LAB 5

OSTEICHTHYES: ACTINOPTERYGII,LATIMERIA, AND DIPNOI

MATERIALS

1. Numerous whole, preserved actinopterygians and lungfish.

2. Whole, preserved yellow perch (Percaflavescens; Percomorpha) fordissection.

3. Mounted skeleton of perch; whole- and head skeletons of other taxa ofactinopterygians.

4. Read Chapter 8 (pages 211-256) in Pough et al. (1999).

"Of all the animals that have lived in the water, none hau§: been so successful as thebony fishes . . . Osteichthyes."

- Edwin Colbert and Michael Morales, 1991

SUMMARY CLASSIFICATION

Osteichthyes is the most diverse group of vertebrates, relative toMyxinoidea, Petromyzontoidea, and Chondrichthyes, with nearly 24,000species of actinopterygian fishes alone! The following phylogeneticclassification reflects the groups covered in this lab. Numerous taxa, however,have been omitted for time and space considerations (Pough" et aI., 1999).

103

INTRODUCTION

105

Four pentadactyluslimbs

Stapes derived fromhyomandibular bone

'0c:c-O

Bile saltsPulmonary circulation

Two-chambered atrium

Nasolachrymal duct

Intemallung structure increasingly complex

CHOANATA

Thin scalesembedded in skin

Diphycercal tailcontinuous withdorsal and anal fins

Paired fins with long muscular lobesextending below body

Pulmonary vein

-415mya­SilurianEndochondral bone

Bony operculumScales adenticulate

Lepidotrichia

Lung derived from gut

GNATHOSTOMATA

r------ OSTEICHTHYES ------..,

SARCOPTERYGII

Scales composedof ganoine

Single dorsal fin

Figure 5.1. A c1adogram showing the relationships among major clades of Osteichthyes. Additionalcharacters, mostly relating to osteology, are not shown (modified from Maisey, 1986).

Lab 5: OSTEICHTHYES

includes only monophyletic groups. Therefore, Osteichthyes refers to the cladethat includes Actinopterygii (ray-finned fishes), Sarcopterygii (coelacanth,lungfishes, and tetrapods), and their most recent common ancestor. Humans arethus members of Osteichthyes. Osteichthyes is diagnosed by the possession ofendochondral bone, a lung derived from the gut, lepidotrichia, adenticulatescales, and a bony operculum on each side of the pharyngeal region.

There are two radically different modes of bone formation in embryos andyoung of vertebrates. The simpler of the two involves the formation of dermalbone, which is formed in the dermal layer of the skin. Craniates and pre-

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LABS FOR VERTEBRATE ZOOLOGY104

Osteichthyes includes Actinopterygii and Sarcopterygii (Latimeria +Dipnoi + Tetrapoda) (Fig. 5.1). Do not be confused between the translation ofthe name Osteichthyes and what the name represents in a phylogenetic sense.Although Osteichthyes literally means "bony fishes," our phylogenetic taxonomy

NeognathiSalmonidae - salmons, trout, charsNeoteleostei - numerous clades, several of which are

omitted hereAcanthopterygii - acanthopterygians

Atherinimorpha - includes flyingfishes,topminnows

Percomorpha - includes seahorses, sculpins,sunfishes, tunas, flounders, manyothers

Osteichthyes - osteichthyansSarcopterygii - sarcopterygians

Latimeria chalumnae - coelacanthChoanata - choanates

Dipnoi -lungfishesTetrapoda - (Lab 6)

Actinopterygii - actinopterygiansPolypterus - bichirs and reedfishActinopteri

Chondrostei - sturgeons and paddlefishesNeopterygii - neopterygiians

Lepisosteidae - garsHalecostomi - halecostomians

Amia calva - bowfinTeleostei - teleosts

Osteoglossomorpha - includes bonytongues, arowanas,knifefishes, elephantfishes

Elopocephala - elopocephalansElopomorpha - includes tarpons, bonefishes, true eelsClupeocephala - clupeocephalans

Clupeomorpha - includes herrings, anchovies, shadsEuteleostei - euteleosts

Esociformes - pikes and mudminnowsOstariophysi - includes minnows, suckers, catfishes,

characins

Unique pharyngealtoothplate fusion

Osteological andmyological features

Teethontongue andparasphenold

Neural arches elongated posteriorlyHomocercal tail (by external appearance)

Premaxilla mobile

Maxillary bone mobile

Cycloid scales

Elongatedjaws

ACTINOPTERYGII

ACTINOPTERI

NEOPTERYGII

HALECOSTOMI

TELEOSTEI

Abbreviated heterocercal tail

Upper pharyngeal teeth consolidated intotooth bearing plates

Teeth inadul Is absent

Rve rows ofbony scu tes

Endochondralboneabsent

Gas bladder derived from lung

Dorsal finletswith spines

Scales composed of ganoineSingle dorsal fin

Elongatedrostrum

Fi~ure 5.2. A c1adogram showing the hypothesized phylogenetic relationships among extantactmopterygians. Modified from Lauder and Liem (1983), Gardiner and Schaeffer (1989), Nelson (1994)and Pough et ai. (1999).

<llCHONDROSTEI J::e- - ELOPOCEPHALA-

(I) & 0<ll E <ll ~

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gnathostome vertebrates (e.g" ostracoderms) had dermal bones covering theirbodies. Dermal bones are usually simple and plate-like and capable of free growthat every surface until adult size is reached. Additionally, dermal bone usually lackscartilage completely. Dermal bone is found over most of the body in mostosteichthyan fishes (e.g., large plates anteriorly, bony scales over the trunk) and isthe dominant bone type of the osteichthyan skull. Endochondral bone, whichincludes the replacement of an embryonic cartilage by an adult bony structure, is asynapomorphy for Osteichthyes. A great portion of the bone is laid down externalto the embryonic cartilage. In general, cartilage grows at either end of the bone andossification (bone formation) begins centrally and spreads, until adulthood, whenossification is completed. At this point, growth of bone ceases. Most of the bones ofthe original endoskeleton are endochondral (e.g., bones derived from the visceralskeleton, most bones of the pectoral girdle and forelimbs, the pelvic girdle andhindlimbs, vertebrae). Many endochondral bones have complicated articulationswith their neighbors, as well as important attachment sites for muscles.

Lungs are one type of respiratory organ through which gas exchangeoccurs in non-aquatic environments. Lungs first appear, during embryogenesis,in the form of a ventral outpocketing of the floor of the throat. Inactinopterygians (ray-finned fishes) and dipnoans (lungfishes), the lungs havea relatively simple morphology with little or no folding. In mostactinopterygians, the lungs have been modified into a single gas bladder (Fig.5.2) which primarily functions in buoyancy control and not for respiration.

The median and paired fins of most osteichthyans contain soft rays thatstiffen the fins. These rays are, in fact, rows of fin scales that have undergonemodification and are called lepidotrichia. True fin spines, such as thosecommonly found in acanthopterygians, were derived from soft rays. Theyoccur in the dorsal, anal, and pelvic fins. .

The bony, dermal scales of extinct jawless fishes were covered with smalldenticles composed of enamel and dentine. Among extant osteichthyans, thescales are adenticulate, meaning the small denticles have been lost. Scales alsotend to have less mass and have become more flexible in various clades ofosteichthyans. Dermal scales are absent in some actinopterygians (e.g.,catfishes), embedded in the skin (e.g., true eels, several dipnoans), or modifiedto form bony plates or scutes (e.g., sturgeons and armored catfishes). Recall thatthe scales of chondrichthyans are dermal denticles (placoid scales) and that theunderlying bony layers have been lost.

The opercula are located between the head and shoulder on either side ofthe body behind the cheek region and consist of four pairs of platelike dermalbones. The main element is the opercular bone, and the other smaller elementsinclude the interoperculum, preoperculum and suboperculum. The opercularapparatus serves as a shield for the gills and as part of the branchial pumpwhich functions in respiration and feeding.

106 LABS FOR VERTEBRATE ZOOLOGY Lab 5: OSTEICHTHYES 107

109

Ql For which taxon is the presence of lungs a synapamarphy?

Lab 5: OSTEICHTHYES

ACTINOPTERYGII

OSTEICHTHYAN DIVERSITY

Palypterus (bichirs and reedfish) is the basal lineage among extantActinopterygii and is the closest extant relative (CER) to Actinopteri (Figs. 5.2and 5.4). There are 10 species of bichirs and one species of reedfish, and alloccur in freshwater bodies in Africa. Examine the specimens of Palypterusavailable to you. Note that their bodies are covered'1With thick, interlocking,multi-layered ganoid scales. Canoid scales are unique to actinopterygians. Alsoobserve the dorsal fin with multiple finlets. Each of the 5-18 finlets has asingle spine to which is attached one or more soft rays (Fig. 5.4). Fishes withinPalypterus have paired ventral lungs which are used in respiration.

Polypterus

Actinopterygii refers to the ray-finned fishes because their fins aresupported entirely by dermal fin rays composed of lepidotrichia. Amongseveral synapomorphies which support the monophyly of this group, twoinclude scales composed of ganoine and a single dorsal fin (Fig. 5.1) Thescales of actinopterygians, like other osteichthyans, are composed of severalbony layers, one of which is comprised of the unique bony material calledganoine. Basal actinopterygians, including Polypterus, Chondrostei, andLepisosteidae, retain the ganoid-type scale. Other actinoptygians possess aderived scale type (cycloid scale) which lacks ganoine (Fig. 5.2). Several extantactinopterygians have two dorsal fins, but this character state is derived withrespect to the basal or earliest diverging actinopterygians which possessed onlyone dorsal fin.

An enormous amount of diversity exists among the extant species ofactinopterygians. In this lab you will inspect some of this amazing andimportant diversity.

LABS FOR VERTEBRATE ZOOLOGY

Increased contact of1 stvertebra with skull bones

NEOGNATHI

ACANTHOPTERYGII

Pelvic and pectoralgirdles joined

Pelvic fins with 1 spineand 5 soft rays

Increased jaw mobility

EUTELEOSTEI

CLUPEOCEPHALA

Nuptial tubercles on head and body

108

In Lab 5, you will investigate non-tetrapod osteichthyans, ir:clud~ngActinopterygii (ray-finned fishes), Latimeria (coelacanth), and DlpnOl

(lungfishes) .

Unique pharyngealtoothplate fusion

Figure 5.3. Phylogenetic relationships of the Clupeocaphala. Modifid (and simplifid) from Lauder and

Liem (1983), Nelson (1994), and Pough et ai. (1996).

Figure 5.4. Actinopterygii: The biehir (Polypterus). Note the multiple dorsal finlets.

ACTINOPTERI

Actinopteri includes all actinopterygian fishes except Polypterus (Fig. 5.2).The lungs have been modified into a single, dorsal gas bladder which primarilyfunctions in hydrostatic or buoyancy control. The respiratory function of the gasbladder is retained in lepisosteids (gars) and fishes of Amia calva (bowfin) andin several other fishes. Several more distantly related actinopterygians also usethe gas bladder for sound production (e.g., catfishes) as well as sound reception(e.g., dupeomorphs and ostariophysines).

CHONDROSTEI

Chondrostei is nested within Actinopteri and is the CER to Neopterygii(Fig. 5.2). Two distinctive clades within Chondrostei are.A~ipe~~~e(p j

if \ (stllrgeofls)alld,rolyodon (paddlefishes) (Fig. 5.5). If available, examine the\$) '~Xtel"narchal"actJrs of preserved specimens. Chondrosteans have ganoid scales

on the upper portion of the caudal fin. Pre-actinopterygian characters include aheterocercal tail and open spirade (except some species sturgeons).

The endoskeleton of chondrosteans lacks endochondral bone and much ofthe dermal bones found in other basal actinopterygians. Additionally, thenotochord persists in adults and vertebral centra are absent.

Q2 What skeletal structure usually replaces the notochord during the ontogeny ofmost a gnathostomes?

B

Figure 5.5. Chondrostei: (A) Sturgeon (Acipenseridae). (8) American paddlefish (Po/yadon).

. If sturgeons ~re a.vailable, observe the five rows of bony scutes, ventrallyOriented protruSlble Jaws, lack of teeth in adults, and four barbels in front ofthe mouth. Protrusible jaws have evolved independently in otheractinopterygians (Pough et al., 1999).

Q3 Considering the nature of the jaws, ventral positi0lj- of the mouth, lack of teeth,and possessIOn of barbels, where and how do you think these fish feed?

There are two species of paddlefish (Fig. 5.5). One is found in the UnitedStates and is a plankton feeder with a non-prostrusible mouth. The Chinesepaddlefish is piscivorous (fish eater) and possesses a protrusible mouth.

I~ available, examine a specimen of the American paddlefish. Closelyexamme the rostrum. This structure is richly innervated with ampuUaryorgans.

110 LABS FOR VERTEBRATE ZOOLOGY Lab 5: OSTEICHTHYES111

NEOPTERYCII

113

Halecostomi includes the monotypic Amia calva (bowin) + Teleostei (Fig.5.2). Halecostomian fishes are diagnosed by several synapomorphies of thecheek, jaw articulation, and opercular bones including a mobile maxilla.Feeding becomes much more specialized with the advent of moveable jawelements, such as the mobile maxilla. Identify the maxilla on the halecostomidskeleton (e.g., yellow perch) available to you. Also, members of Halecostomipossess cycloid scales which are thin, pliable scales formed of a thin sheet ofbone-like material and an underlying fibrous layer. The upper bony layer isusually characterized by concentric ridges that represent growth incrementsduring the life ofthe fish. "

HALECOSTOMI

Q7 Examine the caudal fin. Observe and describe its neopterygian characteristics,and include a sketch below.

Figure 5.6. Lepisosteidae: Gar (Lepisosteus).

Q8 What specific taxon are the gars members ofexclusive ofall other neopterygians?

Lab 5: OSTEICHTHYES

.~~~~31Obtain a preserved specimen of Amia calva (bowfin) (Fig. 5.7). The single

species of bowfin is restricted to freshwater bodies in eastern North Americaand exists in sympatry with gars.

LABS FOR VERTEBRATE ZOOLOGY

Q4 What functions might the rostrum serve?

Lepisosteidae (gars) is a member of Neopterygii and the CER to Teleostei(Figs. 5.2 and 5.6). There are seven extant species of gars and all are restricted tothe New World (North and Central America). This group is easily identified bythe elongated jaws, which are formed, in part, by the toothed infraorbitalbones (Pough et a/., 1999). Gars range from 1 to 4 meters in total length, andtheir multi-layered and interlocking ganoid scales are very similar to theancestral actinopterygian scale type. The overall morphology of gars isspecialized for ambush and swift predation on other fishes.

Neopterygii is the CER to Chondrostei and includes all extantactinopterygian fishes except the chondrosteans and Polypterus (Fig. 5.2). Oneof the more apparent synapomorphies for Neopterygii is that the upper lobe ofthe caudal fin contains an axial skeleton that is reduced in size to produce anearly symmetrical caudal fin. This type of caudal fin is often termed anabbreviated heterocercal tail, and it persists in lepisosteids (gars) and in Amiacalva (bowfin).

112

Q5 How might these gill rakers function in filter feeding?

Lift an operculum and observe the hair-like gill rakers.

JQ6 Carefully observe a preserved gar. From your observations, list at least three (3)· features that would appear to serve as adaptations for an ambush-predator lifestyle.

115Lab 5: OSTEICHTHYES

Osteoglossomorphs possess well-developed teeth on the parasphenoidand tongue bones such that they form a shearing bite. The parasphenoid is oneof the bones comprising the roof of the mouth.

TELEOSTEI

Osteoglossomorpha (arawanas, freshwater butterfly fish, knifefishes, andelephantfishes) is a member of Teleostei and the CER to Elopocephala (Fig.5.2). There are about 217 species in this clade, and they occupy freshwaterhabitats in North America (e.g., Hiodon), South America (e.g., Osteoglossum andArapaima), Africa (e.g., Mormyrus), as well as Australia and Asia.

Q13 How can you explain the disjunct geographical distribution of these taxa? Sincethey all share a common ancestor, how could their present-day distribution havebeen achieved? Is there more than one possible explanation?

Osteoglossomorpha

Teleostei is an extremely diverse group of fishes, with over 23,000 extantspecies. The CER is Amia calva. Teleosts live in an array of habitats, from vastocean depths to high, alpine waters and hot desert springs. Morphologicaldiversity is incredible from any perspective (Paxton and Eschmeyer, 1994).

Teleostei is diagnosed by the presence of a homocercal tail and mobilepremaxillae, among other synapomorphies. The homocercal tail is superficiallysymmetric, but internally the vertebral column, which terminates at the base ofthe fin, tilts upward at its tip where modified posterior neural arches provideadditional support to the dorsal side of the tail. The homocercal tail allows ateleost to swim horizontally without using its paired fins as control surfaces forproducing lift. Pectoral and pelvic fins of teleosts tend to be more flexible,mobile, and diverse in shape, size, and position.

The mobile premaxilla and maxilla allow greater feeding efficiency andspecialization, such as in the process of jaw protrusion and suction feeding(Pough et aI., 1999).

LABS FOR VERTEBRATE ZOOLOGY

Find the lateral line and bony operculum on Amia calva.

Q12 What function do you think the bony operculum serves? Do you think it mighthave more than one function? Why?

114

Qll What is the function of the lateral line system?

Ql0 For which taxa are these two character states synapomorphies?

Q9 Observe the caudal fin on a specimen of Amia calva. How is it similar to thecaudal fin of lepisosteid fishes?

Figure 5.7. Halecostomi: Bowfin (Amia calva).

Q14 How might a shearing bite be advantageous in feeding?

ELOPOCEPHALA

Synapomorphies supporting the monophyletic status of Elopocephala aremostly complex skeletal and muscular (myological) characters (Fig. 5.2). Youmay not be held responsible for these characters in this lab. The two majorcrown clades nested within Elopocephala are Elopomorpha andClupeocephala.

~ Elopomorpha

Elopomorpha includes the tarpons, ladyfish, bonefish, and true eels, and isthe CER to Clupeocephala (Fig. 5.2). Most elopomorphs are marine and eel­like, but some live in freshwater. All elopomorphs have a specialized larvacalled the leptocephalus larva, which typically lives near the open oceansurface for a long period of time (Pough et aI., 1999). This life-history strategymay permit wide and long-distance dispersal, even though the adults may berestricted to shallow inshore habitat\" I

1 HvObserve any true eels (anguilliforms) that may be available.

,.-~=~=~-=~

Q15 How are the dorsal and anal fins different from those of the other fishes you haveobserved? If not visible, what may have been their fates?

Q16 Judging from the shape and morphology of the eel you are observing, describethe type ofhabitat it occupies.

Pelvic girdles and fins are always absent in anguilliforms, and the pectoralfins are often reduced in size or absent.

Q17 What sorts ofenvironmental factors may have selected for the reduction or lossof these fins?

Superficially, eels look like lampreys.

Q18 What visible differences can you detect?

CLUPEOCEPHALA

Clupeocephala is nested within Elopocephala and is the CER toElopomorpha (Fig. 5.2 and 5.3). Clupeocephala is comprised of Clupeomorpha+ Euteleostei. One synapomorphy of Clupeocephala is unique pharyngealtoothplate fusion.

Clupeomorpha

, lifoClupeomorpha includes sardines, anchovies, smelts, herrings, and shads,

and is the CER to Euteleostei (Fig. 5.3). Most species are specialized for feedingon minute plankton with a specialized mouth and gill straining apparatus.They are often found swimming in extremely large schools.

Q19 What may be possible advantages to swimming in large schools?

116 LABS FOR VERTEBRATE ZOOLOGY Lab 5: OSTEICHTHYES 117

119

The crown group consisting of Ostariophysi + Neognathi does not have aformal taxonomic name (Fig. 5.3). Presence of an adipose fin is asynapomorphy for these two taxa. The adipose fin lies on the mid-dorsal lineposterior to the dorsal fin, and it is a small, fleshy rayless structure. (Fig. 5.8).The adipose fin is not present in many of the euteleost fishes (e.g.,acanthopterygians).

Ostariophysi

OSTARIOPHYSI + NEOGNATHI

Ostariophysi includes the predominant freshwater fishes (~65 % of allfreshwater species), inclu.ding characins, carps, minnows, suckers and catfishe~. IYThere are over 6,500 speCIes m thIS clade. Ostariophysines possess asynapomorphy called the Weberian apparatus (Pough et aI., 1999) (Fig. 5.9).This structure is composed of small bones (ossicles) that connect the gasbladder with the inner ear; thus hearing sensitivity is greatly enhanced. TheWeberian apparatus uses the gas bladder as a sound receptor (similar toclupeomorphs) and the chain of bones as conductors.

Q23 What features of the gas bladder are conducive to its function in soundreception?

Figure 5.8. A synapomorphy for the crown group Ostariophysi + Neognathi (Fig. 5.3) is the adipose fin asdepicted on a salmonid species.

Lab 5: OSTEICHTHYESLABS FOR VERTEBRATE ZOOLOGY

Esociformes include the pikes, muskellunge, and mudminnows and is theCER to Ostariophysi + Neognathi. The pikes, of which there are 10 extantspecies, are freshwater fishes with a circumpolar distribution in the Northernhemisphere.

Q22 How is the overall bodyform of pikes similar to gars? What might this indicateabout their lifestyle and feeding habits?

Euteleostei comprises the vast majority of living teleosts. Most euteleostmales develop nuptial tubercles which are composed of epidermal cells andare either keratinized or non-keratinized. These structures may be present onthe head, body, and fins, and provide friction that helps to keep males andfemales in contact during mating. Many lineages comprise this taxon, amongwhich phylogenetic relationships remain uncertain (Nelson, 1994). Only a fewwill be considered here.

EUTELEOSTEI

Esociformes) (p-

118

The gas bladder of clupeomorphs has a pair of anterior extensions whichenter the skull and connect to the inner ear. This synapomorphy allows thegas bladder to serve as a sound receptor which delivers sound signals to theinner ear for increased auditory reception.

Q21 What other basal actinopterygian is afilter-feeding planktivore?

Q20 Lift up the operculum ofa preserved shad or other planktivorous clupeomorph.Observe the relatively long and slender gill rakers. How do you think thesefunction in filter feeding on plankton?

121

Q28 Under what types of conditions might a semelparous life history strategy bemore advantageous to an iterparous strategy?

Many salmon reproduce only once, then die shortly after mating. Animalswhich show this life-history strategy are called semelparous. Organisms thathave the potential to reproduce more than once in a lifetime are iteroparous.

Lab 5: OSTEICHTHYES

Q27 Which basal, vertebrate taxon also has anadromous species?

NEOGNATHI

Salmonidae

Salmonidae includes the familiar salmon, trout, and chars. All salmonidsretain the adipose fin discussed earlier, and many are anadromous. This meansthat adults spawn in freshwater, the juveniles return to the ocean to mature,and then return to freshwater to complete their life cycle.

Q26 Do the catfish have an adipose fin? For which taxon is the adipose fin asynapomorphy?

Neognathi is the CER to Ostariophysi (Fig. 5.3). The basal lineage withinNeognathi is Salmonidae. A synapomorphy for Neognathi is increased contactof the first vertebra with the skull bones. There are several neognathan taxathat will not be considered in this lab due their relatively obscure nature (e.g.,Stomiiformes, Ateleopodiformes, Cyclosquamata, Scopelomorpha,Lampridiomorpha, Polymixiomorpha, and Paracanthopterygii), although thereare some very interesting species in these groups (Nelson, 1994). Salmonidae,Atherinomorpha, and Percomorpha will be introduced.

Intercalcarium

LABS FOR VERTEBRATE ZOOLOGY

TripusScaphum

Claustrum

120

Membranouslabyrinth

Posterior margin of skull

Q25 Examine the barbels surrounding the mouth ofa catfish. What might bepossible functions for these structures? How could you test your hypotheses?

B

Q24 What might have been some of the selective agents for the evolution of theWeberian apparatus?

Figure 5.9. A synapomorphy for Ostariophysi (Fig. 5.3) is the Weberian apparatus, which is a sound­detection system (refer to Pough et aI., 1999, p. 239-241). (A) Lateral view. (8) Dorsal view.

A

ACANTHOPTERYGII

123

Look once again at some of the non-percomorph fishes. How is the position oftheir pelvic fins, relative to their pectoral fins, different from the percomorphsyou have observed?

Q31 Identify advantages to an upturned mouth. Where and how might fishes feedwith mouths such as this?

Percomorpha

'3~lerPercomorpha includes perches, sunfisht;§, mackerel, snappers, tuna,

marlin, barracuda, remoras, cichlids, flounders, and many others, and is theCER to Atherinomorpha (Fig. 5.3). Two synapomorphies include the joining ofthe pelvic girdle firmly to the pectoral girdle and pelvic fins with one spineand five soft rays (Fig. 5.14).

Observe the percomorphs available to you, and look for the two charactersdescribed above.

Q33 Provide explanation(s) for the forward migration of the pelvic fins. Do you thinkthis modification provides functional benefits? How?

Note that members of this clade do not possess an adipose fin. Note alsothe numerous spines on the dorsal fins of many of these fishes.

Q34 Provide possible functions for these dorsal fin spines.

Lab 5: OSTEICHTHYES

IQ32l

V

LABS FOR VERTEBRATE ZOOLOGY

Many atherinomorphs have protrusible, upturned mouths (e.g., topminnows, guppies, swordtails, and pupfishes) (Nelson, 1994). If available,observe these specimens.

122

Q30 Identify one or more possible selective pressures that may have caused theevolution ofgliding fins.

Atherinomorpha includes flying fishes, grunions, needlefishes,guppies,and swordtails, and is the CER to Percomorpha. The atherinomorphshave modified protrusible jaws (Pough et al., 1999).

If available, observe a preserved flying fish. These fishes do not actually flybut glide.

Q29 Which fins on the flying fish are enlarged for gliding?

Atherinomorpha

Acanthopterygii, which comprises the true spiny-rayed fishes, is nestedwithin Neognathi. To complete a survey of actinopterygian diversity in thislab, you will look at representatives of the two major crown clades withinAcanthopterygii: Atherinomorpha and Percomorpha. Synapomorphiessupporting the monophyly of Acanthopterygii concern details of themusculature and skeleton, including a more mobile jaw than other teleosts.This is due in large part to the presence of a well developed ascending processon the premaxilla which allows greater protrusibility (forward movement) ofthe jaws. Acanthopterygians generally possess ctenoid scales with minutespines on the exposed portions of the scales or in a comb-like row on theposterior margin.

.125

Choanata includes Dipnoi (lungfishes) and Tetrapoda (amphibians,reptilians, and mammals). Tetrapoda will be introduced in the next lab (Lab 6).Several synapomorphies diagnose Choanata (Fig. 5.1). Recall that bile, which isproduced by the liver, contains mostly excretory products, includingdecomposed proteins and pigments derived from hemoglobin of aged red~loodcells. Choanates also produce bile salts which are discharged into themtestme and aId a pancreatic enzyme in splitting and absorbing fats. In thechoanate heart a partition develops in the atrium such that the left chambercontains pulmonary blood which has been oxygenated (delivered by thepulmonary vein), and the right chamber receives veinous blood from the sinusvenosus. The atrial division is partial in lungfishes. Limited mixing ofoxygenated and deoxygenated blood occurs in the ventricle. But due to thespiral effect of heart contraction, oxygenated and deoxygenated blood largelyremams separated. Choanates also have nasolacrymal ducts' which extend fromthe nasal cavity to the orbit. These are the tear ducts and they maintain eyemoisture.

CHOANATA

Q37 Provide possible evolutionary explanations for the ossification of the lung in thecoelacanth.

Figure 5.10. Sarcopterygii: Coelacanth (Latirneria chalumnae), a lobed-finned fish.

Lab 5: OSTEICHTHYESLABS FOR VERTEBRATE ZOOLOGY

Latimeria chalumnae, commonly called the coelacanth, (Figs. 5.1 and 5.10)is the sole extant species of a once diverse lineage of coelacanth fishes, and it isthe CER to Choanata, which includes Dipnoi (lungfishes) and Tetrapoda(tetrapods). The coelocanth has only been found in the Indian Ocean near thecoast of Madagascar. One of several synapomorphies is the ossified lung thatno longer functions as a buoyancy or air breathing organ.

Latimeria chalumnae

SARCOPTERYGII

Q36 Consider, again, the shape of these fishes. In what type ofhabitats might youexpect to find them? Would you expect these fishes to have a gas bladder? Why?

.124

Sarcopterygii includes Latimeria chalumnae (coelacanth), Dipnoi(lungfishes), and Tetrapoda (tetrapods) (Fig. 5.1). Synapomorphies include apulmonary vein and paired, muscular lobed-fins extending below the body.The pulmonary vein passes from the lung directly to the atrial cavity of theheart (on the left side) and allows aerated blood to pass directly from the lungsto the heart. Aerated blood is then pumped into the ventricle and from there tovarious parts of the body. The muscular lobed fins of sarcopterygians aresometimes utilized for a walking type of locomotion, which would later beused by the ancestors of tetrapods to invade terrestrial habitats.

Q35 Are these fishes laterally or dorsa-ventrally compressed? How can you tell?

If available, inspect adult specimens of flounders or soles (Pleuronectiformes).These largely marine percomorphs are unusual in that the young initially arebilaterally symmetrical and swim upright, but then undergo metamorphosiswhere the body becomes highly compressed and one eye migrates to the otherside of the cranium. Following metamorphosis, they then lie and swim on theeyeless side.

127Lab 5: OSTEICHTHYES

Q40 The pectoral and pelvic fins (and their respective ;girdles) are synapomophies forwhich taxon?

General Internal Anatomy

DISSECTION OF ADULT PERCH

After obtaining a preserved specimen, identify the mouth, bonyoperculum, dorsal fines), homocercal caudal fin, anal fin, anus, pectoral fins,pelvic fins, soft and spiny rays, and lateral line system (Fig. 5.12).

Identify the oral cavity, teeth, pharynx, gill arches, gill slits, gill lamellae,gill rakers, esophagus, stomach, intestine, liver, heart, gas bladder (asynapomorphy for Actinopteri), myomeres, and kidneys (Fig. 5.13).

General External Anatomy

You probably will use a relatively common and readily accessiblepercomorph, such as the yellow perch (Percaflavescens), to exploreactinopterygian morphology (Figs. 5.12 - 5.15).

Q39 What is a homocercal tail?

The pectoral and pelvic fins of the South American and African lungfishesare tendril-like, which indicates that a common ancestor of these species lostthe muscular lobed fins. The Australian lungfish retains the fleshy, muscularfins of Sarcopterygii and uses these to slowly walk across the bottom of ponds.The caudal fin of dipnoans is diphycercal with the vertebral column extendingstraight back to the tip of the body and the fin developing symmetrically aboveand below it. Another synapomorphy is thin scales embedded in skin.

LABS FOR VERTEBRATE ZOOLOGY126

Figure 5.11. Choanata: Lungfishes (Dipnoi). (A) African lungfish (Protopterus sp.). (B) South Americanlungfish (Lepidosiren paradoxa). (C) Australian lungfish (Neoceratodus forsteri).

c .~

B

A

Q38 What geologic factors may account for the disjunct geographic distribution of

these lungfishes?

Dipnoi includes six species of extant lungfishes (Fig. 5.11), one inAustralia, one in South America, and four in Africa.

Dipnoi

Ceratotrichia

129

Neural spine

Pectoral fin

Lepidotrichia (hard spines)

/ Pterygiophore

. fi'l ments? The gill rakers?What is the function of the gill 1 a ,

, ,f the gas bladder?What is the functLOn 0;

I to in other osteichthyans,. bladder homo ogousWhat structure IS the gasincluding tetrapods?

~.

'. ~~.,::,\

--- _\~ ~ UrostyleL\- ~"~,' ,"'~I Dorsal ribs Anal finPelvic fin Ventral rib

1 erch (Perea flavescens).h . Skeletal system of the yel ow pFigure 5.14. Percomorp a.

Q41

Q42

Q43

Lab 5: OSTEICHTHYES

Ceratotrlchia

Head kidney

DuodenumPancreas

LABS FOR VERTEBRATE ZOOLOGY

. r dorsal finPQ\l.erI9~'_" ••"'~~_Ceratotrichia

Lateral~

Swim bladder

Eye

Bulbous~-"~:';iilIO'l!!:::'-_- arteriosus~lj~~~~~~I~··~"·~·"~:;'i/~··~,.;.~.~~~~~t:::;~:::-~:~:ventriCle Sinus venosus

intestineAnus Fat (covering

- Gonad stomach)

h (Perca flavescens).of the yellow percha' Internal anatomyFigure 5.13. Percomorp .

128

h (Perca flavescens).of the yellow perchao External anatomyFigure 5.12. Percomorp .

Subopercular

Supraocciptial

131

"-',,<-_-Hyomandibular

.:.:-;;.,.~,...:::.'""'__Opercular

Interopercular

1:Tth7-f?~~.--~',---- Preopercular

Frontal

Maxilla --4\-\--

Quadrate

Metapterygoid

Angular _-..:.:::::,~::;;;:=:~~

Premaxilla

Lab 5: OSTEICHTHYES

Figure 5.15. Head skeleton.

Note the extremely large number of bones in the skull (Fig. 5.15). This largenumber is an ancestral condition for vertebrates (as evidenced by extinctfishes). Most of these bones are dermal in embryonic origin, originating fromthe external dermal plates of extinct jawless vertebrates. The palatoquadratecartilage, which forms the upper jaw in elasmobranchs, has been supplantedfunctionally by two dermal bones anteriorly, the premaxilla and maxilla. Thesetwo bones progressively become more mobile in actinopterygians (Figs. 5.2-5.3)and consequently allow greater feeding specializations (Pough et aI., 1999).Posteriorly, the quadrate (Fig. 5.15) and metapterygoid represent the ossifiedremnants of the palatoquadrate. The quadrate serves in jaw articulation in allosteichthyans except in mammals. In a lineage ancestral to mammals, thequadrate evolved into a middle ear bone called the incus. The mandibularcartilage, which forms the lower jaw in elasmobranchs, has been replaced byseveral dermal bones including (among others) the dentary and the smallarticular bone on the posterio-dorsal part of the lower jaw which is the site ofarticulation with the quadrate. Remember the hyoid arch in elasmobranchs? Inosteichthyans, the hyomandibular bone represents the hyomandibularcartilage, and ventrally there are several hyoid bones. In tetrapods, thehyomandibular evolved into the stapes, a middle ear bone. If you have time,identify some of the other bones, just for your enjoyment and self-edification.

Dentary

LABS FOR VERTEBRATE ZOOLOGY

Kidneys?

Stomach?

Liver?

Respiratory gills?

130

Q45 What are lepidotrichia?

Locate the paired, segmented, and branched lepidotrichia in various fins

(Fig. 5.14).

Skeletal System

Q44 For which craniate taxa are the following character states synapomorphies:

QUESTIONS FOR DISCUSSION

133

WEB SITES

<http://www.yorkbiosis.orglzrdocs/zoolinfo/grp_fish.htm>.

Bond, C. E. 1996. Biology of Fishes, 2nd edn. Saunders College Publishing, New York, New York.Colbert, E. H., and M. Morales. 1991. Evolution of the Vertebrates. A History of the Backboned

Animals Through Time. 4th edn. Wiley-Liss, New York, New York.Diana, J. S. 1995. Biology and Ecology of Fishes. Biological Sciences Press, Traverse City, Michigan.Gardiner, B. G., and B. Schaeffer. 1989. Interrelationships of lower actinopterygian fishes.

Zoological Journal of the Linnean Society 97: 135-187.Lauder, G. V, and K. F. Liem. 1983. Patterns of diversity and evolution in ray-finned fishes. In:

Fish Neurobiology, Volume 1, Brain Stem and Sense Organs (Ed. by R G. Northcutt and R. E.Davis), pp. 1-24. The University of Michigan Press, Ann Arbor, Michigan.

Maisey, J. G. 1986. Heads and tails: A chordate phylogeny. Cladistics 3: 201-256.Maisey, J. G. 1996. Discovering Fossil Fishes. Henry Holt and Company, New York, New York.Nelson, J. S. 1994. Fishes of the World. 3rd edn. Wiley and Sons,1New York, New York.Paxton, J. R, and W. N. Eschmeyer (Editors). 1994. Encyclopedia of Fishes. Academic Press, New

York, New YorkPough, F. H., C. M. Janis, and J. B. Heiser. 1999. Vertebrate Life. 5th edn. Prentice-Hall, Upper

Saddle River, New Jersey.Romer, A. S. 1962. The Vertebrate Body, 3rd edn. Saunders College Publishing, New York, New

York.

This Web site (FISH) is supported by BIOSIS, the publisher of BiologicalAbstracts and Zoological Records, and is one of their Internet resource guides inzoology. There are dozens of other links, far too many to list individually(check it out, you'll see!), but some include indexes, resource guides,conservation, newsgroups, fisheries, ichthyology servers, images, museums,organizations, and publications.

REFERENCES

There is a tremendous amount of current information on the biology ofosteichthyans on the Internet. The Web site provided below is especially useful.Also, be certain to inspect the Tree of Life and others from Lab 1.

Lab 5: OSTEICHTHYESLABS FOR VERTEBRATE ZOOLOGY132

Most of the pectoral girdle and all of the pelvic girdle is comprised ofendochondral bone. The dermal elements of the pectoral girdle include theclavicle, cleithrum, and supradeithrum. The supracleithrum attaches thepectoral girdle firmly to the posterior region of the skull. The endochondralbones include the coracoid and scapula.

1. When it comes to the sheer number of species and morphological diversity,extant actinopterygians (~ 24,000 species and counting!) have no equalamong the vertebrates. What might be the explanations for thisphenomenon? In class, derive several hypotheses that could be used toexplain or test your ideas.

2. From your reading assignment, what is the evolutionary utility of sex­reversal in certain teleosts? Why is this life-history trait more common inmarine (reef) species than in freshwater ones?

3. Bone (calcium phosphate) did not have its origin in osteichthyans. Whatreasons (e.g., selective advantages) can you provide to explain the absence(or nearly so) of bone in extant chondrichthyans and chondrosteans and itspresence in most osteichthyans? What is the functional significance ofendochondral ossification?

Q46 What are myomeres and myosepta? For which taxon are these structuressynapomorphies?

The vertebral column is not wen differentiated into distinctive regions,and only the trunk and caudal vertebrae are readily distinguishable. Recall thatthe vertebral column largely replaces the notochord as a central supportingaxis in gnathostomes. As in chondrichthyans (Lab 4), the dorsal arch of thecentrum is the neural arch, and it protects the spinal cord, which passesthrough the neural canal. Ribs attach to the vertebrae along the anteriorportion of the vertebral column and they lie within the myosepta betweenadjacent myomeres. By serving as connectors between the musculature and thevertebrae, ribs render the muscular effort more effective.