRECT CLASSIFICATION.

II. BE ABLE TO GIVE THE COMMON NAME OF EACH GROUP OF ORGANISMS: HAGFISH, LAMPREY, SHARK, SKATE, RAY, RATFISH, LOBE-FINNED FISH, LUNGFISH, COELACANTH, RAY-FINNED FISH, FROG, TOAD, SALAMANDER, CAECILIAN, LIZARD, SNAKE, TURTLE, CROCODILIAN, RATITE BIRD, CARINATE BIRD, MONOTREME, MARSUPIAL MAMMAL, PLACENTAL MAMMAL.

III. KNOW THE BASIC FEATURES OF EACH SUPERCLASS AND CLASS.

IV. IF THERE IS A PARTICULAR THEME PRESENT IN A CLASS ON DISPLAY, UNDERSTAND THE THEME. FOR EXAMPLE, YOU MIGHT BE EXPECTED TO UNDERSTAND THE DIET OF A PARTICULAR BAT BASED ON TOOTH CHARACTERISTICS OR TO UNDERSTAND PROBABLE FOOD CAPTURE FUNCTION OF A PARTICULAR BIRD BASED ON BILL SHAPE.

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OVERVIEW OF VERTEBRATE DIVERSITY

Kingdom Animalia (animals)Phylum Chordata (chordates)

Subphylum Vertebrata (vertebrates)Superclass Agnatha (jawless vertebrates)

Class Myxini (hagfishes)Class Petromyzontida (lampreys)

Superclass Gnathostomata (jawed vertebrates)Class Chondrichthyes (cartilaginous fishes)Class Actinopterygii (ray-finned fishes)Class Sarcopterygii: (lobe-finned fishes—includes the coelacanth

and lungfishes)

Class Amphibia (anurans, caecilians, salamanders)Class Reptilia (snakes, lizards, turtles, crocodilians)Class Aves (birds)Class Mammalia (mammals)

[Two subclasses: 1) monotremes, 2) marsupials & placental mammals]

SUPERCLASS AGNATHA - jawless vertebrates. These animals do not have a lower jaw hinged to the cranium and supported by an internal skeletal element. (Note: your lab book lumps the two agnathan classes listed below into a single Class Agnatha.)

CLASS MYXINI - hagfish. Hagfishes are marine forms and are the only vertebrates with body fluids isotonic to seawater. They are scavengers and feed on dead and dying fishes. They secrete large amounts of mucus (“myxini” means “slime” in Greek) that is used as a defense against predators. Hagfishes are also characterized by rudimentary eyes and three pairs of barbels around the mouth. The species on display in the lab has a single opening for water to exit the body after passing through the pharyngeal gill slits. Other species have separate openings for each individual gill slit.

CLASS PETROMYZONTIDA - lamprey. Lampreys differ from hagfishes in a number of anatomical and physiological features. Adult lampreys have an oral disc, separate external openings for all gill slits and a dorsal median nostril. Lampreys also undergo metamorphosis. (There may be an ammocoetes larva on display.)

SUPERCLASS GNATHOSTOMATA - jawed vertebrates.

CLASS CHONDRICHTHYES - sharks, skates, rays and ratfishes. This class is characterized by the following features: cartilaginous skeleton, placoid scales (and teeth that are similar in structure to the scales), oily liver used for buoyancy, ampullae of Lorenzini which are used to detect tiny electrical fields created by muscular movements. Examine the material that illustrates each of these characteristics and the specimens that illustrate the diversity within the group.

Characteristics of Chondrichthyes: Internal cartilaginous skeleton: notice that the upper jaw is not fused to the cranium.Placoid scales: examine placoid scales under the microscope.Teeth (similar in structure to scales): examine shark jaw

External anatomy of Squalus acanthias: note the following features:ampullae of Lorenzinispiracleseparate, lateral gill openings

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heterocercal tail

Diversity of Chondrichthyes: There are over 625 species of cartilaginous fishes. You will examine only a few representatives.

Sharks: note the laterally placed eyes and broad snout.Skates and Rays: when you examine these specimens, note the spiracle, ventral gill slits and enlarged pectoral fins fused to the head. (Note dorsal denticles, and on the stingray, the enlarged “spine” [all are modified placoid scales].)Ratfishes (also called Chimeras): examine the specimen on demonstration; note the differencesbetween this and the shark:

operculumnaked body (no placoid scales)spine (a modified placoid scale)tooth plates (inside the mouth)

NOTE: THE FOLLOWING TWO CLASSES (Actinopterygii and Sarcopterygii) HAVE TRADITIONALLY BEEN COMBINED IN ONE CLASS—THE OSTEICHTHYES. The recent changes in classification are in both your text and lab manual.

CLASS ACTINOPTERYGII - ray-finned fishes. Ray-finned fishes are characterized by the following features: internal skeleton made of bone (in most), single gill opening covered with an operculum, paired fins supported by dermal rays [they do not have fleshy lobes at the bases of the fins] , air bladder used as a lung or for buoyancy (lost in some). The group is very diverse with over 23,000 species in both freshwater and marine environments. Examine the materials that demonstrate the characteristics of bony fishes and examine examples of diversity. You will not be responsible for the names of the representatives, but be able to recognize them as ray-finned fishes (Class Actinopterygii).

Characteristics of Actinopterygii:Bony skeleton.Scales: Scales of ray-finned fishes all have bone in them, but some have other layers as well. Examine the following types of scales:

ganoid scales - have ganoin, an enamel-like substance, overlying the bone. This scale is from a gar.cycloid scales - are composed of a thin layer of bone arranged in concentric rings (=annuli) that reflect the growth pattern of the fish.ctenoid scales - are like cycloid scales except that they have small tooth-like projections (ctenii) along the exposed edge. The ctenii are thought to help improve hydrodynamic efficiency.

Air bladder: examine the dissected specimen and note the air bladder (also called the swim bladder). In this species the bladder is used for buoyancy.

CLASS SARCOPTERYGII—lobe-finned fishes. Lobe-finned fishes have some features in common with the ray-finned fishes, including a bony skeleton and a single gill opening covered with an operculum; however, their paired fins have a sturdy internal skeleton with muscle within the limb. Usually have air bladder used as a lung.

Lungfishes: Examine the model of an Australian lungfish on demonstration. Note the fleshy lobes on the paired fins. Fishes in this group have a lung (that is homologous to the air bladder you saw earlier) and some species are able to withstand drying of the habitat by encasing themselves in a mucus and mud cocoon and breathing air through exposed nostrils.

Coelacanth: Examine the model of the coelocanth. Note the fleshy lobes at the bases of all the fins. This species is closely related to the lineage that is believed to have given rise to the amphibians.

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CLASS AMPHIBIA - This class includes anurans (=frogs and toads), which account for about 85% of the diversity in the class, salamanders, and an odd “worm-like” form called a caecilian. Amphibians are anamniotes, meaning that there is no amnion membrane to enclose the embryo and keep it from drying out. The eggs must therefore develop in water (or a moist environment). The egg hatches into a gill-breathing larva which, in most species, metamorphoses into a lung-breathing adult. There are species, however, that never metamorphose but retain larval characteristics even after they mature into reproductive adults. This is the phenomenon of neoteny.

Amphibians have smooth, moist skin with no scales, although some species have areas of thickened epidermis (cornified areas) that resemble epidermal scales. The skull is flattened and the vertebral column shows regional specialization for the attachment of limb girdles (this specialization is not evident in vertebral columns of fishes).

Examine the diversity of amphibians on display and note the class characteristics shown in the demonstrations.

CLASS REPTILIA - This class is undoubtedly paraphyletic and newer texts have proposed alternate classifications of the reptiles, which currently include snakes and lizards, turtles, crocodilians, the New Zealand tuatara, and the extinct dinosaurs. These organisms are quite different in many respects, but all were placed in the Class Reptilia based on the presence of epidermal scales, an amniotic egg, direct development (lack of larval stage) and because none has either feathers (which would make it a bird) or hair (which would make it a mammal).

Examine the diversity of living reptiles on display. Note the similarity between snakes and lizards. There are some legless lizards - can you distinguish them from snakes? If so, how? Of the reptilian subgroups, snakes and lizards are more closely related to one another than either is to any other subgroup. The turtles and the crocodilians each represent subgroups that are more distantly related to the snakes and lizards and to each other. In fact, crocodilians are believed to be more closely related to birds than to any other subgroup of reptiles.

CLASS AVES - birds. The Class Aves contains approximately 9000 species extant (=living), of which about 55% belong to one of the 27 orders - the songbirds. All members lay amniotic eggs, usually in a nest constructed of plant material. They possess thin, dry skin covered with feathers. Feathers are unique to this class and probably evolved for insulation; all modern birds are endothermic. All birds are bipedal on their hindlimbs, with the forelimbs modified into wings for flight. Some members of this class have wings that are reduced and they are flightless, but never in the history of the group has the wing secondarily assumed some different locomotion function. Even those that use the wing under water use it in the same way as is done for flight in the atmosphere. As a class, they show far less morphological diversity than is found in any other tetrapod class.

Skeletal features of the class can be seen on the chicken skeleton displayed in the lab:Skull features:

1) Toothless jaws - this feature is found in other classes also, but it only within this class that all members lack teeth.

2) Lower jaw is composed of several bones – birds and all lower classes have jaws made up of many bones.

3) The jaw in birds is covered with a keratinaceous sheath.

Vertebral column features: there is considerable modification in response to the demands of flight. The column is highly rigid, with only the neck and base of the tail moveable.

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4) Uncinate processes (horizontal bony flaps) overlap individual ribs, adding to rigidity of the ribcage during downstroke in flight.

5) A large, keeled sternum attached to the ribs supports large flight muscles. 6) Pygostyle—in birds, most of the tail bone is reduced and fused.7) Synsacrum—in birds, some lumbar, some caudal, and all the sacral vertebrae are

fused.

Pectoral girdle: this structure must be stout in birds in order to withstand the stresses of flight.8) Furcula (“wishbone”)—the clavicles in birds have become fused into a single bone. 7) Corocoid—a powerful bone that acts as a strut between the wings and sternum in

birds. Interestingly enough, monotremes also possess this structure, as do most of the reptiles.

Limbs: 10) The forelimb has been modified into the wing, which has the basic “arm”

elements of all tetrapods, but has been modified.11) The digits have been reduced to three with only one digit remaining

moveable.12) The hindlimb has also been highly modified, with the tibia elongated and the

fibula reduced to a splint.

CLASS MAMMALIA - Mammals are characterized by two unique characteristics: the presence of hair and the production of milk from mammary glands. Other mammalian characteristics include endothermy and (usually) homeothermy, a variety of skin glands (oil, sweat, scent), muscular diaphragm, three middle ear ossicles, secondary palate, ribs only on thoracic vertebrae, only a single bone in each side of the lower jaw, and heterodont dentition.

Examine the material available illustrating several of these features and the variations in characteristics among members of this class. Please use care in handling these specimens. Some are irreplaceable.

There are about 4500 species of mammals divided into two subclasses:1) The egg-laying mammals, called monotremes: There are only three living species, and

they are restricted to Australia and New Guinea. One is the duck-billed platypus, a semiaquatic form, and the other two are spiny anteaters or echidnas. The production of eggs (ovipary), rather than giving birth (vivipary), is a shared primitive characteristic with reptiles. Although these species do produce milk, they lack nipples. The milk is taken from tufts of fur associated with the mammary glands.

2) The second subclass is divided into two major groups, the marsupials and the placental mammals.

Marsupials: This group is known as the pouched mammals. Marsupials get their name from the presence of an abdominal pouch or marsupium for carrying the young (although not all marsupials have a pouch). The developing young are nourished with a primitive placenta much different from other mammals. They are born at an early stage of development, crawl from the vagina to the pouch where they attach to a nipple, and remain there for several weeks. The only species occurring in the United States is the opossum. Most other species of marsupials (about 250) occur in either the Australian region or South America. Look at the specimen of an adult opossum and the preserved newborn young.

Placental Mammals: All mammals other than monotremes and marsupials have a true placenta for nourishment of the developing embryo. This group includes the vast majority of mammals, about 3750 species.

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The placental mammals occur in every habitat on Earth and include members that fly (bats) and those that live entirely underground (e.g. pocket gophers and moles), as well as those that are restricted to aquatic habitats (whales, dolphins, manatees). This group also includes the largest animal ever to have lived, the great blue whale. The placental mammals are divided into about eighteen orders. You are familiar with many of these. Examples of some of the major orders of placental mammals are out for you to examine, including rodents, bats, carnivores, ungulates and primates. Some of the features that distinguish these groups are explained on the cards accompanying the specimens.

The evolution of heterodont dentition has allowed mammals to exploit almost every major feeding niche, including insectivory, frugivory (fruit), granivory (seeds), nectivory (nectar), folivory (leaves), carnivory, and sanguivory (blood). Although they are toothless, the baleen whales even utilize filter feeding by means of thousands of thin strands of material called baleen.

As you examine the specimens on display, note the variations in dental morphology and their relationship to diet.

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