Pore-canal network (“wrinkles”) in ammonoid shell wall (Cephalopoda)

The structure of pristine preserved shells of Mesozoic ammonoids was examined in order to identify whether there are homologous or homoplasic traits in the internal structure of the shell wall that can be used for phylogeny and taxonomy, particularly in regard to episodic growth interruptions and the dorsal shell wall. Different sculptural elements that are usually associated with an interruption in shell growth, like varices, constrictions, flares, parabolae and radial lirae, were analysed to determine whether these have a general ground plan in internal structure or not. Varices and constrictions shows no interruptions in shell growth but have characteristic internal thickenings formed by the nacreous layer. Owing to the general structural conformity of varices and constrictions in the shells of Jurassic and Cretaceous taxa, they are probably homologous traits. Flares, parabolae and radial lirae are characterized by an interruption in growth, they mark the succession of two different shell generations. Parabolae and flares mark an interruption of shell growth caused by the formation of a frill-like, outwardly bent temporary aperture (but differ in their general shape). The outer prismatic layer, the nacreous layer and an apertural prismatic coating (i.e. indicates a mantle cover) build their aperture. Radial lirae are formed by imbrication of two successive sigmoid shell lamellae, formed either by the organic periostracum or the outer prismatic layer. Each lira has a characteristic adorally-projecting, scythe-like appendage arising from its crest. Owing to the general structural and morphological conformity of flares and parabolae it is likely that both represent different expressions of a homologous structure. Morphological transitions imply that parabolae and radial lirae are probably homologous as well. Mesozoic Ammonoidea had different types of the dorsal shell wall. The vast majority of planispirally taxa forms a prismatic reduced dorsal shell wall, consisting of an outer organic component (e.g. wrinkle layer) and the subsequent formed dorsal inner prismatic layer. The latter is only secreted in the rear of the living chamber. Reduced dorsal shell wall construction of Ammonoidea is generally homologous and exists in the early ontogenetic stages of all taxa. Rather few ammonoid taxa reinforce the dorsal shell wall. Some planispirally taxa form a nacreous reduced dorsal shell wall in the rear part of the living chamber, which is reinforced by secondary pair of nacreous and inner prismatic layers. Heteromorph taxa and some planispirally taxa secreted a complete dorsal shell wall at the aperture, i.e. the ventral, lateral and dorsal shell wall form a continum aperturally and adapically. The dorsal shell layers are identical with the ventral shell wall. The broad phylogenetic distribution of dorsally secreted nacre indicates a plesiomorphic relic trait of the orthocone ammonoid ancestors.

The structure of the shell wall, particularly at the apertural margin, is described in the Callovian ammonoid Quenstedtoceras from Lukow, Poland. Ventral and lateral sides of the shell wall show periodic interruptions in shell secretion. As shown in the present study, these interruptions divide the shell wall into calcareous sublayers that are separated by thin intermediate layers of organic substance. In places, the organic layers increase considerably in thickness. The presence of organic layers between the calcareous sublayers increases the amount of organic substance in the shell wall. The shell aperture has a ventral rostrum. At the shell aperture, the shell wall decreases in thickness and forms a sharp-edged, thin, apertural margin that probably retains its shape in the adult stage. In comparison with Nautilus, the shell wall of Quenstedtoceras is much thinner at the aperture, has a longer growth zone and probably does not form a gerontic thickening. The shape of the apertural margin of Quenstedtoceras is also compared with that of the Callovian ammonoid Kosmoceras and of scaphitid ammonoids. Its significance in ammonoid anatomical design and function is discussed.

3.26 - Vestibular System

Le système vestibulaire : anatomie fonctionnelle et comparée, évolution et développement

Second-order vestibular nucleus neurons which were antidromically activated from the region of the oculomotor nucleus (second-order vestibuloocular relay neurons) were studied in alert cats during whole-body rotations in many horizontal and vertical planes. Sinusoidal rotation elicited sinusoidal modulation of firing rates except during rotation in a clearly defined null plane. Response gain (spike/s/deg/s) varied as a cosine function of the orientation of the cat with respect to a horizontal rotation axis, and phases were near that of head velocity, suggesting linear summation of canal inputs. A maximum activation direction (MAD) was calculated for each cell to represent the axis of rotation in three-dimensional space for which the cell responded maximally. Second-order vestibuloocular neurons divided into 3 non-overlapping populations of MADs, indicating primary canal input from either anterior, posterior or horizontal semicircular canal (AC, PC, HC cells). 80/84 neurons received primary canal input from ipsilateral vertical canals. Of these, at least 6 received input from more than one vertical canal, suggested by MAD azimuths which were sufficiently misaligned with their primary canal. In addition, 21/80 received convergent input from a horizontal canal, with about equal number of type I and type II yaw responses. 4/84 neurons were HC cells; all of them received convergent input from at least one vertical canal. Activity of many vertical second-order vestibuloocular neurons was also related to vertical and/or horizontal eye position. All AC and PC cells that had vertical eye position sensitivity had upward and downward on-directions, respectively. A number of PC cells had MADs centered around the MAD of the superior oblique muscle, and 2/3 AC cells recorded in the superior vestibular nucleus had MADs near that of the inferior oblique. Thus, signals with spatial properties appropriate to activate oblique eye muscles are present at the second-order vestibular neuron level. In contrast, none of the second-order vestibuloocular neurons had MADs near those of the superior or inferior rectus muscles. Signals appropriate to activate these eye muscles might be produced by combining signals from ipsilateral and contralateral AC neurons (for superior rectus) or PC neurons (for inferior rectus). Alternatively, less direct pathways such as those involving third or higher order vestibular or interstitial nucleus of Cajal neurons might play a crucial role in the spatial transformations between semicircular canals and vertical rectus eye muscles.

Pitching the head while rotating (PWR) combines periodic activation of the semicircular canals and the otoliths to generate pitch and roll eye deviations and continuous horizontal nystagmus. Monkeys were tested after individual pairs of semicircular canals were plugged and single units were recorded in the vestibular nerve while the animals were sinusoidally pitched 20-40 deg about a spatial horizontal axis with 5- and 16-s periods and simultaneously rotated about a spatial vertical axis at 30-120 deg/s. As previously shown, the steady-state horizontal response disappeared after plugging the vertical semicircular canals, but was maintained when the lateral canals were plugged. When the left anterior and right posterior canal (LARP) pair was left intact, the steady-state response depended on the axis about which the pitching took place. When the axis was normal to the LARP plane, there was no steady-state response. When the pitching axis was perpendicular to the LARP normal, the response was maximal. Firing rates of otolith units were approximately in phase with pitch position, and the addition of rotation about a vertical axis did not change the response. Lateral canal units did not have a steady-state modulation during pitch or constant velocity rotation. During PWR, they oscillated at twice the pitch frequency. This corresponded to the frequency at which the canal was maximally activated as it aligned with the plane of rotation. The amplitude of modulation increased proportionally to rotational velocity, but the phase remained the same. These characteristics were unchanged during roll while rotating (RWR), which induces little continuous nystagmus. Anterior and posterior canal units were maximally excited near pitch-velocity maxima and minima, respectively, during pure pitching. During PWR, however, the phases of both components simultaneously shifted toward each other and toward being in phase with otolith units. The peak excitation tended toward a forward-pitch position when the rotation was to the ipsilateral side, and toward a backward pitch position when the rotation was to the contralateral side. With 120-deg/s rotation during a 16-s pitch period, the phase difference between anterior and posterior canal units was as small as 17 deg. These data support the postulate that the correlation between vertical canal and otolith units is the critical factor in generating continuous unidirectional horizontal nystagmus during PWR.

An endocochliate embryo model for the Mesozoic Ammonitida is proposed based on scanning electron microscopy of the ammonitella (= embryonic shell) stage of well‐preserved Japanese Cretaceous specimens belonging to nine species of five superfamilies. As in other specimens described previously, the ammonitella wall succeeding from the initial chamber ("protoconch") in the species examined consists of the inner prismatic, middle subprismatic and outer prismatic layers, with minute tubercles resting on the outer. Developmental patterns of these structures and their comparison with primary shell formation in modern Nautilus and Spirula suggest that the outer thin prismatic layer with microtubercles was secreted by the exterior epithelium after the completion of the main ammonitella wall by the interior shell gland. Thus, the early ammonite embryo might have had an endocochliate structural plan as in coleoids, and at the time of hatching the overlying mantle epithelium had shifted anteriorly to become an ectocochliate condition.

BackgroundDespite its economic importance, we have a limited understanding of the molecular mechanisms underlying shell formation in pearl oysters, wherein the calcium carbonate crystals, nacre and prism, are formed in a highly controlled manner. We constructed comprehensive expressed gene profiles in the shell-forming tissues of the pearl oyster Pinctada fucata and identified novel shell formation-related genes candidates.Principal FindingsWe employed the GS FLX 454 system and constructed transcriptome data sets from pallial mantle and pearl sac, which form the nacreous layer, and from the mantle edge, which forms the prismatic layer in P. fucata. We sequenced 260477 reads and obtained 29682 unique sequences. We also screened novel nacreous and prismatic gene candidates by a combined analysis of sequence and expression data sets, and identified various genes encoding lectin, protease, protease inhibitors, lysine-rich matrix protein, and secreting calcium-binding proteins. We also examined the expression of known nacreous and prismatic genes in our EST library and identified novel isoforms with tissue-specific expressions.ConclusionsWe constructed EST data sets from the nacre- and prism-producing tissues in P. fucata and found 29682 unique sequences containing novel gene candidates for nacreous and prismatic layer formation. This is the first report of deep sequencing of ESTs in the shell-forming tissues of P. fucata and our data provide a powerful tool for a comprehensive understanding of the molecular mechanisms of molluscan biomineralization.

The fastigial nucleus (FN) receives vestibular information predominantly from Purkinje cells of the vermis. FN in the monkey can be divided in a rostral part, related to spinal mechanisms, and a caudal part with oculomotor functions. To understand the role of FN during movements in space, single-unit activity in alert monkeys was recorded during passive three-dimensional head movements from rostral FN. Seated monkeys were rotated sinusoidally around a horizontal earth-fixed axis (vertical stimulation) at different orientations 15 degrees apart (including roll, pitch, vertical canal plane and intermediate planes). In addition, sinusoidal rotations around an earth-vertical axis (yaw stimulus) included different roll and pitch positions (+/-10 degrees, +/-20 degrees). The latter positions were also used for static stimulation. One hundred fifty-eight neurons in two monkeys were modulated during the sinusoidal vertical search stimulation. The vast majority showed a uniform response pattern: a maximum at a specific head orientation (response vector orientation) and a null response 90 degrees apart. Detailed analysis was obtained from 111 neurons. On the basis of their phase relation during dynamic stimulation and their response to static tilt, these neurons were classified as vertical semicircular canal related (n = 79, 71.2%) or otolith related (n = 25; 22.5%). Only seven neurons did not follow the usual response pattern and were classified as complex neurons. For the vertical canal-related neurons (n = 79) all eight major response vector orientations (ipsilateral or contralateral anterior canal, posterior canal, roll, and nose-down and nose-up pitch) were found in Fn on one side. Neurons with ipsilateral orientations were more numerous and on average more sensitive than those with contralateral orientations. Twenty-eight percent of the vertical canal-related neurons also responded to horizontal canal stimulation. None of the vertical canal-related neurons responded to static tilt. Otolith-related neurons (n = 25) had a phase relation close to head position and were considerably less numerous than canal-related neurons. Except for pitch, all other response vector orientations were found. Seventy percent of these neurons responding during dynamic stimulation also responded during static tilt. The sensitivity during dynamic stimulation was always higher than during static stimulation. Sixty-one percent of the otolith-related neurons responded also to horizontal canal stimulation. These results show that in FN, robust vestibular signals are abundant. Canal-related responses are much more common than otolith-related responses. Although for many canal neurons the responses can be related to single canal planes, convergence between vertical canals but also with horizontal canals is common.

The video head impulse test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However, so far, vHIT has been limited to measurement of the function of the horizontal semicircular canals. The goal of this study was to determine if vHIT can detect vertical semicircular canal dysfunction. Horizontal and vertical eye movements were recorded in response to abrupt, passive, unpredictable head turns (head impulses) in the planes of the vertical semicircular canals by high-speed video (250-Hz sampling rate) together with measures of the head movement. Head impulses were delivered diagonally in the plane of the vertical semicircular canals, whereas gaze was directed along the same plane. Patients with known vestibular loss as shown by previous scleral search coil recording were tested to identify if the vHIT testing could detect the loss. The results of patients with unilateral, bilateral, and individual semicircular canal dysfunction were compared with the results of a healthy control subject. The patient with bilateral vestibular loss had no compensatory slow eye movements in any direction. The patient with unilateral vestibular loss showed reduced response for head impulses activating the canals in their affected right ear (right anterior, right posterior, and right horizontal head impulses). The patient with isolated canal loss showed reduced response for head impulses activating the affected right posterior canal. vHIT detects peripheral deficits of both vertical and horizontal semicircular canal function and is a new tool for measuring dysfunction of individual semicircular canals in vestibular patients.

polymorphs, calcite, aragonite, and vaterite, of which the former two are most commonly observed as biological polymorphs in marine mollusks. The pearl oyster P. fucata can generate these two polymorphs in vivo; calcite crystals in the outer prismatic layer and aragonite crystals in the inner nacreous layer of the shell, under the same physical conditions. These phenomena are a key to solving the enigma of bio-mineralization. The early research on shells of mollusks was mainly carried out by electron-microscopic observation [2–6]. Shells are mainly composed of two distinct layers. The outer prismatic layer shows the honeycomb-like network structure of a polygonal prism. The inner nacreous layer shows a cemented brick or veneer-like multilayer structure. Figure 1 shows a schematic representation of the inner nacreous layer. In this case, part of the brick corresponds to the aragonite crystal and part of the cement corresponds to the organic matrix. The organic matrix was first discovered in 1855 by Fremy [7], and is designated as “conchiolin”. Biochemical research on the organic matrix has recently developed, and now it has become clear that the organic matrix is mainly composed of proteins. Some parts of the organic matrix are soluble in water containing EDTA, and are called the water-soluble organic matrix (WSM). Most parts of the organic matrix are insoluble in water and are called the water-insoluble organic matrix (WISM). The group of Morse and colleagues [8–12] and that of Weiner and colleagues [13– 17] reported that shell proteins existing in the WSM mainly controlled the polymorphs of calcium carbonate crystals. In contrast, the early work of Watabe and Wilbur [18] and Wilbur and Watabe [19] and more recent reports by Wheeler [20] and by Samata et al. [21] showed that WISM proteins were mainly involved in polymorphic control. At present, it is difficult to determine which view is correct, because the groups with opposing views used different materials. The groups of Morse and colleagues [8–12] and Weiner and colleagues

Environmental control of strontium and magnesium in Mytilus

To describe the ontogeny of vertical semicircular canals using computed tomography. We have studied 39 human fetuses aged between 17 and 38 weeks of development through multi-helicoidal CT. The first signs of ossification in the semicircular canals, superior and posterior, are from 19 weeks of development, through two primary ossification centers in each canal, which will take part in the formation of the outer cover oriented towards the middle and posterior brain fossae, respectively. In this process it must be added the intervention of the common branch. Internal bone covers are formed by ossification of the fossa subarcuata in the superior semicircular canal, and from the compact center of the labyrinthine capsule into the posterior canal. The tomographic study has allowed us to demonstrate how ossification follows a variable rate, establishing a period between 21 and 26 weeks where there are completely closed canals with others still open to the brain fossae. The tomographic study of the semicircular canals has enabled us to establish a critical period in its ossification that could explain the etiology of the congenital-type dehiscence.

Objective:Vestibulo-ocular reflex gain at 40, 60, and 80 ms following the head movement start is calculated as the instantaneous gain. The purpose of this study was to investigate the reliability of instantaneous gain values at 40, 60, and 80 ms with testing and retesting in healthy adults.Methods:The study was conducted with Interacoustics EyeSeeCam vHIT (Interacoustics, Denmark), and 42 healthy adults were evaluated twice at half-hour intervals (test and retest) by the same practitioner. Agreement of mean gain, gain asymmetry, and instantaneous gain was evaluated using a paired samples t-test.Results:Mean age of the participants was 33.62±11.17; 38.1% were male and 61.9% were female. In the degree of the agreement, paired sample correlation (r) between test and retest results of the horizontal semicircular canals was found to be higher than those of the vertical semicircular canals. Moreover, the highest correlation between test and retest for instantaneous gain, calculated for only horizontal semicircular canals, was found at 80 ms on each side (0.791; 0.838, right and left, respectively), while the lowest correlation between these parameters was found between the gain asymmetry values.Conclusion:The video head impulse test used in studies calculates the mean gain in approximately at 60 ms. However, the higher correlation between mean gain values at 80 ms in our findings indicates that gain calculation strategies and techniques for latencies should be discussed. Additionally, the low correlation of vertical semicircular canals for mean gain and gain asymmetry between semicircular canal pairs, which clearly shows that more standard and more reliable methods should be developed.

Mussel Mytilus galloprovincialis (Lamarck, 1819) is widespread in the north-western part of the Black Sea, it is the active filter feeders sea water, is an important component of various zoocenoses. Mollusk is the object of fisheries and mariculture. Three phenotypes of mussel are separated on features of distribution of a violet pigment in outer prismatic shell layer: Fa – in a prismatic layer of purple pigment absent; Fb – pigment paints the whole of prismatic layer; Fc – pigment is localized in the form of radial strips alternating with unpigmented zones. The first two forms are interpreted homozygotes, last – heterozygotes.The purpose of the work is to study the distribution of mussels different phenotypic groups on the depths of the Odessa coast.The material for the work were the mussels collected in may 2012 at two stations – on the beach Langeron (depth 3,5 m) and in the area of hydrobiological station of Odessa National Mechnikov University (at a depth of 1 m breakwater; 6 m – fouling stones). Samples were collected with the frame area of 0,01 m2. Total collected and analyzed 459 exemplars of mussels, which were divided into the size groups with an interval of 10 mm.Index deficiency of heterozygotes (D) was calculated according to the equation:D = (Hо– Hс)/Нс ,Hо – the number of heterozygotes observed in the population; Hс – the number of heterozygotes expected by Hardy-Weinberg equation. A positive value means a deficit of heterozygotes D and negative – of their surplus.At a depth of 3,5 m represented only mussels of three size groups. About 52% of the total numbers of mollusks are size class of 20-29 mm, for other two classes remaining accounted to 24%.Among the small mollusks provided only at a depth of 6 m, the dominant were mussels of phenotype Fb (60%); half mussel of phenotype Fa (30%) and 10% – mussels of phenotype Fc. In large size class at a depth of 1 m dominated mussels of phenotype Fb – up to 100%.Mussels of phenotype Fa represent a smaller part of mollusks in almost all researched depths (1, 3,5, and 6 m), respectively, 23, 18 and 25% of the total number.At a depth of 1 m the number of mussels of phenotypes Fb and Fc is almost the same – 40 and 37%. At a depth of 3,5 m the number of these mussels of phenotypes differ slightly – 35 and 47%. Mussels of phenotype Fb, on the contrary, is dominated at a depth of 6 m, they accounted for more than half of the total number of animals – 55%. Analysis of the conformity of actual frequencies of phenotypes with theoretical data calculated by the relation of the Hardy-Weinberg equilibrium using the criterion c2 showed that at depths of 1 and 3,5 m obtained facts were not statistically significant.At a depth of 1,0 and 3,5 m observed a deficit of heterozygotes, and at the 6-meter depth – their surplus.