LAB 5
OSTEICHTHYES: ACTINOPTERYGII,
LATIMERIA, AND DIPNOI
MATERIALS
1. Numerous whole, preserved actinopterygians and lungfish.
2. Whole, preserved yellow perch (Percaflavescens; Percomorpha) for
dissection.
3. Mounted skeleton of perch; whole- and head skeletons of other taxa of
actinopterygians.
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 the
bony fishes . . . Osteichthyes."
- Edwin Colbert and Michael Morales, 1991
SUMMARY CLASSIFICATION
Osteichthyes is the most diverse group of vertebrates, relative to
Myxinoidea, Petromyzontoidea, and Chondrichthyes, with nearly 24,000
species of actinopterygian fishes alone! The following phylogenetic
classification reflects the groups covered in this lab. Numerous taxa, however,
have been omitted for time and space considerations (Pough" et aI., 1999).
103
GNATHOSTOMATA
Osteichthyes - osteichthyans
Sarcopterygii - sarcopterygians
Latimeria chalumnae - coelacanth
Choanata - choanates
Dipnoi -lungfishes
Tetrapoda - (Lab 6)
Actinopterygii - actinopterygians
Polypterus - bichirs and reedfish
Actinopteri
Chondrostei - sturgeons and paddlefishes
Neopterygii - neopterygiians
Lepisosteidae - gars
Halecostomi - halecostomians
Amia calva - bowfin
Teleostei - teleosts
Osteoglossomorpha - includes bonytongues, arowanas,
knifefishes, elephantfishes
Elopocephala - elopocephalans
Elopomorpha - includes tarpons, bonefishes, true eels
Clupeocephala - clupeocephalans
Clupeomorpha - includes herrings, anchovies, shads
Euteleostei - euteleosts
Esociformes - pikes and mudminnows
Ostariophysi - includes minnows, suckers, catfishes,
characins
Neognathi
Salmonidae - salmons, trout, chars
Neoteleostei - numerous clades, several of which are
omitted here
Acanthopterygii - acanthopterygians
Atherinimorpha - includes flyingfishes,
topminnows
Percomorpha - includes seahorses, sculpins,
sunfishes, tunas, flounders, many
others
INTRODUCTION
Osteichthyes includes Actinopterygii and Sarcopterygii (Latimeria +
Dipnoi + Tetrapoda) (Fig. 5.1). Do not be confused between the translation of
the name Osteichthyes and what the name represents in a phylogenetic sense.
Although Osteichthyes literally means "bony fishes," our phylogenetic taxonomy
104
LABS FOR VERTEBRATE ZOOLOGY
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OSTEICHTHYES - - - - - - . . ,
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Single dorsal fin
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Scales composed
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Paired fins with long muscular lobes
extending below body
Pulmonary vein
Endochondral bone
Bony operculum
Scales adenticulate
Lepidotrichia
-415myaSilurian
Lung derived from gut
Figure 5.1. A c1adogram showing the relationships among major clades of Osteichthyes. Additional
characters, mostly relating to osteology, are not shown (modified from Maisey, 1986).
includes only monophyletic groups. Therefore, Osteichthyes refers to the clade
that includes Actinopterygii (ray-finned fishes), Sarcopterygii (coelacanth,
lungfishes, and tetrapods), and their most recent common ancestor. Humans are
thus members of Osteichthyes. Osteichthyes is diagnosed by the possession of
endochondral bone, a lung derived from the gut, lepidotrichia, adenticulate
scales, and a bony operculum on each side of the pharyngeal region.
There are two radically different modes of bone formation in embryos and
young of vertebrates. The simpler of the two involves the formation of dermal
bone, which is formed in the dermal layer of the skin. Craniates and preLab 5: OSTEICHTHYES
105
gnathostome vertebrates (e.g" ostracoderms) had dermal bones covering their
bodies. Dermal bones are usually simple and plate-like and capable of free growth
at every surface until adult size is reached. Additionally, dermal bone usually lacks
cartilage completely. Dermal bone is found over most of the body in most
osteichthyan fishes (e.g., large plates anteriorly, bony scales over the trunk) and is
the dominant bone type of the osteichthyan skull. Endochondral bone, which
includes the replacement of an embryonic cartilage by an adult bony structure, is a
synapomorphy for Osteichthyes. A great portion of the bone is laid down external
to the embryonic cartilage. In general, cartilage grows at either end of the bone and
ossification (bone formation) begins centrally and spreads, until adulthood, when
ossification is completed. At this point, growth of bone ceases. Most of the bones of
the original endoskeleton are endochondral (e.g., bones derived from the visceral
skeleton, most bones of the pectoral girdle and forelimbs, the pelvic girdle and
hindlimbs, vertebrae). Many endochondral bones have complicated articulations
with their neighbors, as well as important attachment sites for muscles.
Lungs are one type of respiratory organ through which gas exchange
occurs in non-aquatic environments. Lungs first appear, during embryogenesis,
in the form of a ventral outpocketing of the floor of the throat. In
actinopterygians (ray-finned fishes) and dipnoans (lungfishes), the lungs have
a relatively simple morphology with little or no folding. In most
actinopterygians, 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 that
stiffen the fins. These rays are, in fact, rows of fin scales that have undergone
modification and are called lepidotrichia. True fin spines, such as those
commonly found in acanthopterygians, were derived from soft rays. They
occur in the dorsal, anal, and pelvic fins.
.
The bony, dermal scales of extinct jawless fishes were covered with small
denticles composed of enamel and dentine. Among extant osteichthyans, the
scales are adenticulate, meaning the small denticles have been lost. Scales also
tend to have less mass and have become more flexible in various clades of
osteichthyans. Dermal scales are absent in some actinopterygians (e.g.,
catfishes), embedded in the skin (e.g., true eels, several dipnoans), or modified
to form bony plates or scutes (e.g., sturgeons and armored catfishes). Recall that
the scales of chondrichthyans are dermal denticles (placoid scales) and that the
underlying bony layers have been lost.
The opercula are located between the head and shoulder on either side of
the body behind the cheek region and consist of four pairs of platelike dermal
bones. The main element is the opercular bone, and the other smaller elements
include the interoperculum, preoperculum and suboperculum. The opercular
apparatus serves as a shield for the gills and as part of the branchial pump
which functions in respiration and feeding.
106
LABS FOR VERTEBRATE ZOOLOGY
ACTINOPTERYGII
ACTINOPTERI
NEOPTERYGII
HALECOSTOMI
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Neural arches elongated posteriorly
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Premaxilla mobile
Maxillary bone mobile
Cycloid scales
Abbreviated heterocercal tail
Upper pharyngeal teeth consolidated into
tooth bearing plates
Gas bladder derived from lung
Scales composed of ganoine
Single dorsal fin
Fi~ure 5.2. A c1adogram showing the hypothesized phylogenetic relationships among extant
actmopterygians. Modified from Lauder and Liem (1983), Gardiner and Schaeffer (1989), Nelson (1994)
and Pough et ai. (1999).
Lab 5: OSTEICHTHYES
107
OSTEICHTHYAN DIVERSITY
CLUPEOCEPHALA
ACTINOPTERYGII
EUTELEOSTEI
NEOGNATHI
ACANTHOPTERYGII
Pelvic and pectoral
girdles joined
Pelvic fins with 1 spine
and 5 soft rays
Increased jaw mobility
Actinopterygii refers to the ray-finned fishes because their fins are
supported entirely by dermal fin rays composed of lepidotrichia. Among
several synapomorphies which support the monophyly of this group, two
include scales composed of ganoine and a single dorsal fin (Fig. 5.1) The
scales of actinopterygians, like other osteichthyans, are composed of several
bony layers, one of which is comprised of the unique bony material called
ganoine. Basal actinopterygians, including Polypterus, Chondrostei, and
Lepisosteidae, retain the ganoid-type scale. Other actinoptygians possess a
derived scale type (cycloid scale) which lacks ganoine (Fig. 5.2). Several extant
actinopterygians have two dorsal fins, but this character state is derived with
respect to the basal or earliest diverging actinopterygians which possessed only
one dorsal fin.
An enormous amount of diversity exists among the extant species of
actinopterygians. In this lab you will inspect some of this amazing and
important diversity.
Polypterus
Increased contact of1 st
vertebra with skull bones
Nuptial tubercles on head and body
Unique pharyngeal
toothplate fusion
Figure 5.3. Phylogenetic relationships of the Clupeocaphala. Modifid (and simplifid) from Lauder and
Liem (1983), Nelson (1994), and Pough et ai. (1996).
Palypterus (bichirs and reedfish) is the basal lineage among extant
Actinopterygii and is the closest extant relative (CER) to Actinopteri (Figs. 5.2
and 5.4). There are 10 species of bichirs and one species of reedfish, and all
occur in freshwater bodies in Africa. Examine the specimens of Palypterus
available to you. Note that their bodies are covered'1With thick, interlocking,
multi-layered ganoid scales. Canoid scales are unique to actinopterygians. Also
observe the dorsal fin with multiple finlets. Each of the 5-18 finlets has a
single spine to which is attached one or more soft rays (Fig. 5.4). Fishes within
Palypterus have paired ventral lungs which are used in respiration.
Ql
For which taxon is the presence of lungs a synapamarphy?
In Lab 5, you will investigate non-tetrapod osteichthyans, ir:clud~ng
Actinopterygii (ray-finned fishes), Latimeria (coelacanth), and DlpnOl
(lungfishes) .
108
LABS FOR VERTEBRATE ZOOLOGY
Lab 5: OSTEICHTHYES
109
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 primarily
functions in hydrostatic or buoyancy control. The respiratory function of the gas
bladder is retained in lepisosteids (gars) and fishes of Amia calva (bowfin) and
in several other fishes. Several more distantly related actinopterygians also use
the 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
if \ (stllrgeo s)a d,rolyodon (paddlefishes) (Fig. 5.5). If available, examine the
fl ll
\$) '~Xtel"narchal"actJrs of preserved specimens. Chondrosteans have ganoid scales
on the upper portion of the caudal fin. Pre-actinopterygian characters include a
heterocercal tail and open spirade (except some species sturgeons).
The endoskeleton of chondrosteans lacks endochondral bone and much of
the dermal bones found in other basal actinopterygians. Additionally, the
notochord persists in adults and vertebral centra are absent.
j
Q2
110
What skeletal structure usually replaces the notochord during the ontogeny of
most a gnathostomes?
LABS FOR VERTEBRATE ZOOLOGY
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, ventrally
Oriented protruSlble Jaws, lack of teeth in adults, and four barbels in front of
the mouth. Protrusible jaws have evolved independently in other
actinopterygians (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 United
States and is a plankton feeder with a non-prostrusible mouth. The Chinese
paddlefish is piscivorous (fish eater) and possesses a protrusible mouth.
I~ available, examine a specimen of the American paddlefish. Closely
examme the rostrum. This structure is richly innervated with ampuUary
organs.
Lab 5: OSTEICHTHYES
111
Q4
What functions might the rostrum serve?
Lift an operculum and observe the hair-like gill rakers.
Q5
How might these gill rakers function in filter feeding?
Figure 5.6. Lepisosteidae: Gar (Lepisosteus).
Q7
Examine the caudal fin. Observe and describe its neopterygian characteristics,
and include a sketch below.
NEOPTERYCII
Neopterygii is the CER to Chondrostei and includes all extant
actinopterygian fishes except the chondrosteans and Polypterus (Fig. 5.2). One
of the more apparent synapomorphies for Neopterygii is that the upper lobe of
the caudal fin contains an axial skeleton that is reduced in size to produce a
nearly symmetrical caudal fin. This type of caudal fin is often termed an
abbreviated heterocercal tail, and it persists in lepisosteids (gars) and in Amia
calva (bowfin).
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 to
the New World (North and Central America). This group is easily identified by
the elongated jaws, which are formed, in part, by the toothed infraorbital
bones (Pough et a/., 1999). Gars range from 1 to 4 meters in total length, and
their multi-layered and interlocking ganoid scales are very similar to the
ancestral actinopterygian scale type. The overall morphology of gars is
specialized for ambush and swift predation on other fishes.
J
Q6
·
112
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.
LABS FOR VERTEBRATE ZOOLOGY
HALECOSTOMI
Halecostomi includes the monotypic Amia calva (bowin) + Teleostei (Fig.
5.2). Halecostomian fishes are diagnosed by several synapomorphies of the
cheek, jaw articulation, and opercular bones including a mobile maxilla.
Feeding becomes much more specialized with the advent of moveable jaw
elements, such as the mobile maxilla. Identify the maxilla on the halecostomid
skeleton (e.g., yellow perch) available to you. Also, members of Halecostomi
possess cycloid scales which are thin, pliable scales formed of a thin sheet of
bone-like material and an underlying fibrous layer. The upper bony layer is
usually characterized by concentric ridges that represent growth increments
during the life ofthe fish.
"
.~~~~31
Obtain a preserved specimen of Amia calva (bowfin) (Fig. 5.7). The single
species of bowfin is restricted to freshwater bodies in eastern North America
and exists in sympatry with gars.
Q8
What specific taxon are the gars members of exclusive of all other neopterygians?
Lab 5: OSTEICHTHYES
113
TELEOSTEI
Figure 5.7. Halecostomi: Bowfin (Amia calva).
Observe the caudal fin on a specimen of Amia calva. How is it similar to the
caudal fin of lepisosteid fishes?
Q9
Teleostei is an extremely diverse group of fishes, with over 23,000 extant
species. The CER is Amia calva. Teleosts live in an array of habitats, from vast
ocean depths to high, alpine waters and hot desert springs. Morphological
diversity is incredible from any perspective (Paxton and Eschmeyer, 1994).
Teleostei is diagnosed by the presence of a homocercal tail and mobile
premaxillae, among other synapomorphies. The homocercal tail is superficially
symmetric, but internally the vertebral column, which terminates at the base of
the fin, tilts upward at its tip where modified posterior neural arches provide
additional support to the dorsal side of the tail. The homocercal tail allows a
teleost to swim horizontally without using its paired fins as control surfaces for
producing 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 and
specialization, such as in the process of jaw protrusion and suction feeding
(Pough et aI., 1999).
Osteoglossomorpha
Find the lateral line and bony operculum on Amia calva.
Ql0
For which taxa are these two character states synapomorphies?
Osteoglossomorpha (arawanas, freshwater butterfly fish, knifefishes, and
elephantfishes) is a member of Teleostei and the CER to Elopocephala (Fig.
5.2). There are about 217 species in this clade, and they occupy freshwater
habitats in North America (e.g., Hiodon), South America (e.g., Osteoglossum and
Arapaima), Africa (e.g., Mormyrus), as well as Australia and Asia.
Q13
Qll
What is the function of the lateral line system?
Q12
What function do you think the bony operculum serves? Do you think it might
have more than one function? Why?
114
LABS FOR VERTEBRATE ZOOLOGY
How can you explain the disjunct geographical distribution of these taxa? Since
they all share a common ancestor, how could their present-day distribution have
been achieved? Is there more than one possible explanation?
Osteoglossomorphs possess well-developed teeth on the parasphenoid
and tongue bones such that they form a shearing bite. The parasphenoid is one
of the bones comprising the roof of the mouth.
Lab 5: OSTEICHTHYES
115
Q14
How might a shearing bite be advantageous in feeding?
Pelvic girdles and fins are always absent in anguilliforms, and the pectoral
fins are often reduced in size or absent.
Q17
What sorts of environmental factors may have selected for the reduction or loss
of these fins?
ELOPOCEPHALA
Synapomorphies supporting the monophyletic status of Elopocephala are
mostly complex skeletal and muscular (myological) characters (Fig. 5.2). You
may not be held responsible for these characters in this lab. The two major
crown clades nested within Elopocephala are Elopomorpha and
Clupeocephala.
~
Superficially, eels look like lampreys.
Q18
What visible differences can you detect?
Elopomorpha
Elopomorpha includes the tarpons, ladyfish, bonefish, and true eels, and is
the CER to Clupeocephala (Fig. 5.2). Most elopomorphs are marine and eellike, but some live in freshwater. All elopomorphs have a specialized larva
called the leptocephalus larva, which typically lives near the open ocean
surface for a long period of time (Pough et aI., 1999). This life-history strategy
may permit wide and long-distance dispersal, even though the adults may be
restricted to shallow inshore habitat\" I
CLUPEOCEPHALA
Clupeocephala is nested within Elopocephala and is the CER to
Elopomorpha (Fig. 5.2 and 5.3). Clupeocephala is comprised of Clupeomorpha
+ Euteleostei. One synapomorphy of Clupeocephala is unique pharyngeal
toothplate fusion.
1 Hv
Observe any true eels (anguilliforms) that may be available.
,.-~=~=~-=~
Q15
Clupeomorpha
How are the dorsal and anal fins different from those of the other fishes you have
observed? If not visible, what may have been their fates?
Q16 Judging from the shape and morphology of the eel you are observing, describe
,
lifo
Clupeomorpha includes sardines, anchovies, smelts, herrings, and shads,
and is the CER to Euteleostei (Fig. 5.3). Most species are specialized for feeding
on 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?
the type of habitat it occupies.
116
LABS FOR VERTEBRATE ZOOLOGY
Lab 5: OSTEICHTHYES
117
Q20
Q21
Lift up the operculum of a preserved shad or other planktivorous clupeomorph.
Observe the relatively long and slender gill rakers. How do you think these
function in filter feeding on plankton?
What other basal actinopterygian is afilter-feeding planktivore?
OSTARIOPHYSI + NEOGNATHI
The crown group consisting of Ostariophysi + Neognathi does not have a
formal taxonomic name (Fig. 5.3). Presence of an adipose fin is a
synapomorphy for these two taxa. The adipose fin lies on the mid-dorsal line
posterior 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
The gas bladder of clupeomorphs has a pair of anterior extensions which
enter the skull and connect to the inner ear. This synapomorphy allows the
gas bladder to serve as a sound receptor which delivers sound signals to the
inner ear for increased auditory reception.
EUTELEOSTEI
Euteleostei comprises the vast majority of living teleosts. Most euteleost
males develop nuptial tubercles which are composed of epidermal cells and
are either keratinized or non-keratinized. These structures may be present on
the head, body, and fins, and provide friction that helps to keep males and
females in contact during mating. Many lineages comprise this taxon, among
which phylogenetic relationships remain uncertain (Nelson, 1994). Only a few
will be considered here.
Esociformes)
Ostariophysi includes the predominant freshwater fishes (~65 % of all
freshwater species), inclu.ding characins, carps, minnows, suckers and catfishe~.
There are over 6,500 speCIes m thIS clade. Ostariophysines possess a
synapomorphy called the Weberian apparatus (Pough et aI., 1999) (Fig. 5.9).
This structure is composed of small bones (ossicles) that connect the gas
bladder with the inner ear; thus hearing sensitivity is greatly enhanced. The
Weberian apparatus uses the gas bladder as a sound receptor (similar to
clupeomorphs) and the chain of bones as conductors.
Q23
What features of the gas bladder are conducive to its function in sound
reception?
(p-
Esociformes include the pikes, muskellunge, and mudminnows and is the
CER to Ostariophysi + Neognathi. The pikes, of which there are 10 extant
species, are freshwater fishes with a circumpolar distribution in the Northern
hemisphere.
Q22
How is the overall bodyform of pikes similar to gars? What might this indicate
about their lifestyle and feeding habits?
Figure 5.8. A synapomorphy for the crown group Ostariophysi + Neognathi (Fig. 5.3) is the adipose fin as
depicted on a salmonid species.
118
LABS FOR VERTEBRATE ZOOLOGY
Lab 5: OSTEICHTHYES
119
IY
Q26
Posterior margin of skull
Do the catfish have an adipose fin? For which taxon is the adipose fin a
synapomorphy?
Claustrum
Membranous
labyrinth
NEOGNATHI
Neognathi is the CER to Ostariophysi (Fig. 5.3). The basal lineage within
Neognathi is Salmonidae. A synapomorphy for Neognathi is increased contact
of the first vertebra with the skull bones. There are several neognathan taxa
that will not be considered in this lab due their relatively obscure nature (e.g.,
Stomiiformes, Ateleopodiformes, Cyclosquamata, Scopelomorpha,
Lampridiomorpha, Polymixiomorpha, and Paracanthopterygii), although there
are some very interesting species in these groups (Nelson, 1994). Salmonidae,
Atherinomorpha, and Percomorpha will be introduced.
A
Scaphum
Tripus
Intercalcarium
Salmonidae
B
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.
Salmonidae includes the familiar salmon, trout, and chars. All salmonids
retain the adipose fin discussed earlier, and many are anadromous. This means
that adults spawn in freshwater, the juveniles return to the ocean to mature,
and then return to freshwater to complete their life cycle.
Q27
Q24
Which basal, vertebrate taxon also has anadromous species?
What might have been some of the selective agents for the evolution of the
Weberian apparatus?
Many salmon reproduce only once, then die shortly after mating. Animals
which show this life-history strategy are called semelparous. Organisms that
have the potential to reproduce more than once in a lifetime are iteroparous.
Q25
120
Examine the barbels surrounding the mouth of a catfish. What might be
possible functions for these structures? How could you test your hypotheses?
LABS FOR VERTEBRATE ZOOLOGY
Q28
Under what types of conditions might a semelparous life history strategy be
more advantageous to an iterparous strategy?
Lab 5: OSTEICHTHYES
121
ACANTHOPTERYGII
Q31
Acanthopterygii, which comprises the true spiny-rayed fishes, is nested
within Neognathi. To complete a survey of actinopterygian diversity in this
lab, you will look at representatives of the two major crown clades within
Acanthopterygii: Atherinomorpha and Percomorpha. Synapomorphies
supporting the monophyly of Acanthopterygii concern details of the
musculature and skeleton, including a more mobile jaw than other teleosts.
This is due in large part to the presence of a well developed ascending process
on the premaxilla which allows greater protrusibility (forward movement) of
the jaws. Acanthopterygians generally possess ctenoid scales with minute
spines on the exposed portions of the scales or in a comb-like row on the
posterior margin.
Percomorpha
Q29
IQ32
l
V
Look once again at some of the non-percomorph fishes. How is the position of
their pelvic fins, relative to their pectoral fins, different from the percomorphs
you have observed?
Which fins on the flying fish are enlarged for gliding?
Q33
Q30
'3~ler
Percomorpha includes perches, sunfisht;§, mackerel, snappers, tuna,
marlin, barracuda, remoras, cichlids, flounders, and many others, and is the
CER to Atherinomorpha (Fig. 5.3). Two synapomorphies include the joining of
the pelvic girdle firmly to the pectoral girdle and pelvic fins with one spine
and five soft rays (Fig. 5.14).
Observe the percomorphs available to you, and look for the two characters
described above.
Atherinomorpha
Atherinomorpha includes flying fishes, grunions, needlefishes,
guppies,and swordtails, and is the CER to Percomorpha. The atherinomorphs
have modified protrusible jaws (Pough et al., 1999).
If available, observe a preserved flying fish. These fishes do not actually fly
but glide.
Identify advantages to an upturned mouth. Where and how might fishes feed
with mouths such as this?
Provide explanation(s) for the forward migration of the pelvic fins. Do you think
this modification provides functional benefits? How?
Identify one or more possible selective pressures that may have caused the
evolution of gliding fins.
Note that members of this clade do not possess an adipose fin. Note also
the numerous spines on the dorsal fins of many of these fishes.
Q34
Provide possible functions for these dorsal fin spines.
Many atherinomorphs have protrusible, upturned mouths (e.g., top
minnows, guppies, swordtails, and pupfishes) (Nelson, 1994). If available,
observe these specimens.
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LABS FOR VERTEBRATE ZOOLOGY
Lab 5: OSTEICHTHYES
123
If available, inspect adult specimens of flounders or soles (Pleuronectiformes).
These largely marine percomorphs are unusual in that the young initially are
bilaterally symmetrical and swim upright, but then undergo metamorphosis
where the body becomes highly compressed and one eye migrates to the other
side of the cranium. Following metamorphosis, they then lie and swim on the
eyeless side.
Q35
Are these fishes laterally or dorsa-ventrally compressed? How can you tell?
Q36
Consider, again, the shape of these fishes. In what type of habitats might you
expect to find them? Would you expect these fishes to have a gas bladder? Why?
Figure 5.10. Sarcopterygii: Coelacanth (Latirneria chalumnae), a lobed-finned fish.
Q37
SARCOPTERYGII
Sarcopterygii includes Latimeria chalumnae (coelacanth), Dipnoi
(lungfishes), and Tetrapoda (tetrapods) (Fig. 5.1). Synapomorphies include a
pulmonary vein and paired, muscular lobed-fins extending below the body.
The pulmonary vein passes from the lung directly to the atrial cavity of the
heart (on the left side) and allows aerated blood to pass directly from the lungs
to the heart. Aerated blood is then pumped into the ventricle and from there to
various parts of the body. The muscular lobed fins of sarcopterygians are
sometimes utilized for a walking type of locomotion, which would later be
used by the ancestors of tetrapods to invade terrestrial habitats.
Latimeria chalumnae
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 is
the CER to Choanata, which includes Dipnoi (lungfishes) and Tetrapoda
(tetrapods). The coelocanth has only been found in the Indian Ocean near the
coast of Madagascar. One of several synapomorphies is the ossified lung that
no longer functions as a buoyancy or air breathing organ.
.124
LABS FOR VERTEBRATE ZOOLOGY
Provide possible evolutionary explanations for the ossification of the lung in the
coelacanth.
CHOANATA
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 is
produced by the liver, contains mostly excretory products, including
decomposed proteins and pigments derived from hemoglobin of aged red
~lood cells. Choanates also produce bile salts which are discharged into the
mtestme and aId a pancreatic enzyme in splitting and absorbing fats. In the
choanate heart a partition develops in the atrium such that the left chamber
contains pulmonary blood which has been oxygenated (delivered by the
pulmonary vein), and the right chamber receives veinous blood from the sinus
venosus. The atrial division is partial in lungfishes. Limited mixing of
oxygenated and deoxygenated blood occurs in the ventricle. But due to the
spiral effect of heart contraction, oxygenated and deoxygenated blood largely
remams separated. Choanates also have nasolacrymal ducts' which extend from
the nasal cavity to the orbit. These are the tear ducts and they maintain eye
moisture.
Lab 5: OSTEICHTHYES
.125
Dipnoi
Dipnoi includes six species of extant lungfishes (Fig. 5.11), one in
Australia, one in South America, and four in Africa.
Q38
What geologic factors may account for the disjunct geographic distribution of
these lungfishes?
The pectoral and pelvic fins of the South American and African lungfishes
are tendril-like, which indicates that a common ancestor of these species lost
the muscular lobed fins. The Australian lungfish retains the fleshy, muscular
fins of Sarcopterygii and uses these to slowly walk across the bottom of ponds.
The caudal fin of dipnoans is diphycercal with the vertebral column extending
straight back to the tip of the body and the fin developing symmetrically above
and below it. Another synapomorphy is thin scales embedded in skin.
DISSECTION OF ADULT PERCH
General External Anatomy
You probably will use a relatively common and readily accessible
percomorph, such as the yellow perch (Percaflavescens), to explore
actinopterygian morphology (Figs. 5.12 - 5.15).
After obtaining a preserved specimen, identify the mouth, bony
operculum, dorsal fines), homocercal caudal fin, anal fin, anus, pectoral fins,
pelvic fins, soft and spiny rays, and lateral line system (Fig. 5.12).
A
B
Q39
What is a homocercal tail?
Q40
The pectoral and pelvic fins (and their respective ;girdles) are synapomophies for
which taxon?
General Internal Anatomy
c
.~
Figure 5.11. Choanata: Lungfishes (Dipnoi). (A) African lungfish (Protopterus sp.). (B) South American
lungfish (Lepidosiren paradoxa). (C) Australian lungfish (Neoceratodus forsteri).
126
LABS FOR VERTEBRATE ZOOLOGY
Identify the oral cavity, teeth, pharynx, gill arches, gill slits, gill lamellae,
gill rakers, esophagus, stomach, intestine, liver, heart, gas bladder (a
synapomorphy for Actinopteri), myomeres, and kidneys (Fig. 5.13).
Lab 5: OSTEICHTHYES
127
. r dorsal fin
PQ\l.erI9~'_"
••"'~~_
Lepidotrichia (hard spines)
Ceratotrichia
/
Pterygiophore
Lateral~
Neural spine
Ceratotrlchia
Eye
Ceratotrichia
.
~
L\~
"~,',"'~
I
'.
---
Pectoral fin
Pelvic fin
Ventral rib
Dorsal ribs
~~.,::,\
_\~ ~
Urostyle
Anal fin
Figure 5.12. Percomorphao. External anatomy of the yellow perch (Perca flavescens).
Figure 5.14. Percomorp h a.. Skeletal system of the yel1ow p erch (Perea flavescens).
Swim bladder
Pancreas
Duodenum
Q41
What is the function of the gill
. fi'l1 aments?, The gill rakers?
Q42
What is the functLOn
,
Q43
What structure IS. the gas bladder homo Iogous to in other osteichthyans,
including tetrapods?
Head kidney
~lj~~~~~~I~··~"·~·"~:;'i/~··~,.; ~.~~~~~t:::;~:::-~:~:ventriCle
~-"~:';iilIO'l!!:::'-_-
0;,f the
gas bladder?
Bulbous
arteriosus
Sinus venosus
intestine
Anus
Fat (covering
Gonad
stomach)
Figure 5.13. Percomorp ha'. Internal anatomy of the yellow perch (Perca flavescens).
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LABS FOR VERTEBRATE ZOOLOGY
Lab 5: OSTEICHTHYES
129
Q44
For which craniate taxa are the following character states synapomorphies:
Respiratory gills?
Stomach?
Liver?
Note the extremely large number of bones in the skull (Fig. 5.15). This large
number is an ancestral condition for vertebrates (as evidenced by extinct
fishes). Most of these bones are dermal in embryonic origin, originating from
the external dermal plates of extinct jawless vertebrates. The palatoquadrate
cartilage, which forms the upper jaw in elasmobranchs, has been supplanted
functionally by two dermal bones anteriorly, the premaxilla and maxilla. These
two 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 ossified
remnants of the palatoquadrate. The quadrate serves in jaw articulation in all
osteichthyans except in mammals. In a lineage ancestral to mammals, the
quadrate evolved into a middle ear bone called the incus. The mandibular
cartilage, which forms the lower jaw in elasmobranchs, has been replaced by
several dermal bones including (among others) the dentary and the small
articular bone on the posterio-dorsal part of the lower jaw which is the site of
articulation with the quadrate. Remember the hyoid arch in elasmobranchs? In
osteichthyans, the hyomandibular bone represents the hyomandibular
cartilage, and ventrally there are several hyoid bones. In tetrapods, the
hyomandibular 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.
Frontal
Premaxilla
Supraocciptial
Kidneys?
"-',,<-_-Hyomandibular
Maxilla
.:.:-;;.,.~,...:::.'""'_ _ Opercular
Skeletal System
Dentary
Locate the paired, segmented, and branched lepidotrichia in various fins
(Fig. 5.14).
Q45
--4\-\--
What are lepidotrichia?
Angular
_-..:.:::::,~::;;;:=:~~
1:Tth7-f?~~.--~',---- Preopercular
Quadrate
Subopercular
Metapterygoid
Interopercular
Figure 5.15. Head skeleton.
130
LABS FOR VERTEBRATE ZOOLOGY
Lab 5: OSTEICHTHYES
131
The vertebral column is not wen differentiated into distinctive regions,
and only the trunk and caudal vertebrae are readily distinguishable. Recall that
the vertebral column largely replaces the notochord as a central supporting
axis in gnathostomes. As in chondrichthyans (Lab 4), the dorsal arch of the
centrum is the neural arch, and it protects the spinal cord, which passes
through the neural canal. Ribs attach to the vertebrae along the anterior
portion of the vertebral column and they lie within the myosepta between
adjacent myomeres. By serving as connectors between the musculature and the
vertebrae, ribs render the muscular effort more effective.
Q46
What are myomeres and myosepta? For which taxon are these structures
synapomorphies?
Most of the pectoral girdle and all of the pelvic girdle is comprised of
endochondral bone. The dermal elements of the pectoral girdle include the
clavicle, cleithrum, and supradeithrum. The supracleithrum attaches the
pectoral girdle firmly to the posterior region of the skull. The endochondral
bones include the coracoid and scapula.
QUESTIONS FOR DISCUSSION
1. When it comes to the sheer number of species and morphological diversity,
extant actinopterygians (~ 24,000 species and counting!) have no equal
among the vertebrates. What might be the explanations for this
phenomenon? In class, derive several hypotheses that could be used to
explain 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 in
marine (reef) species than in freshwater ones?
3. Bone (calcium phosphate) did not have its origin in osteichthyans. What
reasons (e.g., selective advantages) can you provide to explain the absence
(or nearly so) of bone in extant chondrichthyans and chondrosteans and its
presence in most osteichthyans? What is the functional significance of
endochondral ossification?
132
LABS FOR VERTEBRATE ZOOLOGY
WEB SITES
There is a tremendous amount of current information on the biology of
osteichthyans 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.
<http://www.yorkbiosis.orglzrdocs/zoolinfo/grp_fish.htm>.
This Web site (FISH) is supported by BIOSIS, the publisher of Biological
Abstracts and Zoological Records, and is one of their Internet resource guides in
zoology. 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
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 York
Pough, 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.
Lab 5: OSTEICHTHYES
133