Ontogeny of the jaw apparatus and suspensorium of the Tetraodontiformes

Skeletal ontogeny of the Plainfin Midshipman, Porichthys notatus (Percomorphacea: Batrachoidiformes)

Batrachoidiformes are benthic fishes that utilize the undersides of rocks as spawning nests. Their larvae are attached to the nest and nourished by a large yolk sac. The evolutionary shift from feeding, free-swimming larvae to sedentary larvae that are reliant on their yolk sac for nutrition can lead to changes in skeletal development. Batrachoidiformes also have many morphological specializations, such as five pectoral-fin radials (versus four in other acanthomorphs) that are of uncertain homology, the determination of which may have phylogenetic implications. A larval series of Porichthys notatus was collected and its skeletal ontogeny is described. In P. notatus the ossification of the pharyngeal toothplates occurs relatively later than in percomorphs with free-swimming larvae. The posterior basibranchial copula cartilage (= fourth basibranchial) in Porichthys notatus has a unique development among fishes: it initially develops as a paired element at 6.8-7.1 mm NL before fusing posteriorly and forming single median cartilage at 7.4 mm SL. Cartilages of hypobranchial four are transitory, being observed in two specimens of 6.8 and 7.3 mm NL before fusing with ceratobranchial four. The previously identified dorsalmost pectoral radial is a bone formed by a hypertrophied propterygium that ossifies later in development. The earliest stages of P. notatus have three dorsal spines, but during late larval development, the growth of the third dorsal spine is interrupted. The development of P. notatus is compared and discussed in context to that of other acanthomorph.

The teeth and dentition of the filefish (Stephanolepis cirrhifer) revisited tomographically

The upper and lower tooth-bearing jaws of the filefish (Stephanolepis cirrhifer) were scanned using a micro-CT system in order to address the existing gaps between the traditional pictures of the morphology and histology. 2D tomograms, reconstructed 3D models and virtual dissection were employed to examine and evaluate the in situ geometry of tooth implantation and the mode of tooth attachment both separately and collectively. No distinct sockets comparable to those in mammals were evident, but shallow depressions were observed in the premaxillary and the dentary. The opening of the tooth pulp cavity was not simply oriented towards the apparent tooth base in a direction opposite to the tooth apex. The opening was distorted basoposteriorly or basoanteriorly depending on the position of the tooth, and the edge of the pulp cavity opening was barely ankylosed; i.e. the sites of pleurodont ankylosis along the basoposterior or basoanterior edge of the opening appeared to closely match the contour of the shallow depression in the bone. These 3D findings appear to be very informative when considering the phylogeny of tooth attachment, suggesting that micro-CT would be a useful modality concurrent with or in advance of histological investigations.

Life history, distribution and molecular phylogenetics of the Upward-Mouth Spikefish Atrophacanthus japonicus (Teleostei: Tetraodontiformes: Triacanthodidae)

Ninety-six juvenile specimens (37-54 mm standard length; L_S ) of the rarely collected Upward-Mouth Spikefish Atrophacanthus japonicus (Triacanthodidae) were obtained from the stomachs of three Yellowfin Tuna Thunnus albacares collected off Guam in the Mariana Islands in the central Pacific Ocean. These specimens extend the range of A. japonicus eastward into Oceania. We review the systematic characters of the monotypic genus Atrophacanthus and present colour photographs of freshly collected specimens. The diet of the juvenile specimens of A. japonicus consisted of thecosome pteropods and foraminiferans. We present a range map of A. japonicus based on all known specimens and show that specimen size is related to whether specimens were collected in the pelagic zone or on the bottom. Our results support that, compared to all other Triacanthodidae, A. japonicus has an unusually extended pelagic larval and juvenile period, up to 54 mm L_S , before settling to the bottom as adults. Lastly, we provide a multilocus phylogeny addressing the phylogenetic placement of Atrophacanthus based on eight of 11 triacanthodid genera and six genetic markers. Our results reveal that Atrophacanthus is the sister group of Macrorhamphosodes and they provide new insights about the evolutionary history of the family.

A new phylogeny of tetraodontiform fishes (Tetraodontiformes, Acanthomorpha) based on 22 loci

Tetraodontiform fishes represent one of the most peculiar radiations of teleost fishes. In spite of this, we do not currently have a consensus on the phylogenetic relationships among the major tetraodontiform lineages, with different morphological and molecular datasets all supporting contrasting relationships. In this paper we present the results of the analysis of tetraodontiform interrelationships based on two mitochondrial and 20 nuclear loci for 40 species of tetraodontiforms (representing all of the 10 currently recognized families), as well as three outgroups. Bayesian and maximum likelihood analyses of the concatenated dataset (18,682 nucleotides) strongly support novel relationships among the major tetraodontiform lineages. Our results recover two large clades already found in mitogenomic analyses (although the position of triacanthids differ), while they strongly conflict with hypotheses of tetraodontiform relationships inferred by previous studies based on morphology, as well as studies of higher-level teleost relationships based on nuclear loci, which included multiple tetraodontiform lineages. A parsimony gene-tree, species-tree analysis recovers relationships that are mostly congruent with the analyses of the concatenated dataset, with the significant exception of the position of the pufferfishes+porcupine fishes clade. Our findings suggest that while the phylogenetic placement of some tetraodontiform lineages (triacanthids, molids) remains problematic even after sequencing 22 loci, an overall molecular consensus is beginning to emerge regarding the existence of several major clades. This new hypothesis will require a re-evaluation of the phylogenetic usefulness of several morphological features, such as the fusion of several jaw bones into a parrot-like beak, or the reduction and loss of some of the fins, which may have occurred independently more times than previously thought.