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31
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"Chimaeriformes"
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Evolutionary Origin and Phylogeny of the Modern Holocephalans (Chondrichthyes: Chimaeriformes): A Mitogenomic Perspective
With our increasing ability for generating whole-genome sequences, comparative analysis of whole genomes has become a powerful tool for understanding the structure, function, and evolutionary history of human and other vertebrate genomes. By virtue of their position basal to bony vertebrates, cartilaginous fishes (class Chondrichthyes) are a valuable outgroup in comparative studies of vertebrates. Recently, a holocephalan cartilaginous fish, the elephant shark, Callorhinchus milii (Subclass Holocephali: Order Chimaeriformes), has been proposed as a model genome, and low-coverage sequence of its genome has been generated. Despite such an increasing interest, the evolutionary history of the modern holocephalans—a previously successful and diverse group but represented by only 39 extant species—and their relationship with elasmobranchs and other jawed vertebrates has been poorly documented largely owing to a lack of well-preserved fossil materials after the end-Permian about 250 Ma. In this study, we assembled the whole mitogenome sequences for eight representatives from all the three families of the modern holocephalans and investigated their phylogenetic relationships and evolutionary history. Unambiguously aligned sequences from these holocephalans together with 17 other vertebrates (9,409 nt positions excluding entire third codon positions) were subjected to partitioned maximum likelihood analysis. The resulting tree strongly supported a single origin of the modern holocephalans and their sister-group relationship with elasmobranchs. The mitogenomic tree recovered the most basal callorhinchids within the chimaeriforms, which is sister to a clade comprising the remaining two families (rhinochimaerids and chimaerids). The timetree derived from a relaxed molecular clock Bayesian method suggests that the holocephalans originated in the Silurian about 420 Ma, having survived from the end-Permian (250 Ma) mass extinction and undergoing familial diversifications during the late Jurassic to early Cretaceous (170–120 Ma). This postulated evolutionary scenario agrees well with that based on the paleontological observations.
Journal Article
Harriotta avia sp. nov. – a new rhinochimaerid (Chimaeriformes: Rhinochimaeridae) described from the Southwest Pacific
Harriotta avia sp. nov., a new species of long-nose chimaera (Holocephali: Chimaeriformes: Rhinochimaeridae), is described from specimens collected off New Zealand in the Southwest Pacific Ocean. The species is distinguished from its congeners by a combination of the following characters: elongated, narrow and depressed snout up to 56% BDL; long, slender trunk; beak-like vomerine tooth plate; large eye, length 8–12% BDL and height 5–7% BDL; long dorsal spine reaching slightly beyond apex of the dorsal fin; and slender rod-like pelvic claspers. The skin is deciduous, and uniform chocolate brown when intact. Harriotta avia sp. nov. is also distinguished from other Harriotta species based on DNA sequence divergence of the NADH2 gene. Harriotta avia sp. nov. is reported from the New Zealand-Australian region. Conclusions here show that Harriotta raleighana, a presumed globally distributed species, likely comprises several species and the genus Harriotta warrants a revision with specimens representing all ocean basins.
Journal Article
Hidden diversity of the most basal tapeworms (Cestoda, Gyrocotylidea), the enigmatic parasites of holocephalans (Chimaeriformes)
Gyrocotylideans are evolutionary ancient parasitic flatworms, and like their hosts—a relict group of holocephalan fishes (Chimaeriformes)—they are considered to be “living fossils” of a vanished past. However, the species diversity, host associations and biogeography of these most basal tapeworms are poorly known. Herein, we provide evidence of a conspicuous contrast between the genetic and morphological data based on an examination of newly collected and properly processed
Gyrocotyle
specimens (hologenophores) isolated from holocephalans off Taiwan and Argentina. Our molecular data, inferred from three genes (
COI, 28S rRNA, 18S rRNA
), showed unexpected genetic interrelationships among isolates of the genus
Gyrocotyle
, because each of the four genotypes from Taiwan clustered with isolates of distinct gyrocotylideans from the North Atlantic. Three genotypes of
Gyrocotyle
from Taiwan were morphologically almost indistinguishable from each other but represented distinct genetic lineages; a single specimen of
Gyrocotyle
sp. genotype 4 exhibited a clear genetic and morphological distinctness, though its formal description as a new species would be premature. Additionally, specimens of
Gyrocotyle rugosa
Diesing, 1850, from the type host
Callorhinchus callorynchus
from Argentina, provided the first genetic data on the type species of the genus and enabled us to characterise it, which is necessary for future taxonomic studies. The finding of some specimens of
Gyrocotyle
sp. genotype 3 in
Chimaera phantasma
, and another one in
C.
cf.
argiloba
, together with the putative conspecificity of an unidentified gyrocotylidean from
Callorhinchus milii
off Australia and
G. rugosa
from
C. callorynchus
off Argentina, represent evidence that one gyrocotylidean species may parasitise more than one holocephalan host species. Existing taxonomic problems and conflicts between morphological and molecular data on species of
Gyrocotyle
can only be resolved if hologenophores from type hosts and localities of nominal taxa are properly characterised genetically and morphologically.
Journal Article
A New Paleozoic Symmoriiformes (Chondrichthyes) from the Late Carboniferous of Kansas (USA) and Cladistic Analysis of Early Chondrichthyans
The relationships of cartilaginous fishes are discussed in the light of well preserved three-dimensional Paleozoic specimens. There is no consensus to date on the interrelationship of Paleozoic chondrichthyans, although three main phylogenetic hypotheses exist in the current literature: 1. the Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are grouped along with the modern sharks (neoselachians) into a clade which is sister group of holocephalans; 2. the Symmoriiformes are related to holocephalans, whereas the other Paleozoic shark-like chondrichthyans are related to neoselachians; 3. many Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are stem chondrichthyans, whereas stem and crown holocephalans are sister group to the stem and crown neoselachians in a crown-chondrichthyan clade. This third hypothesis was proposed recently, based mainly on dental characters.
On the basis of two well preserved chondrichthyan neurocrania from the Late Carboniferous of Kansas, USA, we describe here a new species of Symmoriiformes, Kawichthys moodiei gen. et sp. nov., which was investigated by means of computerized X-ray synchrotron microtomography. We present a new phylogenetic analysis based on neurocranial characters, which supports the third hypothesis and corroborates the hypothesis that crown-group chondrichthyans (Holocephali+Neoselachii) form a tightly-knit group within the chondrichthyan total group, by providing additional, non dental characters.
Our results highlight the importance of new well preserved Paleozoic fossils and new techniques of observation, and suggest that a new look at the synapomorphies of the crown-group chondrichthyans would be worthwhile in terms of understanding the adaptive significance of phylogenetically important characters.
Journal Article
Lipid composition and partitioning of deepwater chondrichthyans: inferences of feeding ecology and distribution
The composition of lipids and fatty acids was determined for the livers, muscle, pancreas, kidney and stomach fluids of deepwater chondrichthyan species (including 11 squaliformes, 3 chimaeriformes, 1 hexanchiforme and 3 carcharhiniformes) caught as bycatch from continental waters off south-eastern Australia. The lipid class, fatty acid and fatty alcohol composition differed markedly in each tissue and in each species. The lipid and fatty acid composition of large, lipid-rich (38-70% wet weight, ww) livers demonstrated the multifunctional role of this organ in: lipid distribution, storage and biosynthesis, and buoyancy regulation. In the liver, the importance of certain lipids (including squalene, diacylglyceryl ethers, triacylglycerols and to a lesser extent wax esters) as mediators of buoyancy varied according to lifestyle and habitat. Less variability was observed in the muscle profiles, characterized by low lipid content (<1.0% ww) and high relative levels of polar lipids (>70%). The lipid and fatty acid profiles of the kidney and pancreas showed the highest intraspecific variability, suggesting these organs also have complex roles in lipid storage and metabolism. Overall intra- and interspecific differences in the tissue fatty acid profiles could be related to differences in a number of factors including phylogeny, habitat (depth), buoyancy regulation and diet and presumably also reflect different ecological roles. The lipid and fatty acid profiles are the first published for Rhinochimaera pacifica, Chimaera lignaria and Figaro boardmani and the first to demonstrate interspecific variation in lipid profiles of various tissues of deepwater chondrichthyans. The application of multivariate analysis to lipid class and fatty acid tissue profiles in chondrichthyans inferred dietary differences and metabolic preferences between species and habitats. These results have important implications for the future use of fatty acids as dietary tracers in chondrichthyan research.
Journal Article
FIRST RECORDS OF CHIMAERA OPALESCENS (HOLOCEPHALI: CHIMAERIFORMES: CHIMAERIDAE) FROM MADEIRA AND NORTH-WEST AFRICAN COAST
This study reports new findings of Chimaera opalescens Luchetti, Iglésias et Sellos, 2011, which represent new records of this fish from Madeira and Morocco. The specimens were caught at the depths between 800 and 1221 m. Additional specimens deposited in the Natural History Museum of Funchal (MMF) were also studied as a comparative material and the results are reported herein. The new records of C. opalescens extend the previously known area of distribution of this fish further south.
Journal Article
Capture of Hydrolagus cf. purpurescens (Gilbert, 1905) (Chimaeriformes: Chimaeridae) off southeastern Sakhalin
The capture in waters off southeastern Sakhalin of a male of Hydrolagus TL 122 cm is described. It is tentatively identified as Hydrolagus cf. purpurescens, a new species for the fauna and the second representative of the subclass in far eastern waters of Russia. The captured specimen is briefly described and its photographs are published. Unsolved problems of taxonomy of the group purpurescens complex do not permit to make a unanimous determination of this specimen. These problems are discussed and some items concerning the nomenclature of this group are specified.
Journal Article
The first record of the sicklefin chimaera Neoharriotta pinnata (Chimaeriformes: Rhinochimaeridae) in the southern Bay of Biscay (North-East Atlantic)
One specimen of an adult female of the chimaera
Neoharriotta pinnata
was caught in the southern of Bay of Biscay (44° N). Until now, this species has been reported at the coast of West Africa, in the Arabian Sea, the Bay of Bengal and to the south-west of India. It is the first time that this chimaera has been recorded at the latitudes north of the parallel 22° N. This report extends the known habitat of this species considerably.
Journal Article
Ischyodus rayhaasi (Chimaeroidei; Callorhynchidae) from the Campanian-Maastrichtian Fox Hills Formation of Northeastern Colorado, USA
Modern ratfish (chimaeroids) are examples of a poorly documented lineage of cartilaginous fishes that extends back to Triassic time. Here we report on the discovery of abundant remains of the callorhynchid chimaeroid Ischyodus rayhaasi Hoganson and Erickson 2005 from a Campanian-Maastrichtian age locality in the Fox Hills Formation of northeastern Colorado. A second, distinct group of chimaeroid specimens, designated Ischyodus sp., occurs at the same locality and may represent a species separate from I. rayhaasi, an earlier ontogenetic stage, or sexual dimorphism within I. rayhaasi. The presence of chimaeroid fishes is discussed in regard to the paleoecology and paleogeography of the Late Cretaceous Western Interior Seaway.
Journal Article