Descriptive osteology of the family Chaudhuriidae (Teleostei, Synbranchiformes, Mastacembeloidei), with a discussion of its relationships

63 Pages·2003·6.6 MB·English

by  Britz, Ralf

AMERICAN MUSEUM
Novitates
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3418, 62 pp., 29 figures, 7 tables October 29, 2003
Descriptive Osteology of the Family
Chaudhuriidae (Teleostei, Synbranchiformes,
Mastacembeloide1), with a Discussion of
Its Relationships
RALF BRITZ! AND MAURICE KOTTELAT?
ABSTRACT
The little known earthworm eel family Chaudhuriidae consists of nine small to minute
species of Asian freshwater fishes. In this paper, the osteology of seven representatives of the
family is described in detail for the first time. We propose a list of 21 synapomorphies to
support chaudhuriid monophyly. Reductive characters are: loss of basisphenoid, pterosphenoid,
endopterygoid, dermopalatine, pars autopalatina, posttemporal, gill rakers, toothplate on phar-
yngobranchial two, distal pectoral radials, lateral line canals, dorsal- and anal-fin spines and
their supporting pterygiophores, epurals, uroneurals, parhypural, and reduction in numbers of
epicentrals and hypurals. Progressive characters are: presence of a long membrane bone pro-
cess on autosphenotic, a boomerang-shaped ectopterygoid with a long preorbital extension, an
anterior process of membrane bone of the metapterygoid, a unique arrangement of dorsal gill
arch elements, separate foramina for the three trigeminal branches, and a ventromedian keel
on the first vertebra. The new information is used to critically reevaluate previous hypotheses
of chaudhuriid relationships. Finally, the issue of miniaturization in chaudhuriid fishes is ad-
dressed and discussed.
‘Lehrstuhl fiir Spezielle Zoologie, Universitét Tiibingen, Auf der Morgenstelle 28, 72076 Tiibingen, Germany;
and Research Associate, Department of Ichthyology, American Museum of Natural History. Present address: Division
of Fishes, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560. e-mail:
[email protected]
? Case postale 57, 2952 Cornol, Switzerland. e-mail: [email protected]
Copyright © American Museum of Natural History 2003 ISSN 0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3418
INTRODUCTION lications, without justification placed the
three genera in two families, Chaudhuriidae
Chaudhuriidae, or earthworm eels, com-
and Pillaiidae, the latter containing Garo and
prise small to minute, eel-like freshwater
Pillaia. Travers’ (1984b) synonymization of
fishes (fig. 1) distributed in Southeast Asia.
the three chaudhuriid genera was criticized
They usually live among dense vegetation in
by Kottelat and Lim (1994) who retained Pil-
standing or slowly flowing waters (Kottelat
laia as a valid genus. Subsequently, Kullan-
and Lim, 1994; Kerle et al., 2000). Currently,
der et al. (2000) presented evidence for the
the family consists of the following nine spe-
validity of Garo.
cies in six genera: Chaudhuria caudata An-
Travers (1984b) concluded that the three
nandale, 1918; Chaudhuria fusipinnis Kot-
chaudhuriid species known at that time
telat and Britz in Kottelat, 2000; Pillaia
formed a monophyletic lineage with the mas-
indica Yazdani, 1972 (fig. 1); Pillaia kachin-
tacembelid Sinobdella (as Rhynchobdella) si-
ica Kullander, Britz, and Fang, 2000; Garo
khajuriai Talwar, Yazdani, and Kundu, 1977; nensis and transferred the latter taxon from
Nagaichthys filipes Kottelat and Lim in Kot- Mastacembelidae to Chaudhuriidae. Travers’
telat, 1991; Chendol keelini Kottelat and (1984b) changes were criticized by Kottelat
Lim, 1994; Chendol lubricus Kottelat and (1991) and Kottelat and Lim (1994). Johnson
Lim, 1994; Bihunichthys monopteroides Kot- and Patterson (1993) reported problems with
telat and Lim, 1994. Travers’ (1984b) characterization of the
The family Chaudhuriidae was erected by Chaudhuriidae, and Britz (1996), reinvesti-
Annandale (1918) for the small eel-like fish, gating Travers’ (1984b) hypothesis of a
Chaudhuria caudata, from Lake Inle, Bur- monophyletic Chaudhuriidae including Si-
ma. He classified it along with the true eels nobdella, demonstrated that the latter genus
in the order Apodes, as did Whitehouse is a plesiomorphic mastacembelid rather than
(1918). Soon thereafter, Regan (1919) hy- a chaudhuriid.
pothesized a close relationship between the Travers’ (1984a, 1984b) osteological stud-
families Chaudhuriidae and Mastacembeli- ies were based only on two, and Britz’
dae (spiny eels), a view further supported by (1996) account only on one, of the nine
Annandale and Hora (1923). chaudhuriid species because additional ma-
More than 50 years passed until a second terial of the remaining taxa was not available,
species of chaudhuriid was described, Pillaia
and some of the species were not described
indica (Yazdani, 1972), which was subse-
at that time. Recent extensive collections of
quently placed in a separate new family Pil-
well-preserved specimens of chaudhuriids
laiidae (Yazdani, 1976). Talwar et al. (1977)
from different areas in Southeast Asia yield-
described a second species of Pillaia, P. kha-
ed the opportunity to study the osteology of
juriai, transferred four years later to a new
representatives of this poorly known family.
genus Garo by Yazdani and Talwar (1981).
Our investigation has several objectives.
Annandale (1918), Whitehouse (1918), and
First, we provide a detailed description of the
Annandale and Hora (1923) provided more
skeleton of seven of the nine species of
cursory remarks regarding osteology, but
Chaudhuriidae as a reference work for future
Travers (1984a, 1984b) published the first
studies. We then utilize this new information
comprehensive osteological description of
to critically reevaluate and discuss the char-
Chaudhuriidae and Pillaiidae and reviewed
their phylogenetic relationships with Masta- acters that Travers (1984b) listed as synapo-
cembelidae. Travers (1984a, 1984b) consid- morphies for Chaudhuriidae and Mastacem-
ered the differences between Chaudhuria, beloidei. Finally, we address the issue of
Pillaia, and Garo insufficient to keep them miniaturization in chaudhuriid fishes, when
in different genera and families and therefore compared to their closest relatives, the mas-
united the three species in Chaudhuria, fam- tacembelids and synbranchids. A phyloge-
ily Chaudhuriidae. Strangely, Yazdani (1990) netic analysis of chaudhuriids is beyond the
did not discuss or even cite Travers’ (1984a, scope of this paper and will be dealt with in
1984b) two papers and, as in his earlier pub- a forthcoming publication.
2003 BRITZ AND KOTTELAT: OSTEOLOGY OF CHAUDHURIDAE 5
Fig. 1. Pillaia indica, live individuals. A. Adult male, ca. 80 mm. B. Subadult male, ca. 65 mm. C.
Close-up of head of same specimen. D. Close-up of adult male, ca. 85 mm. Note absence of rostral
tentacle.
MATERIALS AND METHODS 34-38 mm), CMK 5510 (1, disarticulated),
CMK 15965 (6, 26.5—42.7 mm); C. fusipin-
Our study is based on the following
nis: CMK 15967 (6, paratypes, 29.7—36.5
cleared and double-stained (C&S) material,
provided length is standard length (SL): Bi- mm); Chendol keelini: AMNH 217795 (10,
hunichthys monopteroides: AMNH 217765 7.5—65 mm), CMK 7949 (1, paratype, 44.2
(1, 42 mm), CMK 7947 (2, paratypes, 31—36 mm), ZRC 17779 (1, ca. 49 mm); C. lubri-
mm), ZRC 16835—-847 (2, disarticulated); cus: CMK 10638 (2, paratypes, 38.2—50
Chaudhuria caudata: AMNH 217415 (1, 40 mm); Nagaichthys filipes: CMK 6660 (1,
mm), CMK 7934 (1, 52 mm), CMK 8241 (6, paratype, 30.8 mm), CMK 9601 (1, 27 mm),
- AMERICAN MUSEUM NOVITATES NO. 3418
CMK 10870 (2, 25-28 mm), CMK 11387 (1, rather seems to have come from additional
28.5 mm); Pillaia indica: USNM 372577 (1, specimens of Chaudhuria caudata that An-
85.8 mm), USNM 372577 (1, 61 mm). Fin nandale and Hora collected during a second
ray counts reported in table 6 for Nagaichth- trip to Lake Inle in 1922 and that were used
ys filipes are based on additional alcohol in part for Annandale and Hora (1923). This
specimens: CMK 11267 (6, 20.7—27.6 mm), interpretation is in accordance with the in-
CMK 10870 (2, 25.5—26.4 mm), CMK 9601 formation provided in the online catalog of
(1, 29.4 mm), CMK 10623 (1, 26.0 mm), the British Museum. There, only one speci-
CMK 16683 (2, 16.6—20.6 mm), CMK men (BMNH 1920.1.20.1) is listed as para-
16705 (3, 27.3-29.0 mm), CMK 16723 (1, type of C. caudata, and those specimens cit-
31.2 mm), CMK 16718 (3, 25.3—27.4 mm). ed by Travers as types (BMNH 1923.3.10.1—
Cleared-and-stained representatives of 4) have no such status. It is unfortunate that
mastacembelid and synbranchid taxa used as Travers (1984a) did not specify if the three
comparative material: Macrognathus panca- C&S specimens agreed in all the characters
lus: AMNH 217414 (8, 4.5-36 mm); Mas- that he described for C. caudata because it
tacembelus erythrotaenia: AMNH 42129 (1, is still unclear if the Thai and Burmese pop-
277 mm); M. sp. (incorrectly labeled as Ma- ulations are conspecific. However, because
crognathus aculeatus): AMNH 097654 (1, he did not mention any differences among
158 mm). Macrotrema caligans: MCZ 47107 the specimens, it may be assumed that no
(2, 172-178 mm); Monopterus albus: major differences existed. Travers’ (1984a)
AMNH 41579 (1, 167 mm); Ophisternon MCZ specimen (MCZ 47058) was collected
aenigmaticum: AMNH 31573 (1, 72 mm); in Thailand. We could not compare Travers’
Synbranchus marmoratus: AMNH 30213 (1, (1984a) description with this specimen to
142 mm), MCZ 52376 (3, 65-140 mm; 1, clarify discrepancies we encountered be-
disarticulated). tween his description of C. caudata and our
We were able to include in our study rep- own material, because it now lacks its head.
resentatives of seven of the nine described We are also not certain if our specimens
chaudhuriid species. Because of scarcity of of Pillaia (fig. 1) actually belong to the spe-
material we could not investigate specimens cies P. indica. They came from a local or-
of Garo khajuriai and Pillaia kachinica. namental fish exporter in Coochbehar in
Some additional remarks on the material are Western Bengal and were purportedly col-
pertinent. We cannot be certain that all our lected not far from this locality. The locality
material from different areas in Southeast for the holotype and three of the paratypes
Asia listed as Chaudhuria caudata is con- of P. indica is Sumer stream of the Khasi
specific with C. caudata from Inle Lake, and Jaintia Hills 22 km north of Shillong (at
Burma. Although we tried hard, we were not 1068 m altitude), and the fourth paratype
successful in obtaining material of this taxon came from a stream at Umshing 13 km north
from the type locality, Lake Inle, from our of Shillong (at 1524 m altitude). Both these
own collecting there or loans from the Zoo- localities are about 240 km from the area of
logical Survey in India. Coochbehar, the source of our specimens.
For his osteological study of the three spe- The specimens of Pillaia at our disposal,
cies known at his time, Travers (1984a, however, can be clearly assigned to this ge-
1984b) had specimens of Pillaia indica and nus on the basis of a single element in the
Chaudhuria caudata, but not of Garo kha- upper jaw (fused maxilla and premaxilla?).
juriai. Concerning Chaudhuria caudata, he They also do not differ substantially in the
studied three specimens, two from BM(NH) characters provided in the original descrip-
that he listed as types (Travers, 1984a: 8) and tion of P. indica (Yazdani, 1972), and we
that were stained with alizarin only and one therefore consider them to be conspecific
from MCZ that was double stained. It is un- with that species. However, we are unable to
likely that the three specimens from explain significant differences between the
BM(NH) are actually types because Annan- osteological features we observed in our
dale (1918) mentioned only four specimens specimens and those described by Travers
in the type series. The BM(NH) material (1984a). These differences will be addressed
2003 BRITZ AND KOTTELAT: OSTEOLOGY OF CHAUDHURIDAE 5
below. Of the two specimens of P. indica CR caudal-fin ray
that Travers (1984a: 43) had on loan from De dentary
the Zoological Survey of India, the larger DHh dorsal hypohyal
specimen (68 mm) was “poorly preserved DR distal radial of pterygiophore
Eb epibranchial
and stained (alizarin only).’’ Thus it is most
Ecpt ectopterygoid
likely, although not stated clearly by Travers
Epo epiotic
(1984a: 43), that his description was based
EthPl ethmoid plate
mainly on the smaller specimen (44.5 mm)
Exoc exoccipital
that “‘has responded well to both stains (aliz- Fe fenestration of neural arches
arin & alcian blue).”’ Fr frontal
FV,9 5
The only other chaudhuriid species de- foramen of first, second, or third
scribed from northern India is Garo khaju- branch of trigeminal nerve
riai. The holotype was collected from rice foramen of facial nerve
foramen of vagal nerve
paddies at Rongrengiri, Garo Hills, Megha-
hypural
laya, the paratype from Baguri (Kaziranga
hypobranchial
Wildlife Sanctuary) Sibsagar district, Upper
hemal spine
Assam. No osteological information is avail-
hyosymplectic cartilage
able for this species, and all other informa- hyomandibular
tion provided in the original description (Tal- interhyal
war et al., 1977) is scarce and unsatisfactory. interhyal cartilage
However, a recently collected specimen from interopercle
Assam assigned to the genus Garo (Kullan- lateral commissure
der et al., 2000) shows that its upper jaw con- lateral ethmoid
lamina orbitonasalis
sists of the usual two paired bones, maxilla
Meckel’s cartilage
and premaxilla. Therefore, it seems we can
mesethmoid
exclude the possibility that we could explain
metapterygoid
the differences between our specimens and
maxilla
Travers’ (1984a) account of P. indica by as-
nasal
suming ours were actually a Garo species. neural spine
One unlikely explanation for the observed opercle
differences is that our specimens from parapophysis
Coochbehar represent an additional yet un- pharyngobranchial
described species of Pillaia. These taxonom- posterior ceratohyal
ic uncertainties can only be resolved once postcleithrum
comparative material of the different species pars metapterygoidea of palatoquad-
involved from the poorly collected area of rate
proximal-middle radial of ptery-
northeastern India becomes available.
giophore
Pmx premaxilla
ABBREVIATIONS
preopercle
ACh anterior ceratohyal Poza postzygapophysis
An angular PQ pars quadrata of palatoquadrate
Ana anguloarticular PR? pectoral radial?
Asph autosphenotic Pro prootic
Bb basibranchial PRPI pectoral radial plate
BbC basibranchial cartilage Prza prezygapophysis
Bh basihyal Psph parasphenoid
Boc basioccipital Pto pterotic
BR branchiostegal ray PU preural centrum
Cb ceratobranchial quadrate
ChC ceratohyal cartilage fin soft ray
Cl cleithrum Ra retroarticular
Cm coronomeckelian RC rostral cartilage
Co coracoid Ri rib
CoC coracoid cartilage Sc scapula
6 AMERICAN MUSEUM NOVITATES NO. 3418
ScC scapular cartilage remnant of the trabecula communis, extends
SccoC scapulocoracoid cartilage back into the orbit (fig. 2B). The ventral cor-
Scl supracleithrum ner of the lateral wing of the lateral ethmoid
Soc supraoccipital bears an articular facet for the lacrimal, the
Sop subopercle
only bone of the circumorbital series devel-
SP spinelike projection on neural arch
oped in chaudhuriids. The lacrimal forms the
in front of neural spine
lateral wall of the nasal capsule (fig. 2B). Its
Sy symplectic
posteriormost part has an ascending process
TH trabecular horn
TrC trabecula communis that contacts the posterior part of the dorsal
TS tectum synoticum anterior lamina of the lateral ethmoid. Slight-
U ural centrum ly anterior to this, the lacrimal has an inci-
UP4 fourth upper pharyngeal toothplate sure that represents the ventral rim of the
V1,2,... first, second, ... vertebra posterior nasal opening. The anterior dorsal
VHh ventral hypohyal
lamina of the lateral ethmoid forms its dorsal
VHhC ventral hypohyal cartilage
rim. In front of the posterior nasal opening
VK ventral keel on first centrum
the lacrimal contacts the anterior lamina of
Vo vomer
the lateral ethmoid and the nasal bone, so
that the orifice is completely surrounded by
RESULTS
bone. In specimens smaller than the one fig-
For the purpose of description, the skele-
ured, the respective bones may leave narrow
ton of chaudhuriids is divided into the fol-
gaps between each other.
lowing major parts: neurocranium; hyopala-
Medially the nasals are separated by the
tine arch and opercular apparatus; hyoid,
unpaired mesethmoid, a thin, vertical, blade-
urohyal, and branchial arches; shoulder gir-
like bone whose anterior end is fused to the
dle with pectoral fin; vertebral column with vomer (fig. 2B). The mesethmoid is con-
dorsal, anal, and caudal fins; and scales, if
nected ventrally by a short cartilaginous rod
applicable.
to the area where the lateral ethmoids meet
in the midline. This cartilage is a remnant of
OSTEOLOGY OF CHENDOL KEELINI the narrow nasal septum found in other chau-
Chendol keelini reaches a size of at least dhuriids and in mastacembelids (see Britz,
57 mm at the type locality in Malaysia (Kerle 1996). A conspicuous rodlike rostral carti-
et al., 2000), but specimens from the popu- lage articulates with the anteriormost dorsal
lation in Jambi, Sumatra, grow to 81.3 mm part of the mesethmoid (fig. 2A, B). The
(ZRC 41666, Tan, personal commun.). It is proximal part of the cartilage, which lies an-
thus the second largest species studied here. terior to the tip of the vomer and between
C. keelini is the only chaudhuriid with scales. the heads of the maxillae, may ossify in larg-
They are confined to the posterior third of er specimens. The vomer underlies the eth-
the body (Kottelat and Lim, 1994; personal moid region as a thin splint of bone. Poste-
obs.). riorly the vomer tapers to a needle-thin pro-
NEUROCRANIUM (fig. 2): The neurocranium cess located in a groove of the parasphenoid
is a solidly ossified case with the widest part and extends along half the length of that
in the occipital region from where it tapers bone (fig. 2C). The anterior end of the vomer,
to the snout. which is indistinguishably fused to the mes-
The ethmoid region consists of four bones. ethmoid, is enlarged and bears two articular
The elongate nasal covers the olfactory or- facets for the maxillary bones.
gan dorsally. It is sutured to the lateral eth- The orbital region, as the area between the
moid, which forms the caudal and dorsolat- otic and the ethmoid part, is dominated in
eral wall of the nasal capsule. The lateral eth- dorsal aspect by the large frontal, which ex-
moid has developed an anterior dorsal lamina tends from the anterior end of the otic region
of membrane bone, which, along with the na- to the anterior part of the orbit (fig. 2A, B).
sal, forms a rigid cover for the nasal organ The paired frontals are sutured to each other
(fig. 2). Where the lateral ethmoids meet in along most of their length and taper toward
the midline, an elongate block of cartilage, a their anterior end where they contact the na-
2003 BRITZ AND KOTTELAT: OSTEOLOGY OF CHAUDHURIDAE 7
Fig, 2 Chendol keelini, AMNH 217795, 65 mm, neurocranium and anterior vertebrae, cartilage in
gray. A. Dorsal view, second vertebra only shown in part. B. Lateral view. C. Ventral view, second
vertebra only shown in part.
sals. There is no trace of a cephalic sensory vator arcus palatini originates. There is no
canal within these bones. The frontal is bor- pterosphenoid or basisphenoid developed.
dered ventrally over most of its length by the The prootic is the dominant bone in the
autosphenotic, and it contacts the prootic an- lateral wall of the cranium (fig. 2B, C). It is
teriorly and pterotic posteriorly (fig. 2B). sutured dorsally to the autosphenotic over
Caudally the frontal reaches the large supra- most of its length, and only its most anterior
occipital. The autosphenotic is an elongate tip contacts the frontal. Ventrally at the pos-
bone tapering toward its anterior end. Its pos- terior two-thirds it is bordered by the paras-
terior part contributes to the anterior articu- phenoid. It encloses or contributes to the fo-
lation for the hyomandibular and in larger ramina for the cranial nerves V,,,; and VII,
specimens it has a ridge from which the le- all of them exiting through separate forami-
8 AMERICAN MUSEUM NOVITATES NO. 3418
na. The prootic also contributes to the ante- traverse the bone. Similar depressions are
rior articulation of the hyomandibular and to also present in the rostral part of the frontals,
the articulatory groove that extends to the on the dorsal face of the nasals and the mem-
pterotic. It also forms a canal for the jugular branous wings of the lateral ethmoid (fig.
vein bridged laterally by a narrow ring of 2A). The intercalar is absent. The postero-
bone, the lateral commissure, situated ventro- ventral part of the otic bulla and the ventral
lateral to the anterior articulation of the hyo- part of the ball-and-socket articulation with
mandibular with the ear capsule. This lateral the first vertebra are formed by the basioc-
commissure represents the anterior border of cipital.
the foramen for the hyomandibular branch of HYOPALATINE ARCH AND OPERCULAR AP-
the facialis nerve. The prootic also houses PARATUS (fig. 3): The hyopalatine arch con-
the anterior part of the auditory bulla. sists of hyomandibular, symplectic, quadrate,
The parasphenoid spans from the orbital metapterygoid, and ectopterygoid. There is
to the occipital region (fig. 2B, C). It is nar- no endopterygoid or palatine (neither dermo-
row in the orbital region, broadest at the level nor autopalatine) developed. The hyoman-
of the anterior articulation of the hyomandib- dibular has three articular heads. The anterior
ular, then tapers again and splits into two head articulates with the autosphenotic/pro-
long, thin arms that extend to the articulation otic, the posterior head with the pterotic, and
of the occipital region with the first vertebra. the opercular head with the opercle. The
Anteriorly it has a shallow ventral groove for crest between the anterior and the posterior
reception of the vomer, which extends over head rests in a groove on the prootic and
half of its length. In the area of the trabecula pterotic to which it is attached by connective
communis in the orbital region, the paras- tissue. The lateral side of the hyomandibular
phenoid slightly curves dorsally, becoming possesses a vertical crest that is bound to the
detached from the underlying vomer. Thus a preopercle by connective tissue (fig. 3A).
narrow gap forms between the two bones. The hyomandibular is pierced by a foramen
The pterotic is situated at the widest part of the hyomandibular trunk of the facial
of the cranium and forms the posterior part nerve. An anterior lamina of membrane bone
of the articulatory groove and articulation for extends toward, but does not contact, the me-
the hyomandibular (fig. 2B, C). The epiotic tapterygoid and ventrally contacts the sym-
is a small cap of bone at the posterodorsal plectic. The symplectic is long and rodlike
corner of the otic capsule. It may possess a and its anterior end fits into a groove in the
posteriorly directed process in larger speci- quadrate (fig. 3B). The latter has a strong
mens to which attach tendons of the trunk posteroventral process of membrane bone
musculature. tightly bound to the preopercle by connective
The broad supraoccipital forms the roof of tissue.
the posterior part of the cranium (fig. 2A, B). A small zone of cartilage separates the
In this large specimen it has a prominent quadrate and metapterygoid (fig. 3). An an-
transverse ridge along its posterior margin terior process of membrane bone from the
for insertion of the trunk musculature. There metapterygoid bridges the gap between this
are no parietals. They are not fused to the bone and the quadrate. The ectopterygoid is
supraoccipital, but are rather lost, as evi- long and narrow and curved like an asym-
denced by our ontogenetic series of C. kee- metrical boomerang. Its posterior end artic-
lini. ulates with the medial part of the quadrate.
The exoccipital forms the posterodorsal The area of the ectopterygoid that turns from
part of the otic bulla, the dorsal part of the an anterodorsal to a more horizontal plane is
ball and socket articulation with the first ver- tightly bound to the lateral ethmoid. The an-
tebra, and the lateral and dorsolateral wall of teriormost tip of the ectopterygoid is directed
the foramen magnum (fig. 2). The paired ex- toward the midline and there is firmly at-
occipitals are separated from each other in tached to the vomer.
the dorsal midline by a cartilaginous area. In The four bones of the opercular apparatus
a dorsal view they may have some small de- are thin and in some areas only weakly os-
pressions in the bone, which may or may not sified (fig. 3A, C). The large opercle articu-
2003 BRITZ AND KOTTELAT: OSTEOLOGY OF CHAUDHURIDAE
lop Sop
Pop
1mm
Fig. 3. Chendol keelini, AMNH 217795, 65 mm, cartilage in gray. A. Hyopalatine arch, lateral view.
B. Upper and lower jaws, lateral view. C. Hyopalatine arch, medial view. D. Upper and lower jaws,
medial view.
lates with the opercular head of the hyoman- is well ossified in its anterodorsal part, which
dibular. It has a prominent ridge on its inner is connected to the hyomandibular, the sym-
side that extends from the articulation with plectic, and the posteroventral process of the
the hyomandibular caudoventrally (fig. 3C). quadrate. Ossification is weaker in its pos-
The subopercle is a thin, weakly ossified terior area. The interopercle is located medial
plate ventral to the opercle. The preopercle and ventral to the preopercle; it is wide in
10 AMERICAN MUSEUM NOVITATES NO. 3418
the posterior part and attenuates rostrally to elongate bone with a cartilaginous tip (fig.
a tip (fig. 3C) from which the interoperculo- AD).
retroarticular ligament originates. The anter- There are six well-developed long bran-
odorsal area of this bone is better ossified chiostegal rays, four articulating with the an-
than the caudoventral area. terior and two with the posterior ceratohyal
The upper jaw comprises the maxilla and (fig. 4A, B). The four posterior rays articu-
premaxilla, which are tightly bound together late with the lateral face and the anterior ones
(fig. 3B, D). The premaxilla bears teeth along with the medial face of the ceratohyals. If the
its ventral margin. The maxilla is toothless branchiostegal membrane is folded, the two
with a wide posterior part that tapers anteri- anterior rays come to lie medial to the cera-
orly. Its anterior head articulates with the tohyals along their whole length and thus are
ventrolateral face of the rostral tip of the separated from the posterior four rays.
The urohyal (fig. 4C) is bladelike with a
fused mesethmoid/vomer. The dentary op-
poses the premaxilla and bears teeth along vertical lamina of bone and two anterior pro-
its dorsal margin. Its posterior end bifurcates cesses that attach to the ventral hypohyals by
ligaments.
into a winglike dorsal coronoid process that
There are three ossified basibranchials (fig.
is ligamentously attached to the medial side
4D), with the first being shorter than the sec-
of the posterior end of the maxilla, and a
ond and third. The latter ends between the
long posteroventral process that runs along
third hypobranchials. There are three hypo-
the anguloarticular (fig. 3D). The latter bone
branchials of different shape. The first hypo-
articulates posteriorly with the quadrate.
branchial is a short rodlike bone. It articu-
From its widest part it tapers anteriorly and
lates with the anterior third of the second
ends at the base of the bifurcation of the den-
basibranchial. The second hypobranchial
tary. The posteroventral corner of the angu-
bears a ventrally directed, cartilaginously
loarticular is capped by the small retroarti-
tipped process at its anterior end. It articu-
cular, to which the ligament from the inter-
lates with the anterior third of the third bas-
opercle is attached. Meckel’s cartilage is still
ibranchial. The third hypobranchial bears
well developed and visible in a medial view
several teeth on its dorsal surface. Its anterior
of the lower jaw. Dorsal to its posterior end
end also has a ventrally directed anterior pro-
lies the small round coronomeckelian bone.
cess. The posteriomedial part of hypobran-
HyYoimp, UROHYAL, AND BRANCHIAL ARCHES
chial 3 is produced into a short broad caudal
(fig. 4): The interhyal is relatively large (fig.
process with a cartilaginous tip. This articu-
4A, B). Its upper tip articulates with the hy-
lates with the fourth basibranchial, a small
opalatine arch at the cartilaginous area be-
nodule of cartilage that articulates posteriorly
tween hyomandibular and symplectic and its
with the cartilaginous anterior tip of cerato-
lower tip with the posterior end of the pos-
branchial 4 (fig. 4D). All ceratobranchials are
terior ceratohyal. The latter bone is separated
elongate rodlike bones. Ceratobranchial 5
from the anterior ceratohyal by a cartilagi-
bears numerous conical teeth on its dorsal
nous strip. This strip is bridged on the medial
surface.
side by a strong caudally directed dorsal pro- There are four epibranchials whose lateral
cess of the anterior ceratohyal that fits into a ends articulate with the respective cerato-
groove of the posterior ceratohyal (fig. 4B). branchials (fig. 4D). Epibranchials 1 and 2
The anterior ceratohyal has a wide hind part are short, thin, and rodlike. The medial end
that tapers at about half its length. The dorsal of epibranchial | articulates with the anterior
and ventral hypohyals are small ossifications end of pharyngobranchial 2; the medial end
capping the rostral end of the anterior cera- of epibranchial 2 articulates with the poste-
tohyal (fig. 4A, B). The ventral hypohyal rior end of the same pharyngobranchial and
also serves as point of attachment for the lig- the anterior end of pharyngobranchial 3. Epi-
ament from the urohyal. The dorsal hypohyal branchial 3 is also rodlike but bears a dor-
articulates with the basihyal and extends pos- sally directed uncinate process that articu-
teriorly beyond the posterior tip of the ven- lates with a similar process on epibranchial
tral hypohyal. The basihyal is a stout and 4. The latter has a club-shaped medial tip for