<Emphasis Type="Italic">Icriodus marieae</Emphasis>, a new icriodontid conodont species from the Middle Devonian

A new conodont species, Icriodus marieae, is described from pelagic limestone beds of the Carnic Alps (Austria). Specimens are obtained from the upper part of the Valentin Formation (Central Carnic Alps) and range from the latest Eifelian to middle Givetian. Significantly differing from other icriodontid conodonts is that the icriodontan element of the new species develops only three denticles on either lateral denticle row, which are constricted to the central part of the element. The anterior part of the element is free of lateral row denticles and consists of two to four denticles, which have a fan-shaped outline in lateral view. The anterior part as well as the posterior part (consisting of cusp and two to three pre-cusp denticles) is higher than the denticles of the central part of the element. Shape analysis confirms that the parameters chosen for landmarks (element size relation and denticle setting) show little variation between different specimens.     

DESCRIPTION OF EUBRANCHUS LINENSIS NEW SPECIES (NUDIBRANCHIA), WITH REMARKS ON DIAULY IN NUDIBRANCHS

A new species of nudibranch, Eurbranchus liensis, is described,from specimens collected from the southern Iberian Peninsula.The coloration of this species is characterized by the presenceof blood-red patches over the whole body and opaque white pigmentationon the tips of the cerata, rhinophores and oral tentacles, aswell as along the side of the foot. The jaws are denticulateand the triseriate radula has lateral teeth with a small secondarycusp. The rachidian tooth usually has four denticles on eachside. The reproductive system has a prostate and there is astylet at the end of the penis. The diaulic condition in theEubranchidae and in other families of nudibranchs is discussed. (Received 15 August 1989; accepted 24 February 1989)     

Autonomous requirements for the segment polarity gene armadillo during Drosophila embryogenesis

Embryos hemizygous for armadillo produce a "segment polarity" phenotype in which the naked posterior two-thirds of each segment is replaced by denticles with reversed polarity. Small patches of homozygous arm cells induced by mitotic recombination also form such denticles, indicating that the changes in cellular fate observed in homozygous arm embryos are autonomous at the level of single cells. Clonally derived arm patches do not, however, show the characteristic arm polarity reversals, arguing that this feature of the phenotype depends on cell interactions in fully mutant embryos. Few, if any, clones were found in the posterior-most regions of the naked cuticle, and none were found in the posterior compartments of the thorax.     

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three‐dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro‐CT scanning, gel‐based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro‐CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver‐like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond‐like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading‐to‐trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.     

Developmental origins of complex radular characters in the Muricidae: the bifid rachidian edge

Muricid gastropod radulae are more complex than those of most other neogastropods, especially in the number and variety of cusps, denticles, and interlocking mechanisms. How this complexity evolved, however, is unknown. Morphological gaps between higher taxa within the Muricidae are substantial, and there are few unambiguous intermediates. Here, we use developmental data from the Patagonian trophonine muricid Trophon geversianus to investigate the evolution of an unusual condition in which there are two marginal cusps at each end of each central rachidian tooth, rather than one or none as in most muricids. Trophon geversianus begins ontogeny with one marginal cusp (the inner marginal cusp), but a second (the outer marginal cusp) appears later, arising from separation of the rachidian base edge from the radular membrane rather than through bifurcation or lateral migration of pre‐existing cusps. Truncation of development (i.e., paedomorphosis) at this second developmental phase in a trophonine ancestor provides an explanation for the lack of transitional forms between most adult trophonine muricids, which have the plesiomorphic condition of one marginal cusp, and sister group ocenebrine muricids, which have the derived condition of two marginal cusps.     

Tree species, root decomposition and subsurface denitrification potential in riparian wetlands

Patches of organic matter have been found to be important `hotspots' of denitrification in both surface and subsurface soils, but the factors controlling the formation and maintenance of these patches are not well established. We compared the concentration of patches of organic matter and root biomass in the subsurface (saturated zone) beneath poorly drained riparian wetland soils at four sites in Rhode Island, USA - two dominated by red maple (Acer rubrum) and two dominated by white pine (Pinus strobus). Denitrification enzyme activity (DEA) and carbon (C) content of patch material were compared between sites and between patches with different visual characteristics. Root decomposition was measured in an 8-week ex-situ incubation experiment that compared the effects of water content, root species, and soil matrix origin on CO₂ evolution. We observed significantly greater concentrations of patches at 55 cm at one red maple site than all other sites. DEA and percent C in patches was generally higher in patches than matrix soil and did not vary between sites or by patch type. White pine roots decomposed at a faster rate than red maple roots under unsaturated conditions. Our results suggest that faster root decomposition could result in lower concentrations of patches of organic material in subsurface soils at sites dominated by white pine. Tree species composition and root decomposition may play a significant role in the formation of patches and the creation and maintenance of groundwater denitrification hotspots in the subsurface of riparian wetlands. Abbreviations: DEA – denitrification enzyme activity; DOC – dissolved organic carbon; PD – poorly drained; RM-1 – red maple-1 site; RM-2 – red maple-2 site; WP-1 – white pine-1 site; WP-2 – white pine-2 site.     

Motheaten, an immunodeficient mutant of the mouse. I. Genetics and pathology.

A new recessive mutation, motheaten (me), is on chromosome 6, 21.9 +/- 4.3 recombination units distal to white (Miwh). Mice homozygous for the new mutation have neutrophilic lesions of the skin beginning as early as day 1, and pneumonitis with many macrophages in the alveoli as early as day 3. They suffer high mortality from birth onward and none has survived longer than 8 weeks. The lymph nodes may be enlarged, but the thymus, Reyer's patches, and lymphatic tissue of the spleen are much reduced in size. Lymph nodes, spleen, and Peyer's patches lack lymphatic nodules. The lymph nodes and spleen contain many plasma cells. There are increased numbers of neutrophils and monocytes in the peripheral blood, and increased numbers of neutrophils in bone marrow at the expense of red cell precursors. Hematopoietic tissue in the spleen is increased and appears more active than normal. Motheaten mice appear to have an immune deficiency beginning very shortly after birth.     

New ischnacanthid acanthodians from the Early Devonian of Australia, with comments on acanthodian interrelationships

Rockycampacanthus milesi n.gen., n.sp. is described from a single jaw from the Rocky Camp member of Lower Devonian Buchan Group, E Victoria. Rockycampacanthus differs from other ischnacanthiforms in having large multicuspidate teeth with dual rows of secondary cusps forming a posteromesial flange, a mesial tooth row beginning opposite the fourth cusp of the main tooth row, and in the gnathal bone being deepest in the anterior half. Taemasacanthus erroli n. gen., n. sp. is described from several jaw bones from the Lower Devonian Murrumbidgee Group, New South Wales. Taemasacanthus has a well developed posterolabial flange with secondary cusps developed, vertical rows of denticles on the cusps of the main tooth row and a well developed mesial tooth row separated from the main row by a prominent ridge. The labial face of the jaw has a circular ridge which may have supported labial cartilages. The complex mandibular joint in climatiforms, acanthodiiforms and some primitive sharks differs from the simple jaw articulation of ischnacanthids. It is suggested that ischnacanthids are the plesiomorphic sister group to climatiforms plus acanthodiiforms. The interrelationships of ischnacanthids, climatiforms and acanthodiforms are discussed.     

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm dentition. A consensus view emerged that a dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crown-group gnathostomes are suggested to derive from the pharyngeal denticle whorls, at least in sharks, with the patterning mechanisms co-opted to the oral cavity. A comparable co-option is suggested for the Placodermi.     

A new assemblage of freshwater sharks (Chondrichthyes: Elasmobranchii) from the Upper Triassic of India

This study reports the first occurrence of a varied xenacanth assemblage from the Upper Triassic Tiki Formation of India, based on multiple well-preserved isolated teeth. Based on distinct tooth morphology, two species of the genus Mooreodontus are described: M. indicus and a new species, M. jaini. The new species is diagnosed based on a tricuspid crown containing two stout, slightly diverging lateral cusps pointing in the same direction, a high median cusp, crown-base angle almost at 90°, large, rounded, apical button with several foramina and multiple, 8–9 coarse vertical cristae on all the cusps. Dental anomaly in the form of a partial quadri-cuspidate xenacanthid tooth is present in the collection. Another group of xenacanthid teeth have bicuspid crowns with two upright, asymmetric cusps, where the mesial cusp is thicker than the distal one, and consistently lack a median cusp. Such distinct bicuspid tooth morphology is usually present in Palaeozoic forms and is reported for the first time from the Late Triassic. It is considered to belong to a new taxon, Tikiodontus asymmetricus nov. gen., nov. sp., of indeterminate family. Distinctive tooth histology also differentiates the two Indian genera Mooreodontus and Tikiodontus nov. gen. from other xenacanthid taxa. In addition, the Tiki assemblage has yielded multiple chondrichthyan dermal denticles, which may be subdivided into two morphotypes based on their robustness and presence/absence of linear ridges on the fused cusps. India holds a unique position in terms of its Late Triassic freshwater shark fauna, as it exhibits distinct Laurasian affinities. These freshwater sharks had restricted occurrences in other parts of the Gondwanan landmass.     

By the teeth of their skin, cavefish find their way

Teeth and skin teeth (denticles), collectively named odontodes, are usually associated with the physical roles of cutting, protection or drag reduction in fishes [1,2]. These structures are composed of a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel [3]. Odontodes arise from neural crest cells and epithelium and are often innervated [1-3]. However, little is known about their possible sensory function. Here, we demonstrate for the first time a mechanosensory role for denticles in a cavefish endemic to a fast water flow cave. All fishes gather hydrodynamic information via specialized sense organs called neuromasts [4-6]. Some fishes are especially attentive to such type of information [5] and until now hypertrophy of the neuromast system has been reported as the main constructive sensory adaptation in cavefishes [6,7]. We expect that the mechanosensory nature of denticles highlighted in this cave fish species might reflect a widespread sensory role for these structures in other animals.     

A possible dominant white gene in Jersey cattle

A white heifer ("Snow") was born in 1991 from coloured registered Jersey parents. She produced six calves sired by coloured Jersey bulls: three white bull calves, two white heifer calves, and one coloured bull calf. One of the white bull calves was mated with 40 Hereford × Friesian yearling heifers (white face, predominantly black body with some white patches). The 38 resulting calves included 16 white and 22 coloured calves. Twelve of the 16 white calves were heifers and four were bulls. Red or black spotting was recorded on some white calves. The results are consistent with an autosomal dominant mutant causing the white phenotype. The mutation appears to have arisen spontaneously in Snow, then passing to her white progeny and white grand-progeny. The white individuals varied from entirely white in a few cases, to most having some residual small areas of red or black pigmentation in patterns not typical of other reported white spotting patterns of cattle.     

Structure and topographic distribution of oral denticles in elasmobranch fishes

The placoid scales, or denticles, of the external epidermis of elasmobranchs are well known as a hard protective coat over the skin to reduce abrasion or as elements to reduce hydrodynamic drag. However, the structure and function of denticles within the oral cavity is uncertain. Using stereological and scanning electron microscopy, this study examines the structure and distribution of oral denticles in a range of elasmobranchs. Of the batoids analyzed, only members of the Rhinobatidae possessed oral denticles, with no denticles found in the members sampled in the Gymnuridae or Dasyatidae. In contrast, oral denticles were located in all the selachians examined, except for members of the Orectolobidae. Within the selachians, the denticles of the Carcharhinidae have a grooved surface and a central spine, which is angled toward the posterior of the mouth. These denticular adaptations are beneficial to reduce hydrodynamic drag, an advantage for these free-swimming species with ram ventilation. Alternatively, members of the Hemiscyllidae have broad bulbous denticles that often overlap, providing a hard surface to protect the epithelium from abrasion during the consumption of hard-bodied prey. The distribution and high number of oral denticles appears to spatially compromise the capacity for oral (taste) papillae to populate the oropharyngeal cavity but provides increased friction and grip on prey items as they are manipulated within the mouth.     

FOUR NEW SPECIES OF TAMBJA BURN, 1962 (NUDIBRANCHIA: POLYCERIDAE) FROM THE INDO-PACIFIC

The genus Tambja previously included 24 described species. Fournew species, T. tentaculata n. sp., T. gabrielae n. sp., T.zulu n. sp. and Tambja victoriae n. sp., from the Indo-Pacificare described. Tambja tentaculata n. sp., from Guam, is theonly known species in the genus with well developed, dorsolaterallygrooved, oral tentacles. Its inner lateral teeth have a bifidinner cusp with two long, sharp denticles. The oral tentaclesof T. tentaculata are more typical of Roboastra species, whilethe shape of the inner lateral teeth is more typical of Tambja.Nevertheless, the arrangement of the two cusps of the innerlateral teeth and the presence of a rachidian tooth withoutdenticles and with a central notch at the anterior edge, typicalof the species of the genus Tambja, suggest the placement withinthis genus. Tambja gabrielae n. sp., from Indonesia and PapuaNew Guinea, has dark green to dark brown ground colour withbright yellow patches scattered on the body. Tambja zulu n.sp. from Durban, South Africa, is characterized by a black groundcolour with slender yellow longitudinal lines. Tambja victoriaen. sp. is a new species from Papua New Guinea and Australiathat has frequently been misidentified as Roboastra arika, characterizedby its blue body colour and yellow lines. The four species aredistinguishable based on differences in body coloration, ofcharacters of the radula and of the reproductive system. Anoverview on distinguishing features of all known Indo-PacificTambja species is presented. (Received 21 June 2004; accepted 20 January 2005)     

Testing microstructural adaptation in the earliest dental tools

Conodont elements are the earliest vertebrate dental structures. The dental tools on elements responsible for food fracture—cusps and denticles—are usually composed of lamellar crown tissue (a putative enamel homologue) and the enigmatic tissue known as ‘white matter’. White matter is unique to conodonts and has been hypothesized to be a functional adaptation for the use of elements as teeth. We test this quantitatively using finite-element analysis. Our results indicate that white matter allowed cusps and denticles to withstand greater tensile stresses than do cusps comprised solely of lamellar crown tissue. Microstructural variation is demonstrably associated with dietary and loading differences in teeth, so secondary loss of white matter through conodont phylogeny may reflect changes in diet and element occlusal kinematics. The presence, development and distribution of white matter could thus provide constraints on function in the first vertebrate dental structures.     

Genetic analysis of the position of meiosis in <Emphasis Type="Italic">Porphyra haitanensis</Emphasis> Chang et Zheng (Bangiales,Rhodophyta)

Crossing experiments were carried out between artificial pigmentation mutants and the wild type in Porphyra haitanensis Chang et Zheng to ascertain where meiosis occurs in its life history by confirming whether the color segregation and the color-sectored blades appear in F₁ gametophytic blades developed from conchospores which are released from heterozygous conchocelis. Two red-type pigmentation mutants (R-10 and SPY-1) were used as the female parent. Their blades are red or red orange in color, thinner than the wild type and weak in elasticity, and have no denticles on their margins. The wild type (W) was used as the male parent; its blades are light brown in color, thick and good in elasticity, and have many marginal denticles. The F₁ gametophytic blades developed from conchospores which were released from heterozygous conchocelis produced in the crosses of R-10(♀)×W(♂) and SPY-1(♀)×W(♂) showed two parental colors (R and W) and two new colors (R', lighter in color than R; W', wild-type-like color and redder than W). Linear segregation of colors occurred in the F₁ blades, forming color-sectored blades with 2–4 sectors. In the color-sectored blades, R and R' sectors were thinner than W and W' sectors, and had weak elasticity and no denticles on their margins, whereas W and W' sectors were thick and had good elasticity and many marginal denticles. Of the F₁ gametophytic blades, 95.2–96.7% were color-sectored and only 3.3–4.8% were unsectored. These results indicate that meiosis of P. haitanensis occurs during the first two cell divisions of a germinating conchospore, and thus it is considered that the initial four cells of a developing conchosporeling constitute a linear genetic tetrad leading to the formation of a color-sectored blade. The new colors of R' and W' were recombinant colors due to the chromosome recombination during the first cell division in meiosis. It is considered that color phenotypes of the two mutants used in this paper were result of two (or more) recessive mutations in different genes, and that they also have mutations concerned with blade thickness and formation of marginal denticles, which are linked with the color mutations.     

Teeth outside the mouth in teleost fishes: how to benefit from a developmental accident

SUMMARY Evolution proceeds by the selection of characters that enhance survival rates so that the long-term outcome for a species is better adaptation to its environment. These new characters are "accidentally" acquired, mostly through mutations leading to modifications of developmental events. However, changes that lead to the ectopic expression of an organ are rare and, whereas their subsequent selection for a new role is even more rare, such a scenario has apparently occurred for denticles in some teleost fish. Small, conical denticles are present, mainly on the dermal bones of the head, in a few, unrelated lineages of living teleosts. Here, I show that the morphology and structure of the denticles in Atherion elymus , an atheriniform, is similar to those of teeth inside the oral cavity. These denticles are not derived evolutionarily from odontodes of early vertebrates, nor do they represent a re-expression as such (i.e., a long-lasting ability to make odontodes outside the oral cavity). Teeth and odontodes are homologous organs but the origin of the denticles is to be found in teeth, not in odontodes. The denticles are simply teeth that form outside the mouth, probably derived from a sub-population of odontogenically pre-specified neural crest cells. These "accidental" extra-oral teeth have arisen independently in these lineages and were selectively advantageous in a hydrodynamic context.     

A fourth teleost lineage possessing extra-oral teeth: the genus atherion (teleostei; atheriniformes)

In the course of an evolutionary and developmental study on the dermal skeleton, our attention was drawn to the existence of denticles located outside the oral cavity in the atheriniform species Atherion elymus. These denticles, attached to the surface of most dermal bones of the head, are especially numerous on the snout, chin and the undersides of the lower region of the head, where they are aligned forming a crenulated keel. Using light, scanning and transmission electron microscopy, we clearly demonstrate the dental (vs bony) nature of these denticles. They are small, conical elements mostly oriented backwards and are not ankylosed to the bone support. Ligaments originating from the internal and external surface of the base of the dentine cone link the denticles to the attachment bone, which itself merges with the bone support below. The denticles have the same form and structure as teeth, from which they differ only in having a larger base and a pulp cavity that is nearly completely filled with secondary dentine by centripetal deposition. This suggests that the denticles have a longer functional history than teeth. Atherion is now the fourth teleost lineage found to develop such denticles on the head.     

Scanning electron microscopy of the lip denticiles of Ascaris suum adults of known ages.

Purebred Hampshire pigs, farrowed and maintained under conditions precluding extraneous helminth infection, were exposed to a single dose of 10,000 Ascaris suum infective eggs. The pigs were killed at intervals of 28, 41, 55, 86, 115, 145, 175, and 206 days after infection. At necropsy, no gross lesions were found in the lungs or livers of infected pigs. The worms were recovered from the small intestine, identified, counted, and fixed. The heads were excised, critical point dried, mounted en face, and examined by scanning electron microscopy. Worms 28 to 115 days old had unworn denticles that were triangular when viewed laterally but blunt when viewed tangentially. Wearing of the denticles was observed first with 145-day-old worms; wearing increased with age both in numbers of denticles affected and in degree of wear so that by 206 days after inoculation, almost all denticles in the center of the lip were worn. Worn denticles appear truncated when viewed from any angle. The denticles outside the central area were not affected by wear. The size of the denticles varies not only between specimens of the same age, but also on each specimen. However, average denticle size is directly related to the size and, accordingly, to the age of the worm. External to each denticle is a corresponding depression that we have called the denticular groove. One 28-day-old specimen had some extra denticles aligned irregularly along the lip; this irregularity gave the appearance of a double row. The denticles of the two subventral lips are similar to those of the dorsal and are equally affected by wear. There was no detectable difference in denticles of male and female worms. Since wear can now be specifically correlated with age, we conclude that the denticles are functional and become worn through use. Consequently, adult A. suum may be an even more injurious pathogen than heretofore supposed.