Morphological analysis of the hagfish heart. II. The venous pole and the pericardium

The morphological characteristics of the venous pole and pericardium of the heart were examined in three hagfish species, Myxine glutinosa, Eptatretus stoutii, and Eptatretus cirrhatus. In these species, the atrioventricular (AV) canal is long, funnel‐shaped and contains small amounts of myocardium. The AV valve is formed by two pocket‐like leaflets that lack a papillary system. The atrial wall is formed by interconnected muscle trabeculae and a well‐defined collagenous system. The sinus venosus (SV) shows a collagenous wall and is connected to the left side of the atrium. An abrupt collagen‐muscle boundary marks the SV‐atrium transition. It is hypothesized that the SV is not homologous to that of other vertebrates which could have important implications for understanding heart evolution. In M. glutinosa and E. stoutii, the pericardium is a closed bag that hangs from the tissues dorsal to the heart and encloses both the heart and the ventral aorta. In contrast, the pericardium is continuous with the loose periaortic tissue in E. cirrhatus. In all three species, the pericardium ends at the level of the SV excluding most of the atrium from the pericardial cavity. In M. glutinosa and E. stoutii, connective bridges extend between the base of the aorta and the ventricular wall. In E. cirrhatus, the connections between the periaortic tissue and the ventricle may carry blood vessels that reach the ventricular base. A further difference specific to E. cirrhatus is that the adipose tissue associated with the pericardium contains thyroid follicles. J. Morphol. 277:853–865, 2016. © 2016 Wiley Periodicals, Inc.     

Variability in the Presence of Elastic Fibre-like Structures in the Ventral Aorta of Agnathans (Hagfishes and Lampreys)

This paper investigates whether elastic fibre-like structures are present in the ventral aorta of hagfishes and lampreys. Fibres, which are morphologically similar to the elastic fibres of gnathostomatous (jawed) vertebrates, are shown to be present in the ventral aorta of the hagfish Paramyxine atami, and also, but to a lesser extent, the dorsal aorta of this species and the ventral aorta of another hagfish, Eptatretus stouti.The ‘elastic’ tissue formed irregular sheet-like aggregates, comprising well-defined amorphous material surrounded by tubular microfibrils, whose diameters ranged from 10 to 15 nm. While this tissue was most abundant in the same region of the aortae as that occupied by the elastica interna in the blood vessels of gnathostomes, it was also found deeper in the wall of these blood vessels. Although tubular microfibrils were found in the ventral aorta of the hagfish Myxine glutinosaand the lamprey Geotria australis, these were never associated with well–defined, amorphous material. This parallels the results of previous studies on Myxine glutinosaand another species of lamprey, Petromyzon marinus.Thus, the elastic fibre–like tissues found in the ventral aortae of P. atamiand E. stoutiprovide the first examples of such structures in this region in agnathan vertebrates.     

Plasma cells in adult Atlantic hagfish,Myxine glutinosa

Summary Hagfishes, the most primitive vertebrates, are of special interest for the evolution of immune responses. Eptatretus stoutii, the Pacific hagfish, is able to mount cellular and humoral immune responses but all attempts to demonstrate in them the presence of plasma cells have failed. In the present study we demonstrate for the first time plasma cells identifiable by ultrastructural criteria in the pronephros, a primitive lymphohaemopoietic organ, of Myxine glutinosa, the Atlantic hagfish.     

Review and phylogeny of the New Zealand hagfishes (Myxiniformes: Myxinidae), with a description of three new species

Hagfishes from New Zealand are reviewed and a phylogeny proposed using morphological and genetic data (DNA sequences of cytochrome c oxidase subunit I gene, COI, and the small subunit RNA, 16S). E ptatretus cryptus sp. nov. was previously confused with Eptatretus cirrhatus (Forster in Bloch & Schneider, 1801) because of their similar morphology, and is found from the Three Kings Islands to Stewart Island and in the eastern part of the Chatham Rise (at depths of 96–922 m). E ptatretus poicilus sp. nov. is endemic to the Three Kings Islands, where it is common and associated with soft sediment and deep‐sea coral‐sponge habitats (114–842 m). N eomyxine caesiovitta sp. nov. is a slender hagfish found along the east coast of the North Island south to the Chatham Rise (430–1083 m). A neotype is erected for E. cirrhatus (type locality: Breaksea Sound, Fiordland), occurring widely in New Zealand coastal, shelf, and slope waters (1–922 m), but not at the Three Kings Islands. Eptatetrus goliath Mincarone & Stewart, 2006, Neomyxine biniplicata (Richardson & Jowett, 1951), and Nemamyxine elongata Richardson, 1958 are further described using additional material. Rubicundus eos (Fernholm, 1991) is still only known from the holotype (type locality: Challenger Plateau). Genetic results showed that the New Zealand Eptatretus species form a monophyletic group within the subfamily Eptatretinae, indicating likely speciation from a single common ancestor within the area. E ptatretus poicilus sp. nov. is the sister species of E. cirrhatus, and E . cryptus sp. nov. is closely associated with the clade formed by these two species. Eptatretus goliath is most closely associated with Eptatretus minor Fernholm & Hubbs, 1981 (Gulf of Mexico), these two species basally diverging within New Zealand hagfishes. The endemic genus Neomyxine forms a well‐supported monophyletic group of as yet uncertain position within the phylogenetic tree. A key to the New Zealand hagfishes, fresh colour photographs, distribution maps, and in situ video recordings are presented. © 2015 The Linnean Society of London     

Morphometics and Gonadal Development of the Hagfish Eptatretus cirrhatus in New Zealand

Hagfishes have been the target of commercial fisheries in many areas of the world, with the catch processed for leather and for human consumption. A fishery has been operating in New Zealand waters for the last six years, harvesting the bearded hagfish, Eptatretus cirrhatus. The fishery has thus far been unregulated. Based on samples collected dockside over a two-year period, this report expands the morphometric database for this species, provides information on the size and weight of the harvested animals, determines the sizes at the onset of gonadal development and the minimum sizes at sexual maturation for males and females, and indicates that E. cirrhatus, like most other hagfish species, has no specific breeding season. Although females appear in the population at smaller sizes, the sex ratio for mature animals is 1:1 and the sizes of the largest males and females are comparable. The changes observed in sex ratio as a function of TL suggest differences in the timing and rates of gonadal development in females versus males rather than protogyny. Based on the size of the eggs, the number of eggs per female, the proportion of the population that contains large eggs, and the number of postovulatory females, it is clear that E. cirrhatus, like other hagfish species, are potentially vulnerable to overexploitation.     

Reproductive biology and ecology of Pacific hagfish (Eptatretus stoutii) and black hagfish (Eptatretus deani)

The reproductive biology of Pacific hagfish Eptatretus stoutii (Lockington, 1878) and black hagfish Eptatretus deani (Evermann & Goldsborough, 1907) was assessed using current and historical data. Our results found that the reproductive characteristics of both hagfish species reflect those of K-selected species, which tend to live long and exhibit slow growth rates, low fecundity (approximately 20 eggs per female) and late maturity. Additionally, females of both species commence maturation prior to males. This study provides a population profile for both species of hagfish, but further assessments are needed to effectively manage a sustainable hagfish fishery.     

Review of the Australian hagfishes with description of two new species of Eptatretus (Myxinidae)

This paper revises and updates taxonomic and distributional information about hagfishes (Myxinidae) from Australia. It covers five species of the genus Eptatretus: Eptatretus cirrhatus known from eastern Australia and also distributed around New Zealand, Eptatretus longipinnis endemic to South Australia, Eptatretus strahani originally described from the Philippines and reported here as a new record from Western Australia and two new species described herein as Eptatretus alastairi and Eptatretus gomoni, both from Western Australia. Eptatretus alastairi is distinguished from all congeners by the unique combination of the following characters: six pairs of gill pouches; three‐cusp multicusps on the anterior and posterior rows of cusps; anterior unicusps 9–12; posterior unicusps 8–11; total cusps 48–56; prebranchial pores 13–16; branchial pores 5–6; trunk pores 50–55; tail pores 11–13; total pores 83–88; two bilaterally symmetrical nasal‐sinus papillae in the dorsal surface of the nasal sinus. Eptatretus gomoni is distinguished from all congeners by the unique combination of the following characters: eight pairs of gill pouches; three‐cusp multicusps on the anterior and two‐cusp multicusps on the posterior row of cusps; anterior unicusps 10–11; posterior unicusps 9–10; total cusps 50; prebranchial pores 12–13; branchial pores 7–8; trunk pores 57–58; tail pores 14–15; total pores 91–93; no nasal‐sinus papillae. An identification key for the Australian species of Eptatretus is also provided.     

Highly repetitive DNA sequences that are restricted to the germ line in the hagfish Eptatretus cirrhatus: a mosaic of eliminated elements

The New Zealand hagfish, Eptatretus cirrhatus, is known to eliminate parts of its chromosomes during embryogenesis from presumptive somatic cells. Electrophoresis of germ line and somatic DNAs of this species, after treatment with the restriction endonucleases DraI and EcoRI, revealed three fragments of DNA that were restricted to the germ line. DNA filter hybridization experiments demonstrated that these fragments were present almost exclusively in the germ line DNA of E. cirrhatus and that they were highly and tandemly repeated. Thus, these DNA fragments appeared to be eliminated during embryogenesis. Moreover, one fragment (a DraI fragment) cross-hybridized with the germ line DNA from other species of hagfish, namely, Eptatretus okinoseanus and Paramyxine atami. Molecular cloning and sequence analysis revealed that the DraI fragment was composed mainly of closely related sequences of 85 bp in length and that this sequence was about 75% homologous to the sequence of EEEo2 (eliminated element of E. okinoseanus 2) which is a germ line-restricted and highly repetitive sequence that was isolated previously from E. okinoseanus. The other two fragments were composed of three families of closely related sequences that were 172 bp long (designated EEEc1), 61 bp long (EEEc2) and 54 bp long (EEEc3). Fluorescence in situ hybridization experiments revealed that each eliminated element was distributed on several chromosomes that are limited to germ cells. EEEo2 was dispersed on 12 C-band-positive chromosomes. EEEc1 and EEEc3 were dispersed on all C-band-positive and several C-band-negative chromosomes. By contrast, EEEc2 was located to terminal regions of several C-band-negative chromosomes. These results suggest that the eliminated chromosomes in hagfish are mosaics of highly repeated, germ line-restricted families of DNA sequences. Received: ██; in revised form: 25 October 1997 / Accepted: ██     

Ependymal Absorption of Peroxidase into the Third Ventricle of the Hagfish Eptatretus burgeri (Girard)

Abstract The ependymal cells of both dorsal and ventral walls lining the lumen of the neurohypophysis of the hagfish, Eptatretus burgeri, absorb peroxidase injected into the third ventricle. Peroxidase diffuses rapidly into the connective tissue separating the neurohypophysis from the adenohypophysis, and also into the connective tissue located between the cell nests of the adenohypophysis.     

The partial sequence of the first 30 residues from the amino-terminus of hemoglobin B in the hagfish,Eptatretus stoutii: Homology with lamprey hemoglobin

Summary The partial sequence of the first 30 residues from the amino-terminus of hemoglobin B in the hagfish,Eptatretus stoutii, has been determined. Considerable homology was found between this sequence and the corresponding sequence of lamprey hemoglobin. Both hagfish and lamprey hemoglobins have an additional segment of 9 residues at the amino-terminus as compared with mammalian hemoglobins.This work was initiated at the University of Texas at Austin, and continued in Dr. Charles Yanofskey's laboratory at Stanford University.     

The Different Vascular Patterns of Slime Glands in the Hagfishes,Myxine glutinosa Linnaeus and Eptatretus stouti Lockington A Scanning Electron Microscope Study of Vascular Corrosion Casts*

The vascular patterns of the epidermally derived slime glands of the Atlantic hagfish, Myxine glutinosa, and of the Pacific hagfish, Eptatretus stouti, have been studied by scanning electron microscopy of vascular corrosion casts. In Myxine a simple two-dimensional vascular network sheaths the slime glands, while in Eptatretus there is also a great number of capillary loops of different lengths arising from the sheathing network and extending into the interior of the glands. These basic differences in slime glands vascular patterns are thought to reflect substantially different physiological behaviour of the slime glands in Myxine and Eptatretus.     

Hagfish phylogeny and taxonomy,with description of the new genus Rubicundus (Craniata,Myxinidae)

A recent phylogenetic analysis of the Myxinidae based on the 16S rRNA gene resulted in synonymization of Paramyxine with Eptatretus. This created homonymy of Paramyxine fernholmi with Eptatretus fernholmi and Paramyxine wisneri with Eptatretus wisneri. In order to resolve this nomenclatural dilemma, we made a more extensive phylogenetic assessment of the Myxinidae and examined the nomenclature of the family. We used 75 sequences (37 of which new for this study) of a 561 bp fragment of the 16S rRNA gene, representing 33 species, and 72 sequences (37 of which new for this study) of a 687 bp fragment of the cytochrome c oxidase subunit I (COI) gene, representing 23 species, to reconstruct the phylogeny of Myxinidae. The monophyly of the subfamily Myxininae, traditionally characterized by having a single pair of external gill openings, was rejected (0.50 Bayesian posterior probability) by the 16S analysis, but supported by the COI and combined COI+16S analyses (0.99 and 0.81 Bpp, respectively). The monophyly of the subfamily Eptatretinae, characterized by having several pairs of external gill openings, was not supported by the 16S analysis and rejected by the COI and combined COI+16S analysis due to the placement of Eptatretus lopheliae as the earliest branch of Myxinidae (0.71 and 0.57 Bpp, respectively). Eptatretus lopheliae and Eptatretus rubicundus formed a monophyletic group and were allocated to a new genus, Rubicundus, characterized by the presence of an elongated tubular nostril and reddish coloration. A new monotypic subfamily, Rubicundinae, was proposed for Rubicundus. The synonymy of the genera Paramyxine and Quadratus with Eptatretus was confirmed. E. fernholmi is renamed Eptatretus luzonicus. Eptatretus wisneri was renamed Eptatretus bobwisneri. Petromyzon cirrhatus Forster, 1801, Homea banksii Fleming, 1822, and Bdellostoma forsteri Müller, 1836 are synonyms, but no type specimens are known to exist. Petromyzon cirrhatus was designated as type species of Eptatretus, conserving present usage. Gastrobranchus dombeyi Shaw, 1804 has priority over other names for Chilean myxinids. Bdellostoma stoutii was designated as type species of Polistotrema Gill. The validity of the Western Atlantic Myxine limosa as distinct from the Eastern Atlantic Myxine glutinosa was confirmed.     

In Search of the Hagfish Thymus

The Pacific hagfish, Eptatretus stoutii, is capable of a varietyof immunologic responses including allograft rejection and serumantibody production to soluble and cellular antigens. Interesthas revived in the morphology of hagfish lymphoid tissues. Thesearch for a thymus in young specimens has resulted in the discoveryof a phagocytic and antigen-receptive cell population associatedwith the pharyngeal velar muscles. We suggest that a protothymusor precursor of the thymus of higher vertebrates may be containedwithin this velar muscle complex.     

Morphometric classification of neurosecretory granules in the neurohypophysis of the hagfish,Eptatretus burgeri

Summary Neurosecretory axons in the neurohypophysis of the hagfish, Eptatretus burgeri, were statistically classified into six types according to the size of secretory granules. These types are comparable with those in higher vertebrates. The concentration of each axon type is different in three regions: anterior dorsal wall, posterior dorsal wall, and ventral wall. The regional differences of the hagfish neurohypophysis are discussed in relation to the regional differentiation of the tetrapod neurohypophysis into the median eminence and the pars nervosa.We wish to express our appreciation to Professor Hideshi Kobayashi for the guidance of this study. It was aided by grants from the Ford Foundation and the Ministry of Education to Professor H. Kobayashi, and also by grants from the Population Council, New York and the Ministry of Education to Professor S. Ishii.     

Immunohistochemical localization of bioactive peptides and amines associated with the chromaffin tissue of five species of fish

Biogenic peptides and amines associated with the chromaffin tissue in Atlantic cod (Gadus morhua), rainbow trout (Oncorhynchus mykiss), European eel (Anguilla anguilla), spiny dogfish (Squalus acanthias) and Atlantic hagfish (Myxine glutinosa) were identified utilizing immunohistochemical techniques. Within the posterior cardinal vein (PCV) in cod, trout and eel, a subpopulation of chromaffin cells displayed immunoreactivity to tyrosine hydroxylase (TH) and dopamine--hydroxylase (DH) but not to phenylethanolamine-N-methyltransferase (PNMT). TH-like immunorectivity was observed within cells in hagfish hearts. Nerve fibres displaying vasoactive intestinal peptide (VIP) immunoreactivity and pituitary adenylyl cyclase activating peptide (PACAP) immunoreactivity innervated cod, trout and ell chromaffin cells. In eel, neuropeptide Y (NPY)-like and peptide YY (PYY)-like immunoreactivity was located within cells in the PCV, including chromaffin cells. Serotonin-like immunoreactivity was observed within eel and cod chromaffin cells and in hagfish hearts. In the dogfish axillary bodies, nerves displaying TH-like, VIP-like, PACAP-like, substance P-like and galanin-like immunoreactivity were observed. These results are compared with those of other vertebrates, and potential roles for these substances in the control of catecholamine release are suggested.     

Eptatretus strickrotti n. sp. (Myxinidae): first hagfish captured from a hydrothermal vent

A single hagfish (Myxinidae, Eptatretus) specimen was recently captured at a hydrothermal vent site on the East Pacific Rise (38 degrees S). This is the first capture of a member of the jawless fishes (agnathans) from a hydrothermal vent site. The specimen differs from all congeners by the very slender body (depth 2.9% of total length), the paired and median ventral nasal sinus papillae, and the presence of 10 afferent branchial arteries on the medial ventral aorta. It is further unique because of a combination of the following features: slime pore counts; paired dorsal nasal sinus papillae; 12 gill pouches and gill apertures; posterior left side of body widely separated from pharyngocutaneous duct; 3/2 multicusp configuration; ventral aorta bifurcated anteriorly between 2nd and 3rd gill pouches (counted from the snout toward the heart); and pink coloration. The specimen is here described as a new species named Eptatretus strickrotti. Molecular 16S rRNA data places this new species as the basal-most species of Eptatretus, providing important new insight to the evolution of hagfishes as a whole.     

The Complete Mitochondrial Genome of the Hagfish Myxine glutinosa: Unique Features of the Control Region

The complete sequence of the mitochondrial DNA of the hagfish Myxine glutinosa has been determined. The hagfish mtDNA (18,909 bp) is the longest vertebrate mtDNA determined so far. The gene arrangement conforms to the consensus vertebrate type and differs from that of lampreys. The exceptionally long (3628-bp) control region of the hagfish contains the typical conserved elements found in other vertebrate mtDNAs but is characterized by a large number of putative hairpins, which can potentially fold into a highly compact secondary structure that appears to be unique to hagfish. The comparison of the mtDNAs of two M. glutinosa specimens, excluding the control region, shows a 0.6% divergence at the nucleotide level as a sample of intraspecies polymorphism. Received: 21 August 2000 / Accepted: 2 March 2001     

The chromosomes of some lower chordates

The chromosomes of three species of lower chordates were examined using a squash technique on small pieces of testis. Ciona intestinalis, a tunicate of the order Enterogona, has fourteen pairs of minute chromosomes. Styela plicata, a tunicate of the order Pleurogona, has sixteen pairs of chromosomes whose total size is approximately twice that of the Ciona chromosomes and about 10% of that of a typical mammalian complement. The hagfish, Eptatretus stoutii, of the suborder Myxinoidea, order Cyclostomata, has twenty-four pairs of chromosomes and what appear to be one to four small supernumeraries in some animals. The hagfish chromosomes are large, approaching the size of a typical mammalian complement. These size relationships agree in general with a concept of a small ancestral vertebrate genome which evolved into the larger present day genomes through a series of duplications of genetic material.This work was supported in part by Grant No. 247-701 from the San Diego State College Foundation.     

FMRFamide-like immunoreactivity in the brain of the Pacific hagfish,Eptatretus stouti (Myxinoidea)

Summary The distribution of FMRFamide-like immunoreactivity was investigated in the brain of a myxinoid, the Pacific hagfish,Eptatretus stouti, by means of immunocytochemistry. In the forebrain, labelled cell bodies occurred in the infundibular nucleus of the hypothalamus and some closely adjacent nuclei. Labelled fibers formed a diffuse network in the forebrain, but there was no evidence for the presence of intracerebral ganglionic cells of the terminal nerve or a central projection of the terminal nerve. In the hindbrain, a group of labelled cells was found in the trigeminal sensory nucleus. A distinet terminal arborization occurred in the ventrally adjacent nucleus A of Kusunoki and around the nuclei of the branchial motor column. These findings suggest that FMRFamide may play a role in the central control of branchiomotor activity.