Morphology and feeding in tadpoles of Ceratophrys cranwelli (Anura: Leptodactylidae)

This paper provides data on the skeleton, musculature, buccal apparatus, buccopharyngeal cavity and diet of Ceratophrys cranwelli tadpoles, and attempts to contribute to the knowledge of relations between morphology and ecology in anuran larvae. Both in morphological characters and feeding habits, these tadpoles are very similar to other species within the genus. They possess many of the structural features usually found in predaceous tadpoles: strong, keratinized jaw sheaths and keratodonts, reduced buccal papillation, high values of in‐lever arm proportion and buccal floor area, well‐developed ceratohyals, and hypertrophied jaw muscles. Food sources consist of other tadpoles, microcrustaceans, larvae of insects, plant fragments, as well as rotifers and microalgae. As facultative carnivores, they are likely to play an important role in regulating the aquatic communities of the ephemeral ponds where they develop.     

Ventilation and the origin of jawed vertebrates: a new mouth

This study investigates the origin of jaws by re-assessing homologies between the oropharyngeal regions of Agnatha and Chondrichthyes. In accordance with classical theory, jaws are interpreted as the most anterior arches of the ventilatory branchial basket. It is proposed that jaws first enlarged for a ventilatory function, i.e. closing the jaws prevented reflux of water through the mouth during forceful expiration. Next, they enlarged further to grasp prey in feeding. As they enlarged, the jaws tilted forward, squeezing the ancestral oral cavity in front of them ('old mouth') into a slit between the jaws and lips. Simultaneously, the anterior part of the pharynx behind the jaws was pulled forward and became a 'new mouth' (the buccal part of the buccopharyngeal cavity of gnathostomes). During the transition to gnamostomes, the premandibular cheeks and lips of the old mouth remained in place, and are represented in ammocoete lampreys, chimaeroids, and sharks. The stages in the evolution of gnathostomes, driven by selection for increasing activity, are modelled as: ancestral vertebrate (with unjointed branchial arches) to early pre-gnathostome (jointed internal arches and stronger ventilation) to late pre-gnadiostome (with mouth-closing, ventilatory 'jaws') to early gnathostome (feeding jaws).     

Determination of feeding mode in fishes: the importance of using structural and functional feeding studies in conjunction with gut analysis in a selective zooplanktivore Chirostoma estor estor Jordan 1880

Anatomical and histological studies of the endangered atherinid Chirostoma estor estor reveal that the species is ideally adapted to feeding on zooplankton. It has a superior protractile mouth with short unicuspid mandibular teeth. The buccal cavity is a highly adapted branchial sieve with branchial spines which develop in complexity with age to form a continuous flexible interdigitated mat. The filter bed has many of the characteristics of a cross-flow filter, which is ideal for a continuously feeding and filtering animal as the filter bed will not readily become occluded. The aggregates from the cross-flow filter pass to the rear of the buccal cavity where they are triturated by well-developed pharyngeal teeth. The species has a short intestine (<0·3 × body length) with no histological evidence of stomach-like structures, no pyloric caecae and with trypsin-like enzymes operating at high pH. Feeding trials with natural plankton showed a sequence of particle size selection as the animals grow, with older animals taking cladocerans up to 700 μm in diameter. Although some adults occasionally take small fish prey, cumulatively, the present studies indicate that the fish is a zooplankton feeder throughout all its life stages.     

Buccal oscillation and lung ventilation in a semi-aquatic turtle, Platysternon megacephalum

Movements of the hyobranchial apparatus in reptiles and amphibians contribute to many behaviors including feeding, lung ventilation, buccopharyngeal respiration, thermoregulation, olfaction, defense and display. In a semi-aquatic turtle, Platysternon megacephalum, x-ray video and airflow measurements from blowhole pneumotachography show no evidence that above water hyobranchial movements contribute to lung inflation, as in the buccal or gular pump of amphibians and some lizards. Instead, hyobranchial movements produce symmetrical oscillations of air into and out of the buccal cavity. The mean tidal volume of these buccal oscillations is 7.8 times smaller than the mean tidal volume of lung ventilation (combined mean for four individuals). Airflow associated with buccal oscillation occurs in the sequence of inhalation followed by exhalation, distinguishing it from lung ventilation which occurs as exhalation followed by inhalation. No fixed temporal relationship between buccal oscillation and lung ventilation was observed. Periods of ventilation often occur without buccal oscillation and buccal oscillation sometimes occurs without lung ventilation. When the two behaviors occur together, the onset of lung ventilation often interrupts buccal oscillation. The initiation of lung ventilation was found to occur in all phases of the buccal oscillation cycle, suggesting that the neural control mechanisms of the two behaviors are not coupled. The pattern of occurrence of both buccal oscillation and lung ventilation was found to vary over time with no obvious effect of activity levels.     

Functional morphology of the feeding apparatus,feeding constraints,and suction performance in the nurse shark Ginglymostoma cirratum

The nurse shark, Ginglymostoma cirratum, is an obligate suction feeder that preys on benthic invertebrates and fish. Its cranial morphology exhibits a suite of structural and functional modifications that facilitate this mode of prey capture. During suction‐feeding, subambient pressure is generated by the ventral expansion of the hyoid apparatus and the floor of its buccopharyngeal cavity. As in suction‐feeding bony fishes, the nurse shark exhibits expansive, compressive, and recovery kinematic phases that produce posterior‐directed water flow through the buccopharyngeal cavity. However, there is generally neither a preparatory phase nor cranial elevation. Suction is generated by the rapid depression of the buccopharyngeal floor by the coracoarcualis, coracohyoideus, and coracobranchiales muscles. Because the hyoid arch of G. cirratum is loosely connected to the mandible, contraction of the rectus cervicis muscle group can greatly depress the floor of the buccopharyngeal cavity below the depressed mandible, resulting in large volumetric expansion. Suction pressures in the nurse shark vary greatly, but include the greatest subambient pressures reported for an aquatic‐feeding vertebrate. Maximum suction pressure does not appear to be related to shark size, but is correlated with the rate of buccopharyngeal expansion. As in suction‐feeding bony fishes, suction in the nurse shark is only effective within approximately 3 cm in front of the mouth. The foraging behavior of this shark is most likely constrained to ambushing or stalking due to the exponential decay of effective suction in front of the mouth. Prey capture may be facilitated by foraging within reef confines and close to the substrate, which can enhance the effective suction distance, or by foraging at night when it can more closely approach prey. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Osteology,myology and feeding mechanism of Astronotus ocellatus (Pisces,Perciformes)

Summary Astronotus ocellatus captures its prey by creating a negative pressure in the buccal cavity which is caused by its quick expansion. Once the prey has been accommodated, the buccal cavity undergoes a compression which may propel the prey towards the pharyngeal jaws for mastication. The motion picture recordings indicate retracted premaxillae at the beginning of food intake followed by a maximum attainment of mouth gape and then mastication. During the maximum opening of the mouth the premaxillae are protruded and dentaries are at maximum depression. These events are followed by activities such as buccopharyngeal cavity expansion, bulging on the ventral surface of the head, and prominent curvature on the ventral surface anterior to the urohyal, caused by the upward movement of the glossohyal. Based on the cinematographic results, it may be inferred that the maximum mouth gape is caused by the sternohyoid-hyoid-interopercular-mandible coupling, and not by the opercular apparatus-mandible coupling, as the latter acts after the full descent of the lower jaw. Impression of the expanded buccopharyngeal cavity has been made by a paraffin mold technique, which confirms the displacement of the buccopharyngeal elements during expansion of the cavity.     

The suction mechanism of the pipid frog,Pipa pipa (Linnaeus, 1758)

Most suction‐feeding, aquatic vertebrates create suction by rapidly enlarging the oral cavity and pharynx. Forceful enlargement of the pharynx is powered by longitudinal muscles that retract skeletal elements of the hyoid, more caudal branchial arches, and, in many fish, the pectoral girdle. This arrangement was thought to characterize all suction‐feeding vertebrates. However, it does not exist in the permanently aquatic, tongueless Pipa pipa , an Amazonian frog that can catch fish. Correlating high‐speed (250 and 500 fps) video records with anatomical analysis and functional tests shows that fundamental features of tetrapod body design are altered to allow P. pipa to suction‐feed. In P. pipa , the hyoid apparatus is not connected to the skull and is enclosed by the pectoral girdle. The major retractor of the hyoid apparatus arises not from the pectoral girdle but from the femur, which lies largely within the soft tissue boundaries of the trunk. Retraction of the hyoid is coupled with expansion of the anterior trunk, which occurs when the hypertrophied ventral pectoral elements are depressed and the urostyle and sacral vertebra are protracted and slide forward on the pelvic girdle, thereby elongating the entire trunk. We suggest that a single, robust pair of muscles adduct the cleithra to depress the ventral pectoral elements with force, while modified tail muscles slide the axial skeleton cranially on the pelvic girdle. Combined hyoid retraction, axial protraction, and pectoral depression expand the buccopharyngeal cavity to a volume potentially equal to that of the entire resting body of the frog. Pipa may be the only tetrapod vertebrate clade that enlarges its entire trunk during suction‐feeding.     

Buccal oscillation and lung ventilation in a semi-aquatic turtle, Platysternon megacephalum

Movements of the hyobranchial apparatus in reptiles and amphibians contribute to many behaviors including feeding, lung ventilation, buccopharyngeal respiration, thermoregulation, olfaction, defense and display. In a semi-aquatic turtle, Platysternon megacephalum, x-ray video and airflow measurements from blowhole pneumotachography show no evidence that above water hyobranchial movements contribute to lung inflation, as in the buccal or gular pump of amphibians and some lizards. Instead, hyobranchial movements produce symmetrical oscillations of air into and out of the buccal cavity. The mean tidal volume of these buccal oscillations is 7.8 times smaller than the mean tidal volume of lung ventilation (combined mean for four individuals). Airflow associated with buccal oscillation occurs in the sequence of inhalation followed by exhalation, distinguishing it from lung ventilation which occurs as exhalation followed by inhalation. No fixed temporal relationship between buccal oscillation and lung ventilation was observed. Periods of ventilation often occur without buccal oscillation and buccal oscillation sometimes occurs without lung ventilation. When the two behaviors occur together, the onset of lung ventilation often interrupts buccal oscillation. The initiation of lung ventilation was found to occur in all phases of the buccal oscillation cycle, suggesting that the neural control mechanisms of the two behaviors are not coupled. The pattern of occurrence of both buccal oscillation and lung ventilation was found to vary over time with no obvious effect of activity levels.     

Comparative morphology of the feeding basket of five species of Euphausia (Crustacea,Euphausiacea) in the western North Pacific,with some ecological considerations

The feeding basket morphology and stomach content analyses of five Euphausia species (E. recurva, E. nana, E. pacifica, E. mutica and E. similis) were compared to elucidate their feeding ecology. The filter areas of feeding basket of E. pacifica and E. nana were proportionally larger than those of others in the size classes 13-20 mm and <13 mm, respectively, suggesting a high filtering efficiency in these species at each size class. Based on the secondary setal distance, it is suggested that there are three types of feeding basket in five Euphausia species. One is the fine mesh (<5 μm) of E. pacifica and E. nana; a second is the medium (10-20 μm) of E. recurva and E. mutica; and the third is the coarse (20-30 μm) of E. similis. The ability to feed on particles <5 μm would give both species, E. pacifica and E. nana, a great advantage over other species when number of flagellates is high. Stomach content analyses indicated a more omnivorous feeding mode in E. mutica, E. recurva and E. similis and a more herbivorous in E. pacifica and E. nana. This is in agreement with morphological studies of feeding baskets. Increments in the primary and secondary setal distances with increasing size of four Euphausia species, except E. pacifica, were evident, reflecting interspecific differences in food particle sizes utilized. In E. pacifica, however, the morphological similarity should produce intraspecific competition in diet. This revised version was published online in September 2006 with corrections to the Cover Date.     

Prey capture in the pike-perch,Stizostedion lucioperca (teleostei,percidae): A structural and functional analysis

Summary The pike-perch,Stizostedion lucioperca, uses both suction and grasping during feeding. Type, size, and position of prey and predator determine the movement of catching. This is concluded from simultaneous motion analysis, electromyography, and the record of pressures inside the buccopharyngeal cavity during feeding. The EMG incorporates 24 muscles of the head, including the branchial basket and the anterior body musculature. When the pike-perch begins to feed acceleration and expansion of the head parts determine the negative buccopharyngeal pressure and therefore the suction force applied to different preys. Not the head muscles, but the epaxial and hypaxial body musculatures provide the main force for the rapid expansion of the head through movements of the neurocranium, pectoral girdle, and hyoid arch. Despite the lack of a true neck, the pike-perch is able to move its neurocranium in all directions to aim the suction force. The experiments revealed that ventral and lateral movements aid in the ingestion of a big prey after it has been grasped with the teeth. The head muscles are active as regulators of the opening movements and in the closing movements. Variable overlaps of ab- and adductor activity show that their contraction patterns are interdependent. Variations in the recorded pressures can be related largely to a series of EMGs showing different starting moments of adductor contraction. In this progressive series two patterns were distinguished, and their accompanying movements were compared and related to the type of prey. According to the feeding behavior and morphology, the pike-perch is classified as a rapacious predator. Comparison with some other voracious fishes shows that besides the total length of the lower jaw and the dentigerous area, the construction and dentition of the upper jaws and the anterior suspensorial and neurocranial parts are also important features of this ecological type. However it appears that the fishes selected for this comparison use suction rather than the teeth as the main means of catching the smaller, but commonly eaten prey. The teeth prevent escape after capture by sucking and they increase the maximum prey size that can be caught. In this group, the head ofStizostedion appears to be comparatively well adapted to sucking with grasping adaptations.     

Branchial arches of suspension–feeding Oreochromis esculentus: sieve or sticky filter?

Only 4% of 600 particles slid on or adhered to buccopharyngeal surfaces of Oreochromis esculentus . Only a minute quantity of mucus was visible during feeding (0·6% of 68 224 video frames; 30 frames s^–1), and very few particles were retained in this mucus. Filtration by mucus entrapment on the branchial arches is rejected as a mechanism of particle retention in this species. Since particles contacted the branchial arches infrequently, and the inter–raker spaces are too large to retain particles less than approximately 50 μm, sieving by gill rakers as a particle retention mechanism is rejected also. Unlike the suspension–feeding congener O. niloticus, O. esculentus does not use branchial arches to retain food particles by sieving or by mucus entrapment.     

The mechanism of ultraplanktonic entrapment in anuran larvae

Tadpoles of several different genera were fed graded suspensions of uniform polystyrene particles to determine the lower size limit of particles that could be ingested. Certain tadpoles can extract suspended particles as small as 0.126 μ in diameter from the water. In terms of particle size, this is an efficiency comparable to the best mechanical sieves that can currently be produced by man. A mechanism for ultrasplanktonic entrapment is proposed on the basis of scanning electron micrographs of the secretory ridges in the branchial food traps of Rana catesbeiana before and after feeding. Xenopus tadpoles in yeast suspensions modify their clearance and buccal pumping rates in response to varying food concentrations. This may be an adaptation for maintaining a constant input of food mass to the tissues that extract the food from the water. Variability in the lower size limit of filterable particles among tadpoles of different genera correlates with the availability of suspended matter in the microhabitat where these tadpoles may be found.     

Early ontogeny of Galeichthys feliceps from the south east coast of South Africa

The early development of Galeichthys feliceps (Valenciennes, 1840) was investigated using a combination of incubator-reared embryos and embryos removed from the buccal cavities of wild-caught parents. The eggs were 15·7 mm in diameter and the average brood size was 49. Hatching occurred at an advanced developmental state after approximately 75–80 days, when branchial and fin differentiation were complete. Exogenous feeding began within the adult buccal cavity shortly after hatching. The young were released as juveniles after approximately 140 days, at a total length of 54 mm.     

Form and function of the feeding apparatus in Eutardigrada (Tardigrada)

Tardigrade feeding apparatus is a complex structure with considerable taxonomic significance that can be schematically divided into four parts: buccal ring, buccal tube, stylet system, and pharynx. We analyzed the fine morphology and the tridimensional organization of the tardigrade buccal?Cpharyngeal apparatus in order to clarify the relationships between form and function and to identify new characters for systematic and phylogenetic studies. We conducted a comparative analysis of the cuticular structures of the buccal?Cpharyngeal apparatuses of twelve eutardigrade species, integrating data obtained by SEM and LM observations. Morphological diversity was observed and new cuticular structures such as the stylet coat of the stylet system were identified. The synthesis of the buccal?Cpharyngeal apparatus during molting was also analyzed obtaining a clear developmental sequence of its resynthesis. These findings lead us to redefine the previous interpretations of the functioning mechanisms of the buccal?Cpharyngeal apparatus and provide a more specific relationship between tardigrade diet and the anatomy of their feeding apparatuses. In addition, the detection by energy-dispersive X-ray spectroscopy of calcium in the stylets, buccal tube, and placoids of eutardigrade species (i.e., Milnesium tardigradum, Paramacrobiotus richtersi) indicates that CaCO₃ incrustations are not an exclusive feature of heterotardigrades and lead to suppose that this trait was present in the ancestors of both classes.     

Regulation of diurnal filter feeding by a novel gill structure in Amblypharyngodon melettinus (Teleostei,Cyprinidae)

A unique gill structure, apparently associated with filter feeding on phytoplankton and suspended microdetritus, has been found in Amblypharyngodon melettinus, an abundant small Cyprinidae of Sri Lanka. The gill lamellae, the site of gas exchange, are bordered by a double row of fine appendices which are spread over the interlamellar gaps during daytime, but folded up at night. A respiratory function of the appendices can be excluded. The changing position of appendices correlates with the diurnal pattern of feeding (day) and swimming (night). The mechanism for movement of the appendices consists of hinge-like joints formed from the basement membranes of pavement cells, driven by variation in lamellar blood pressure. Food collection is based on both an efficient hydrosol filter produced by dense populations of clavate mucous cells of the buccopharyngeal epithelia and the lamellar appendices which cause a slower and more turbulent water current in the buccopharyngeal cavity. This may ensure the proper contact of food particles with the sticky mucous surface before they leave the buccopharyngeal cavity. The uniqueness of this structure is that the filter can be switched off during periodically occurring periods of high oxygen demand (high swimming activity at night) probably benefiting the process of respiration.     

The Bearing of Filter Feeding on the Water Pumping Mechanism of Xenopus Tadpoles (Anura: Pipidae)

Abstract New findings on the functional anatomy of filter feeding have permitted some clarification of water flow through tadopoles. The dorsal velar apparatus projects downward from the roof of the buccopharynx and consists of three mucosal pads and three vanes on both sides of the midline. At least four functions may be ascribed to the dorsal velar apparatus. 1. Each pad and its complementary vane fit so flush into each of the three bilateral filter cavities that exhalent water must flow in thin sheets over the filter plates before its exit via the pharyngeal clefts. 2. Like hydrofoils, the vanes deflect water and prevent strong currents from disorganizing the mucous food cords. 3. When tadpoles cease water pumping, the plugging effect of the dorsal velar apparatus in the filter cavities helps to occlude the pharyngeal clefts. 4. Secretions of dorsal velar glands, especially on the surface of the velar pads, may assist the mucus of the ventral velum to entrap suspended food. Other findings concern the M3b muscle, which helps to elevate the buccopharyngeal floor during expiration; the lack of cilia, but presence of low glandular elevations on the ventral velum; the reduction of the exits from the pharyngeal clefts 2 and 3 into a single valvular exit controlled by the B2b and B2c muscles; and the probable absence of a mechanical feeding function for the oral tentacles.     

Functional morphology of the branchial basket of ascidia paratropa (Tunicata,Ascidiacea)

Summary The filtering surface of the branchial basket of Ascidia paratropa (Huntsman, 1912) consists of two adjacent and connected sheets. The stigmatal surface is loosely folded. The secondary gill screen, composed of ciliated longitudinal vessels with primary and secondary papillae, is connected to the stigmatal surface on the inside of the branchial basket. Continuous mucus secretion results in a net with elastic and adhesive properties, and a pore size of less than 0.5 m in its longest dimension. Net production cannot be interrupted by external mechanical stimuli. The net is usually supported by and transported across the secondary screen, forming a filtering surface that parallels the undulations of the stigmatal surface; however, localized muscular activity of the dorsal laminar fold and longitudinal vessels are also involved in mucous net transport. Squirts occur more frequently than in many species. At these times the net is transported as a flat sheet, independent of the secondary screen. Squiring does not interrupt continuous feeding activity.