Significance of the suture line in cephalopod taxonomy revealed by 3D morphometrics in the modern nautilids Nautilus and Allonautilus.

Assessing the taxonomic importance of the suture line in shelled cephalopods is a key to better understanding the diversity of this group in Earth history. Because fossils are subject to taphonomic artifacts, an in-depth knowledge of well-preserved modern organisms is needed as an important reference. Here, we examine the suture line morphology of all known species of the modern cephalopods Nautilus and Allonautilus. We applied computed tomography and geometric morphometrics to quantify the suture line morphology as well as the conch geometry and septal spacing. Results reveal that the suture line and conch geometry are useful in distinguishing species, while septal spacing is less useful. We also constructed cluster trees to illustrate the similarity among species. The tree based on conch geometry in middle ontogeny is nearly congruent with those previously reconstructed based on molecular data. In addition, different geographical populations of the same species of Nautilus separate out in this tree. This suggests that genetically distinct (i.e., geographically isolated) populations of Nautilus can also be distinguished using conch geometry. Our results are applicable to closely related fossil cephalopods (nautilids), but may not apply to more distantly related forms (ammonoids).

The utility of micro-computed tomography for the non-destructive study of eye microstructure in snails.

Molluscan eyes exhibit an enormous range of morphological variation, ranging from tiny pigment-cup eyes in limpets, compound eyes in ark clams and pinhole eyes in Nautilus, through to concave mirror eyes in scallops and the large camera-type eyes of the more derived cephalopods. Here we assess the potential of non-destructive micro-computed tomography (µ-CT) for investigating the anatomy of molluscan eyes in three species of the family Solariellidae, a group of small, deep-sea gastropods. We compare our results directly with those from traditional histological methods applied to the same specimens, and show not only that eye microstructure can be visualised in sufficient detail for meaningful comparison even in very small animals, but also that µ-CT can provide additional insight into gross neuroanatomy without damaging rare and precious specimens. Data from µ-CT scans also show that neurological innervation of eyes is reduced in dark-adapted snails when compared with the innervation of cephalic tentacles, which are involved in mechanoreception and possibly chemoreception. Molecular tests also show that the use of µ-CT and phosphotungstic acid stain do not prevent successful downstream DNA extraction, PCR amplification or sequencing. The use of µ-CT methods is therefore highly recommended for the investigation of difficult-to-collect or unique specimens.

Spiral Form of the Human Cochlea Results from Spatial Constraints.

The human inner ear has an intricate spiral shape often compared to shells of mollusks, particularly to the nautilus shell. It has inspired many functional hearing theories. The reasons for this complex geometry remain unresolved. We digitized 138 human cochleae at microscopic resolution and observed an astonishing interindividual variability in the shape. A 3D analytical cochlear model was developed that fits the analyzed data with high precision. The cochlear geometry neither matched a proposed function, namely sound focusing similar to a whispering gallery, nor did it have the form of a nautilus. Instead, the innate cochlear blueprint and its actual ontogenetic variants were determined by spatial constraints and resulted from an efficient packing of the cochlear duct within the petrous bone. The analytical model predicts well the individual 3D cochlear geometry from few clinical measures and represents a clinical tool for an individualized approach to neurosensory restoration with cochlear implants.

A study of the type series of Nautilus pompilius Linnaeus, 1758 (Mollusca, Cephalopoda, Nautilida).

Few animals are treasured by zoologists more than Nautilus, and Nautilus pompilius Linnaeus, 1758, the type species of the genus, in particular. However, the type series of this species has not been studied in great detail. According to the rules of zoological nomenclature the type series consists of all the specimens included by the author in the new nominal taxon at the time of description (whether directly or by bibliographic reference), and any evidence, published or unpublished, may be taken into account to determine what specimens are included. The type series of Nautilus pompilius includes specimens in the Linnean Society of London, the University Museum in Uppsala, and specimens figured by pre-Linnaean authors indicated by reference by Linnaeus (1758). One specimen in London and four specimens in Uppsala, which are still extant, are likely to have been known to Linnaeus at the time when he prepared the 10th Edition of Systema Naturae (Linnaeus 1758), although none of these specimens was specifically mentioned by him. Even though it is widely believed that Linnaeus (1767) designated as lectotype a specimen figured by Rumphius (1705) in his D'Amboinsche Rariteitkamer, referred to in the Systema Naturae, this presumed lectotypification is not valid because Linnaeus did not explicitly indicate that any particular specimen was considered to be the type of the species. Later lectotype designations of Rumphius' illustrations are invalid because they show three different specimens. It seems that the best approach, given the quality of the material and the lack of clarity as to its type status, would be to apply to the ICZN asking to set aside all previous type fixations and designate a neotype, preferably a DNA sequenced specimen of known provenance.

An unusual occurrence of Nautilus macromphalus in a cenote in the Loyalty Islands (New Caledonia).

Exploration of a landlocked cenote on Lifou (Loyalty Islands) revealed 37 shells of the cephalopod Nautilus macromphalus Sowerby, 1849, in saltwater on the cenote floor, approximately 40 m below the water surface. The occurrence of these shells is unusual because N. macromphalus is restricted to the open marine waters surrounding the island. All of the shells are mature, and nearly all of them are unbroken, with faded red-brown color stripes. We analyzed seven shells to determine their age. Radiocarbon dating yielded ages of 6380±30 to 7095±30 y BP. The 238U-series radionuclides 210Pb (half-life  = 22.3 y) and 226Ra (half-life  = 1600 y) also were measured. Two of the samples showed radioactive equilibrium between the nuclides, consistent with the old radiocarbon dates, but the other five samples showed excess 210Pb. When corrected for radioactive decay, the 226Ra activities were much greater than those found in living Nautilus. We conclude that exposure to high activities of 222Rn and 226Ra in the salty groundwater of the cenote altered the activities originally incorporated into the shells. Human placement of the shells in the cavity is rejected based on their radiocarbon age and the geometry of the cenote. The most probable explanation is that the animals entered the flooded karstic system through a connection on the seaward side at approximately 7,000 y BP, during an interval of slowly rising sea level. Unable to find an exit and/or due to anoxic bottom waters, the animals were trapped and died inside. The open connection with the sea persisted for ∼700 y, but after ∼6400 y BP, the connection was lost, probably due to a roof collapse. This is a rare example of Nautilus in a karstic coastal basin and provides a minimum age for the appearance of N. macromphalus in the Loyalty Islands.

Nautilus: craniotomia dinâmica - nova técnica cirúrgica e resultados preliminares / Nautilus-shaped dynamic craniotomy: a new surgical technique and preliminary results

INTRODUÇÃO: Considerando-se que as craniossinostoses são afecções basicamente suturais, o fato de o cérebro estar aprisionado em um compartimento fechado, que não possui a complacência necessária para acompanhar seu crescimento, se constitui no desafio principal de seu tratamento. O objetivo do tratamento é restabelecer a complacência da sutura estenótica e corrigir a deformidade craniana compensatória. Este trabalho propõe a associação de osteotomia helicoide à distração osteogênica proporcionada pelo uso das molas distratoras para remodelar defeitos craniofaciais causados por craniossinostoses. MÉTODO: Entre julho de 2010 e julho de 2012, foram tratados 10 pacientes portadores de craniossinostoses, sendo 5 oxicefalias, 3 escafocefalias, 1 turricefalia e 1 trigonocefalia. O tratamento consistiu na aplicação de molas de Lauritzen, para corrigir a deformidade primária da craniossinostose, com a associação de craniotomia helicoide em forma de Nautilus nos sítios de deformação secundária do crânio, sem descolamento dural. RESULTADOS: Foi observada resolução da deformidade craniana e remissão dos sinais clínicos de hipertensão intracraniana. Nenhum paciente apresentou complicações, como fístula liquórica, infecção local, seroma ou hematoma. CONCLUSÕES: A associação da osteotomia helicoide com a distração ou contração promovida pelas molas permitiu remodelar ativamente o crânio, facilitando a acomodação do conteúdo cerebral no continente craniano.

INTRODUCTION: Considering that craniosynostosis is a suture-related condition, the main challenge for its treatment is the fact that the brain is located in a closed compartment that does not have the required adaptability to accommodate its growth. The goal of treatment is to restore stenotic suture adaptability and correct the compensatory cranial deformity. This paper proposes the combined use of spiral osteotomy with distraction osteogenesis by the use of distracting springs to remodel craniofacial defects caused by craniosynostosis. METHODS: Between July 2010 and July 2012, 10 patients with craniosynostosis were treated: 5 with oxycephaly, 3 with scaphocephaly, 1 with turricephaly, and 1 with trigonocephaly. The treatment consisted of the application of Lauritzen springs to correct the primary craniosynostosis defect in combination with a nautilus-shaped spiral craniotomy at the secondary deformation sites without dural detachment. RESULTS: Resolution of cranial deformity and remission of the clinical signs of intracranial hypertension were observed. None of the patients had complications such as cerebrospinal fluid fistula, local infection, seroma, or hematoma. CONCLUSIONS: The combined use of spiral osteotomy with spring-mediated distraction or contraction enables active reshaping of the skull and facilitates accommodation of the brain by the cranial cavity.

A biphasic memory curve in the chambered nautilus, Nautilus pompilius L. (Cephalopoda: Nautiloidea).

Cephalopods are an exceptional taxon for examining the competing influences of ecology and evolutionary history on brain and behaviour. Coleoid cephalopods (octopuses, cuttlefishes and squids) have evolved specialised brains containing dedicated learning and memory centres, and rely on plastic behaviours to hunt prey effectively and communicate intricate visual displays. Their closest living relative, the primitive nautilus, is the sole remnant of an ancient lineage that has persisted since the Cambrian. Nautilus brains are the simplest among the extant cephalopods, and the absence of dedicated learning and memory regions may represent an ancestral condition. It is assumed that the absence of these regions should limit memory storage and recall in nautilus, but this assumption has never been tested. Here we describe the first evidence of learning and memory in chambered nautilus (Nautilus pompilius). Using a Pavlovian conditioning paradigm, we demonstrate that chambered nautilus exhibits temporally separated short- and long-term memory stores, producing a characteristic biphasic memory curve similar to that of cuttlefishes. Short-term memory persisted for less than 1 h post-training, whereas long-term memory was expressed between 6 and 24 h after training. Despite lacking the dedicated neural regions that support learning and memory in all other extant cephalopods, nautilus expressed a similar memory profile to coleoids. Thus the absence of these regions in the nautilus brain does not appear to limit memory expression, as hypothesised. Our results provide valuable insights into the evolution of neural structures supporting memory.

Adhesive mechanisms in cephalopods: a review.

Several genera of cephalopods (Nautilus, Sepia, Euprymna and Idiosepius) produce adhesive secretions, which are used for attachment to the substratum, for mating and to capture prey. These adhesive structures are located in different parts of the body, viz. in the digital tentacles (Nautilus), in the ventral surface of the mantle and fourth arm pair (Sepia), in the dorsal epidermis (Euprymna), or in the dorsal mantle side and partly on the fins (Idiosepius). Adhesion in Sepia is induced by suction of dermal structures on the mantle, while for Nautilus, Euprymna and Idiosepius adhesion is probably achieved by chemical substances. Histochemical studies indicate that in Nautilus and Idiosepius secretory cells that appear to be involved in adhesion stain for carbohydrates and protein, whilst in Euprymna only carbohydrates are detectable. De-adhesion is either achieved by muscle contraction of the tentacles and mantle (Nautilus and Sepia) or by secretion of substances (Euprymna). The de-adhesive mechanism used by Idiosepius remains unknown.

Thriving at high hydrostatic pressure: the example of ammonoids (extinct cephalopods).

Ammonoids are a group of extinct mollusks belonging to the same class of the living genus Nautilus (cephalopoda). In both Nautili and ammonoids, the (usually planospiral) shell is divided into chambers separated by septa that, during their lifetime, are filled with gas at atmospheric pressure. The intersection of septa with the external shell generates a curve called the suture line, which in living and most fossil Nautili is fairly uncomplicated. In contrast, suture lines of ancient ammonoids were gently curved and during the evolution of the group became highly complex, in some cases so extensively frilled as to be considered as fractal curves. Numerous theories have been put forward to explain the complexity of suture ammonoid lines. Calculations presented here lend support to the hypothesis that complex suture lines aided in counteracting the effect of the external water pressure. Additionally, it is suggested that complex suture lines diminished shell shrinkage caused by water pressure, and thus aided in improving buoyancy. Understanding the reason for complex sutures in ammonoids represents an important issue in paleobiology with potential applications to the problem of the resistance of hollow mechanical structures subjected to high pressure.

Structure and composition of the septal nacreous layer of Nautilus macromphalus L. (Mollusca, Cephalopoda).

The nacreous layer of Mollusca is the best-known aragonitic structure and is the usual model for biomineralization. However, data are based on less than 10 species. In situ observations of the septal nacreous layer of the cephalopod Nautilus shell has revealed that the tablets are composed of acicular laths. These laths are composed of round nanograins surrounded by an organic sheet. No hole has been observed in the decalcified interlamellar membranes. A set of combined analytical data shows that the organic matrices extracted from the nacreous layer are glycoproteins. In both soluble and insoluble matrices, S amino acids are rare and the soluble organic matrices have a higher sulfated sugar content than the insoluble matrices. It is possible that the observed differences in the structure and composition of the nacreous layers of the outer wall and septa of the Nautilus shell have a dual origin: evolution and functional adaptation. However, we have no appropriate data as yet to answer this question.