The Pharyngeal Bones and Teeth of Catostomid Fishes
Joseph T. Eastman
American Midland Naturalist, Vol. 97, No. 1. (Jan., 1977), pp. 68-88.
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The Pharyngeal Bones and Teeth of Catostomid Fishes
JOSEPH T. EASTMAN
Section of Morphology, Division of Biological and Medical Sciences, Brown University, Providence, Rhode Island 02912 ABSTRACT:Examination of the pharyngeal apparatus of 22 species
of catostomids reveals three types of bones and teeth associated with different dietary habits. The mollusk feeders Moxostoma hubbsi and M .
carinatum have 21-42 large, molariform teeth on each of the heavy
pharyngeal bones. The teeth occlude with a chewing pad borne by the
basioccipital and are well-adapted for crushing shells. Most catostomids
(other Moxostoma, Cycleptus, Hypentelium, Lagochila, Catostomus,
Chasmistes, Erimyzon, Xyrauchen and Minytrema) have 43-90 moderately compressed teeth arranged in comblike fashion on each bone. These
species feed primarily on benthic macroinvertebrates including aquatic
insect larvas and small mollusks. I n addition to mastication, the teeth
of this group probably serve to manipulate and hold food during the
rejection of inorganic matter inadvertently taken in with the food. The
teeth of Ictiobus and Carpiodes are extremely small and numerous (134184)., and the pharyngeal bones are correspondingly delicate. These
specle5 are microphagous filtm feeders with a well-developed selectory
apparatus consisting of gill rakers, gill arches and palatal organ. The
teeth are capable of masticating small food items and may also function
as strainers.
An analytical key based only on pharyngeal bone and tooth characteristics is provided, and the bones and teeth of several species are illustrated. Catostomid pharynqeal bones and teeth have some limited use
in specimen identification. They are usually reliable a t the tribe or genus
level. In certain trophically specialized forms (Moxostoma hubbsi, M .
carinatum and Ictiobus cyprinellus) they are significant at the species
level.
INTRODUCTION
Freshwater fishes of the family Catostomidae, commonly known
as suckers, are represented by 11 genera with about 63 species in North
and Central America and the single relict genus Myxocyprinus in
China. Catostomids probably diverged from a cyprinid ancestor sometime before the Eocene (Uyeno and Smith, 1972). Most are suctorial
bottom-feeders with small, extensible, ventroterminal mouths. These
fishes lack both oral teeth and a stomach. They do, however, possess
pharyngeal teeth arranged in a single row on each of the two pharyngeal bones located posterior to the fourth pair of gill arches.
Certain aspects of catostomid morphology are well-documented;
for example, osteological information for some species has been provided by Sagemehl (1891) , Edwards (1926), Gregory (1933), Nelson
(1948, 1949, 1955), Ramaswami (1957), Weisel (1960, 1967a), Branson (1962), Smith (1966) and Smith and Koehn (1971). However,
catostomid pharyngeal bones and teeth, of considerable trophic and
possible taxonomic significance, have never been adequately treated.
Le Sueur (1817) was aware of the existence of catostomid pharyngeal bones and teeth, but only later did ichthyologists begin to recognize
the potential taxonomic value of these structures (Agassiz, 1855;
Bleeker, 1860; Cope, 1870; Jordan, 1878). More recently, fossilized
catostomid pharyngeal bones and teeth have been found in several
localities in the southwestern United States (C. L. Smith, 1954, 1958;
G. R. Smith, 1963). This family represents the second-most abundant
fish group in North American Pleistocene deposits, and most of these
fossils are osteologically indistinguishable from living species (Miller,
1965) . Therefore, descriptions of pharyngeal structures from Recent
species provide valuable information for interpreting material from
archaeological (Trautman, 3 957 :262) and paleontological (cf. Rutte,
1962, for Old World cyprinids) sites.
With the exception of comments by Forbes (1888: 440-441) and
Forbes and Richardson (1908 :63-64), the structural diversity of catostomid pharyngeal bones and teeth has generally not been appreciated
by ichthyologists, nor has their form in the various species been related
to diet or to specializations in ancillary pharyngeal structures. I undertook this investigation to rectify this situation as well as to assess the
utility of pharyngeal bones and teeth in specimen identification. All 11
American genera are represented in the study. Special emphasis is
accorded to Moxostoma carinatum, Catostomus commersoni and
Carpiodes cyprinus because the pharyngeal morphology of each of these
species is considered typical of one of the three levels of trophic adaptation seen in the pharyngeal complex.
AND METHODS
MATERIALS
For the most part, the 22 species (135 specimens) used in this study
represent a typical Great Lakes assemblage of catostomids (Table I ) .
Many were collected from the waters of Minnesota with a 0.25-inch
mesh seine. Most of the Moxostoma, Ictiobur and Carpiodes cyprinus
were netted in Lake St. Croix, Washington Co., Minn., by a commercial fisherman. Other northern species were borrowed from the James
Ford Bell Museum of Natural History at the University of Minnesota.
Rare species were obtained from Cornell University (CU) ; Museum
of Comparative Zoology, Harvard University (MCZ) ; University of
Michigan Museum of Zoology (UMMZ) ; University of Oklahoma
Museum of Zoology (UOMZ) ; and National Museum of Natural History, Washington, D. C. (USNM) .
Pharyngeal bones were removed, thoroughly cleaned of adhering
tissue, dehydrated in ethanol, and degreased in acetone. The number
of teeth per bone was counted with the aid of a dissecting microscope.
Broken and missing teeth were included in the count. In addition, the
pharyngeal region was dissected in representatives of all but the rare
species (Moxostoma hubbsi, M. valenciennesi, Ictiobus niger, Xyrauchen texanus and Lagoclzila lacera). Most specimens studied were
sexually mature adults.
Whenever possible, gut contents were examined and major groups
of food items were identified. For rare species, however, it was necessary to refer to the literature (Forbes. 1888; Forbes and Richardson,
1908; Carlander, 1969) for dietary information.
Illustrations were prepared with the use of a drawing tube attachment on a Wild M-7 stereomicroscope. The pharyngeal bones of some
species were too large to be drawn by this method; in such cases, the
specimens were photographed and a tracing was made from a print.
In order to assure uniformity in illustrative procedures, the bones were
positioned so that the surface facing posteriorly in life, Chu's (1935)
ventral surface, was nearest the illustrator. I n many species the presence of numerous small, dorsal teeth made it impossible for the illustrations to reflect the correct tooth count as given in Table 1. Illustrations of the most ventral tooth of each species are also provided. Many
catostomid teeth bear conical projections or hooks on their anterior
(inner) margins; these are subject to wear, however, and are shown
only when they are a constant and diagnostic feature in a given species.
The catostomid classification used in this paper is that of Hubbs
(1930). This was amended by Nelson (1948, 1949) and subsequently
employed by Miller (1958). Figures 8-21 are arranged according to
this sequence.
Skull bone nomenclature is that of Harrington (1955) with the
exception that the pharyngobranchials are referred to as infrapharyngobranchials (Nelson, 1969). Weisel's (1960) work on the skull of
Catostomus macrocheilus was also helpful. Although the pharyngeal
bone nomenclature proposed by Chu (1935) was formulated with
respect to cyprinids, it is employed here because it is easily adaptable
to catostomid bones.
Pharyngeal tissues studied histologically were fixed in 10% formalin
with subsequent dehydration in ethanol, clearing in xylene, and embedding in paraffin. Sections were cut to a thickness of 6 pm and then
stained with hematoxylin and eosin or Weigert's elastica (for sirnultaneous demonstration of collagen, elastin and muscle). Mounting
was in Permount.
GENERAL
A NATOMY
OF THE PHARYNGEAL
REGION
The pharyngeal bones and teeth.-Fish teeth are generally involved
in the seizing, manipulating, masticating and swallowing of food. Catostomid pharyngeal teeth participate in all but the first of these actions.
The teeth are arranged in a single row on each of the two pharyngeal
bones. These falcate bones, representing fifth ceratobranchials, are
joined at their ventral tips to each other and to ventral gill arch elements by means of a cartilaginous copula. There are only muscular
connections between the pharyngeal bones and the skull, vertebral
column and pectoral girdle.
Cyprinoid pharyngeal teeth are unusual among vertebrate teeth in
that the "enamel organs" are of endodermal rather than ectodermal
origin, developing from the deeper columnar layer of the pharyngeal
epithelium representing the endoderm of the primitive foregut
(Edwards, 1929). The crowns of the teeth are probably composed
entirely of dentin (Cheprakova, 1958). This material, termed modified
dentin by Peyer (1968), functionally substitutes for enamel in most
teleost teeth. Bony ankyloses, several millimeters long, unite the crowns
to the pharyngeal bone. The ankyloses are partially resorbed by osteoclasts prior to tooth loss and reformed during tooth replacement.
~atostomidpharyngeal teeth are replaced continuously throughout
life. Weisel's (196713) study of the form and attachment sequence of
the teeth in larval and juvenile Catostomus indicates that the replacement is rapid at these stages of life with at least the first and second
generations of replacement teeth resembling the conical hooked teeth
of immature cyprinids.
.I n most catostomids the form of the teeth varies with their position
on the bone. The more dorsally situated teeth are generally more
distinctly hooked on the anterior (inner) margin than are the ventral
teeth. Masticatory activity, however, may sometimes obliterate the
hooks. Conversely, recently ankylosed crowns may not have worn
sufficiently to exhibit the flat masticatory surfaces characteristic of, for
example, the teeth of Moxostoma hubbsi and M . carinatum (Figs. 14i E \
IJ).
There is considerable interspecific variation in the number of
pharyngeal teeth (Table 1 ) . The number of teeth per bone is related
to tooth size. Species with large teeth have a relatively small number
of teeth whereas species with small teeth have a large number. Although
sample sizes were too small to permit an analysis of intraspecific variation in tooth number, ranges of the magnitude expressed in Table 1 can
probably be considered normal for a species. Once maturity is reached,
there is no indication that larger individuals of a species have more
teeth than smaller individuals.
T h e basioccipital bone.-In the basicranial region adherent pharyngeal structures such as the basioccipital (Figs. 1-6) reflect feeding a d a p
tations in the different species. The catostomid basioccipital differs
from that of cyprinids in that it is more delicate, with the pharyngeal
process extending anteriorly to serve, along with the epibranchials, as
support for the large palatal organ (see below). In cyprinids, however,
the pharyngeal process projects posteriorly from the masticatory process
and serves as a point of origin for the retractor muscles of the pharyngeal bones (Eastman, 1971). This large ventral part of the basioccipital surrounding the dorsal aorta probably represents the fused
hemal arches of anterior vertebrae (Goodrich, 1930:592).
Catostomids generally lack the chewing pad characteristically associated with the cyprinid basioccipital. The only exceptions are Moxostoma carinatum and M . hubbsi, species with heavy pharyngeal bones
and large, molarifonn teeth (Figs. 1, 4, 14-15). Instead of being
lozenge-shaped, as in cyprinids, the pad in these species is crescentshaped with its lateral margins extending dorsally so as to permit
occlusion of all teeth with the pad. The masticatory process is continuous anteriorly and posteriorly with the pharyngeal process. The
anterior projections of the pharyngeal process supporting the palatal
organ are small and slightly fenestrated. The pharyngeal process
TABLE
1.-Pharyngeal
Species
(and location if uncommon)
teeth and diet in some catostomidsl
Mean no. of
teethhone
(with range)
Moxostoma hubbsi ( C U 52914) (Fig. 15)
M . carinatum (Fie. 14)
21 (20-22)
42 (35-51)
~ > p e A t e l i u mGgrica;s TFig. 18)
Lagochila lacera (UMMZ 177430) (Fig. 17)
Catostomus catostomus
44 (40-51)
46 (43-48)
53 (49-57)
C. commersoni (Fig. 19)
Chasmistes breuirostris (Fig. 20)
Moxostoma macrolepidotum
Erimyzon oblongus (UOMZ 39969) (Fig. 12)
Moxostoma erythrurum (Fig. 16)
M . valenciennesi (CU 64101)
Xyrauchen texanus (USNM 48124) (Fig. 21)
Moxostoma duquesnei
Minytrema melanops (Fig. 13)
..
No.
individuals
examined
Tooth and bone
type (see text)
1
1
2
2
2
2
2
2
2
65
67
71
73
81
85
(56-76)
(56-79)
(68-74)
(72-74)
(73-90)
(75-91)
2
2
2
2
2
2
Moxqstomn anisurum Ictiobus niger (MCZ 2323 & 18363) 2
3
I. bubalus (Fig. 10)
I. cyprinellus (Fig. 9 )
Carpiodes cyprinus (Fig. 11)
3
3
3
C. velifer
C. carfiio
3
3
Diet
Large bivalve
Large bivalve
Aquatic insect
Aquatic insect
mollusks
mollusks
larvae
larvae
........................ Aquatic insect larvae,
Entomostraca, small gastropod & bivalve mollusks
As in C. catostomus
........................ Aquatic insect larvae,
small gastropod & bivalve
mollusks, Entomostraca
Entomostraca
As in M . macrolepidotum
As in M . macrolepidotum
Diatoms, filamentous algae
As in M. macrolepidotum
Aquatic insect larvae, bivalve
mollusks (Sphaerium)
As in M . macrolepidotum
Entomostraca, aquatic insect
larvae, Sfihaerium
As in I. niger
Entomostraca, chironornids
Entomostraca, chironomids,
diatoms, filamentous algae,
duckweed ( W o l f i a )
As in C. cyprinus
As in C". cvorinus
Species are arrangeci according to increasing number of teeth; no phylogenetic inference is intended
A posterior to the chewing pad is heavy and blunt (Fig. 4), giving origin
to pharyngeal bone retractor muscles.
In the majority of catostomids, as exemplified by Catostomus commersoni (Figs. 2, 5 ) , the anterior projections of the pharyngeal process
are relatively larger and more cancellous than in Moxostoma carinatum
and M. hubbsi. In C. commersoni these light, irregularly latticed projections comprise the anterior two-thirds of the ventral portion of the
bone and serve to support the palatal organ. Each projection is rounded
to the contour of the organ, the lateral margin being flared dorsally,
and suspended ventral to the main portion of the basioccipital by a
single strut of bone. The two projections unite posteriorly to form a
dense, trabecular protuberance giving origin to the retractor muscles.
The sizable palatal organ of Carpiodes and Ictiobus is supported
by an extremely large and delicate bony complex (Figs. 3, 6) suspended
from the sharp midline keel of the parasphenoid and basioccipital. The
anterior two-thirds consists of four pairs of epibranchials and three
pairs of infrapharyngobranchials. The posterior pair of infrapharyngobranchials is small and poorly ossified. The epibranchials (Fig. 7)
curve markedly toward the midline of the body. Their dorsal portions
are expanded into large, cancellous, hook-shaped processes forming
the bulk of this bony complex. The small infrapharyngobranchials
border the anterior and lateral margins of the aortic canal (Fig. 6 ) .
Although these gill arch elements are not synostotic, they are united
by fibrous connective tissue and move as a unit. They are attached to
each side of the keel of the parasphenoid as well as to laterally projecting knobs near the anterior margin of the first pair of epibranchials.
This gill arch complex is synarthrodially articulated with the pharyngeal process of the basioccipital-a short, fragile latticework with dorsally curled lateral margins. The retractor muscles are not present in
Carplodes, hence the pharyngeal process is not drawn out posteriorlv
nor is its margin composed of compact bone.
The palatal organ.-This thick, fleshly structure, attached to the
ventral surfaces of the parasphenoid and basioccipital, forms the roof
of the pharynx. According to Cole (1944), Aristotle was aware of the
cyprinoid palatal organ, but it remained for Weber (1827) to describe
its innervation by the glossopharyngeal and vagus nerves and its importance in gustation.
The catostomid palatal organ is generally thicker dorsoventrally
than that of a cyprinid of the same size. The size differential is attributable to the greater amount of striated muscle in the catostomid
organ. In most cyprinids, adipose tissue predominates in this structure.
There are no striking histological differences among the palatal
organs of Moxostoma carinatum, Catostomus commersoni and Carpiodes cyprinus. The tunica mucosa is in the form of squarish, flattopped papillae consisting of nonkeratinized stratified squamous epithelium underlaid by a thin, collagenous lamina propria forming the
core of each papilla. The epithelium contains many unicellular mucous
glands as well as taste buds (see below). The collagenous fibers of the
Flgs. 1-2.-Anterolateral
views of the left side of the neurocrania and
pharyngeal bones of Moxostoma carinatum ( 1 ) and Catostomus commersoni
( 2 ) . Note the molariform pharyngeal teeth and the chewing pad in M. carinatz~m. T h e fenestrated nature of the pharyngeal process of the basioccipital
is evident in C. commersoni
bones-of Carpiodes cyprinus. T h e four rieht epibranchials are intact and
partially visible; the ventral portions of the left epibranchials have been cut to
expose the expanded dorsal portions (arrows) that support the palatal organ
Fiqs. 4-6--Ventral views of the neurocrania of M o x o s t o m a c a r i n a t u m ( 4 ) ,
C a t o s t o m u s c o m m e r s o n i ( 5 ) and Carpiodes cyprinus ( 6 )
LIST OF ABBREVIATIOSS
FOR FIGS. 1-6
A 0 - aortic canal in basioccipital; BO - basioccipital; C P - chewing pad;
EB - epibranchial; E O - exoccipital; E P O - epiotic; F - frontal; IPB i n f r a ~ h a r y n ~ o b r a n c h i aO
l ;P I S - opisthotic; P - pitted surface of pharyngeal
bone (Chu, 1 9 3 5 ) ; PPBO - pharyngeal process of basioccipital; P R O prootic; PS - parasphenoid; P T O - autopterotic (fused to supratemporal) ;
PTS - pterosphenoid; PV - prevomer; SPH - autosphenotic; S T F - subtemporal fossa; V - ventral surface of pharyngeal bone (Chu, 1935); V I I foramen for facial nerve; I X - foramen for glossopharyngeal nerve; X foramen for vagus nerve.
lamina propria are contiguous with those of the thin tunica submucosa.
Adjacent to the submucosa is the thickest part of the organ consisting
of circularly, longitudinally and obliquely oriented striated muscle fasciculi with interspersed adipose tissue, blood vessels and nerves.
Taste bud counts differ among catostomids. I found an average of
51 buds in 1-cm sections of the palatal organ of Moxostoma carinatum.
Weisel (1962) counted 62 per cm in Catostornu.~catostomus, while
Miller and Evans (1965) reported 17 buds per 1.3 mrn section ( = 131
buds per cm) in Carpiodes velifer.
Large numbers of taste buds are indicative of the important role
the palatal organ plays in food selection. Most catostornids are bottomfeeders taking in inorganic material that must be separated from food
to be swallowed. Gustatory information perceived by the taste buds is
the initial step in effecting this separation. In addition, the striated
muscle in the organ permits contraction, thereby altering the pharyngeal volume and facilitating ejection or swallowing of material.
A N D DIET
PHARYNGEAL
APPARATUS
Each of the 22 species studied can be assigned to one of three different categories (Table 1) with reference to the structure of the
pharyngeal apparatus (teeth, bones and adnexae) as related to diet.
Type 1.-The mollusk feeders Moxostoma hubbsi and M . carinatum have large molariform teeth with wide, flat grinding surfaces.
The teeth are borne by extremely heavy pharyngeal bones rendered
mobile by seven pairs of well-developed muscles. The bones, especially
in M . hubbsi, are tightly united by interdigitations of the ventral tips
(Fig. 15) . This arrangement is presumably advantageous in stabilizing
the bones and sustaining the force of the bite, important considerations
in shell-crushing. A solid occlusal surface for crushing is provided by
a crescent-shaped chewing pad attached to the basioccipital. When
the pharyngeal bones are elevated and retracted, the teeth oppose the
pad (Fig. 1 ) ) crushing interposed food items.
The palatal organ is relatively thin, and the pharyngeal process of
the basioccipital is correspondingly small. Consequently, the pharyngeal lumen is large, enabling the passage of whole mollusks to the
region of the teeth. The gill rakers are short and widely spaced. Determinate selection of small food items appears to be relatively unimportant in these two specialized mollusk feeders.
Type 2.-In the second and most common condition, represented
by the majority of the species, the pharyngeal apparatus is adapted to
permit moderate mastication. Thus, in species of the genera Moxostoma
(except M. hubbsi and M , carinatum), Cycleptus, Hypentelium, Lagochila, Catostomus, Chasmistes, Erimyron, Xyrauchen and Minytrema,
the apparatus may be considered structurally intermediate between the
extremes of M , hubbsi and M . carinatum (mollusk feeders) and Ictiobus and Carpiodes (microphagous filter feeders). The diet of this
group (Table 1) consists of aquatic insect larvae, small, thin-shelled
mollusks and Entomostraca.
In these species the pharyngeal teeth number from 43 to 90 and
are arranged in a comblike fashion on the bones. The teeth are dorsoventrally compressed with moderate to small grinding surfaces. Many
of the teeth have a small conical projection on their anterior margins.
There is a striking size differential between the dorsal and ventral
teeth; those on the ventral one-half of the bone are several times larger
than more dorsally situated teeth. There is no chewing pad in these
species. The teeth occlude with the posterior part of the palatal organ.
The gill arches are molded to the contours of the palatal organ
and the gill rakers in this group are longer and more closely set than
those of Moxostoma hubbsi and M . carinatum. Although there are no
taste buds on the gill rakers of Catostomus macrocheilus (Weisel,
1960), it is conceivable that they are present in this location in some
catostomids (e.g., Type 3 below), because Iwai (1964) noticed numerous taste buds on the anterior surfaces of the gill rakers and gill
arches in certain cyprinids. He noted that this arrangement is advantageous in filter feeding.
I n this second group of catostomids, the utility of the pharyngeal
teeth in mastication is variable. Weisel (1960, 1962) questioned the
masticatory capability of the teeth of Catostomus. Although he admits
that the teeth could be involved in some weak crushing action against
the palatal organ, he feels that they serve primarily, along with the gill
rakers, as strainers. I doubt, however, that the teeth function efficiently
as strainers. I n all fresh and fixed specimens I examined, the mucosa
surrounding the teeth is higher than the teeth although there is a
striated muscularis presumably conferring some mobility to the mucosa.
Normally, however, the teeth would be below the mucosa, a poor
location for effective utilization as strainers. I t is unlikely that the
mucosa would interfere with mastication because occlusion of the teeth
with the palatal organ would result in mucosal flattening.
Stewart (1926) was also concerned about the role of the pharyngeal teeth in mastication. He found that aquatic insect larvae eaten
by Catostomus commersoni entered the intestine unfragrnented and
concluded that the teeth were not adapted to crushing food. It must
be remembered, however, that the insect exoskeleton is resilient and
that catostomid teeth, unlike those of some cyprinids, are not suited
to tearing and puncturing food. Catostomus commersoni has no difficulty in crushing the thin-shelled mollusks that constitute a significant
part of its diet in certain geographic areas. With regard to lighter food
items, such as insect larvae, it is possible that the teeth serve to manipulate and hold the food against the palatal organ. Bottom-feeding
catostomids take in mud and other inorganic matter that is usually
ejected from the mouth and pharynx. Holding food in the posterior
pharynx is therefore a necessary procedure during the "spitting" maneuver resulting from pharyngeal contraction initiated by the palatal
organ. The small conical projections on the anterior margins of most
catostomid teeth would help to pin food to the palatal organ during
this process.
T y p e 3.-The third type of pharyngeal apparatus, as seen in Ictiobus and Carpiodes, is poorly suited for mastication. The teeth are
numerous (134-184), very small, greatly compressed dorsoventrally,
and short in anteroposterior extent. The pharyngeal bones are very
light and delicate, especially in Carpiodes. They are curved posteriorly,
the concavity opening anteriorly, and the dorsal tips are directed
anteroventrally. This curving serves to mold the bones around the
lateral and dorsal aspects of the palatal organ such that the bones
resemble gill arches in form and position (Fig. 3 ) . The arched shape,
close approximation to the palatal organ, and poorly developed musculature allow only slight movement of the pharyngeal bones of these
species. I n addition, a fibrous attachment links the fourth epibranchials
with a tubercle on the lateral surface near the dorsal tips of the pharyngeal bones. This connection further inhibits independent action on the
part
.
.. the bones while ensuring that they move in conjunction with
of
the gill arches.
The size of the teeth and the form and attachments of the bones
indicate that these structures are not subject to significant masticatory
stresses, and therefore are probably not involved in the crushing of
hard food items. The diet of these fishes, consisting mainly of Entomostraca, chironomids, algae and other plant material, supports this
contention. This type of food requires little mastication, and the size
of the teeth and the force of the bite are probably sufficient to partially
crush the carapaces of copepods, ostracods and cladocerans. The frequency with which mud is found in the intestines of Ictiobus and
Carpiodes indicates that decaying animal and plant material extracted
from the bottom are common dietary items. The palatal organ permits
separation of the organic and inorganic components although some
mud is inadvertently swallowed. The numerous small teeth would certainly be capable of performing any mastication required by this soft
material and also of manipulating and holding food during the spitting
reflex. I t is possible that the teeth may also be involved, along with
the gill rakers, in straining (see below).
Whereas most ictiobine species are bottom feeders, Ictiobus cyprinellus probably occupies both the bottom and limnetic plankton-feeding
niches (Johnson, 1963). That it is more of a planktivor than the other
species of Ictiobus is supported by the preponderance of Entomostraca
in its diet. Moreover, the gill rakers form a more effective sieve, the
pharyngeal teeth are smaller and more numerous, and the pharyngeal
bones are more delicate than in I . niger and I . bubalus. Some masticatory ability is necessary in these latter two species, however, since
their diet includes, in addition to Entomostraca, soft-bodied aquatic
insect larvae and small bivalve mo!lusks. The teeth are correspondingly
larger
than in I . cyprinellus.
- and the bones more rugged
-.Hard food items requiring mastication are generally not included
in the diet of Carpiodes (Table 1). Some plant material is taken, and
the intestine of Carpiodes is longer and more highly coiled than in
Ictiobus (Berner, 1948), probably reflecting the greater dietary impor-
tance of vegetable matter as well as the larger amount of mud ingested
by the former.
Ictiobus and Carpiodes are equipped to strain small food items from
water and bottom material by a specially adapted filtering mechanism
consisting of palatal organ, gill rakers and gill arches. The thick palatal
organ has numerous taste buds and high dorsally projecting lateral
margins. Miller and Evans (1965) regard Carpiodes and Ictiobus as
capable of sorting food in the mouth and pharynx because of the many
taste buds in these locations and the large vagal brain lobes receiving
fibers from these buds. The relatively inflexible gill arches are closely
opposed to the lateral and dorsal aspects of the palatal organ. The gill
rakers are long, slender, closely set and rough-surfaced. The curvature
of the ,gill arches ensures that the gill rakers, and their contained food
items, can touch the epithelium of the palatal organ. These modifications result in the effective sieving ability necessary for both limnetic
plankton feeding and bottom foraging. The pharyngeal bones and
teeth of Ictiobus and Carpiodes are not adapted to rigorous mastication. Instead, these species possess modifications of ancillary pharyngeal structures that allow the determinate selection and efficient straining of small food items.
The morphological divergence of the pharyngeal apparatus associated with trophic specialization (microphagous filter feeding or mollusk feeding) is easily recognized. However, with the exception of the
Ictiobinae and Moxostoma hubbsi and M . carinaturn among the Catostominae, most catostomids have retained a more generalized, and presumably ancestral, type of pharynqeal apparatus. Most of these latter
species are bottom foragers with Type 2 pharyngeal bones and teeth
(see above). This condition allows flexibility in feeding habits because ,teeth of this type may be employed in the manipulatibn and
mastication of a variety of riverine and lacustrine benthic organisms
includinq insect larvae, small mollusks and plant material. The ability
to exploit this rich bottom habitat is probably partially responsible for
the extensive radiation and success of certain catostomine groups with
Type 2 bones and teeth. For example. of the 57 catostomids recognized
bv Bailey (1970), 46 (81%) are members of the tribes Catostomini or
Moxostomatini. Most species in these tribes have Type 2 bones and
teeth.
USE OF PHARYNGEAL
BONESAND TEETH
IN
SPECIMENIDENTIFICATION
T o assess the utility of catostomid pharyngeal bones and teeth in
specimen identification, I constructed an analytical key to the various
species employing only pharyngeal bone and tooth features. Many additional rnorphologic and meristic characters would, of course, be used
in conventional taxonomic work. This approach is useful, however.
when confronted with the problem of identifying a limited amount of
skeletal material such as might be found at a paleontological or an
archaeological site. Catostomid pharyngeal bones and teeth are frequently included among such material (C. L. Smith, 1954, 1958; G. R.
Smith, 1963). I n addition, they are often found intact among the
stomach c,ontents of piscivorous fishes.
By way of summary and as a means of presenting descriptive data,
an artificial (and not strictly dichotomous) key is provided below.
A Key to the Genera and Some Species of American Catostomids Based Solely oln Features of the Pharyngeal Bones and Teeth la. Bones compressed anteroposteriorly; flat in cross section; great curvature of
dorsoventral axis approximates semicircle with concavity opening anteriorly;
dorsal tips directed anteroventrally; usually delicate, light in weight; more
2
than 100 teeth/bone ....................................................................................
lb. Bones not compressed anteroposteriorly; triangular in cross section; dorsoventral axis not curved; dorsal tips not directed anteroventrally; usually
moderate to heavy in weight; less than 100 teeth/bone ........................
3
2a. Bones extremely compressed anteroposteriorly; thin and cancellous especially
near lateral margin; pitted surface (Fig. 11, P ) faces posteriorly; ventral
tips short; teeth extremely small and numerous 169-184 (150-190) ;
extremely narrow mediolaterally; no great size differential among teeth
................................................................................
Carpiodes spp. (Fig. 11)
2b. Bones compressed anteroposteriorly; thin; pitted surface (Fig. 9, P ) faces
posterolaterally; ventral tips very long; teeth small and numerous 152
(129-1 73) ; narrow mediolaterally ; ventral teeth larger than dorsal
teeth ................................................................
Ictiobus cyprinellus (Fig. 9)
2c. Bones slightly compressed anteroposteriorly; almost triangular in cross section; relatively heavy; pitted surface faces anterolaterally; ventral tips short;
teeth Small and numerous 134-142 ( 115-167) ; narrow mediolaterally;
ventral teeth larger than dorsal teeth ............................ Ictiobus niger and
I. bubalus (Fig. 10)
3a. Bones massive and heavy; large molariform teeth with wide, flat grinding
surfaces; usually less than 42 teeth/bone .................................................. 4
3b. Bones intermediate in weight; teeth arranged in comblike fashion; usually
small grinding surfaces on ventral teeth; conical projections or hooks on
anterior (inner) margins of dorsal teeth; usually more than 42 teeth/
5
bone ................................................................................................................
4a. Medial margins of ventral tips of bones interdigitated; 21 (20-22) teeth/
bone with four or five teeth on ventral one-half of bone ................................
............................................................................ Moxostoma hubbsi (Fig. 15)
4b. Medial margins of ventral tips of bones not interdigitated; 42 (35-51)
teeth/bone with seven teeth on ventral one-half of bone ............................
....................................................................Moxostoma carinatum (Fig. 14)
5a. 43 (40-45) teeth/bone; teeth relatively large with 15 on ventral one-half
of bone; ankyloses long with height of teeth decreasing from ventral to
dorsal; bones moderately heavy with ventral tips deep anteroposteriorly
..............................................................................
Cycleptus elongatus (Fig. 8 )
5b. 44-46 (40-51) teeth/bone
5b'. Teeth delicate with conical projections on anterior margins of all teeth;
small grinding surfaces: bones light and delicate; very flat (uncurved)
anteroposteriorly; dorsal one-half squarish; ventral tips round and not
deep anteroposteriorly .................... Hypentelium nigricans (Fig. 18)
5b". Teeth small and delicate with hooks on anterior margins of all teeth;
no grinding surfaces; bones light and delicate; slightly curved antero-
posteriorly; dorsal one-half rounded; ventral tips truncate and deep
anteroposteriorly ..........................................Lagochila lacera (Fig. 17 )
5c. 53-56 (49-57) teeth/bone; ventral teeth large with well-developed grinding
surfaces; dorsaI teeth with conical projections on anterior margins; bones
moderately heavy; wide mediolaterally; pitted surface well-developed;
lateral margin rough .......................................... Catostomus catostomus,
C . commersoni (Fig. 19) and
Chasmistes bsevirostris (Fig. 20)
5d. 60-90 (49-102) teeth/bone; small grinding surfaces on ventral teeth; dorsal
teeth with conical projections on anterior margins; bones intermediate in
Fig. 7.-Anterior
view of the third right epibranchial of Carpiodes
cyprinus. Crosshatching represents fibrous tissue
Figs. 8-9.-Cyclefitus
elongatus ( 8 ) and Zctiobus cyprinellus ( 9 )
Figs. 8-21.-The views depicted in Figs. 8-21 are: left-the ventral surface
(Chu, 1935) of the pharyngeal bones; center-the medial aspect of the most
ventral tooth on the left pharyngeal bone with the demarcation between the
tooth and bony ankylosis drawn; and right-the relative size of the dorsal surface of the most ventral tooth on the left bone. The bones depicted in Figs.
9-11 have been rotated medially by about 30' so as to permit more accurate
representation of their curvature and thinness.
size and weight ................................................ Moxostoma macrolepidotum, M . erythrurum (Fig. 16),
M. valenciennesi,
M . duquesnei and
M. anisurum
5e. 65 (56-76) teeth/bone; bones intermediate i n size and weight; lateral margins sharp; ventrally directed protuberances near dorsal tips; anterior and
posterior margins o f ventral tips thin and sharp .........................................
Erimyton oblongus (Fig. 1 2 )
5 f . 73 (72-74) teethlbone; bones very similar t o Catostomus and Chasmistes
(see 5c above) but more delicate and not as wide; teeth smaller ............
.......................................................................... Xyrauchen texanus (Fig. 2 1 )
5g. 85 (75-91) teeth/bone; bones and teeth very similar to Erimyton oblongus
(see 5e above) ........................................ Minytrema melanops (Fig. 1 3 )
Based on my study of descriptive anatomy resulting in the preceding
key, I was able to draw the conclusions presented below concerning
Figs. 10-12.-Zctiobus
bubalus ( l o ) , Carpiodes cyprinus ( 11 ) and Erimyton oblongus ( 1 2 ) the utility of catostomid pharyngeal bones and teeth in specimen identification.
The delicate, curved bones and numerous, small teeth render the
pharyngeal apparatus of the Ictiobinae distinctive among catostomids.
Carpiodes and lctiobus are easily distinguished from each other at the
generic level. However, separation of all species in these two genera
is not possible. The bones and teeth of the three Carpiodes species are
identical, but Ictiobus cyprinellus is easily separated from I. bubalus
and I. niger, two species with very similar bones and teeth.
Although the bones and teeth of the three tribes included in the
Catostorninae are similar, they differ enough to allow separation for
purposes of identification. Those of the Moxostomatini and Catostolnini are more similar to each other than either is to the Erimyzonini. The narrow bones with ventrally directed protuberances near
the dorsal tips mark the Erimyzonini as distinct from the other two
tribes. Within this tribe, it is difficult to separate Erimyzon from
Minytrema.
Among the Moxostomatini, Moxostoma hubbsi and M . carinatum
Figs. 13-15.-Minytrema
melanops (13), Moxostoma carinatum (14)
and Moxostoma hubbsi ( 1 5 )
are unique because of their heavy bones and molarifom teeth adapted
to crushing mollusk shells. This resemblance, however, has evolved
independently and these two species, members of different subgenera,
are not closely related (Robins and Raney, 1956). Although their diets
are similar, each species has distinctive pharyngeal bones, those of M.
hubbsi being heavier with fewer and larger teeth than in M. carinatum.
I studied five other species of Moxostoma but was not able to note any
outstanding differences in the form of the bones and teeth. The teeth
of M. valenciennesi are, however, larger than those of the other four
species. While the tooth counts differ among Moxostoma species, additional knowledge of intraspecific variation in the counts is desirable
before they can be regarded as reliable. Lagochila and Hypentelium
have similar but separable bones and teeth.
In the Catostomini, I was not able to distinguish the species of
Catostomus (sensu stricto), or to separate Catostomus (s.s.) from
Chasmistes, using only bones and teeth. My sample did not include
species of the subgenus Pantosteus. These similarities may be
explained, at least in part, by the fact that Catostomus is of rather
Figs. 16-18.-Moxostoma erythrurum (16), Lagochila lacera ( 1 7 ) and H y ~ e n t e l i u mnigricans ( 18) recent (late Pliocene) origin (Uyeno and Miller, 1965) and not greatly
diversified with respect to pharyngeal morphology. Although more
delicate, the bones and teeth of Xyrauchen fit the general tribal pattern
and probably reflect the herbivorous diet (Carlander, 1969) of this
species.
These findings, then, indicate that catostoxnid pharyngeal bones
and teeth are reliable for specimen identification at the specific, generic
or tribal levels, depending on the particular subgroup under consideration. I n most instances, therefore, they supplement other morphologic
and meristic information and are, by themselves, inadequate for species
diagnoses.
Acknowledgments.-Financial support for this study was provided by a Biomedical Sciences General Research Support Grant from Brown University. For
the loan of specimens I am grateful to: James C. Underhill and the late
Samuel Eddy, University of Minnesota; Loren G. Hill, University of Oklahoma;
Karel F. Liem and Robert Schoknecht, Harvard University; Fred Martini,
Cornell University; Gerald R. Smith, University of Michigan; Stanley H. Weitzman, National Museum of Natural History; and Carolee Bussjaeger, University
of Oklahoma Health Sciences Center.
Figs. 19-21.-Catostomus commersoni (19), Chasmistes brevirostris
(20) and Xyrauchen texanus (21)
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