The structure and development of the jaw adductor musculature in the turtle Chelydra serpentina

The investigation of the development of the trigeminal jaw adductor musculature in the turtle Chelydra serpentina documents the early aggregation of muscle rudiments around the innervating nerve branches, probably a consequence of inductive interaction. This may explain the early continuity of the intramandibularis with the intermandibularis muscle. Several aspects of muscle development differ in the turtle as compared to lizards. These differences highlight the fact that conjectures of homology, based on a static topographical correspondence of adult structures, cannot capture the dynamics of the developmental process. The intramandibularis muscle of turtles, comparable to that of crocodiles, represents a plesiomorphous structure which is not homologous to the intramandibularis muscle of lacertoid lizards, a derived feature of the Lacertoidea. A derived feature of the chelonian jaw adductor musculature is the posterodorsal expansion of the external adductor along a supraoccipital crest, developing according to a pattern of Haeckelian recapitulation. Muscle development serves to corroborate the concept of a monophyletic Eureptilia, including diapsids and synapsids, as opposed to the (paraphyletic) Anapsida. The impact of the differentiation of the external adductor into a pulley system on cranial kinesis is analysed in biomechanical terms.     

Tanaidacea (Crustacea) of the north-east Atlantic: the subfamily Pseudotanainae (Pseudotanaidae) and the family Nototanaidae

Sixteen species of the tanaidacean subfamily Pseudotanainae and three of the family Nototanaidae have been recorded from shallow and deep waters in the north-east Atlantic. Six new species of Pseudotanais, and the new genera Mystriocentrus, Parapseudotanais and Bathytanaissus are described. The species Pseudotanais affinis is re-described, and a cladistic analysis of the ‘affinis’ species-group is presented. Pseudotanais is a eurybathic genus and individuals of this taxon are common in the region. The Nototanaidae is poorly represented in the deep-sea, and the present record is the first for the Northern Hemisphere.     

Tanaidacea (Crustacea) of the north-east Atlantic: the subfamily Pseudotanainae (Pseudotanaidae) and the family Nototanaidae

Sixteen species of the tanaidacean subfamily Pseudotanainae and three of the family Nototanaidae have been recorded from shallow and deep waters in the north-east Atlantic. Six new species of Pseudotanais , and the new genera Mystriocentrus, Parapseudotanais and Bathytanaissus are described. The species Pseudotanais affinis is re-described, and a cladistic analysis of the 'affinis' species-group is presented. Pseudotanais is a eurybathic genus and individuals of this taxon are common in the region. The Nototanaidae is poorly represented in the deep-sea, and the present record is the first for the Northern Hemisphere.     

A comparative ontogenetic study of the tetraodontiform caudal complex

Konstantinidis P. and Johnson, G. D. 2012. A comparative ontogenetic study of the tetraodontiform caudal complex. —Acta Zoologica (Stockholm) 93 : 98–114. Interpretation of the caudal complex of adult Tetraodontiformes has proven problematic because of the consolidation of the component elements. Here, we show that an ontogenetic approach offers considerable elucidation of the homology of the caudal complex, resulting in a new understanding of the grundplan of these fishes. The reductions of structures of the caudal complex are interpreted in a phylogenetic context. The caudal skeleton of larval triacanthodids resembles that of many adult percomorphs; however, during subsequent development epural 3 disappears, while epural 2 is reduced so that it can hardly be distinguished from the uroneural remnants. Juvenile triacanthids have an epural 2 that is lost in ontogeny, and the cartilaginous parhypural becomes integrated into the large hypural plate. In ostraciids and diodontids, the parhypural is absent throughout development. The hypural plates of adult balistids, monacanthids and tetraodontids have a conspicuous diastema between the dorsal and ventral portions. However, in early stages of the former two, the dorsal and ventral portions are continuous in cartilage proximally and remain fused in the adults. In tetraodontids, the two hypurals are separate from their initial appearance in cartilage and never fuse, raising the question of homology of the individual hypurals among the different families.     

Retracted: Evolution and development of the homocercal caudal fin in teleosts

The vertebrate caudal skeleton is one of the most innovative structures in vertebrate evolution and has been regarded as an excellent model for functional morphology, a discipline that relates a structure to its function. Teleosts have an internally‐asymmetrical caudal fin, called the homocercal caudal fin, formed by the upward bending of the caudal‐most portion of the body axis, the ural region. This homocercal type of the caudal fin ensures powerful and complex locomotion and is thought to be one of the most important evolutionary innovations for teleosts during adaptive radiation in an aquatic environment. In this review, we summarize the past and present research of fish caudal skeletons, especially focusing on the homocercal caudal fin seen in teleosts. A series of studies with a medaka spontaneous mutant have provided important insight into the evolution and development of the homocercal caudal skeleton. By comparing developmental processes in various vertebrates, we propose a scenario for acquisition and morphogenesis of the homocercal caudal skeleton during vertebrate evolution.     

Development of the axial skeleton in wolffish, Anarhichas lupus (Pisces, Anarhichadidae), at different temperatures

The ontogeny of the axial skeleton, in particular the caudal skeleton, is described from embryos to adult specimens in common wolffish, Anarhichas lupus. The eggs were incubated at constant temperatures of 7.0, 11.0 and 13.0 °C. High egg mortality and structural changes in skeletal development (fusion of parts, absence of distal radials and most of dorsal and anal fin rays, abnormal neural arches and dorsal fin rays) were observed at 13 °C. The frequencies of some anomalies were lower at 11 °C than at 13 °C. The main reason of structural changes of the skeleton at high temperature is the breaking of normal correlations between developmental rates of some cartilaginous structures and other tissues and organs of the embryo. These data suggest an epigenetic mechanism of skeletal evolution.     

Mites of the family Hyadesiidae (Acari: Astigmata) from New Zealand

Keys are provided to families of Hyadesioidea, to genera of Hyadesiidae, and to all species of this family known from the New Zealand subregion. A new species of Amhyadesia , two new species of Hyadesia sensu stricto , and four new species of a newly defined subgenus of Hyadesia (Parahyadesia) are described.     

Comparative osteology of the Danio (Cyprinidae: Ostariophysi) axial skeleton with comments on Danio relationships based on molecules and morphology

Danio is a diverse group of small, colourful and easily bred freshwater fishes native to Southern Asia. Biological interest in danios has increased in recent years because the zebrafish, Danio rerio , has become an important model organism, particularly for studies of vertebrate developmental biology and genetics. Though several phylogenetic studies of Danio have been done on a subset of Danio species, the resulting phylogenies conflict in detail. To examine the utility of osteology for systematics of this group at the species level, we studied the axial skeleton for 11 species of Danio. We analyse our morphological data alone and combined with DNA sequence data for five gene sequences generated in earlier phylogenetic studies. The axial skeleton of Danio exhibits 14 characters that prove useful in phylogenetic analysis. Both molecular and morphological data support the monophyly of the danios included in our analysis and both data sets support the monophyly of two subclades: a deep-bodied group and a slender-bodied group. Separate analysis of molecular and morphological data sets show that the molecular data resolves relationships within the slender subclade whereas the topology of the deep-bodied subclade is determined by morphological data.  © 2002 The Linnean Society of London. Zoological Journal of the Linnean Society , 2002, 135 , 529–546.     

Appendicular skeleton in Bachia bicolor (Squamata: Gymnophthalmidae): osteology,limb reduction and postnatal skeletal ontogeny

The osteology of the appendicular skeleton and its postnatal development are described in Bachia bicolor, a serpentiform lizard with reduced limbs. The pectoral girdle is well developed and the forelimb consists of a humerus, ulna, radius, five carpal elements (ulnare, radiale, distal carpals 4–3, centrale), four metacarpals (II, III, IV, V) and phalanges (phalangeal formula X‐2‐2‐2‐2). In the hindlimb, the femur is small and slender, and articulates distally with a series of ossified amorphous and extremely reduced elements that correspond to a fibula, tibia and proximal and distal tarsals 4 and 3. The pelvic girdle consists of ischium, pubis and ilium, but its two halves are widely separated; the ilium is the least reduced element. We describe the ossification and development during postnatal skeletal ontogeny, especially of epiphyseal secondary centres, ossifications of carpal elements, apophyseal ossifications and sesamoids. Compared to other squamates, B. bicolor shows an overall reduction in limb size, an absence of skeletal elements, a fusion of carpal elements, an early differentiation of apophyseal centres, and a low number of sesamoids and apophyseal centres. These observations suggest that the reductions are produced by heterochronic changes during postnatal development and probably during embryonic development; therefore the appendicular skeleton exhibits a pattern of paedomorphic features.     

Gonads ofCarassius auratus (teleosts) in organ culture: A new technique and the effects of testosterone

Summary The use of a semi-natural medium (Eagle’s MEM supplemented with chicken embryo extract) appears to be satisfactory for ovarian and testicular fragment cultures ofCarassius auratus. The male germ cells show a normal degeneration which might be attributed to a lack of pituitary hormones: gonadotropic and, possibly, somatotropic hormone. The ovarian fragments maintain a normal organization during 21 days of culture. Only the occytes in late vitellogenesis massively atresiate at the beginning of culture. The addition of fetal bovine serum to this medium produces surprising effects on the testicular explants, particularly on the spermatogonial mitoses. This might be attributed to the presence of STH and androgen in the serum. The modifications of ovarian explants, on the other hand, are identical to those observed with Eagle’s MEM supplemented with chicken embryo extract. M 199 has been tested as a synthetic medium; the preliminary results are encouraging. Testosterone, when added to the semi-natural medium, permits complete spermatogenesis in the testicular fragments during the 21 days of culture, but does not produce any effect on the ovarian explants.     

The postcranial skeleton of Kingoria nowacki (von Huene) (Therapsida: Dicynodontia)

A new specimen of Kingoria nowacki (von Huene) with a complete pelvic girdle and hindlimb is reconstructed and the method of locomotion analysed. It is concluded that the hindlimb was modified from the normal dicynodont pattern in a direction comparable to that of advanced mammal-like reptiles which are presumed to have given rise to mammals. The pectoral girdle also had a modified form, but the humerus was probably conservative in its morphology. The hindlimb stride relied on protraction and retraction to effect movement while the forelimb relied on long axis rotation of the humerus. Possible reasons for the difference in morphology and function of the fore-and hindlimbs are discussed, and a functional sequence for the generation of the Kingoria pelvic girdle from that of other Permian dicynodonts is suggested.     

The phylogeny and systematics of European predacious Syrphidae (Diptera) based on larval and puparial stages

The external larval morphology of predacious Syrphidae is examined and compared with that of other groups of syrphids. Predacious larvae form a distinctive, monophyletic group. Relationships among 29 of the 34 European genera and subgenera are analysed using cladistic methods based on larval and puparial characters. Interpretation of the cladogram suggests that, within Syrphinae, a system of five tribes can be recognized and that a major trend has been a shift from ground layer to arboreal larval habitats, with an increasing degree of obligate dependence on soft-bodied Homoptera as prey. Generic diagnoses with biological and taxonomic notes are given and a key to genera based on larvae and puparia is provided.     

Echinoid Spines from the Anisian (Middle Triassic) of Qingyan, South- western China

Echinoid remains from the Triassic of China are described for the first time. The Middle Triassic of Qingyan in Guizhou Province, south-western China, has yielded nine taxa of primary spines; seven of these come from the lower Upper Anisian. Because all of the spines are disarticulated, the material is treated only parataxonomically. 'Cidaris' lineola (Bather) and 'Cidaris' wissmanni (Desor) are species originally described from the alpine Triassic of Europe. 'Cidaris' bangtoupoensis sp. nov., 'Cidaris' wachangpoensis sp. nov., 'Cidaris' venustespinosa sp. nov., 'Cidaris' fangchui sp. nov., 'Cidaris' gu sp. nov., 'Cidaris' mafengpoensis sp. nov. and 'Cidaris' sp. A are so far known only from Qingyan. Palaeoautecological interpretations based on the shapes of the spines fit well with the fact that the echinoids from Qingyan are part of highly diverse fossil associations which represent the remains of communities that lived in a protected, shallow-marine, stable soft-bottom habitat. The rather high diversity of the echinoid spines in terms of the number of both taxa and general types of shape shows that the echinoids, after nearly becoming extinct at the end of the Palaeozoic, began a new phase of adaptive radiation in the Anisian at the latest.     

Leis' conundrum: homology of the clavus of the ocean sunfishes. 2. Ontogeny of the median fins and axial skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae)

One of the most conspicuous characters of the ocean sunfishes, family Molidae, is the punctuation of the body by a deep, abbreviated, caudal fin-like structure extending vertically between the posterior ends of the dorsal and anal fins, termed the clavus by Fraser Brunner. Homology of the clavus has been a matter of debate since the first studies on molid anatomy in the early 1800s. Two hypotheses have been proposed: 1) It is a highly modified caudal fin; 2) It is formed by highly modified elements of the dorsal and anal fins. To resolve this homology issue, we studied the ontogeny of the molid vertebral column and median fins and compared it to that of a less morphologically derived gymnodont (see Part 1 of this study), a member of the family Tetraodontidae. We show that in molids the chorda never flexes during development, that the claval rays form from the posterior ends of the dorsal and anal fins toward the middle, thus closing the gap inward, and that elements of the molid clavus have an identical development and composition as the proximal-middle and distal radials of the regular dorsal and anal fins. We thus conclude that the molid clavus is unequivocally formed by modified elements of the dorsal and anal fin and that the caudal fin is lost in molids.     

The morphology and evolution of the ventral gill arch skeleton in batoid fishes (Chondrichthyes: Batoidea)

The ventral gill arch skeleton was examined in some representatives of batoid fishes. The homology of the components was elucidated by comparing similarities and differences among the components of the ventral gill arches in chondrichthyans, and attempts were made to justify the homology by giving causal mechanisms of chondrogenesis associated with the ventral gill arch skeleton. The ceratohyal is present in some batoid fishes, and its functional replacement, the pseudohyal, seems incomplete in most groups of batoid fishes, except in stingrays. The medial fusion of the pseudohyal with successive ceratobranchials occurs to varying degrees among stingray groups. The ankylosis between the last two ceratobranchials occurs uniquely in stingrays, and it serves as part of the insertion of the last pair of coracobranchialis muscles. The basihyal is possibly independently lost in electric rays, the stingray genus Urotrygon (except U. daviesi) and pelagic myiiobatoid stingrays. The first hypobranchial is oriented anteriorly or anteromedially, and it varies in shape and size among batoid fishes. It is represented by rami projecting posterolaterally from the basihyal in sawfishes, guitarfishes and skates. It consists of a small piece of cartilage which extends anteromedially from the medial end of the first ccratobranchial in electric rays. It is a large cartilaginous plate in most of stingrays. It is absent in pelagic myliobatoid stingrays. The remaining hypobranchial cartilages also vary in shape and size among batoid fishes. Torpedo and possibly the Jurassic Belemnobalis and Spathobatis possess the generalized or typical chondrichthyan ventral gill arch structure in which the hypobranchials form a Σ-shaped pattern. In the electric ray Hypnos and narkinidid and narcinidid electric rays, the hypobranchial components are oriented longitudinally along the mid-portion of the ventral gill arches. They form a single cartilaginous plate in the narkinidid electric rays, Narcine and Diplobatis. In guitarfishes and skates, the second hypobranchial is unspecialized, and in skates, it does not have a direct contact with the second ceratobranchial. In both groups, the third and fourth hypobranchials are composed of a small cartilage which forms a passage for the afferent branches of the ventral aorta and serve as part of the insertion of the coracobranchialis muscle. In sawfishes and stingrays, the hypobranchials appear to be included in the medial plate. In sawfishes, the second and third components separately chondrify in adults, but the fourth component appears to be fused with the middle medial plate. In stingrays, a large medial plate appears to include the second through to the last hypobranchial and most of the basibranchial copulae. The medial plate probably develops independently in sawfishes and stingrays. Because the last basibranchial copula appears to be a composite of one to two hypobranchials and at least two basibranchial copulae, the medial plate may be formed by several developmental processes of chondrogenesis. More detailed comparative anatomical and developmental studies are needed to unveil morphogenesis and patternings of the ventral gill arch skeleton in batoid fishes.