Oral Hood Research Articles

In the sea slug Melibe leonina the posterior nerves communicate stomach distention to inhibit feeding and modify oral hood movements.

The sea slug Melibe leonina is an excellent model system for the study of the neural basis of satiation, and previous studies have demonstrated that stomach distention attenuates feeding. Here we expanded on this work by examining the pathway communicating stomach distention to the central nervous system and the effects of distention on motor output. We found that the posterior nerves (PN), which extend posteriorly from the buccal ganglia and innervate the stomach, communicate stomach distention in Melibe. PN lesions led to increased feeding duration and food consumption, and PN activity increased in response to stomach distention. Additionally, the percentage of incomplete feeding movements increased with satiation, and PN stimulation had a similar impact in the nerves that innervate the oral hood. These incomplete movements may be functionally similar to the egestive, food rejecting motions seen in other gastropods and enable Melibe to remain responsive to food, yet adjust their behavior as they become satiated. Such flexibility would not be possible if the entire feeding network were inhibited.

The Digestive Diverticula in the Carnivorous Nudibranch, Melibe leonina, Do Not Contain Photosynthetic Symbionts.

SynopsisA number of nudibranchs, including Melibe engeli and Melibe pilosa, harbor symbiotic photosynthetic zooxanthellae. Melibe leonina spends most of its adult life on seagrass or kelp, capturing planktonic organisms in the water column with a large, tentacle-lined oral hood that brings food to its mouth. M. leonina also has an extensive network of digestive diverticula, located just beneath its translucent integument, that are typically filled with pigmented material likely derived from ingested food. Therefore, the focus of this project was to test the hypothesis that M. leonina accumulates symbiotic photosynthetic dinoflagellates in these diverticula. First, we conducted experiments to determine if M. leonina exhibits a preference for light, which would allow chloroplasts that it might be harboring to carry out photosynthesis. We found that most M. leonina preferred shaded areas and spent less time in direct sunlight. Second, we examined the small green circular structures in cells lining the digestive diverticula. Like chlorophyll, they exhibited autofluorescence when illuminated at 480 nm, and they were also about the same size as chloroplasts and symbiotic zooxanthellae. However, subsequent electron microscopy found no evidence of chloroplasts in the digestive diverticula of M. leonina; the structures exhibiting autofluorescence at 480 nm were most likely heterolysosomes, consistent with normal molluscan digestion. Third, we did not find evidence of altered oxygen consumption or production in M. leonina housed in different light conditions, suggesting the lack of any significant photosynthetic activity in sunlight. Fourth, we examined the contents of the diverticula, using HPLC, thin layer chromatography, and spectroscopy. The results of these studies indicate that the diverticula did not contain any chlorophyll, but rather harbored other pigments, such as astaxanthin, which likely came from crustaceans in their diet. Together, all of these data suggest that M. leonina does sequester pigments from its diet, but not for the purpose of symbiosis with photosynthetic zooxanthellae. Considering the translucent skin of M. leonina, the pigmented diverticula may instead provide camouflage.

Discovery of two ‘chimeric’ Gastrotricha and their systematic placement based on an integrative approach

AbstractSublittoral sand from the islands of Sardinia (Italy) and Flores (Azores) – separated by more than 3700 km linear distance and 8 years between two independent sampling campaigns – yielded conspicuous specimens of two bizarre, yet undescribed, species of the marine gastrotrich clade Macrodasyida. These gastrotrichs combine several character traits that were already known from two, non-related genera. Morphological data were carefully analysed and digitally documented, and nuclear and mitochondrial DNA sequences were used for phylogenetic inference. The results of these analyses claim for the erection of a new genus. Specimens of the new taxon have a body length of less than 400 µm and are characterized by a wide, funnel-shaped mouth opening shielded dorsally by an oral hood and possess a posterior peduncle that ends with a Y-shaped pair of appendages that carry the posterior adhesive tubes. Further tubes occur as anterior, ventrolateral and lateral series; the gonads are unpaired and there is a set of two accessory reproductive organs. Molecular phylogenetic analyses confirm the results of former studies and clearly place the new taxon in Thaumastodermatidae. We hereby propose the establishment of Chimaeradasys gen. nov. and describe C. oligotubulatus sp. nov. from the Azores and C. polytubulatus sp. nov. from Sardinia.

Hox gene expression during development of the phoronid Phoronopsis harmeri

BackgroundPhoronida is a small group of marine worm-like suspension feeders, which together with brachiopods and bryozoans form the clade Lophophorata. Although their development is well studied on the morphological level, data regarding gene expression during this process are scarce and restricted to the analysis of relatively few transcription factors. Here, we present a description of the expression patterns of Hox genes during the embryonic and larval development of the phoronid Phoronopsis harmeri.ResultsWe identified sequences of eight Hox genes in the transcriptome of Ph. harmeri and determined their expression pattern during embryonic and larval development using whole mount in situ hybridization. We found that none of the Hox genes is expressed during embryonic development. Instead their expression is initiated in the later developmental stages, when the larval body is already formed. In the investigated initial larval stages the Hox genes are expressed in the non-collinear manner in the posterior body of the larvae: in the telotroch and the structures that represent rudiments of the adult worm. Additionally, we found that certain head-specific transcription factors are expressed in the oral hood, apical organ, preoral coelom, digestive system and developing larval tentacles, anterior to the Hox-expressing territories.ConclusionsThe lack of Hox gene expression during early development of Ph. harmeri indicates that the larval body develops without positional information from the Hox patterning system. Such phenomenon might be a consequence of the evolutionary intercalation of the larval form into an ancestral life cycle of phoronids. The observed Hox gene expression can also be a consequence of the actinotrocha representing a “head larva”, which is composed of the most anterior body region that is devoid of Hox gene expression. Such interpretation is further supported by the expression of head-specific transcription factors. This implies that the Hox patterning system is used for the positional information of the trunk rudiments and is, therefore, delayed to the later larval stages. We propose that a new body form was intercalated to the phoronid life cycle by precocious development of the anterior structures or by delayed development of the trunk rudiment in the ancestral phoronid larva.

<strong>First evidence of autofluorescence of a cell mass in developing temnopleurid sea urchins</strong>

The pigment cells of some sea urchin embryos emanate autofluorescence in response to light irradiation. However, it is unclear if this feature is maintained throughout larval development. In the present study we observed embryos and larvae of the temnopleurid sea urchins Temnopleurus hardwickii, T. reevesii, T. toreumaticus and Mespilia globulus exposed to light irradiation, and compared our findings with those of a strongylocentroid, Hemicentrotus pulcherrimus. After exposure to ultraviolet irradiation for a few minutes, there was a strong signal from the temnopleurid sea urchins. The signal was detected from a cell mass that is part of the adult (juvenile) rudiment, formed during development of the prism to the two-armed larval stage and not from pigment cells. This signal was observed in both live and formalin-fixed specimens. Fluorescence was also detected from the digestive organs, coelomic pouches, the ciliary band on the oral hood, from some yellowish-green cells and ectodermal cells, although there were some differences among species. In live H. pulcherrimus larvae, the amniotic cavity that is part of the adult rudiment emanated autofluorescence in response to ultraviolet irradiation. These results indicate that the autofluorescence observed in the cell mass of temnopleurid sea urchins is caused by a different mechanism than previously described. This feature may be a useful marker to trace development of the cell mass.

Restoration of the Topological Organization of the Trigeminal System Following Trigeminal Nerve Root Injury in the Lamprey

Two issues were examined regarding the trigeminal system in larval lampreys: (1) for normal animals, double labeling was used to confirm that the trigeminal system has a topological organization; (2) following trigeminal nerve root transections, double labeling was used to test whether the topological organization of the trigeminal system is restored. First, for normal animals, Alexa 488 dextran amine applied to the medial oral hood (anterior head) labeled trigeminal motoneurons (MNs) in the ventromedial part of the trigeminal motor nuclei (nVm) and axons of trigeminal sensory neurons (SNs) in the ventromedial part of the trigeminal descending tracts (dV). Also, Texas red dextran amine (TRDA) applied to the lateral oral hood labeled trigeminal MNs in the dorsolateral nVm and sensory axons in the dorsolateral dV. These results confirm the topological organization of the trigeminal system of normal lampreys. Second, following trigeminal nerve root transections, the physical integrity of the nerves was restored during growth of trigeminal sensory and motor axons. In addition, double labeling indicated a restoration and refinement of the topological organization of the trigeminal system with increasing recovery times, but mainly for nVm. Despite the paucity of growth of trigeminal sensory axons in dV even at long recovery times (12–16 wks), a substantial percentage of experimental animals recovered trigeminal-evoked swimming responses and trigeminal-evoked synaptic responses in reticulospinal (RS) neurons. Following trigeminal nerve root injury, several mechanisms, including axonal guidance cues, probably contribute to the substantial restoration of the topological organization of the lamprey trigeminal system.

A new species of the genusTetranchyroderma(Gastrotricha: Macrodasyida: Thaumastodermatidae) from Korea, with a peculiar pentancrous armature

Abstract. Surveys of marine gastrotrichs on the coast of South Korea yielded a new species of the genus Tetranchyroderma, bearing 5-pronged hooks as a cuticular armature. Tetranchyroderma hummoni is characterized by a dorsal armature adorned with pentancres, whose central tines are about twice as long as peripheral tines. The new species is also characterized by bearing 3 large and broad papillae per side along boundary row of pentancres on oral hood, a pair of rod-like cephalic tentacles, and a pair of modified pestle organs. Moreover, this new species is clearly distinguished from its congeners by the number of dorsal, dorsolateral and ventrolateral cirratum-type tubes (6−10, 13−19, and 9−14 per side, respectively), and by a pair of foot-like ventral adhesive tubes. The description of the new species belonging to the genus Tetranchyroderma is based on detailed illustrations and scanning electron microscopy. We also provide a short account on the variability within the species, including the morphologica...

Descending propriospinal neurons mediate restoration of locomotor function following spinal cord injury.

In the lamprey following spinal lesion-mediated interruption of long axonal projections of reticulospinal (RS) neurons, sensory stimulation still elicited relatively normal locomotor muscle burst activity, but with some coordination deficits. Computer models incorporating the spinal lesions could mimic many aspects of the experimental results. Thus, after disruption of long-axon projections from RS neurons in the lamprey, descending propriospinal (PS) neurons appear to be a viable compensatory mechanism for indirect activation of spinal locomotor networks.

The influence of stomach distention on feeding in the nudibranch mollusk Melibe leonina

Although research on satiation has revealed much about the effect of sensory inputs on motivational state, we have yet to fully understand exactly how satiating signals influence the neural circuits underlying specific behaviors. One organism that is well suited for addressing this question is the nudibranch Melibe leonina, because its feeding activity is easily quantified, it has translucent skin that makes the stomach easy to observe, and it has large, identifiable neurons that are very suitable for subsequent analysis of the neural correlates of satiation. In this study our goal was to document the time course of satiation in Melibe, and determine if stomach distention contributes to satiation. When exposed to brine shrimp (Artemia), Melibe immediately commenced stereotypic oral hood movements to capture prey, and continued to do so for approximately five hours. Individuals eventually stopped, despite the continued presence of food, and the slowing and eventual termination of oral hood closures was correlated with distension of the stomach caused by the ingested Artemia. We obtained further evidence that stomach distension is one of the underlying causes of satiation by injecting artificial non-nutritive food into the stomach, and by cutting open part of the stomach wall to prevent it from filling and distending. The first treatment caused satiation to occur more rapidly, while the second treatment delayed satiation. Both results demonstrate that in Melibe stomach distention has a major impact on the motivation to feed. These findings provide the framework for subsequent studies designed to determine precisely how stomach distention influences feeding circuits.

First description of a gastrotrich with four scale types, including feathered biancres, a novel find for Gastrotricha

A new species of Tetranchyroderma, T. garraffonii, is described from sublittoral sediments off the coast of Florida, USA. The new species possesses mixed scale types in the form of feathered biancres – a novel discovery for the genus – as well as feathered triancres and ordinary triancres. Biancres consist of a round scale base, a pair of ancre shafts that arise individually from a v-shaped cuticular ridge on the scale, and feathered ancres. Triancres are similar in appearance but have a different ridge pattern. Ordinary triancres occurred in two forms on the lateral sides of the body: a bowl-shaped ancre and a ‘pitchfork’ shaped ancre. Other distinguishing characteristics of the new species include the presence of cephalic tentacles, a papillated fringe to the oral hood, and a single pair of lateral and dorsolateral adhesive tubes at the posterior end. Confocal microscopy verified the presence of a muscular caudal organ and partly muscular vas deferens.

Late Alk4/5/7 signaling is required for anterior skeletal patterning in sea urchin embryos.

Skeletal patterning in the sea urchin embryo requires a conversation between the skeletogenic primary mesenchyme cells (PMCs) and the overlying pattern-dictating ectoderm; however, our understanding of the molecular basis for this process remains incomplete. Here, we show that TGF-β-receptor signaling is required during gastrulation to pattern the anterior skeleton. To block TGF-β signaling, we used SB431542 (SB43), a specific inhibitor of the TGF-β type I receptor Alk4/5/7. Treatment with SB43 during gastrulation blocks anterior PMC positioning and the formation of the anterior skeleton, but does not perturb general ectoderm specification or development. This is the first example of a signaling event required for patterning of a specific part of the skeleton. Alk4/5/7 inhibition does not prevent the formation of a mouth, although SB43-treated plutei display reduced feeding ability, presumably due to the loss of the structural support for the mouth conferred by the anterior skeleton. Both Univin and Nodal are potential ligands for Alk4/5/7; however, Nodal is unilaterally expressed on only the right side, whereas Univin is bilaterally expressed in the ectoderm adjacent to the anterior skeleton during the relevant time period. Our results demonstrate that Univin is both necessary and sufficient for secondary skeletal development in a control background, consistent with the hypothesis that Univin is a relevant Alk4/5/7 ligand for anterior skeletal patterning. Taken together, our data demonstrate that Alk4/5/7 signaling during gastrulation is required to direct PMCs to the oral hood, and suggest that Univin is a relevant ligand for this signaling event.

About the Cover.

Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverMelibe leonina (small inset on cover), is a nudibranch that is most often found in seagrass meadows and kelp beds along the West Coast of the United States and Canada. It feeds on small prey that it captures using rhythmic movements of its large oral hood. Occasionally it can also be observed floating in the water column or swimming using rhythmic lateral flexions of its entire body. Previous studies have demonstrated that it will swim, and crawl, most often at night. In this issue, the paper by James Newcomb, Winsor Watson, and their students, describes how the locomotion of this species is influenced by a circadian clock that might be associated with its eyes.M. leonina has relatively clear skin, so light can easily reach its eyes. The eyes are located on the brain, which is unusual for gastropods. The main picture shows a M. leonina brain that has been removed and pinned out in a dish of saline where it can be kept alive and will continue to express certain behaviors such as swimming. The eyes have black pigment associated with them; the two white spots lateral to the eyes are neurons with a white pigment. All the other round objects are the cell bodies of individual neurons. The clear structures leaving the brain are nerves.M. leonina has been used by a number of scientists to study the neural basis of behavior because, as is evident from the picture of its brain, its neurons are very large, and readily identifiable. The size, color, and consistent location of these neurons, such as the pair of white pigmented cells adjacent to the eyes, make it possible to insert microelectrodes into individual neurons and record their activity, both in intact animals and in isolated brains. Because the eyes are on the brain, these isolated brains, like intact animals, will express swimming activity more in the dark than in the light. In their article, the authors demonstrated that if the eyes of this species are removed, it is still able to synchronize its daily rhythms to the natural light-dark cycle, suggesting that it probably has other, extraocular, photoreceptors. However, without their eyes, individuals do not exhibit circadian rhythms of locomotion in constant darkness, suggesting that these organs may contain an element of the endogenous biological clock.In view of these facts, this nudibranch provides a good model system for investigating the connection between biological clocks and the neural circuitry underlying behaviors that are expressed with a circadian rhythm.Credits: Large image, Winsor Watson III, University of New Hampshire; inset, James N. Newcomb, New England College; layout, Beth Liles, Marine Biological Laboratory. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 227, Number 3December 2014 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv227n3cover © 2014 by Marine Biological Laboratory. All rights reserved.PDF download Crossref reports no articles citing this article.

Discovery of fossil lamprey larva from the Lower Cretaceous reveals its three-phased life cycle.

Lampreys are one of the two surviving jawless vertebrate groups and one of a few vertebrate groups with the best exemplified metamorphosis during their life cycle, which consists of a long-lasting larval stage, a peculiar metamorphosis, and a relatively short adulthood with a markedly different anatomy. Although the fossil records have revealed that many general features of extant lamprey adults were already formed by the Late Devonian (ca. 360 Ma), little is known about the life cycle of the fossil lampreys because of the lack of fossilized lamprey larvae or transformers. Here we report the first to our knowledge discovery of exceptionally preserved premetamorphic and metamorphosing larvae of the fossil lamprey Mesomyzon mengae from the Lower Cretaceous of Inner Mongolia, China. These fossil ammocoetes look surprisingly modern in having an eel-like body with tiny eyes, oral hood and lower lip, anteriorly positioned branchial region, and a continuous dorsal skin fin fold and in sharing a similar feeding habit, as judged from the detritus left in the gut. In contrast, the larger metamorphosing individuals have slightly enlarged eyes relative to large otic capsules, thickened oral hood or pointed snout, and discernable radials but still anteriorly extended branchial area and lack a suctorial oral disk, which characterize the early stages of the metamorphosis of extant lampreys. Our discovery not only documents the larval conditions of fossil lampreys but also indicates the three-phased life cycle in lampreys emerged essentially in their present mode no later than the Early Cretaceous.

Development of oral and branchial muscles in lancelet larvae ofBranchiostoma japonicum

The perforated pharynx has generally been regarded as a shared characteristic of chordates. However, there still remains phylogenetic ambiguity between the cilia-driven system in invertebrate chordates and the muscle-driven system in vertebrates. Giant larvae of the genus Asymmetron were reported to develop an orobranchial musculature similar to that of vertebrates more than 100 years ago. This discovery might represent an evolutionary link for the chordate branchial system, but few investigations of the lancelet orobranchial musculature have been completed since. We studied staged larvae of a Japanese population of Branchiostoma japonicum to characterize the developmental property of the orobranchial musculature. The larval mouth and the unpaired primary gills develop well-organized muscles. These muscles function only as obturators of the openings without antagonistic system. As the larval mouth enlarged posteriorly to the level of the ninth myomere, the oral musculature was fortified accordingly without segmental patterning. In contrast, the iterated branchial muscles coincided with the dorsal myomeric pattern before metamorphosis, but the pharynx was remodeled dynamically irrespective of the myomeric pattern during metamorphosis. The orobranchial musculature disappeared completely during metamorphosis, and adult muscles in the oral hood and velum, as well as on the pterygial coeloms developed independently. The lancelet orobranchial musculature is apparently a larval adaptation to prevent harmful intake. However, vestigial muscles appeared transiently with the secondary gill formation suggest a bilateral ancestral state of muscular gills, and a segmental pattern of developing branchial muscles without neural crest and placodal contributions is suggestive of a precursor of vertebrate branchiomeric pattern.

Marine Gastrotricha of Little Cayman Island with the description of one new species and an initial assessment of meiofaunal diversity

Surveys of littoral and sublittoral sediments from diverse marine environments around Little Cayman Island (LCI) have produced the first records of gastrotrichs from one of the most remote West Indian islands in the Greater Antilles ecoregion of the Tropical Northwest Atlantic. Forty-six stations ranging from littoral to 40 m depth yielded 18 morphospecies from 10 genera (7 Macrodasyida, 3 Chaetonotida) representing six families of Gastrotricha. At least one species is new to science and is described here. Oregodasys caymanensis n. sp. is described from multiple stations around the island from 1.5 to 15 m depth. The new species belongs to a group of species with posterior cirri, but can be distinguished by the possession of six rod-like cephalic tentacles on the oral hood and the presence of pigmented y-cells. Nine previously described morphospecies from other Caribbean and global locations were present around LCI: Aspidiophorus cf. paramediterraneus, A. tentaculatus, Chaetonotus aff. apechochaetus, C. cf. atrox, C. cf. dispar (Chaetonotidae); Diplodasys rothei (Thaumastodermatidae); Macrodasys cf. ommatus and Urodasys viviparus (Macrodasyidae); and Paraturbanella pacifica (Turbanellidae). We also encountered further unidentified morphospecies of Chaetonotida from the genus Xenotrichula and from six genera of Macrodasyida (Diplodasys, Megadasys, Macrodasys, Oregodasys, Paraturbanella, Tetranchyroderma). In addition to new geographic records of Gastrotricha, we provide the first general survey of meiofauna from Little Cayman Island including new geographic records for several taxa.

NOTES ON OCCURRENCE. FEEDING AND SWIMMING BEHAVIOUR OF NOTARCHUS INDICUS AND MELIBE. BUCEPHALA AT ELAT, RED SEA (MOLLUSCA: OPISTHOBRANCHIA)

ABSTRACT The simultaneous occurrence of algae and the slugs Notarchus indicus and Melibe bucephala in Elat is pointed out. Both slugs are calm-water types and profit from the detritus layer on the algae. Notarchus indicus scrapes off the food from more or less flat surfaces using its radula. Melibe bucephala, which has no radula, is conspicuous for its specialized method of taking detritus from filamentous substrates. This feeding behaviour is permitted by a special organ, the oral hood, which can take in soft tender food particles by enclosing them. Melibe bucephala swims by bending its body laterally. Notarchus indicus swims by the propulsive thrust of a water jet expelled from the parapodial cavity. It is suggested that Notarchus indicus in the adult stage is regularly distributed to new habitats by swimming and floating in sea currents.

Tetranchyroderma bronchostylus sp. nov., the first known gastrotrich (Gastrotricha) with a sclerotic canal in the caudal organ

A new species of Tetranchyroderma (Macrodasyida: Gastrotricha) is described from coarse sediments at 9 m depth at Capron Shoals, Florida. Tetranchyroderma bronchostylus sp. nov. is distinguished primarily by the presence of a sclerotic canal within the accessory caudal organ, and represents the first species of Tetranchyroderma described with such a feature. The following combination of characters further distinguish this species from its congeners: an oral hood with a scalloped margin, paired cephalic tentacles, paired sensorial organs, a pentancrous cuticle, three pairs of dorsolateral adhesive tubes, one pair of ventrolateral adhesive tubes in the pharyngeal region and up to 11 pairs of ventrolateral tubes in the trunk region, and one pair of lateral adhesive tubes close to the paired caudal pedicles.

New Species of the Thorny Catfish Genus Leptodoras (Siluriformes: Doradidae) from Rio Fresco, Xingu Basin, Brazil

Abstract A new species of the thorny catfish genus Leptodoras (family Doradidae) is described. The new species shares three characters with its congeners, the modified oral hood with distinct upper labial extensions, the first gill arch with enlarged accessory lamellae extending well onto medial face of gill filaments, and the pelvic fin inserted in anterior half of body. The new species is distinguished from congeners by having a large dark submarginal blotch on distal half of dorsal-fin spine and anteriormost dorsal-fin branched rays, lower labial extension of modified oral hood extending more posteriorly than upper labial extension, relatively few midlateral scutes, gas bladder moderately sized (not reduced), paired bony capsules on anteriormost vertebrae reduced to paired cup-like laminar ossifications separated by a triangular septum, pair of small, swelling-like diverticula on each side of the anterior chamber of gas bladder, a well-developed anterior nuchal plate, and nuchal foramina present. The n...

Ultrastructure of feathered triancres in the Thaumastodermatidae and the description of a new species of Tetranchyroderma (Gastrotricha: Macrodasyida) from Australia

Tetranchyroderma adeleae sp. nov. is described from North Stradbroke Island, eastern Australia, where it is present in low abundance in the clean, coarse sediments of Cylinder beach. The species is characterized by the presence of epidermal glands on the oral hood and three pairs of dorsolateral cirrata. This is also the first described species of Tetranchyroderma with mixed ancre types that consist of both ordinary triancres and feathered triancres. Ordinary triancres are present on the ventrolateral margins of the body while feathered triancres adorn the dorsal side. Details of the ultrastructure of the cuticle in T. adeleae sp. nov. and a species of Pseudostomella are compared to each other and the cuticle of additional species of Thaumastodermatidae. At the ultrastructural level, feathered triancres are composed of a thickened endocuticular base with three tines (shafts) that give rise to pointed, feather-shaped scales. The structure of the base, tines and scales reveals a finely granular construction without noticeable substructure. The ultrastructure of feathered triancres is similar to that of ordinary triancres and broadly similar to feathered triancres in other species. However, differences are noted in the contour of the feathered scales that are not detected with light microscopy. Future studies of the thaumastodermatid cuticle using scanning electron microscopy are warranted to provide enhanced three-dimensional resolution and insight into their evolution.

New species of thorny catfish, genus Leptodoras Boulenger (Siluriformes: Doradidae), from Tapajós and Xingu basins, Brazil

A new species of thorny catfish (family Doradidae) is described as a member of genus Leptodoras Boulenger by having a modified oral hood and first gill arch with enlarged accessory lamellae extending well onto medial face of gill filaments. The new species is distinguished by three characteristics unique within Leptodoras: gas bladder moderately sized (not reduced) with simple walls (diverticula absent), and paired bony capsules on anteriormost vertebrae reduced to paired cup-like laminar ossifications separated by triangular septum. The new species was discovered from material recently collected in the Tapajós basin at Serra do Cachimbo and in the headwaters of rio Xingu. The species description is supplemented by a detailed osteological description, discussion on its placement among congeners, and a re-evaluation of the diagnosis of Leptodoras and its relationships with sister taxon Anduzedoras oxyrhynchus. In addition, the distributions of several species of Leptodoras are expanded based on recent collecting efforts and identification of museum specimens not previously studied.