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Acoustic signaling by fishes has been recognized for millennia, but is typically regarded as comparatively rare within ray-finned fishes; as such, it has yet to be integrated into broader concepts of vertebrate evolution. We map the most comprehensive data set of volitional sound production of ray-finned fishes (Actinopterygii) yet assembled onto a family level phylogeny of the group, a clade representing more than half of extant vertebrate species. Our choice of family-level rather than species-level analysis allows broad investigation of sonifery within actinopterygians and provides a conservative estimate of the distribution and ancestry of a character that is likely far more widespread than currently known. The results show that families with members exhibiting soniferous behavior contain nearly two-thirds of actinopterygian species, with potentially more than 20,000 species using acoustic communication. Sonic fish families also contain more extant species than those without sounds. Evolutionary analysis shows that sound production is an ancient behavior because it is present in a clade that originating circa 340 Ma, much earlier than any evidence for sound production within tetrapods. Ancestral state reconstruction indicates that sound production is not ancestral for actinopterygians; instead, it independently evolved at least 27 times, compared to six within tetrapods. This likely represents an underestimate for actinopterygians that will change as sonifery is recognized in ever more species of actinopterygians. Several important ecological factors are significantly correlated with sonifery – including physical attributes of the environment, predation by members of other vertebrate clades, and reproductive tactics – further demonstrating the broader importance of sound production in the life history evolution of fishes. These findings offer a new perspective on the role of sound production and acousticcommunication during the evolution of Actinopterygii, a clade containing more than 34,000 species of extant vertebrates.

Atlantic Cutlassfish, Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger-shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro-CT scanning to study 92 specimens of T. lepturus from the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement in T. lepturus depending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement in T. lepturus to 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions.

The ranges of two rare species of deep-water dragonets—the Spotfin Dragonet Foetorepus agassizii (Goode and Bean, 1888) and the Palefin Dragonet Foetorepus goodenbeani Nakabo and Hartel, 1999—overlap on the outer continental shelf of North America in the Mid Atlantic Bight. We studied more than 450 specimens collected between 2009–2015 by the Northeast Fisheries Science Center to photographically document these species, better characterize their geographic and depth distributions, and describe aspects of their reproductive biology. The two species occurred in a small subset of locations within the sampled area (81 of 6,225 stations). Although F. agassizii and F. goodenbeani occur within a similar geographic region, F. agassizii occurs at greater depths, on average 33 m deeper, than F. goodenbeani. Collection locations and depths in spring and fall were similar, suggesting that F. agassizii and F. goodenbeani do not migrate seasonally, perhaps because they occur in habitats with stable year-round temperatu...

Suction feeding and gill ventilation in teleosts are functionally coupled, meaning that there is an overlap in the structures involved with both functions. Functional coupling is one type of morphological integration, a term that broadly refers to any covariation, correlation, or coordination among structures. Suction feeding and gill ventilation exhibit other types of morphological integration, including functional coordination (a tendency of structures to work together to perform a function) and evolutionary integration (a tendency of structures to covary in size or shape across evolutionary history). Functional coupling, functional coordination, and evolutionary integration have each been proposed to limit morphological diversification to some extent. Yet teleosts show extraordinary cranial diversity, suggesting that there are mechanisms within some teleost clades that promote morphological diversification, even within the highly integrated suction feeding and gill ventilatory systems. To investigate this, we quantified evolutionary integration among four mechanical units associated with suction feeding and gill ventilation in a diverse clade of benthic, primarily suction-feeding fishes (Cottoidei; sculpins and relatives). We reconstructed cottoid phylogeny using molecular data from 108 species, and obtained 24 linear measurements of four mechanical units (jaws, hyoid, opercular bones, and branchiostegal rays) from micro-CT reconstructions of 44 cottoids and 1 outgroup taxon. We tested for evolutionary correlation and covariation among the four mechanical units using phylogenetically corrected principal component analysis to reduce the dimensionality of measurements for each unit, followed by correlating phylogenetically independent contrasts and computing phylogenetic generalized least squares models from the first principle component axis of each of the four mechanical units. The jaws, opercular bones, and branchiostegal rays show evolutionary integration, but the hyoid is not positively integrated with these units. To examine these results in an ecomorphological context, we used published ecological data in phylogenetic ANOVA models to demonstrate that the jaw is larger in fishes that eat elusive or grasping prey (e.g., prey that can easily escape or cling to the substrate) and that the hyoid is smaller in intertidal and hypoxia-tolerant sculpins. Within Cottoidei, the relatively independent evolution of the hyoid likely has reduced limitations on morphological evolution within the highly morphologically integrated suction feeding and gill ventilatory systems.

Prior to European contact, South Pacific islanders used serrated shark teeth as components of tools and weapons. They did this because serrated shark teeth are remarkably effective at slicing through soft tissues. To understand more about the forms and functions of serrated shark teeth, we examined the morphology and histology of tooth serrations in three species: the Tiger Shark (Galeocerdo cuvier), Blue Shark (Prionace glauca), and White Shark (Carcharodon carcharias). We show that there are two basic types of serrations. A primary serration consists of three layers of enameloid with underlying dentine filling the serration's base. All three species studied have primary serrations, although the dentine component differs (orthodentine in Tiger and Blue Sharks; osteodentine in the White Shark). Smaller secondary serrations are found in the Tiger Shark, formed solely by enameloid with no contribution from underlying dentine. Secondary serrations are effectively "serrations within serrations" that allow teeth to cut at different scales. We propose that the cutting edges of Tiger Shark teeth, equipped with serrations at different scales, are linked to a diet that includes large, hard-shelled prey (e.g., sea turtles) as well as smaller, softer prey such as fishes. We discuss other aspects of serration form and function by making analogies to man-made cutting implements, such as knives and saws.

We investigated food preferences of Atlantic Hagfish (Myxine glutinosa) in Bigelow Bight in the Gulf of Maine by deploying traps at three moderate depths (ranging from 61 m to 132 m) using different types of bait (fish, crabs, and clams) singly and in mixtures. We counted the numbers of specimens caught in each trap, recorded their individual weights and lengths, and noted the presence of eggs. Bait containing fish consistently attracted the greatest number of hagfish, while invertebrate-based baits were less effective: there was a nine-fold increase in catch rate for traps containing fish bait compared to traps containing only clam bait, and no hagfish were caught using only crab bait. Atlantic Hagfish appear to be adept at detecting even small quantities of fish because baits consisting of 10% fish and 100% fish were equally effective. Even at the relatively shallow and closely adjacent depths sampled we found longer and heavier hagfish at the deepest sampling sites, and individuals from those sites had...

This study describes the teeth, dentition, and tooth replacement pattern of the Gulper Shark, Centrophorus granulosus, using histology and micro-CT scanning. Tooth microstructure and the orthodont histotype of C. granulosus are described and illustrated, and tooth morphology is discussed in the context of squaliform phylogenetic studies. Dental characters previously used to study squaliform interrelationships need revision. The dentitions of adult and near-term pups are documented to illustrate ontogenetic changes in tooth morphology as well as the pattern of tooth replacement. Based on the positions of replacement teeth in each tooth file, the replacement pattern of the palatoquadrate dentition is best described as phased sinusoidal replacement. This study also documents the monognathic and dignathic heterodonty of pups and adults, confirming previously published descriptions of heterodonty that have proven to be of taxonomic significance. A revised dental formula is provided that better reflects the too...

The goosefish, Lophius americanus, is a dorso-ventrally compressed marine fish that spends most of its life sitting on the substrate waiting to ambush prey. Species in the genus Lophius have some of the slowest ventilatory cycles recorded in fishes, with a typical cycle lasting more than 90s. They have a large gill chamber, supported by long branchiostegal rays and ending in a siphon-like gill opening positioned underneath and behind the base of the pectoral fin. Our goals were to characterize the kinematics of gill ventilation in L. americanus relative to those of more typical ray-finned fishes, address previous assertions about ventilation in this genus, and describe the anatomy of the gill opening. We found that phase 1 of ventilation (during which both the buccal and gill chamber are expanding) is greatly increased in duration relative to that of typical ray-finned fishes (ranging from 62 to 127s), and during this phase, the branchiostegal rays are slowly expanding. This slow expansion is almost visually imperceptible, especially from a dorsal view. Despite this unusually long phase 1, the pattern of skeletal movements follows that of a typical actinopterygian, refuting previous assertions that Lophius does not use its jaws, suspensorium, and operculum during ventilation. When individuals were disturbed from the sediment, they tended to breathe more rapidly by decreasing the duration of phase 1 (to 18-30s). Dissections of the gill opening revealed a previously undocumented dorsal extension of the adductor hyohyoideus muscle, which passes from between the branchiostegal rays, through the ventro-medial wall of the gill opening, and to the dorsal midline of the body. This morphology of the adductor hyohyoideus shares similarities with that of many Tetraodontiformes, and we suggest that it may be a synapomorphy for Lophiiformes+Tetraodontiformes. The specialized anatomy and function of the gill chamber of Lophius represents extreme modifications that provide insight into the potential limits of the actinopterygian gill ventilatory system.

Teeth are a potentially rich source of character data for phylogenetic studies of living and fossil sharks, but there are many uncertainties about the homologies of tooth loci as well as structural details of teeth in different taxa. Here, we provide new developmental data on the so-called lateral cusplets of the teeth in Lamniformes. We studied the five living species of Lamnidae (Lamna nasus, L. ditropis, Isurus oxyrinchus, I. paucus, and Carcharodon carcharias) and a more basal lamniform, the Sand Tiger Carcharias taurus, using light microscopy and micro-CT scanning. We also studied a single skeletal specimen of the smalltooth Sand Tiger, Odontaspis ferox. Structures in the teeth of juvenile White Sharks, C. carcharias, were interpreted as lateral cusplets in some previous studies, but we show that they develop differently from lateral cusplets in the teeth of Lamna and Carcharias. We conclude that the structures in Carcharodon are not homologous to the lateral cusplets of Lamna and Carcharias taurus a...

Adult Atlantic Wolffish, Anarhichas lupus, have a heterodont oral dentition consisting of long caniniform teeth in the symphysial regions of the dentaries and premaxillae and large molariform teeth posteriorly on the dentaries, dermopalatines, and vomer. Teeth are ankylosed to the bone of attachment. Wolffish use the caniniform teeth to capture prey including molluscs, crustaceans, echinoderms, and, less commonly, fishes. Prey are transported posteriorly and crushed between the molariform teeth. The molariform teeth of adults fit closely together despite individually variable shapes and sizes in a space-filling pattern that we term anamestic. Adult wolffish have an unusual tooth replacement pattern in which teeth are lost and subsequently replaced all at once, a pattern called simultaneous replacement. We used dissection, osteology, histology, and micro-computed tomography (CT) to study tooth replacement in a series of Anarhichas lupus from the western North Atlantic. Tooth development is intraosseous, wi...

Two incomplete shark teeth were recovered during archaeological excavation of a historic fishing station on Smuttynose Island, ME. Specimens were identified to the species-level using non-destructive computed tomography (CT) imaging techniques. Their external and internal morphology is described and illustrated. Both teeth are from large sharks in the Order Lamniformes. The larger specimen is a developing tooth from the upper jaw of a Carcharodon carcharias (White Shark). The second specimen is a broken tooth from the lower jaw of a Lamna nasus (Porbeagle). The Smuttynose excavations provide an opportunity to examine faunal assemblages and the island's historic 17th-through 19th-century fisheries. Criteria for identifying teeth of common pelagic sharks of the Western North Atlantic are offered, and the role of sharks in the historic Gulf of Maine fishery is discussed.

A phylogenetic survey is a powerful approach for investigating the evolutionary history of a morphological characteristic that has evolved numerous times without obvious functional implications. Restricted gill openings, an extreme modification of the branchioste- gal membrane, are an example of such a characteristic. We examine the evolution of branchiostegal membrane morphology and highlight convergent evolution of restricted gill openings. We surveyed specimens from 433 families of actinopterygians for branchiostegal membrane morphology and measured head and body dimensions. We inferred a relaxed molecular clock phylogeny with branch length estimates based on nine nuclear genes sampled from 285 species that include all major lineages of Actinopterygii. We calculated marginal state reconstruc- tions of four branchiostegal membrane conditions and found that restricted gill openings have evolved independ- ently in at least 11 major actinopterygian clades, and the total number of independent origins of the trait is likely much higher. A principal component analysis revealed that fishes with restricted gill openings occupy a larger morphospace, as defined by our linear measurements, than do fishes with nonrestricted openings. We used a decision tree analysis of ecological data to determine if restricted gill openings are linked to certain environments. We found that fishes with restricted gill openings repeat- edly occur under a variety of ecological conditions, although they are rare in open-ocean pelagic environ- ments. We also tested seven ratios for their utility in dis- tinguishing between fishes with and without restricted gill openings, and we propose a simple metric for quantifying restricted gill openings (RGO), defined as a ratio of the distance from the ventral midline to the gill opening rela- tive to half the circumference of the head. Functional explanations for this specialized morphology likely differ within each clade, but its repeated evolution indicates a need for a better understanding of diversity of ventilatory morphology among fishes. J. Morphol. 000:000-000, 2015.

Sexual dimorphism in mammals typically is reduced in monogamous species relative to polygynous species, with promiscuous species being intermediate. This pattern of dimorphism characterizes adult behavior and body mass of prairie voles, a monogamous species, when compared with meadow voles, a closely related polygynous or promiscuous species. We examined whether the pattern also applies to young of the two species by observing individual pups living in family groups in seminatural environments. Observations during the second week of life revealed no sex differences in pup behavior or body mass. However, we detected species differences in suckling behavior, jockeying for position within the huddle (especially among males), and body mass that replicate and extend our previous observations. These data indicate that patterns of sexual dimorphism associated with different mating systems may not be evident in juvenile mammals, but that species differences in behavior and body mass can be obvious at this stage.

Monogamous parents are predicted to invest equally in male and female offspring whereas polygynous parents in good condition are predicted to invest more in male than female offspring. Sex-biased parental investment can occur in three ways: (1) mothers and fathers invest different amounts of care in their offspring (effect of parent sex); (2) parents invest different amounts of care in male and female offspring (effect of offspring sex); and (3) one parent, but not the other, invests different amounts of care in male and female offspring (interaction between parent sex and offspring sex). Studies of parent–offspring interactions in rodents have focused on either effect of parent sex or effect of offspring sex, but not the interaction between parent sex and offspring sex, and most studies have examined only one species. We studied prairie voles (Microtus ochrogaster), a monogamous species, and meadow voles (M. pennsylvanicus), a polygynous (or promiscuous) species, under laboratory conditions designed to simulate field conditions. For each species, we recorded the frequency and duration with which mothers and fathers licked their male and female offspring. We found that meadow vole fathers licked male offspring for longer durations than female offspring. However, prairie vole fathers, prairie vole mothers, and meadow vole mothers did not lick male and female pups for different durations. From the standpoint of the pups, male prairie vole pups, female prairie vole pups, and female meadow vole pups were licked for longer durations by their mothers than by their fathers. In contrast, for male meadow vole pups there was no difference in the duration with which they were licked by mothers and fathers. We also detected effects of litter size: as litter size increased, the frequency and duration of pup licking decreased for mothers and increased for fathers. For duration (but not frequency) of pup licking, these changes were more dramatic in meadow voles than in prairie voles. Our data are generally consistent with predictions that monogamous parents, such as prairie voles, should invest equally in male and female offspring whereas polygynous (or promiscuous) parents, such as meadow voles, should invest more in male offspring when conditions are favourable. Our data also highlight the complexity of parent–offspring interactions in rodents and emphasize the need to examine whether male and female offspring within a species differ in their behaviour or ability to obtain parental care.

Following dispersal from 1 group, individuals may join other established social groups. Such intergroup transfer may increase access to potential mates and decrease mate competition. We used data from 402 individuals to examine patterns of intergroup transfer in prairie voles (Microtus ochrogaster). Nearly 32% of established social groups (single female units, male–female pairs, or communal groups of at least 2 adults of the same sex) were joined by 1 or more individuals. Most individuals (76%) that joined social groups were wanderers that were either unmarked, recently marked during grid trapping, or marked transients; 70% were males. Joining a group was not contingent upon recent disappearance of residents. Total number of residents positively affected the probability of a female joining a social group, whereas number of adult female residents and population density negatively affected it. Some individuals (24%) moved directly from one group to another without an intervening wandering stage; we refer to these instances of intergroup transfer as direct transfers. Most direct transferers moved into nearby groups, but not the closest group. Males were more likely than females to directly transfer into groups with potential mates and without potential competitors. Thus, males directly transferred in a manner consistent with maximizing reproductive opportunities. In contrast, 25% of females directly transferred into groups without potential mates and 96% into groups with at least 1 adult female. Females may be less constrained by group composition with respect to potential mates because wandering males, with which females can mate, are prevalent. All-male groups almost never occur in our population, so females probably cannot avoid joining groups with competitors.

Sturgeons of the family Acipenseridae comprise 25 extant species, making it the most species-rich extant family of basal (i.e., nonteleostean) actinopterygians. Because of their basal position within Actinopterygii, the anatomical study of sturgeons has a long and rich history, although there remains much to be discovered. Here we describe and illustrate the skeletal anatomy of the shortnose sturgeon, Acipenser brevirostrum, as a representative of the family Acipenseridae. Acipenser brevirostrum, which is distributed along the east coast of North America, is a relatively small species of sturgeon, reaching a maximum of just over 1 m in total length. Our study is based on 105 skeletal and 147 alcohol-stored specimens representing a broad range of ontogenetic stages (ca. 18 to 1000+ mm TL). This study emphasizes the bony portions of the skeleton, their ontogeny, and parts of the skeleton that persist as cartilaginous elements into the adult stage; the earliest stages of development of the chondrocr...

Summary Domestic mammals exhibit diversity in suckling behaviour, yet little is known about suckling in most wild species, including rodents with tenacious nipple attachment. This behaviour, whereby young cling tightly to nipples, has been interpreted as an adaptation to competition within and among litters for nipples and milk. Comparative studies of suckling behaviour of tenacious and non-tenacious species are lacking, however, as are studies placing patterns of suckling in a phylogenetic context. We compared suckling in prairie voles (Microtus ochrogaster; tenacious nipple attachment), woodland voles (= pine voles, M. pinetorum; tenacious nipple attachment) and meadow voles (M. pennsylvanicus; non-tenacious nipple attachment). We hypothesized that suckling behaviour of meadow voles differs from that of the other two species. We found that meadow vole pups display higher frequencies of nipple attachment, shorter durations of nipple attachment (significantly different from prairie voles only), more frequent nipple-switching, and no preference for nipple pairs (prairie vole and woodland vole young preferred the hindmost nipples). Mapped onto a phylogeny, our data suggest a suite of behavioural characters associated with suckling in prairie and woodland voles (tenacious nipple attachment, preference for hindmost nipples, and infrequent nippleswitching) and highlight diversity of suckling behaviour among closely related species.

Total parental expenditure of mammals and birds has been predicted to increase with litter or brood size, but data from rodents provide little support for this prediction. We examined the effects of natural variation in litter size on parental nest attendance in pine (= woodland), prairie, and meadow voles housed in seminatural environments. In all 3 species, mothers spent less time in the nest with large litters than with small; time spent in the nest by fathers was unaffected by litter size. We suggest that failure to meet the prediction of increased parental expenditure with increased litter size reflects basic differences in the manner in which mammals and birds feed altricial young.

Little is known about sex differences in parental behavior of biparental mammals and if mates in such species coordinate care of young. We studied parental care displayed by prairie voles (Microtus ochrogaster) under seminatural laboratory conditions during the first 3 d of life of their offspring. Through direct observations and videotaping, we monitored members of male-female pairs to determine if sex differences in early parental behavior exist and if mothers and fathers coordinate visits to the nest. To assess the impact of fathers on survival of pups and behavior of mothers, we also examined parental care displayed by single females toward their young. Male and female members of breeding pairs differed dramatically in degree of parental care. Females spent more time in the nest with young and licked them more frequently than did males. Additionally, females maintained the nest more frequently than did males, whereas they maintained runways less frequently. Although coordination of visits to the nest was not perfect between members of pairs, pups of pairs were left alone for less time than were pups of single females. Parental behavior displayed by paired and single females did not differ, nor did survival of their young to day 3 or 15. We suggest that provision of ample space and cover to vole parents rearing young in captivity promotes expression of sex differences in parental behavior, but that even seminatural conditions are not sufficient to yield benefits of father presence to survival of young. Under more challenging conditions, such as cold temperatures or presence of predators, benefits of father presence might emerge.

We used intensive live trapping over a 1-y period to investigate the general ecology of a population of Norway rats (Rattus norvegicus) inhabiting a barn in east-central Illinois. At the start of our study in April 1986, the population contained 10 adult females and three adult males. The population increased and exhibited two peaks of about 100 individuals, one peak in late June and the other in late October 1986. Reproduction ceased during the late autumn and winter, and the population declined to only one adult male and one adult female by spring 1987. Increases in the number of rats represented young born at the barn, not adult rats moving into the population; decreases in population size likely resulted from predation rather than dispersal. Females first captured as adults persisted longer at the barn than did males and females first captured as juveniles or subadults; the few males first captured as adults persisted the shortest time of all age and sex classes. Young males gained body mass more rapidly than did young females. Wounding and parasitism by botflies occurred at relatively low levels. Our data indicate that a rat population with negligible immigration and seasonal breeding can exhibit dramatic changes in numbers, and that live-trapping at weekly intervals can yield high recapture rates useful for examining growth rates, survival and other basic life history characteristics.

Tooth replacement poses many questions about development, pattern formation, tooth attachment mechanisms, functional morphology and the evolution of vertebrate dentitions. Although most vertebrate species have polyphyodont dentitions, detailed knowledge of tooth structure and replacement is poor for most groups, particularly actinopterygians. We examined the oral dentition of the bluefish, Pomatomus saltatrix, a pelagic and coastal marine predator, using a sample of 50 individuals. The oral teeth are located on the dentary and premaxillary bones, and we scored each tooth locus in the dentary and premaxillary bones using a four-part functional classification: absent (A), incoming (I), functional (F=fully ankylosed) or eroding (E). The homodont oral teeth of Pomatomus are sharp, deeply socketed and firmly ankylosed to the bone of attachment. Replacement is intraosseus and occurs in alternate tooth loci with long waves of replacement passing from rear to front. The much higher percentage of functional as opposed to eroding teeth suggests that replacement rates are low but that individual teeth are quickly lost once erosion begins. Tooth number increases ontogenetically, ranging from 15-31 dentary teeth and 15-39 premaxillary teeth in the sample studied. Teeth increase in size with every replacement cycle. Remodeling of the attachment bone occurs continuously to accommodate growth. New tooth germs originate from a discontinuous dental lamina and migrate from the lingual (dentary) or labial (premaxillary) epithelium through pores in the bone of attachment into the resorption spaces beneath the existing teeth. Pomatomus shares unique aspects of tooth replacement with barracudas and other scombroids and this supports the interpretation that Pomatomus is more closely related to scombroids than to carangoids.

Lobotes surinamensis is a widely distributed marine perciform and is the sole member of the family Lobotidae, which has unclear phylogenetic affinities. In this paper we describe and illustrate a mode of tooth replacement in Lobotes that we name “grouped” tooth replacement. Lateral oral teeth are replaced intraosseously, i.e., developing replacement teeth can clearly be seen beneath them within both the dentary and premaxillary bones. In contrast to the more typically seen pattern of alternate replacement, the replacement teeth of Lobotes develop as a group within the bone, lying directly beneath the group of teeth that they will replace. Within each tooth replacement group, the teeth show an anteroposterior gradient in age. Within the category of fully functional teeth there is a clear anterior to posterior gradient of eruption within a tooth group. Grouped tooth replacement may be a synapomorphy of Lobotes and Datnioides. As in Lobotes, the lateral oral teeth of Datnioides also are replaced int...

We describe methods for preparing dry skeletons of virtually any osteichthyan species with a well-ossified skeleton, including very large specimens (e.g., > 1 m Megalops atlanticus). Our approach differs from those conventionally used to prepare skeletons of tetrapods in that (1) fairly complete dissection of the specimen is required at the outset of processing; and (2) we use an alcohol dehydration step to rapidly dry the specimen. Similar techniques can be used to prepare well-calcified chondrichthyan skeletons. We also outline the steps for making Ridewood dissections of the skull. Dry, partially articulated skeletons prepared by these methods can be stored indefinitely in acid-free containers in an environmentally controlled space (21 C ± 3 C; Rh = 40% ± 5%) in pest-proof specimen cases. Although a truism of anatomical research is that you cannot learn everything from studying one specimen or one type of preparation, partially articulated dry skeletons are useful for research ranging from phy...

Little is known about the behavior of male and female rodents at parturition. We documented behavior during and immediately after parturition in prairie voles (Microtus ochrogaster), a species characterized by extensive biparental care during the preweaning period. To assess the role of males in parturition and their effect on maternal behavior, we studied parturient behavior of male‐female pairs and females recently separated from their mates. We studied 12 births under seminatural conditions. For each birth, we scored behavior beginning with birth of the 1st offspring, using 3 h of continuous videotape records. Time from birth of the 1st offspring to birth of the last was always ,1 h. Female prairie voles were aggressive toward their mates and effectively excluded them from the nest for most, if not all, of the period of parturition. Thus, measures of parental behavior were much higher for females than for males in breeding pairs. Females permitted males back into the nest about 1 day after parturition. The behavior at parturition of paired and single females was similar. Our data indicate that females may limit the role of males in parturition and care of newborn young, even in species with extensive paternal investment.

†Protopsephurus liui Lu, 1994, from the Lower Cretaceous Yixian Formation of China, is both the oldest and the most primitive paddlefish (polyodontid) known. It was originally described based on a partial skeleton, a partial skull, and two partial trunk regions, leaving much of the species' osteology unknown. Here, based on the type specimens and many newly discovered well-preserved skeletons, we describe this species in detail. †Protopsephurus is clearly a polyodontid based on several characters including: (1) the presence of stellate bones; (2) the presence of a series of long median dorsorostral and ventrorostral bones; (3) extreme elongation of the snout; (4) the presence of anterior, middle and posterior divisions of the fenestra longitudinalis; and (5) the presence of “microctenoid” scales (defined here). Within Polyodontidae, †Protopsephurus (which forms the monotypic series †Protopsephuri) lacks several characters derived for all other Polyodontidae (=Polyodonti). In contrast to †Protopse...

The lower jaw of a gymnodont fish collected from the lower Eocene Cambay Shale Formation in Gujarat Province, western India, has fused dentaries without a beak and a remarkable series of teeth that are unique among all known fossil and living Tetraodontiformes. The teeth are molariform, with raised spokes radiating inward from the emarginated peripheral edge of the crown. Tooth development is intraosseous, with new teeth developing in spongy bone before they erupt and attach to the dentary by pedicels. Although many of the 110 tooth loci in the fossil have lost their teeth, in life the teeth would have grown to fit tightly together to form a broad and continuous crushing surface. The estimated age of the Cambay Shale vertebrate fauna is ca. 54.5 Ma, making the jaw the second oldest confirmed gymnodont fossil. Preliminary comparisons with extant taxa of gymnodonts with fused dentaries (e.g., Diodon, Chilomycterus, and Mola) show detailed similarities in jaw structure, but further study of the denti...

Elasmobranchs exhibit two distinct arrangements of mineralized tissues in the teeth that are known as orthodont and osteodont histotypes. Tra- ditionally, it has been said that orthodont teeth main- tain a pulp cavity throughout tooth development whereas osteodont teeth are filled with osteodentine and lack a pulp cavity when fully developed. We used light microscopy, scanning electron microscopy, and high-resolution micro-computed tomography to compare the structure and development of elasmobranch teeth representing the two histotypes. As an example of the orthodont histotype, we studied teeth of the blue shark, Prionace glauca (Carcharhiniformes: Carcharhinidae). For the osteodont histotype, we studied teeth of the great white shark, Carcharodon carcharias (Lamni- formes: Lamnidae). We document similarities and dif- ferences in tooth development and the microstructure of tissues in these two species and review the history of definitions and interpretations of elasmobranch tooth histotypes. We discuss a possible correlation between tooth histotype and tooth replacement and review the history of histotype differentiation in sharks. We find that contrary to a long held misconception, there is no orthodentine in the osteodont teeth of C. carcharias. J. Morphol. 276:797-817, 2015. V C 2015 Wiley Periodicals, Inc.

The comparative osteology, phylogenetic relationships, and historical biogeography of all known taxa of fossil and living amiid fishes (Halecomorphi: Amiidae) are investigated in detail. Previously, the detailed osteology of nearly all fossil amiids was unknown. We present the first well-supported comprehensive phylogeny for fossil and living amiid fishes. We synthesize clearly documented phylogenetic data on amiids and other halecomorph fishes with other historical phenomena such as ontogeny, historical biogeography, stratigraphic paleontology, and paleoecology (both “stationary” and “historical”). We also use our study of halecomorph fishes as a platform to explore several fundamental methodological and theoretical concepts important to phylogenetic/evolutionary investigations. These concepts pertain mainly to (1) the use of comparative empirical data to interpret various historical patterns and (2) the practice of integrating fossil and living species together in original (i.e., non-literature...

Electroreception is an ancient subdivision of the lateral line sensory system, found in all major vertebrate groups (though lost in frogs, amniotes and most ray-finned fishes). Electroreception is mediated by 'hair cells' in ampullary organs, distributed in fields flanking lines of mechanosensory hair cell-containing neuromasts that detect local water movement. Neuromasts, and afferent neurons for both neuromasts and ampullary organs, develop from lateral line placodes. Although ampullary organs in the axolotl (a representative of the lobe-finned clade of bony fishes) are lateral line placode-derived, non-placodal origins have been proposed for electroreceptors in other taxa. Here we show morphological and molecular data describing lateral line system development in the basal ray-finned fish Polyodon spathula, and present fate-mapping data that conclusively demonstrate a lateral line placode origin for ampullary organs and neuromasts. Together with the axolotl data, this confirms that ampullary organs are ancestrally lateral line placode-derived in bony fishes.

A large sample of embryological material of the North American paddlefish Polyodon spathula (Acipenseriformes: Polyodontidae) confirms that early development in Polyodon is very similar to that reported for the sister group of Polyodontidae, the sturgeons (Acipenseridae). Polyodon illustrates many basic aspects of acipenseriform (and actinopterygian) head development that have not been adequately described. In this paper, we provide an overview of external features of cranial development using scanning electron microscopy. The observations are correlated with staging schemes previously proposed for paddlefishes and other acipenseriforms. Events that occur after the start of neurulation (stage 19) to the start of feeding (stage 46) are emphasized. New information on the structure and folding of the mandibular and hyoid segments permits an understanding of the early development of the pharyngeal region. In addition, we offer new descriptions of the hatching gland, the olfactory organ, the sensory barbel, and the initiation of paddle outgrowth. We also comment on the mode of origin of the hypophysis, and refute the notion that it is derived from the lips of the anterior neuropore as suggested in older literature. This information sets the stage for future comparative and experimental studies of the embryology of basal actinopterygians. © 1992 Wiley-Liss, Inc.

Metabolic rate, branchial morphology, and modes of gill ventilation were studied in young (2-10 g) North American paddlefish, Polyodon spathula, with anatomical, behavioral, and physiological methods. Polyodon lacks the oral and opercular valves that are typical for fishes that rely on a buccal pump system to ventilate the gills, and the jaw opening system of Polyodon is poorly suited for regular pumping movements. Unrestrained, undisturbed juvenile paddlefishes swim constantly at a mean speed of 1.1-1.5 body lengths · $s^{-1}$ (bls). The maximum speed sustainable for > 10 min is 1.6-1.8 bls. When forced to swim at slow speeds in flow tanks or water tunnels, ventilation of the gills by buccal pumping occurs at a frequency of 50-80 · $min^{-1}$. As swimming speed increases, buccal ventilation becomes intermittent and continuous ram ventilation occurs above 0.6-0.8 bls, which means that Polyodon is essentially an obligate ram ventilator under normal conditions. Oxygen consumption ($\dot{M}O_{2}$), carbon di...

Improved structural and functional interpretations regarding the dermal skeleton of Paleozoic lungfishes (Dipnoi) can be derived from a direct comparison of Recent and fossil tissues. In particular, skin from the snout of adult Australian lungfish (Neoceratodus forsteri) contains horizontal plexuses and vertical capillary loops which resemble in structure, size and density components of the cosmine layer in such Paleozoic lungfishes as Dipterus valenciennesi and Chirodipterus australis. In addition to these dermal papillae, the skin of the snout also contains ampullary electroreceptors, goblet cells, compound mucus glands, and terminal branches and openings of the mechanoreceptive lateral line system. Pore canal systems of fossil lungfishes previously have been interpreted as housing electroreceptors or other cutaneous sense organs of the lateral line system. In contrast, we regard pore canal systems as evidence of a complex cutaneous vasculature involved in the deposition of mineralized tissues. Prevailing ideas on the structure and biological role of cosmine are reinterpreted, including the theory that electroreceptors played an important part in the origin of the dermal skeleton.

The development of the cardiovascular system has been analysed in embryos of the little skate, Raja erinacea, ranging in age from 27 to 144 days after spawning. Circulation starts at the end of the first month. At that time, the heart is S-shaped, there is no differentiation between ventricle and conus arteriosus and no valve formation is detectable. Complete differentiation of the central circulatory system and its valves was observed at about 40 days after spawning, although there are changes in proportion that occur before hatching. In the smallest embryos used for physiological studies, 27 days post-spawning (0.01–0.03g body mass), circulation of blood was observed and heart rate was 35–40 beats min−1. Heart rate increased with development, reaching a maximum of 65–68 beats min−1 at a body mass of 0.2 g (60 days post-spawning) and then slowly decreased until just prior to hatching. Ventricular diastolic pressure remained below 0.1 kPa throughout development whereas ventricular systolic pressure increased significantly with increasing body mass. In small embryos (0.1g) serial flap valves in the conus separated the ventral aorta from the diastolic ventricle, and the conus supported ventral arterial blood pressure because of its elastic properties.

The kinematics of tongue projection by terrestrial adult California newts, Taricha torosa (Rathke, 1833), are described based upon high-speed cinematography. Tongue projection results from coupled anterior movements of the ceratohyals and branchial arches. Four distinct periods are defined during a projection sequence: preparation, tongue projection, tongue recovery and mouth closing. Key anatomical correlates of projection are described, with special emphasis on the mobility of the hyoid arch. Adult Taricha (Gray, 1850) have lost the mandibulo-hyoid ligament and reduced additional connective tissues present in larvae. These changes decouple the hyoid arch from mouth opening and release the ceratohyals to participate in a tongue projection system distinct from those of ambystomatids and plethodontids. These phylogenetic differences pose questions about the evolution of tongue projection systems in terrestrial urodeles. Currently available data are consistent with the interpretation that terrestrial urodeles have independently evolved specialized tongue projection systems at least twice: the ceratohyal-stable mode of plethodontids and the ceratohyal-mobile system of newts. In all cases, an essential underlying (= plesiomorphic) feature is the presence of the depressor mandibulae muscle. We regard this pathway for mouth opening as a prerequisite which liberated the hyobranchium for alternative function. Comprehensive studies of the mandibulo-hyoid ligament and depressor mandibulae will be vital to modelling the evolution of specialized tongue projection systems of urodeles.

Polypterid fishes are considered the basalmost group of extant actinopterygians and may be a direct link to understanding the systematics and evolution of the first bony fishes. Several investigations have been conducted on one member genus, Polypterus; however, since the first specimens of its sister taxon Erpetoichthys calabaricus were described, remarkably little work has been done on the species. We review terminology critical to understanding cranial morphology in polypterids and present a new description of the skull of E. calabaricus as observed through classical methods of skeletal preparation, X-radiographic microfocus computed tomography, and 3D-digital reconstruction. Differences among E. calabaricus and at least three species of Polypterus (P. bichir, P. senegalus, and P. endlicheri), besides the gross variation in size, include an overall elongation of the skull roof observable in most elements of E. calabaricus with a shortening of most associated processes. In addition, several elements present in species of Polypterus are absent in E. calabaricus. As a result, Polypterus should not be used as a proxy for the family Polypteridae to the exclusion of E. calabaricus in phylogenetic studies, which examine early actinopterygians. Each should be treated separately, to resolve inter- and intrarelationships of Polypteridae.

increased demand has recently driven the price of black market smoked sturgeon as high as $ 26 a kilogram. With poachers standing to gain roughly a third of this price [besides the much higher price of caviar], a large fish could be worth thousands of dollars. Gary Hamilton in Canadian Geographic, July/August 1996, p. 62

In their paper in this volume Bemis et al. (1997) ask: ‘How many valid species of Acipenser should we recognize?’ Although a partial answer to this question is presented in their Table 5, we discovered in the course of preparing this volume that some additional commentary is needed. In fact, there are two questions: (1) how many species should be recognized? and (2) what scientific names should be used for some of the species? The sympatric distributions of most species of sturgeons set the stage for much confusion about species boundaries, but the situation is actually much more complicated. Confusion about the number of species of sturgeons living within the same basin can result from the often close morphological and meristic similarities of certain species of Acipenser, particularly during juvenile period. Moreover, we still have remarkably inadequate knowledge of the comparative anatomy of the species of Acipenser: no modern study has ever attempted a comprehensive examination of all species, and it is impossible to rely on literature for the sorts of comparisons that must be made (for more on this general problem, see Grande & Bemis 1991, 1997). Most classical descriptions and comparative anatomical studies relied upon small sample sizes. Voucher specimens of large sturgeons are especially rare in most historical collections, and type specimens (if available at all) are seldom prepared in ways that are suitable for making detailed anatomical comparisons (e.g., many skins are simply overstuffed with straw, so that all internal structures are lost). Intraspecific morphological and meristic polymorphisms occur in all species of acipenserids, and in most cases we have very poor knowledge of differences that develop during ontogeny, particularly changes in such features as the shape of the rostrum (Bemis et al. 1997). Another problem is the ease of hybridization between different species of sturgeons (reviewed in Birstein et al. 1997 this volume). In many of these cases, it is not easy to discriminate between parental species and the hybrids.

We present an overview of the global distribution of all 27 living species of Acipenseriformes in an attempt to understand their biogeographic history and the range of life history patterns displayed by different species. Our biogeographic analysis (based on the most recent phylogenetic analysis including fossil Acipenseriformes) suggests that Acipenseriformes originated in Europe, and that early diversification took place in Asia. Acipenseriformes do not have a common life history; variation within and between species is the rule rather than exception. The few relatively well-known case studies (e.g., Caspian Sea sturgeons, European Atlantic sturgeons in the Gironde system, and shortnose and North American Atlantic sturgeons in rivers of the east coast of America) greatly influence what we think we know about sturgeon biology. Our present level of phylogenetic understanding does not allow us to determine whether anadromy or potamodromy is the plesiomorphic life history pattern for Acipenseriformes. We propose that rivers in which spawning occurs must be the central unit for biogeographic analysis of living Acipenseriformes. After mapping these rivers, we recognized nine biogeographic provinces for acipenseriforms. Some repeated historical patterns emerge from this analysis, but, again, we are limited by our current understanding of phylogenetic relationships within the genus Acipenser in particular. Distribution and biogeographic data are central to deciding where to make new efforts to update existing status information for acipenseriform species. We single out a widely ranging and highly variable species, Acipenser ruthenus, as particularly intriguing, for it spans three of our nine biogeographic provinces, and apparently has different life history patterns in different river systems. Finally, we note new areas in need of basic research, particularly the need for more detailed descriptions and analyses of life histories of different populations of sturgeons.

Acipenseriformes occupy a special place in the history of ideas concerning fish evolution, but in many respects, phylogenetic studies of the group remain in their infancy. Even such basic questions as the monophyly of Acipenser (the largest genus) are unanswered. We define relationships based on comparative osteology, which allows us to incorporate well-preserved fossils into analyses. Acipenseriformes has existed at least since the Lower Jurassic (approximately 200 MYBP), and all fossil and recent taxa are from the Holarctic. Phylogenetic relationships among Paleozoic and Early Mesozoic actinopterygians are problematic, but most workers agree that Acipenseriformes is monophyletic and derived from some component of ‘paleonisciform’ fishes. (‘Paleonisciformes’ is a grade of primitive non-neopterygian actinopterygians, sensu Gardiner 1993.) Taxa discussed in comparison here are: †Cheirolepis, Polypterus, †Mimia. †Moythomasia, †Birgeria, †Saurichthys, Lepisosteus and Amia. We review generic diversity within the four nominal families of fossil and recent Acipenseriformes (†Chondrosteidae, †Peipiaosteidae, Polyodontidae, and Acipenseridae), and provide a cladogram summarizing osteological characters for those four groups. Monophyly of the two extant families is well-supported, but there are no comprehensive studies of all of the known species and specimens of †Chondrosteidae and †Peipiaosteidae. As a result, sister-group relationships among †Chondrosteidae, †Peipiaosteidae, and Acipenseroidei (= Polyodontidae + Acipenseridae)are unresolved. We discuss five features fundamental to the biology of acipenseriforms that benefit from the availability of our new phylogenetic hypothesis: (1) specializations of jaws and operculum relevant to jaw protrusion, feeding, and ram ventilation; (2) anadromy or potamodromy and demersal spawning; (3) paedomorphosis and evolution of the group; (4) the biogeography of Asian and North American polyodontids and scaphirhynchines; and (5) the great abundance of electroreceptive organs in the rostral and opercular regions. Finally, we summarize our nomenclatural recommendations.

This volume is dedicated to the memory of Leo Semenovich Berg (1876–1950), a Russian ichthyologist and geographer. In the foreword to the English translation of Berg's remarkable treatise, ‘Nomogenesis or evolution according to law’, Theodosius Dobzhansky wrote: ‘Berg was one of the outstanding intellects among Russian scientists. The breadth of his interests and the depth as well as the amplitude of his scholarship were remarkable. He had the reputation of being a ‘walking library’, because of the amount of information he could produce from his memory’ (Dobzhansky 1969, p. xi). Berg was prolific, publishing 217 papers and monographs on ichthyology, 30 papers on general zoology and biology, 20 papers on paleontology, 32 papers on zoogeoegraphy, 320 papers and monographs on geography, geology, and ethnography, as well as 290 biographies, obituaries, and popular articles (Berg 1955, Sokolov 1955).

Through its secretion of melatonin, the pineal complex of vertebrates exerts a range of physiological effects including regulation of circadian rhythms, seasonal reproduction, metamorphosis, and body color change. Little is known about phylogenetic differences in the distribution and characteristics of melatonin binding sites in fishes. We used in vitro autoradiography to examine binding of [2-125I]iodomelatonin (IMEL) in 20-micron frozen sections of amphioxus (Branchiostoma lanceolatum), Atlantic hagfish (Myxine glutinosa), larval and adult lamprey (Petromyzon marinus), little skate (Raja erinacea), and rainbow trout (Oncorhynchus mykiss). Tissue was incubated with IMEL in the presence or absence of unlabeled melatonin (1 muM, in order to assess nonspecific binding). A concentration of 32 pM IMEL was used for single point assays and competition studies. No specific binding was found in hagfish or amphioxus, which lack a pineal complex. In the optic tecta of lamprey, skate, and trout, IMEL binding is highly specific (melatonin >> N-acetylserotonin > 5- methoxytryptophol >> serotonin). Scatchard analysis revealed that the tectal binding sites are of high affinity (Kd = 36, 38, and 50 pM) and low capacity (Bmax = 8.1, 19.8, and 21.8 fmol/mg protein) in lamprey, skate, and trout, respectively. In adult lampreys, intense specific IMEL binding is found in the optic tectum (layer I > II > III) and preoptic nucleus (pars parvocellularis > magnocellularis). Binding was less intense and consistent in the same areas of ammocoete brain. In skates and trout, intense specific binding is found in optic tectum, lateral geniculate body, diencephalic preoptic and suprachiasmatic nuclei, basal hypothalamus, and the medial pallium. These results indicate that specific melatonin binding sites are present in all craniate taxa examined except in hagfish. Although we cannot rule out the possibility that melatonin receptors are secondarily lost in hagfish, their absence in amphioxus makes this unlikely. We speculate that melatonin actions in early vertebrates may have included regulation of visual and endocrine responses to light.

Prelude to Sturgeon Biodiversity and Conservation E.K. Balon. Sturgeon Biodiversity and Conservation: An Introduction W.E. Bemis, et al. Part 1: Diversity and Evolution of Sturgeons and Paddlefishes. An Overview of Acipenseriformes W.E. Bemis, et al. Osteology and Phylogenetic Interrelationships of Sturgeons (Acipenseridae) E.K. Findeis. Phylogeny of the Acipenseriformes: Cytogenetic and Molecular Approaches V.J. Birstein, et al. How Many Species are there within the Genus Acipenser? V.J. Birstein, W.E. Bemis. Part 2: Biology and Status Reports on Sturgeons and Paddlefishes. Sturgeon Rivers: An Introduction to Acipenseriform Biogeography and Life History W.E. Bemis, B. Kynard. Past and Current Status of Sturgeons in the Upper and Middle Danube River K. Hensel, J. Holcik. Endangered Migratory Sturgeons of the Lower Danube River and its Delta N. Bacalbasa-Dobrovici. Present Status of Commercial Stocks of Sturgeons in the Caspian Sea Basin R.P. Khodorevskaya, et al. Species Structure, Contemporary Distribution and Status of the Siberian Sturgeon, Acipenser baerii G.I. Ruban. Endemic Sturgeons of the Amur River: Kaluga, Huso dauricus, and Amur Sturgeon, Acipenser schrenckii M.L. Krykhtin, V.G. Svirskii. Biology, Fisheries, and Conservation of Sturgeons and Paddlefish in China Q. Wei, et al. Biology and Life History of Dabry's Sturgeon, Acipenser dabryanus, in the Yangtze River P. Zhuang, et al. Observations on the Reproductive Cycle of Cultured White Sturgeon, Acipenser transmontanus S.I. Doroshov, et al. Contemporary Status of the North American Paddlefish, Polyodon Spathula K. Graham. Life History and Status of the Shovelnose Sturgeon, Scaphirhynchusplatorynchus K.D. Keenlyne. The Status and Distribution of Lake Sturgeon, Acipenser fulvescens, in the Canadian Provinces of Manitoba, Ontario and Quebec: a Genetic Perspective M.M. Ferguson, G.A. Duckworth. Lake Sturgeon Management in the Menominee River, a Wisconsin-Michigan Boundary Water T.F. Thuemler. Life History, Latitudinal Patterns, and Status of the Shortnose Sturgeon, Acipenser brevirostrum B. Kynard. Status and Management of Atlantic Sturgeon, Acipenser oxyrinchus, in North America T.I.J. Smith, J.P. Clugston. Atlantic and Shortnose Sturgeons of the Hudson River: Common and Divergent Life History Attributes M.B. Bain. Biological Characteristics of the European Atlantic Sturgeon, Acipenser sturio, as the Basis for a Restoration Program in France P. Williot, et al. Part 3: Controversies, Conservation and Summary. Sturgeons in the Aral Sea Ecological Catastrophe I. Zholdasova. Threatened Fishes of the World: Pseudoscaphirhynchus spp. (Acipenseridae) V.J. Birstein. Molecular Analysis in the Conservation of Sturgeons and Paddlefish I.I. Wirgin, et al. Sensitivity of North American Sturgeons and Paddlefish to Fishing Mortality J. Boreman. Alternatives for the Protection and Restoration of Sturgeons and their Habitat R.C.P. Beamesderfer, R.A. Farr. Threatened Fishes of the World: Scaphirhynchus suttkusi Williams & Clemmer, 1991 R.L. Mayden, B.R. Kuhajda. Threatened Fishes of the World: Scaphirhynchus albus (Forbes & Richardson, 1905) R.L. Mayden, B.R. Kuhajda. Sturgeon Poaching and Black Market Caviar: A Case Study A. Cohen. The Threatened Status of Acipenseriform Fishes: A Summary B.J. Birstein, et al. Species and Subject Index.

We have investigated structure and function of the external gill filaments, which occur transiently in the embryonic little skate, Raja erinacea. Approximately 25-30 days after spawning (body mass 0.03-0.05 g) external gill filaments appear as an outgrowth from the caudal side of the gill arches. These filaments are thread-like, each containing one afferent and one efferent blood vessel, and by day 70-75 (body mass 0.4-0.5 g) they reach their maximum size at a length of about 1 cm and a blood vessel diameter of 70-80 microns. Subsequent resorption of the filaments is characterized by a decrease in both length and diameter of the blood vessel. By day 90-95 (body mass 0.9-1.0 g) the external gill filaments are completely resorbed and replaced by internal gills. Blood velocity, measured in these external filaments, increased with development from 0.1 mm.sec-1 to about 0.7 min.sec-1, and decreased again during resorption. Blood flow, calculated therefrom with blood vessel diameter, showed a similar maximum curve. A model analysis supports the hypothesis that in a full grown filament respiratory gas exchange is mainly perfusion-limited and can contribute significantly to the total oxygen uptake of the embryo. Analysis of the results indicates, however, that the gill filaments are not adequate as a gas exchange organ for later developmental stages.

New observations based on a serial reconstruction of histological sections of a prenatal coelacanth demonstrate that, in contrast to previous reports, the basicranial muscle is innervated by the abducent nerve rather than the vagal nerve. A detailed account of the course of the abducent nerve and its terminal arborizations in the basicranial muscle and lateral rectus muscle is provided. This finding bears on the phylogenetic derivation of the basicranial muscle in sarcopterygians, its possible homologues in other vertebrates, and patterns of head segmentation in craniates.