A resonant squid-inspired robot unlocks biological propulsive efficiency.

Elasticity has been linked to the remarkable propulsive efficiency of pulse-jet animals such as the squid and jellyfish, but reports that quantify the underlying dynamics or demonstrate its application in robotic systems are rare. This work identifies the pulse-jet propulsion mode used by these animals as a coupled mass-spring-mass oscillator, enabling the design of a flexible self-propelled robot. We use this system to experimentally demonstrate that resonance greatly benefits pulse-jet swimming speed and efficiency, and the robot's optimal cost of transport is found to match that of the most efficient biological swimmers in nature, such as the jellyfish Aurelia aurita The robot also exhibits a preferred Strouhal number for efficient swimming, thereby bridging the gap between pulse-jet propulsion and established findings in efficient fish swimming. Extensions of the current robotic framework to larger amplitude oscillations could combine resonance effects with optimal vortex formation to further increase propulsive performance and potentially outperform biological swimmers altogether.

Acoustically evoked potentials in two cephalopods inferred using the auditory brainstem response (ABR) approach.

It is still a matter of debate whether cephalopods can detect sound frequencies above 400 Hz. So far there is no proof for the detection of underwater sound above 400 Hz via a physiological approach. The controversy of whether cephalopods have a sound detection ability above 400 Hz was tested using the auditory brainstem response (ABR) approach, which has been successfully applied in fish, crustaceans, amphibians, reptiles and birds. Using ABR we found that auditory evoked potentials can be obtained in the frequency range 400 to 1500 Hz (Sepiotheutis lessoniana) and 400 to 1000 Hz (Octopus vulgaris), respectively. The thresholds of S. lessoniana were generally lower than those of O. vulgaris.

Reflectins: the unusual proteins of squid reflective tissues.

A family of unusual proteins is deposited in flat, structural platelets in reflective tissues of the squid Euprymna scolopes. These proteins, which we have named reflectins, are encoded by at least six genes in three subfamilies and have no reported homologs outside of squids. Reflectins possess five repeating domains, which are highly conserved among members of the family. The proteins have a very unusual composition, with four relatively rare residues (tyrosine, methionine, arginine, and tryptophan) comprising approximately 57% of a reflectin, and several common residues (alanine, isoleucine, leucine, and lysine) occurring in none of the family members. These protein-based reflectors in squids provide a marked example of nanofabrication in animal systems.

Microscopia electrónica de fibras nerviosas gigantes / Electron microscopy of giant nerve fibers

El presente trabajo es una revisión breve sobre los detalles ultraestructurales de las fibras nerviosas gigantes y su posible correlación con hallazgos fisiológicos hechos en el axón gigante del calamar. Tanto en secciones finas, como en réplicas obtenidas por crío-fractura, el aspecto más llamativo ha sido la gran cantidad de membranas apareadas que llenan la capa de Schwann. Estas membranas limitan hendiduras intercelulares permeables que conectan la superficie axónica con el espacio extracelular del endoneuro, dejando, así, al axolema como la única barrera continua interpuesta entre el axoplasma y el exterior de la neurona. Se ha observado, tanto en las secciones como en las réplicas, zonas de adosamiento íntimo del axón y de su célula de Schwann a nivel d elos llamados complejos estructurales, en los cuales aparecen involucradas las membranas plasmáticas de ambas células adyacentes. Estas zonas podrían constituir la expresión morfológica del acoplamiento funcional dado a conocer en la misma preparación. Además, la célula de Shwann parece ser muy activa a juzgar por la cantidad de perfiles de exo-endocitosis observados en todas sus superficies de fractura. Finalmente, las células del endoneuro aparecen diferentes en los varios tipos de fibras gigantes estudiados: en el calamar, ellas se muestran como células esponjosas, mientras que en la langosta, ellas exhiben una cantidad extraordinaria de imágenes de exo-endocitosis entremezcladas con algunas uniones epiteliales de baja resistencia y con uniones estrechas incompletas. Por último, en el camarón de río, la célula endoneurales muestran el mismo aspecto que el de la glía adaxónica

Microscopia electrónica de fibras nerviosas gigantes / Electron microscopy of giant nerve fibers

El presente trabajo es una revisión breve sobre los detalles ultraestructurales de las fibras nerviosas gigantes y su posible correlación con hallazgos fisiológicos hechos en el axón gigante del calamar. Tanto en secciones finas, como en réplicas obtenidas por crío-fractura, el aspecto más llamativo ha sido la gran cantidad de membranas apareadas que llenan la capa de Schwann. Estas membranas limitan hendiduras intercelulares permeables que conectan la superficie axónica con el espacio extracelular del endoneuro, dejando, así, al axolema como la única barrera continua interpuesta entre el axoplasma y el exterior de la neurona. Se ha observado, tanto en las secciones como en las réplicas, zonas de adosamiento íntimo del axón y de su célula de Schwann a nivel d elos llamados complejos estructurales, en los cuales aparecen involucradas las membranas plasmáticas de ambas células adyacentes. Estas zonas podrían constituir la expresión morfológica del acoplamiento funcional dado a conocer en la misma preparación. Además, la célula de Shwann parece ser muy activa a juzgar por la cantidad de perfiles de exo-endocitosis observados en todas sus superficies de fractura. Finalmente, las células del endoneuro aparecen diferentes en los varios tipos de fibras gigantes estudiados: en el calamar, ellas se muestran como células esponjosas, mientras que en la langosta, ellas exhiben una cantidad extraordinaria de imágenes de exo-endocitosis entremezcladas con algunas uniones epiteliales de baja resistencia y con uniones estrechas incompletas. Por último, en el camarón de río, la célula endoneurales muestran el mismo aspecto que el de la glía adaxónica (AU)

[Electron microscopy of giant nerve fibers]. / Microscopia electrónica de fibras nerviosas gigantes.

The present paper is a brief review on the ultrastructural details of giant nerve fibers and their possible correlation to some physiological findings which have been reported in the squid giant axon. In both, thin sections and freeze-fracture replicas, the most striking feature is the exceeding amount of paired membranes populating the Schwann cell layer. These membranes represent permeable intercellular clefts connecting the axon surface to the endoneurial extracellular space, thus leaving the axolemma as the only continuous barrier between the axoplasm and the neuron exterior. Close apposition of the axon and Schwann cell at the level of structural complexes involving both cells plasma membranes are observed in sections and replicas. These zones could represent the morphologic expression of the functional coupling reported in the same preparation. Besides, the Schwann cell appears to be very active according to the amount of exo-endocytotic profiles seen in all its fracture faces. Finally, the endoneurial cells are different in the various giant fibers studied: in the squid they appear as spongy cells, whereas in the lobster they exhibit an extraordinary amount of exo-endocytosis mixed with some gap and a few incomplete tight junctions, and in the crayfish they present the same features as the adaxonal glia.

Polarity orientations of microtubules in squid and lobster axons.

Polarity orientations of microtubules in periaxolemmal and internal regions of squid and lobster axons were determined in order to test the hypothesis that regional differences in particle transport are produced by differentially distributed microtubule subclasses. Over 95% of the microtubules in all regions of the axons investigated were oriented with plus ends located distally, pointing away from axonal somata, and there were no significant differences in orientation ratios in periaxolemmal and internal axoplasm. In axonal sheath glial cells of lobsters, microtubules were found to be oriented parallel to axonal microtubules and to have approximately equally mixed polarities. The results for axonal microtubules did not support the possibility of subclasses of axonal microtubules.