Pharyngeal Teeth Research Articles

A revised generic taxonomy for Far East Asian minnow Rhynchocypris and dace Pseudaspius

The Far East Asian dace and minnow clade Pseudaspininae of Leuciscidae sensu stricto, as recognized by molecular phylogeny, comprises three genera, viz. Oreoleuciscus, Rhynchocypris (removed from Phoxinus), and Pseudaspius (including hitherto Tribolodon spp.). Descriptions of Rhynchocypris and Pseudaspius are revised following comparison with Oreoleuciscus as well as with two Eurasian genera Leuciscus and Phoxinus. Eurasian Leuciscus is distinguished from the other genera by having fewer than 60 longitudinal scales and Phoxinus by having a comb-like scale patch between the pectoral fin and opercle. Far East Asian Oreoleuciscus is unique in having a single pharyngeal teeth row, Rhynchocypris in having the anal fin base originating under the posterior end of the dorsal fin base, and Pseudaspius in having axillary scales on pelvic fin base.

Evolutionary developmental genetics of teeth and odontodes in jawed vertebrates: a perspective from the study of elasmobranchs.

Most extant vertebrates display a high variety of tooth and tooth-like organs (odontodes) that vary in shape, position over the body and nature of composing tissues. The development of these structures is known to involve similar genetic cascades and teeth and odontodes are believed to share a common evolutionary history. Gene expression patterns have previously been compared between mammalian and teleost tooth development but we highlight how the comparative framework was not always properly defined to deal with different tooth types or tooth developmental stages. Larger-scale comparative analyses also included cartilaginous fishes: sharks display oral teeth and dermal scales for which the gene expression during development started to be investigated in the small-spotted catshark Scyliorhinus canicula during the past decade. We report several descriptive approaches to analyse the embryonic tooth and caudal scale gene expressions in S. canicula. We compare these expressions wih the ones reported in mouse molars and teleost oral and pharyngeal teeth and highlight contributions and biases that arise from these interspecific comparisons. We finally discuss the evolutionary processes that can explain the observed intra and interspecific similarities and divergences in the genetic cascades involved in tooth and odontode development in jawed vertebrates.

Three new species of Syllis Savigny in Lamarck, 1818 (Annelida: Syllidae) from the south coast of South Africa.

Over the last five decades, only two new species of Syllis (Syllidae, Annelida) have been described from South Africa, suggesting a greatly underestimated richness and the expectation that many more indigenous species still remain undescribed. In this paper, we describe three new species from algal turf along a rocky shore on the south coast of South Africa. All three species are characterised by having pseudo-simple chaetae by loss of blade and enlargement of shafts together with compound heterogomph bidentate falcigers. Syllis zahri sp. nov. (up to 5 mm long) is characterised by light pink to light brown colouration on its prostomium and anterior chaetigers, dark transverse bars that fade towards the posterior region, superior anterior chaetae having short spines and posterior parapodia with distally hollow aciculae. Syllis jaylani sp. nov. (up to 7 mm long) is narrow anteriorly, relatively wider at midbody and tapers posteriorly toward the pygidium, has a pharyngeal tooth slightly back from the anterior margin, strongly bidentate chaetae with teeth perpendicular to the main shaft, thin sinuose bidentate ventral simple chaetae with a serrated edge and pseudo-simple chaetae with a serrated edge in anterior parapodia. Syllis bunaa sp. nov. (up to 9 mm long) shows a characteristic dark brown colouration on its prostomium and anterior region, is distinctly rounded dorsally, and has unidentate or minutely bidentate chaetae, up to three pseudo-simple chaetae on parapodia along the whole body and posterior ventral simple chaetae that are thick with rounded tips or sinuose with a serrated inner edge.

Expression patterns of ectodysplasin and ectodysplasin receptor during early dental development in zebrafish

This study aims to study the expression patterns of ectodysplasin (EDA) and ectodysplasin receptor (EDAR) during the early development of zebrafish and provide a foundation for further research of the Eda signaling pathway in tooth development. Total RNA was extracted from zebrafish embryos at 48 hours postfertilization (hpf) and then reverse transcribed for cDNA library generation. The corresponding RNA polymerase was selected for the synthesis of the digoxin-labeled antisense mRNA probe of zebrafish pharyngeal tooth specific marker dlx2b and Eda signaling-associated genes eda and edar in vitro. The three sequences were ligated into a pGEMT vector with a TA cloning kit, and polymerase chain reaction (PCR) was applied to linearize the plasmid. The resultant PCR sequences were used as templates for synthesizing Dig-labeled mRNA probe dlx2b, eda, and edar. Zebrafish embryos were collected at 36, 48, 56, 60, 72, and 84 hpf, then whole mount in situ hybridization was performed for the detection of eda and edar expression patterns. Then, their expression patterns at 72 hpf were compared with the expression pattern of dlx2b. The mRNA antisense probes of dlx2b, eda, and edar were successfully obtained. The positive signals of eda and edar were observed in zebrafish pharyngeal tooth region at 48-72 hpf and thus conform to the signals of dlx2b in the positive regions. The ligand eda and edar, which are associated with the Eda signaling pathway, are strongly expressed only at the pharyngeal tooth region in zebrafish from tooth initiation to the morphogenesis stage. Thus, the Eda signaling pathway may be involved in the regulation of the early development of zebrafish pharyngeal teeth.

Treatment with synthetic glucocorticoid impairs bone metabolism, as revealed by in vivo imaging of osteoblasts and osteoclasts in medaka fish

Glucocorticoids (GCs) play an important role in the stress reaction and function in the development of multiple tissues in our body. When given chronically in supraphysiologic doses, GCs are associated with orthodontic tooth movement, with serious side effects and particularly adverse effects on bone metabolism. However, the effects of steroids on bone cell dynamics are incompletely understood. Therefore, in this present study we examined the participation of osteoblasts and osteoclasts in osterix-DsRed/TRAP-EGFP double transgenic (Tg) medaka treated with synthetic GCs. Chronic continuous administration of prednisolone (PN) significantly reduced the fluorescence signals in the whole body of both osterix-DsRed and TRAP-EGFP medaka at 18 days, and those of the pharyngeal bone and tooth region at 32 days. To examine the capacity of the medaka for fracture healing during chronic administration of PN, we caused a fracture of a part of the bony fin ray at 18 days after the initiation of PN continuous administration. The bone fracture healing was significantly delayed by 32 days, accompanied by decreased signal area of both osterix-DsRed and TRAP-EGFP compared with that of the control. Next, to investigate the effect of acute administration of GC on the fracture healing, we started administration of dexamethasone (DX) immediately after the bone fracture, and this administration lasted during the 11 days of fracture healing. The results showed that the TRAP-EGFP-positive osteoclasts were reduced in area, but not the osterix-DsRed-positive osteoblasts. Lastly, to confirm the function of the glucocorticoid receptor in bone healing, we generated glucocorticoid receptor 2-deficient medaka (gr2−/−). The fluorescent signal area of osterix-DsRed and TRAP-EGFP were increased at bone fracture sites in these fish, and DX treatment of them decreased the TRAP-EGFP signal area compared with that for the control fish. Our results indicate that GRs negatively regulated osteoclast recruitment and the accumulation of osteoblasts in bone fracture healing.

Fish, amphibian and reptilian assemblage from the middle Miocene locality Gračanica—Bugojno palaeolake, Bosnia and Herzegovina

This paper presents the first fossil fish, amphibian and reptilian fauna from Bosnia and Herzegovina Dinarides. The fauna of ectothermic vertebrates of the Bugojno palaeolake, dated to 15.2–14.0 Ma, composes of killifishes (Cyprinodontiformes indet.), a barb (Barbini indet. (aff. Barbus), a crocodile newt (Chelotriton sp.), a painted frog (Latonia sp.) and a crocodile (Alligatoroidea indet. [?Diplocynodon]). The crocodile remains are confined to the lower part of the section corresponding to the swamp deposit (unit 1). The remaining fauna, which includes fishes and amphibians, come from the upper lacustrine unit 2. A possible Barbus (Barbini indet. (aff. Barbus)) could represent one of the oldest fossil records of the genus found in Europe, which composes of skeletal elements and pharyngeal teeth. The crocodile newt (Chelotriton sp.) represents the first record of this group from the area. For the first time, fossil tadpoles of the genus Latonia are described in this paper, which, moreover, are the first record of tadpole for both the family Discoglossidae and clade of discoglossoid frogs. The crocodile remains, identified as Alligatoroidea indet., should belong to the genus Diplocynodon, which will be tested later on a better preserved material. The fossils, coming from the lacustrine interval, are referred to the deeper water facies. Taphonomic observations of the fossil remains suggest relatively short phase of decay of the animal bodies and their (probably quick) sedimentation in the deeper parts of the lake, with poor oxygen content.

Do Coral Reefs Promote Morphological Diversification? Exploration of Habitat Effects on Labrid Pharyngeal Jaw Evolution in the Era of Big Data.

Coral reefs are complex marine habitats that have been hypothesized to facilitate functional specialization and increased rates of functional and morphological evolution. Wrasses (Labridae: Percomorpha) in particular, have diversified extensively in these coral reef environments and have evolved adaptations to further exploit reef-specific resources. Prior studies have found that reef-dwelling wrasses exhibit higher rates of functional evolution, leading to higher functional variation than in non-reef dwelling wrasses. Here, we examine this hypothesis in the lower pharyngeal tooth plate of 134 species of reef and non-reef-associated labrid fishes using high-resolution morphological data in the form of micro-computed tomography scans and employing three-dimensional geometric morphometrics to quantify shape differences. We find that reef-dwelling wrasses do not differ from non-reef-associated wrasses in morphological disparity or rates of shape evolution. However, we find that some reef-associated species (e.g., parrotfishes and tubelips) exhibit elevated rates of pharyngeal jaw shape evolution and have colonized unique regions of morphospace. These results suggest that while coral reef association may provide the opportunity for specialization and morphological diversification, species must still be able to capitalize on the ecological opportunities to invade novel niche space, and that these novel invasions may prompt rapid rates of morphological evolution in the associated traits that allow them to capitalize on new resources.

Possible species-flock scenario for the evolution of the cyprinid genus Capoeta (Cypriniformes: Cyprinidae) within late Neogene lake systems of the Armenian Highland.

We studied 4 Ma old isolated pharyngeal teeth from lake sediments of Çevirme (Tekman Palaeolake, Erzurum Province). Based on shape characters defined for 3D models of modern species, we found that the Pliocene lake constitutes sympatric occurrence of four Capoeta species (C. cf. umbla, C. cf. baliki, C. cf. sieboldi and C. sp. sevangi/capoeta), whose modern relatives belong to a monophyletic clade inhabiting today three different drainage systems of this region (Euphrates River, Kura River and Black Sea). We interpreted this high local diversity of closely related species in terms of the species-flock model. The Tekman palaeolake was a part of an unrecognized extended late Miocene to Pliocene palaeolake system in the present-day Armenian Highland, which has been disrupted by Pliocene tectonic activities. Surface uplift of the Armenian Highland contributed to the very characteristic biogeographic distribution and endemism of Capoeta in West Asian drainage systems. Thus, we proposed a species-flock scenario for the evolution and dispersal of the cyprinid genus Capoeta in a huge unrecognized palaeolake system in the present-day Armenian Highland.

Characteristics for the External Identification of Black Carp From Grass Carp

AbstractBlack Carp Mylopharyngodon piceus and Grass Carp Ctenopharyngodon idella are morphologically similar species native to eastern Asia and imported to North America as biological control organisms. Preferred identification methods are coloration and pharyngeal tooth form. Grass Carp possess serrated teeth and Black Carp molariform teeth. Examination of pharyngeal teeth causes extensive damage to a specimen and is labor and time intensive. Coloration can vary within a species and fades with preservation. We present a suite of external characteristics consisting of a truss network canonical variate analysis of distance measurements among landmarks on the lateral view of the head of each fish, the ratio of head length to mouth width, the visible presence of the premaxilla viewed dorsally with the mouth fully closed, and anterior lateral line angles among scales. Canonical variate analysis suggested that Grass Carp have a deeper head at the preoperculum and Black Carp a more elongate head relative to the preoperculum and eye. Comparisons of head length to mouth width ratio, visibility of the premaxilla dorsally with the mouth fully closed, and anterior lateral line angles all served as external characteristics of species, but outliers were present for each method. Because of the plastic morphology of wild populations, we suggest that a combination of characters be applied for identification.

Phylogenetic relationships of Cypriniformes and plasticity of pharyngeal teeth in the adaptive radiation of cyprinids.

The Cypriniformes comprise approximately 4,200 species accounting for 25% of the diversity of all freshwater fish, which is widely distributed across the world's continents except Antarctica, South America, and Australia. The highest species diversity is found in Southeastern Asia. Despite its remarkable species diversity and broad-scale geographic patterns of distribution, the evolutionary history of this major freshwater fish group remains largely unresolved. To gain insight of the evolutionary history of Cypriniformes, we present a phylogeny of this group using 1 mitochondrial gene and 15 nuclear genes comprising a total of 14,061 bp. Bayesian inference using all gene fragments yielded a well resolved phylogeny, which is mostly consistent with topologies obtained from Maximum Likelihood analyses. Our results further confirmed the monophyly of Cypriniformes and seven constituent subclades including Cyprinidae, Catostomidae, Gyrinocheilidae, Balitoridae, Cobitidae, Nemacheilidae, and Botiidae. Bayesian divergence time analysis indicated that the origin of the Cypriniformes was about 193 Mya during the early Jurassic, coinciding with the onset of the Pangaea breakup. The basal divergence of Cypriniformes is 154 Mya during the late Jurassic. Our findings from molecular divergence and biogeographical analysis indicate the most likely initial geographical range of the ancient Cypriniformes was both East and South Asia (Southeastern area of Mesozoic Laurasia). Moreover, the burst in species diversity in Cyprinidae afforded by the nearly worldwide colonization is possibly in response to the plasticity of pharyngeal dentition. The present study demonstrates that the Cypriniformes was about 193 Mya during the early Jurassic, coinciding with the onset of the Pangaea breakup. The plasticity of pharyngeal dentition of cyprinids might contribute to the burst and radiation of this lineage. The phylogenetic and biogeographic analyses in this study help to improve our understanding of the evolutionary history of this diverse and important freshwater fish group.

The complex trophic anatomy of silver carp, Hypophthalmichthys molitrix, highlighting a novel type of epibranchial organ

Hypophthalmichthys molitrix, silver carp, is an invasive Asian carp that has become increasingly widespread and ecologically destructive within the upper Mississippi River Basin. Its complex trophic anatomy may help explain the apparent efficiency with which they consume phytoplankton, outcompeting native filter feeders. This cypriniform species is characterized by trophic synapomorphies that include a palatal organ, loss of upper pharyngeal jaws, and a hypertrophied lower pharyngeal jaw. However, in silver carp these structures have become greatly modified and diverge from the more basal condition that characterizes species such as goldfish. The trophic apparatus of silver carp is composed of discrete structures that are functionally coupled: filtering plates, paired epibranchial organs (EBO), a modified palatal organ composed of large muscular folds that interdigitate with the filtering plates, and hypertrophied lower pharyngeal jaws and teeth. The filtering plates fill a significant portion of the buccal cavity, especially since the distal parts of these filtering plates make up a key component of the EBOs. EBOs, food aggregating structures found in many teleosts, are thought to have independently evolved at least six times. Ranging in complexity from small slits on the dorsal wall of the pharyngeal cavity to exceedingly intricate spiraling structures, EBOs are morphologically diverse among filter-feeding fishes. Despite this morphological diversity and broad taxonomic distribution, little is known regarding the functional anatomy of the EBO. Moreover, the EBO in silver carp is distinct from the organs previously described in other species, being created by four independent pharyngeal involutions (instead of the more typical one or two) that form spiral-shaped pharyngeal tubes surrounded by circumferential muscle. On each side of the head greatly hypertrophied hyomandibulae and opercles are connected to the anterior cartilaginous caps of the bilateral EBOs via enlarged muscles. Given that these fish are pump filter feeders we hypothesize that the opercula may compress and expand the EBOs during pumping causing food to be moved posteriorly toward the pharyngeal jaws.

A late Miocene (Hemphillian) freshwater fish (Osteichthyes) fauna from Mobile County, Alabama, USA

ABSTRACT Systematic descriptions of North American Miocene freshwater fishes are extremely uncommon, with those from the Gulf Coastal Plain region being completely absent. In this study we examined 324 historically collected freshwater fish elements derived from the late Miocene (Hemphillian) Mauvilla fossil site located in Mobile County, Alabama, USA. Analysis of these elements confirmed the presence of three unequivocal taxa including Atractosteus sp. cf. A. spatula, Ictalurus spp., and Aplodinotus grunninens. The preserved elements consisted of spines, pharyngeal bones, pharyngeal teeth, and scales, likely indicating a taphonomic bias towards large individuals with robust elements. The co-occurrence of these three taxa indicate they were derived from a medium-to-large river fish assemblage, suggesting that one or more of the rivers that constitute the nearby Mobile Basin may have been present in the region during the late Miocene. Molecular divergence estimates and morphological similarity to modern representatives both support the presence of these extant taxa in the late Miocene, and the examined remains represent some of the earliest fossil occurrences of these extant taxa. These three taxa also represent the first biogeographic occurrence of each in the late Miocene of both Alabama and the Gulf Coastal Plain of North America and helps to improve our understanding of Miocene freshwater fish assemblages.

Six New Species of the Cichlid GenusOtopharynxfrom Lake Malaŵi (Teleostei: Cichlidae)

The endemic Lake Malaŵi cichlid genus Otopharynx is increased from 14 species to 20 by the description of six new species collected from inshore sandy or intermediate rocky/sandy areas or trawled in depths to 59 m. Otopharynx alpha is distinguished from congeners by its unique melanin pattern with suprapectoral spot discrete but supraanal and precaudal spots connected to form a stripe, and by its distinctively shaped pharyngeal bone with numerous small, crowded teeth. Otopharynx mumboensis, thought to be endemic to Mumbo Island, is separated from most congeners by a suprapectoral spot placed entirely below the upper lateral line, and from all others by the combination of 13 gill rakers, pharyngeal bone with posterior margin nearly straight, crowns of all pharyngeal teeth in the median columns broadened and flattened, head length 30.9–32.2% SL, body depth 35.5–36.1% SL, and lower jaw 35.7–36.2% HL. Otopharynx styrax has a more elongate body (depth 24.3–28.6% SL) than any congener. Otopharynx aletes can be diagnosed by the combination of a suprapectoral spot overlapping the upper lateral line, seven or eight vertical bars below the dorsal-fin base, 10 or 11 gill rakers, 34–36 scales in the lateral line, lower pharyngeal bone with molariform posteromedian teeth, and caudal peduncle length 1.6–2.0 times its depth. Otopharynx panniculus is diagnosed by the combination of a prominent square suprapectoral spot spanning subdorsal bars 3 to 4, no dorsal midline spots, 13–15 gill rakers, 31–33 scales in the lateral line, 15 or 16 dorsal-fin spines, absence of a lacrimal notch, and slightly enlarged teeth in the median columns of the lower pharyngeal bone. Otopharynx peridodekamost closely resembles O. panniculus and shares the loss of the lacrimal notch, but has 34–35 scales in the lateral line and 11–13 gill rakers. Photographs of living or freshly collected specimens of five of the new species are provided.

Adaptive Evolution of the Eda Gene and Scales Loss in Schizothoracine Fishes in Response to Uplift of the Tibetan Plateau

Schizothoracine is the predominant wild fish subfamily of the Tibetan plateau (TP). Their scales, pharyngeal teeth and barbels have gradually regressed with increasing altitude. Schizothoracine have been divided into three groups: primitive, specialized and highly specialized. Ectodysplasin-A (Eda) has been considered as a major gene that contributes to the development of skin appendages. The present study cloned the Eda genes of 51 Schizothoracine fish species which represent the three groups and five Barbinae species. Phylogenetic analyses indicated that Eda may have acted as the genetic trigger for scale loss in the Schizothoracine. Furthermore, 14 single nucleotide polymorphisms (SNPs) and two deletions (18 bp and 6 bp in size), were also detected in the Eda coding sequence of the highly specialized group compared to the primitive group. The same SNPs and two indels result in four non-synonymous and two G-X-Y and 1 XY motif indels, which possibly contribute to significant structure changes in the Eda gene. The domain including (G-X-Y)n motif in the Eda gene is relatively conserved amongst teleosts. Based on the above results, we hypothesize that the evolution of Eda gene might be associated with the scale loss in Schizothoracine fishes in response to the phased uplift of the TP.

Gross morphology and scanning electron microscopy of the Bagrus Bayad (Forskal, 1775) oropharyngeal cavity with emphasis to teeth-food adaptation.

Bagrus Bayad (Forskal, 1775) is a bottom feeder fish feeds on different food items. Its oral cavity anatomy has many types of teeth adapted to the capacity and varieties of feeding. The aim of the present study was to use the gross anatomy and scanning electron microscopy to identify the anatomical characteristic, especially of the teeth and taste buds distributed on the roof and floor of the oropharyngeal cavity. The results clarified that Bagrus Bayad has two types of teeth; curved pointed and blunt teeth of different sizes. The teeth appeared on epithelial protrusions. The pharyngeal region had upper and lower pharyngeal teeth, the upper arranged into two oval prominences while the lower ones arranged into two triangular areas. The higher number of the pointed teeth is prove the carnivorous nature of the Bagrus Bayad. Three types of taste bud (I, II, & III) were found in the oropharyngeal cavity. The tongue present in the floor and free from teeth and characterized by the presence of taste bud type I and II. Many microridges of different arrangement observed on the surface epithelium of oropharyngeal cavity. The upper and lower valve characterized by the microridges, pores and taste buds. The knowledge of the nature of the oropharyngeal cavity of the Bagrus Bayad helps in identifying new and better methods for feeding in aquaculture.

Genetic Dissection of a Supergene Implicates Tfap2a in Craniofacial Evolution of Threespine Sticklebacks.

In nature, multiple adaptive phenotypes often coevolve and can be controlled by tightly linked genetic loci known as supergenes. Dissecting the genetic basis of these linked phenotypes is a major challenge in evolutionary genetics. Multiple freshwater populations of threespine stickleback fish (Gasterosteus aculeatus) have convergently evolved two constructive craniofacial traits, longer branchial bones and increased pharyngeal tooth number, likely as adaptations to dietary differences between marine and freshwater environments. Prior QTL mapping showed that both traits are partially controlled by overlapping genomic regions on chromosome 21 and that a regulatory change in Bmp6 likely underlies the tooth number QTL. Here, we mapped the branchial bone length QTL to a 155 kb, eight-gene interval tightly linked to, but excluding the coding regions of Bmp6 and containing the candidate gene Tfap2a Further recombinant mapping revealed this bone length QTL is separable into at least two loci. During embryonic and larval development, Tfap2a was expressed in the branchial bone primordia, where allele specific expression assays revealed the freshwater allele of Tfap2a was expressed at lower levels relative to the marine allele in hybrid fish. Induced loss-of-function mutations in Tfap2a revealed an essential role in stickleback craniofacial development and show that bone length is sensitive to Tfap2a dosage in heterozygotes. Combined, these results suggest that closely linked but genetically separable changes in Bmp6 and Tfap2a contribute to a supergene underlying evolved skeletal gain in multiple freshwater stickleback populations.

Effects of thyroid hormones on vertebral numbers in two cyprinid fish species:Rutilus rutilus(Linnaeus, 1758) andAbramis brama(Linnaeus, 1758)

Previous studies revealed that thyroid hormones (TH) are crucial regulators of fish development and that manipulation of the thyroid gland function can induce developmental heterochronies. These heterochronies are known to be responsible for changes in the number of serially repeating skeletal elements, such as scales, fin rays and pharyngeal teeth. The present study demonstrates that thyroid function manipulation provokes heterochronies in the development of the fish axial skeleton. We studied the variation of the total vertebral numbers as well as the vertebral numbers in different regions of axial skeleton as influenced by manipulation of level of thyroid hormone in two cyprinid species – the common roach Rutilus rutilus (Linnaeus, 1758) and bream Abramis brama (Linnaeus, 1758). As a result, the numbers of total and caudal (more rarely, abdominal) vertebrae were significantly altered. TH-treated fish demonstrated a reduced number of vertebrae at an earlier completion of calcification and at a smaller body size. This finding agrees well with the concept of pleomerism sensu C. C. Lindsey (1975). Another effect of TH on the phenotype of the axial skeleton was the frequent increase in the number of vertebrae in the caudal skeleton (four in place of the normal three) because of non-fusions in the urostyle.

Supernumerary teeth in the pharyngeal dentition of slow-developing zebrafish (Danio rerio , Hamilton, 1822)

Heterochrony, which is a change in the developmental rate and timing, is one of the mechanisms proposed to explain alterations in meristic characters, such as the variation in the numbers of skeletal elements between individuals within a population. To verify the possible role of heterochrony in the evolutionary transformation of the cyprinid pharyngeal tooth formula, the development of the pharyngeal dentition in zebrafish (Danio rerio) was studied under the influence of deficiency of thyroid hormones at 28°C and standard zebrafish rearing conditions. Thiourea was used to decrease the level of thyroid hormones, a treatment known to cause retardation of several developmental processes, including skeletal development and tooth formation. Retarded development resulted in a high degree of variability as well as left – right asymmetry in the dentition. Supernumerary teeth developed; these were either extending a tooth row anteriorly or were added lateral to a tooth row, or both. An addition laterally resembled the start of formation of an accessory tooth row. Compared to younger individuals, older zebrafish showed a higher number of supernumerary teeth, often associated with a broadened attachment zone on the jaws. Both anteriorly and laterally positioned supernumerary teeth were regularly displayed. These results support the hypothesis that heterochrony can affect dental characters in cyprinids, as has been suggested in the development of the skull, caudal fin and the Weberian apparatus.

A Field Observation of Rotational Feeding by Neogobius melanostomus

Neogobius melanostomus, the round goby, was recorded by underwater video feeding on crushed dreissenid mussels at a depth of 12 m in Georgian Bay of Lake Huron, a Laurentian Great Lake. In the video, gobies used rotational or twist feeding to tear away particles from crushed mussels. At least 43 examples of this feeding maneuver occur in the video. Up to 120 gobies m-2 were visible at a time in the video. Mean standard length of gobies appearing in the video was 37 mm. Mean standard length of fish exhibiting twist feeding was larger, 48 mm. Mean size of intact mussels in visible clusters was about 10×20 mm, a size which exceeds the gape width of the largest gobies observed in the video. Neogobius melanostomus is known to use twisting to wrest small attached mussels from the substrates which can be crushed by their pharyngeal teeth. I surmise that the behavior observed in the video is an opportunistic manifestation of this inherent behavioral adaptation to overcome gap limitation and exploit a temporary windfall of food.

Sinorhodeus microlepis, a new genus and species of bitterling from China (Teleostei: Cyprinidae: Acheilognathinae).

A new genus and species, Sinorhodeus microlepis gen. et sp. nov., is described from a tributary of the Yangtze River, in Chongqing City, China. Sinorhodeus gen. nov. can be distinguished from four closely related genera, Paratanakia, Pseudorhodeus, Rhodeus, and Tanakia, by the following combination of characters: pharyngeal teeth 0,0,4-4,0,0, longitudinal scales 41-46, white spots on dorsal-fin rays absent, a black blotch on dorsal fin in juvenile absent, and less developed wing-like yolk sac projections in larvae. Phylogenetic analysis of one mitochondrial gene and six nuclear genes supports the establishment of the new genus.