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The handedness of a given oblique muscle is opposite to that of the other member of the pair on the opposite side of the arm. In addition, on a given side, the handedness of the external and internal oblique muscles is the same and is opposite to that of the median oblique muscle. The external and the median oblique muscles have their origin and insertion on the oral and aboral connective tissue sheets. The fiber angles of the median and external oblique muscles are similar to the fibrous connective tissue layers to which they attach mean angles for O.

The fibers of the inner oblique muscles do not show a distinct origin and insertion and instead appear to interdigitate with the longitudinal and transverse musculature. Surrounding the intrinsic muscle of the arm is a thin layer of circular muscle with fibers arranged circumferentially around the arm. The layer is thickest on the aboral side of the arm, covers the aboral connective tissue sheet and extends toward the oral side of the arm, wrapping the external oblique muscles and inserting on the oral connective tissue sheet Kier and Stella, Support and movement in octopus arms is achieved in a similar manner to that described above for the arms and tentacles of decapods and relies on the resistance to volume change of the musculature of the arms.

The arms are capable of a remarkable diversity and complexity of movements Gutfreund et al. Octopus arms are notable because these deformations may be quite localized or they may occur over the entire length of the arm. In addition, they may occur at one location or at multiple locations on an individual arm. Bending movements can occur in any plane and torsional movements are observed in either direction.

The stiffness in tension, compression, bending and torsion is also under active control by the animal Kier and Stella, Since the arm tissue resists volume change, a decrease in cross section must result in an increase in length. This decrease in cross-section is likely created by contraction of the muscle fibers of the transverse muscle mass.

The elongation created can either be localized, involving only a portion of the transverse muscle, or it can occur over the entire length of the arm. The thin circular muscle layer is also oriented so that its contraction will elongate the arm, but its physiological cross-sectional area is quite small and thus the force it could produce for elongation is small.

One possible role for the circular muscle layer is in providing arm tonus for maintaining posture Kier and Stella, Shortening likely involves contraction of the longitudinal muscle bundles that extend the entire length of the arm. Since the arm resists volume change, shortening of the arm results in an increase in cross-section and thus causes elongation of the transverse and circular muscle fibers. The transverse and longitudinal muscle fibers thus function as antagonists and produce the force required for re-elongation of one another Kier and Stella, The muscle activation required for bending movements is similar to that described above for bending of decapod arms.

Active bending requires selective contraction of the longitudinal muscle bundles along the side of the arm that represents the inside radius of the bend. The support required to resist the longitudinal compressional force that would otherwise simply shorten the arm is provided by the transverse muscle mass. Active bending movements thus require simultaneous contraction of the transverse and longitudinal muscle. Bending may also occur if the transverse muscle decreases the cross-section while the longitudinal muscle on one side of the arm again, the inside radius of the bend maintains a constant length.

As described above for decapod arms, the two examples provided here probably represent endpoints on a continuum of relative shortening of the transverse and longitudinal muscle. Abrupt bends, as have been observed in some behaviors Sumbre et al. The arms of octopus provide an interesting contrast to both the tentacles and arms of decapods. As described above, the tentacles function primarily in elongation and shortening while the arms of decapods exhibit little length change and instead produce bending movements.

The arms of octopuses incorporate both bending and length change Hanassy et al. This can be achieved using the same musculature, the transverse and longitudinal muscle fibers, by simply altering their pattern of activity; sequential activity during elongation and shortening and simultaneous activity during bending Kier and Stella, Based on simple engineering considerations, the force generated by the arm during bending movements is greater if the longitudinal muscle fibers are located as far as possible from the neutral plane of the arm.

The longitudinal muscle is indeed located away from the central axis of the arm. In addition, longitudinal muscle bundles are located around the entire periphery of the cross-section of the intrinsic muscle which allows bending stresses to be exerted in any plane.

The transverse muscle is most robust in the aboral portion of the arm, which is consistent with its role in supporting and producing oral bending the most common mode of forceful bending in conjunction with the longitudinal muscle bundles on the oral side Kier and Smith, ; Kier and Stella, In addition of active bending movements, co-contraction of the transverse and longitudinal muscle increases the flexural stiffness of the arm. Such a pattern of activation is a component of the reaching behavior that has been described by Hochner, Flash and coworkers Gutfreund et al.

As in the arms of decapods, torsional movements are generated by contraction of the oblique muscles. The crossed fiber helical connective tissue arrays are a key component of the helical system of muscle and connective tissue as they transmit the force generated by the oblique muscles.

The external and median oblique muscle pairs on each side of the arm and the associated cross-fiber connective tissue array represent both a left- and a right-handed helical system and thereby allow torsional forces to be generated in either direction, consistent with observations of twisting of the arms in either direction. Co-contraction of the external and median oblique muscle systems likely increases the torsional stiffness of the arm.

The torsional moment is greater if the oblique muscles are located as far from the neutral axis as possible. The external and median oblique muscles are indeed located away from the neutral axis. The functional role of the internal oblique muscles is unclear since they are more central so would be less effective in generating a torsional moment and they have the same handedness as the external oblique. Future work involving electromyography of the internal oblique muscles during arm movement and force production would be of interest in order to determine their biomechanical role Kier and Stella, Octopus arms provide an example of the highly localized movements and deformations that are possible in appendages that rely on muscular hydrostatic mechanisms.

In comparison with a conventional hydrostatic skeleton, localized activation of muscle fibers has a localized effect, rather than the more generalized effect of increasing the hydrostatic pressure of a large fluid filled cavity. Deformations can occur in many directions at any location or at multiple locations and the arms must therefore have the neuromuscular control required to activate selectively small groups of muscle fibers and to precisely modulate their force production.

Indeed, the motor units of the transverse and longitudinal muscle are small and there does not appear to be electrical coupling between the fibers Matzner et al.

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In addition, muscle fiber activation can be controlled directly by neural activity, thereby providing precise modulation of muscle force production Matzner et al. The difficulty with such a system, however, is the potential complexity of motor control that is required. Recent studies are providing important insights into motor pathways and mechanosensory mechanisms Gutfreund et al. The majority of the musculature of the arms and tentacles of coleoid cephalopods, and indeed that of the entire animal, is obliquely striated Hanson and Lowy, ; Hoyle, , ; Amsellem and Nicaise, ; Chantler, ; Nicaise and Amsellem, ; Budelmann et al.

This striation pattern is common in the invertebrates, occurring in at least 14 phyla Thompson et al. In obliquely striated muscle fibers, the thick and thin myofilaments are arranged in a staggered array, forming a helical or oblique pattern of A-bands containing thick filaments , I-bands containing thin filaments and Z material or dense bodies anchor the thin myofilaments. Thus, the fibers lack the transverse banding pattern observed in longitudinal section that characterizes cross-striated muscle fibers.

In transverse sections, however, the fibers show a similar sequence of banding to that observed in longitudinal sections of cross-striated muscle; the staggered arrangement of myofilaments means that a single transverse section passes through I-bands, A-bands, and Z material in a single fiber. The myofilaments surround a central core containing mitochondria and the single cell nucleus. The size of the mitochondrial core varies. In the mantle and in the fins of squids there are distinct zones that include either mitochondria-rich fibers with large cores or fibers with fewer mitochondria and smaller cores.

The mitochondria rich fibers are analogs of the red muscle of vertebrates, operating primarily aerobically and used in repetitive movements, while the mitochondria-poor fibers are anaerobic, white muscle analogs that are recruited for short term maximal efforts Bone et al. The fibers of the arms and tentacles of coleoids that have been studied are predominantly the mitochondria-poor fibers, but additional work is needed to examine this issue.

The striation angle increases as the fiber shortens and decreases as the fiber is elongated. Schematic diagram of a cephalopod obliquely striated muscle fiber. Note that a cross-section of an obliquely striated muscle cell shows an analogous sequence of bands to those seen in a longitudinal section of a cross-striated fiber. It is likely that in bilaterians, striated muscle evolved independently multiple times Oota and Saitou, ; Schmidt-Rhaesa, ; Burton, ; Chiodin et al.

There are examples both of derivation of cross-striation from oblique striation and derivation of oblique striation from cross-striation Schmidt-Rhaesa, Thus, ultrastructural similarity does not necessarily indicate common evolutionary origin and the evolutionary relationships of eumetazoan striated muscle remain unclear Steinmetz et al.

The fibers of the transverse muscle mass of the arms of the loliginid squid Doryteuthis pealeii and the ommastrephid squid Illex illecebrosus are obliquely striated Kier, These fibers have been examined in the most detail so the description that follows will focus on their ultrastructure. Recent preliminary investigations of the ultrastructure of the fibers of the transverse muscle mass of the arms of the cuttlefish Sepia officinalis and of Octopus bimaculoides Shaffer and Kier, have shown similar ultrastructure to that of the arms of squid but additional work is needed.

The fibers are surrounded by an amorphous, electron-dense extracellular material Kier, ; Feinstein et al. Electron micrograph of transverse section of obliquely striated muscle fibers of the transverse muscle of the arm of Doryteuthis pealeii. Regularly spaced junctional feet are visible in the peripheral coupling labeled PC. The terminal cisternae occur where the Z elements and associated sarcoplasmic reticulum SR approach the sarcolemma.

Electron micrograph of longitudinal section of obliquely striated muscle fibers of the transverse musculature of the arm of Illex illecebrosus. The long axis of the muscle fiber is oriented horizontally on the page. The intramyoplasmic zones of sarcoplasmic reticulum SR and dense bodies arrows are oriented at a small angle with respect to the horizontally oriented thick filaments.

The sarcoplasmic reticulum is present in three zones. A peripheral zone of sarcoplasmic reticulum is present in the sarcoplasm adjacent to the sarcolemma. Specialized peripheral couplings are present between the sarcolemma and the outer portion of the membrane of the terminal cisternae of the sarcoplasmic reticulum in this zone and are common where the Z elements are adjacent to the sarcolemma.

Regularly spaced junctional feet are present in the space between the sarcolemma and the membrane of the sarcoplasmic reticulum. A second zone of sarcoplasmic reticulum is present in the plane of the Z elements and consists of a network of units that are elongated parallel to the longitudinal axis of the fiber. This intramyoplasmic zone of sarcoplasmic reticulum is interspersed between the dense bodies that form the Z material in these cells.

A third zone of sarcoplasmic reticulum is present surrounding the mitochondrial core. The fibers lack a transverse tubular system so the peripheral couplings described above likely function in excitation contraction coupling in a manner similar to that of the triad of a vertebrate skeletal muscle fibers Kier, It is challenging to obtain accurate measurements of thick filament length in these cells due to the difficulty of obtaining exactly longitudinal sections.

In a study where special care was taken during sectioning, the thick filaments of the transverse muscle mass of the arms of D. The muscle fibers of the transverse muscle mass of the tentacles of D. Recent preliminary investigation of the transverse muscle mass of the tentacles of the cuttlefish S. Unlike the obliquely striated cells of the arms, the mitochondria are not in the core and instead are located peripherally in the cell, immediately beneath the sarcolemma.

The tubules of the sarcoplasmic reticulum are restricted to the same area as the mitochondria, immediately beneath the sarcolemma. The cells thus lack transverse tubules invaginated tubules and the fibers are not subdivided into myofibrils. The sarcoplasmic reticulum forms specialized couplings with the sarcolemma in a manner similar to that described above for the obliquely striated fibers of the arms.

The coupling includes regularly spaced electron dense junctional feet in the space between the outer membrane of the sarcoplasmic reticulum and the sarcolemma. The peripheral couplings of one fiber are often aligned with those of adjacent fibers Kier, Electron micrograph of transverse section of the cross-striated muscle fibers of the transverse muscle mass of the tentacle of Doryteuthis pealeii. Mitochondria M are located immediately beneath the sarcolemma.

The outer membrane of the sarcoplasmic reticulum SR makes specialized contacts or peripheral couplings PC with the sarcolemma. Note that the A band thick filaments in cross-section passes in and out of the section plane in a single fiber. Electron micrograph of longitudinal section of cross-striated muscle fibers of the transverse musculature of the tentacle of Doryteuthis pealeii. The outer membrane of the sarcoplasmic reticulum SR forms peripheral couplings PC with the sarcolemma. The inset shows a higher magnification view of a peripheral coupling in which junctional feet arrows are visible.

Note that the Z-disc Z is diffuse and sometime follows an angled course across the fiber. The thick filaments have an electron-lucent core when observed in transverse section, in contrast to the core of the thick filaments in the obliquely striated muscle fibers of the arms, which are electron dense. This may be related to the greater paramyosin content of the thick filaments of the obliquely striated muscle fibers since paramyosin occupies the core Kier and Schachat, The thick filament length of the transverse muscle fibers of D.

The Musculature of Coleoid Cephalopod Arms and Tentacles

The fibers lack an M band, a structure present in vertebrate and arthropod cross striated muscle which is located in the center of the A band where thick filaments are bound together by cross-links. The sarcomeres of the tentacle fibers are often observed to be sheared so that the Z disc, A bands, and I bands are not perpendicular to the long axis and instead follow an angled or curved course across the diameter Kier, The Z disc of the transverse muscle fibers of the tentacles is not as regularly arranged as it is in vertebrate and arthropod muscle fibers and instead appears to be a loose grouping of electron-dense material rather than the organized network observed in the Z discs of vertebrates and arthropods Kier, The ultrastructural differentiation of the transverse muscle of the arms and tentacles of squid is especially relevant for consideration of arm and tentacle regeneration Kier, Transverse striation of the tentacle muscle cells appears at approximately 3 weeks and the adult ultrastructure is present 4—5 weeks after hatching.

High speed video recordings of prey capture show correlated behavioral changes. During the first 2—3 weeks after hatching, Sepioteuthis lessoniana hatchlings exhibit a different prey capture behavior from the adults that involves a rapid jet forward and capture of the prey with splayed arms. It is not until 4—5 weeks after hatching that the rapid tentacular strike is employed Kier, It is unknown if a similar sequence of differentiation occurs during regeneration of the tentacles.

Transverse A and longitudinal B sections of fibers from the transverse muscle of the arm arm III , and transverse C , and longitudinal D sections of muscle fibers from the transverse muscle of the tentacle. The cells at this stage in both the arm and the tentacle are obliquely striated. The tentacle cells at this stage C,D show mitochondria M in the core and rows of tubules of the sarcoplasmic reticulum S extending into the center of the cells.

The longitudinal muscle fibers of the arms and tentacles have not been studied in detail with electron microscopy. In previous work on the transverse muscle, the longitudinal muscle bundles are often included in sections so basic observations of their structure have been made. In the arms and in the tentacles they appear to be obliquely striated muscle fibers with ultrastructural characteristics that are similar to those of the transverse muscle of the arms described above Kier, As described above, the muscle fibers of the transverse muscle of the arms provide support for the relatively slow bending movements while those of the tentacle are responsible for extremely rapid elongation during the prey strike.

In order to characterize their contractile properties, Kier and Curtin dissected small bundles of fibers from the transverse muscle mass of the arms and the tentacles of D. The length-force relationship, force-velocity relationship and stimulus frequency-force relationship were determined for both the tentacle and the arms fibers. The force-velocity relationship of the two fibers was dramatically different. A significant difference in the response to electrical stimulation was also observed.

A significant difference in peak tetanic tension was also observed: The length-force relationship of the arm and the tentacle fibers was found to be similar and no difference was observed in the relationship during twitch vs. High levels of resting tension were observed in both fiber types when they were extended beyond optimal length. The high resting tension appeared to damage the preparations so it was not possible to characterize the descending limb of the length tension curve Kier and Curtin, The high resting tension is consistent with a recent study of the mantle muscle of D.

Force is expressed relative to the isometric force of the preparation mean of repeat twitches for the tentacle and repeat ms, 50 Hz tetani for the arm, Doryteuthis pealeii. The lines were fitted to the data using Hill's single hyperbolic function. From Kier and Curtin The differences in contractile properties between the arm and the tentacle transverse muscle of squid are dramatic, especially with respect to the shortening velocity of the transverse tentacle muscle described above. What specializations of the tentacle muscle fibers are responsible for the high shortening velocity observed?

Kier and Schachat compared the myofilament protein compositions from the arms and tentacles of the loliginid squid Sepioteuthis lessoniana in order to ascertain the possible role of differences in biochemical composition in tuning the contractile properties of these fibers. Samples of myofilament proteins were extracted from the transverse muscle of the arms and the transverse muscle of the tentacles and compared using sodium dodecyl sulfate polyacrylamide electrophoresis SDS-PAGE; See Kier and Schachat, for details.

Of particular relevance for considerations of shortening velocity, no differences in the myosin light chains and myosin heavy chains were observed. In addition, no differences in the myosin heavy chain were resolved using myosin purified from each fiber type and compared using several low percentage gel techniques and also using V8 protease and cyanogen bromide peptide mapping techniques See Kier and Schachat, for details.

A difference was observed in the content of the thick filament protein paramyosin, which was higher in the obliquely striated arm muscle, and is consistent with previous research showing a correlation between paramyosin content and thick filament length Levine et al. Thus, the same techniques that have been employed to document the remarkable biochemical heterogeneity of vertebrate muscle fiber types revealed remarkably few differences in myofilament protein composition between the arm and tentacle fibers, in spite of dramatically different contractile properties.

Photograph of a silver-stained SDS-polyacrylamide gel Note that the protein composition of the arm and tentacle transverse muscles is remarkably similar. For comparison, identically prepared myofilament extracts of an erector spinae muscle ES a fast muscle and a soleus muscle S a slow muscle from a New Zealand White rabbit were run in adjacent lanes. From Kier and Schachat The biochemical techniques describe above are unlikely to resolve highly conserved isoforms of proteins that differ in only a few amino acids.

This is relevant to the present discussion because a study Matulef et al. The two alternatively spliced myosin mRNAs for the two isoforms differ in the ATP-binding loop so could potentially impact myosin function and thus muscle fiber contractile properties. Kier and Schachat used semi-quantitative RT-PCR with primers that spanned the alternatively spliced region in order to explore the relative abundance of mRNA for the two myosin heavy chain isoforms in the arm transverse muscle and the tentacle transverse muscle of the squid D. Thus, the low levels of the alternatively spliced isoform along with the lack of significant difference in the levels in the tentacle vs.

To resolve the issue of potential differences in the myosin heavy chain composition of the arms and tentacles, Shaffer and Kier conducted a full analysis of the myosin heavy chain sequence from the transverse muscle of the tentacles and from the transverse muscle of the arms of D.

Transcripts of the myosin heavy chain were sequenced from these muscles and in addition from mantle, fin and funnel retractor musculature. This research showed that the myosin heavy chain was identical in all of the muscles analyzed. In addition to the analysis of squid musculature, Shaffer and Kier analyzed the myosin heavy chain transcript sequences and expression profiles from the arm, tentacle, mantle, funnel retractor and fin of the cuttlefish Sepia officinalis and from the arm, mantle, funnel retractor, and buccal mass musculature of Octopus bimaculoides.

Four myosin isoforms were identified in S. Thus, it appears unlikely that tissue-specific expression of myosin isoforms occurs. Specialization of the tentacle transverse muscle fibers for high shortening velocity appears to have involved primarily ultrastructural modifications. Given the lack of biochemical specialization and the lack of evidence for tissue-specific expression of myosin isoforms, the cross-bridge cycling rate and interfilamentary sliding velocity of the arm and tentacle muscle are likely to be similar.

As described above, the shortening velocity of the fibers of the transverse tentacle muscle was 10 times greater than that of the transverse arm muscle. This dramatic difference in properties is most likely primarily due to differences in the thick filament lengths of the two fiber types. The thick filaments in the tentacle fibers were found to be one tenth the length of those of the arm fibers and thus the tentacle fibers have ten times as many elements in series, per unit length. Because shortening velocities of elements in series are additive Huxley and Simmons, ; Josephson, , based simply on the relative thick filament and sarcomere proportions, the maximum shortening velocity of the tentacle fibers would be expected to be ten times that of the arm muscle fibers.

The musculature and connective tissue of the arms and tentacles of coleoid cephalopods is arranged in a complex, three-dimensional array. Support and movement in these structures depends on a form of hydrostatic skeletal support, referred to as a muscular hydrostat, in which the musculature serves both for force generation and as the support for movement. Because the muscle and other tissue of the arms and tentacles resist volume change, any decrease in one dimension must result in an increase in another. Since the arms and tentacles possess muscle fibers running in all three dimensions, active control of all dimensions can be achieved, allowing great diversity and complexity of movement, including elongation, shortening, bending and torsion.

In addition to deformation and movement, these appendages are also capable of active control of tensile, compressive, bending, and torsional stiffness. The musculature of these appendages is predominantly obliquely striated with relatively long myofilaments.

The exception is the transverse muscle of the tentacles of squid and cuttlefish, which is responsible for remarkably rapid elongation during the prey capture strike. This muscle exhibits cross striations and unusually short thick filaments and sarcomeres. Its shortening velocity is an order of magnitude higher than the obliquely striated fibers of the arms, most likely due to these ultrastructural differences since biochemical comparisons reveal remarkable similarity in the proteins of the myofilament lattice and identical myosin heavy chain sequences in the cross-striated and obliquely striated fibers.

Additional research on the mechanisms and control of regeneration is of particular interest, given the remarkable complexity of the arrangement of the muscle and connective tissues of these appendages. The author confirms being the sole contributor of this work and approved it for publication. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Whitfield for assistance with the figures. National Center for Biotechnology Information , U. Front Cell Dev Biol. Published online Feb Author information Article notes Copyright and License information Disclaimer. Received Nov 25; Accepted Feb 1. The use, distribution or reproduction in other forums is permitted, provided the original author s or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.

No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. Abstract The regeneration of coleoid cephalopod arms and tentacles is a common occurrence, recognized since Aristotle. Introduction Regeneration in cephalopods has been recognized since Aristotle Bello, and was initially observed in individuals collected with arms or tentacles in the process of regeneration Verrill, ; Brock, ; Lange, Muscle morphology and biomechanics The arrangement of the musculature of the arms and tentacles and indeed that of the body of coleoid cephalopods is characterized by a three-dimensional array of muscle fibers Kier, ; Zell, ; Kier and Thompson, Squid and cuttlefish tentacles In squid and cuttlefish, one pair of the ten appendages surrounding the mouth, termed tentacles, is specialized for capturing prey.

Open in a separate window. Biomechanics of support and movement in the tentacles Support and movement relies on the fact that the muscle and other tissues do not undergo significant change in volume in response to changes in pressure Kier, ; Kier and Smith, ; Smith and Kier, Squid and cuttlefish arms The arms of squid and cuttlefish serve important roles in prey handling, manipulation of objects, swimming, and reproduction.

Biomechanics of support and movement in squid and cuttlefish arms One of the most important arm movements, bending, requires selective contraction of the longitudinal muscle on the side of the arm representing the inside radius of the bend. Octopodid arms The eight arms of octopuses serve a variety of functions including prey capture, locomotion, manipulation of objects, grooming, burying, copulation, defense, chemosensing, and tactile sensing.

Morphology and microanatomy of the musculature of octopodid arms Three divisions of the musculature of the arms of octopuses were recognized by Graziadei , including 1 the intrinsic musculature of the suckers Kier and Smith, , ; Tramacere et al. Biomechanics of support and movement in octopus arms Support and movement in octopus arms is achieved in a similar manner to that described above for the arms and tentacles of decapods and relies on the resistance to volume change of the musculature of the arms.

Ultrastructure and specialization of the muscle of cephalopod arms and tentacles Ultrastructure of cephalopod muscle The majority of the musculature of the arms and tentacles of coleoid cephalopods, and indeed that of the entire animal, is obliquely striated Hanson and Lowy, ; Hoyle, , ; Amsellem and Nicaise, ; Chantler, ; Nicaise and Amsellem, ; Budelmann et al. Ultrastructure of the transverse muscle mass of the arms of decapods and octopodids The fibers of the transverse muscle mass of the arms of the loliginid squid Doryteuthis pealeii and the ommastrephid squid Illex illecebrosus are obliquely striated Kier, Ultrastructure of the transverse muscle mass of the tentacles of decapods The muscle fibers of the transverse muscle mass of the tentacles of D.

Development and differentiation of the transverse muscle of the arms and tentacles The ultrastructural differentiation of the transverse muscle of the arms and tentacles of squid is especially relevant for consideration of arm and tentacle regeneration Kier, Ultrastructure of the longitudinal muscles of the arms and tentacles of coleoids The longitudinal muscle fibers of the arms and tentacles have not been studied in detail with electron microscopy. Contractile properties of the transverse muscle of the arms and tentacles of squid As described above, the muscle fibers of the transverse muscle of the arms provide support for the relatively slow bending movements while those of the tentacle are responsible for extremely rapid elongation during the prey strike.

Mechanisms responsible for differences in contractile properties of arm and tentacle transverse muscle The differences in contractile properties between the arm and the tentacle transverse muscle of squid are dramatic, especially with respect to the shortening velocity of the transverse tentacle muscle described above. Biochemical comparison of arm and tentacle transverse muscle Kier and Schachat compared the myofilament protein compositions from the arms and tentacles of the loliginid squid Sepioteuthis lessoniana in order to ascertain the possible role of differences in biochemical composition in tuning the contractile properties of these fibers.

Myosin isoforms in cephalopod muscle The biochemical techniques describe above are unlikely to resolve highly conserved isoforms of proteins that differ in only a few amino acids. Ultrastructural specialization for fast contraction Specialization of the tentacle transverse muscle fibers for high shortening velocity appears to have involved primarily ultrastructural modifications.

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Summary The musculature and connective tissue of the arms and tentacles of coleoid cephalopods is arranged in a complex, three-dimensional array. Author contributions The author confirms being the sole contributor of this work and approved it for publication. Conflict of interest statement The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments I thank S. Sur un cas de regeneration chez Sepioteuthis lessoniana Lesson, On regeneration of the tentacular arm of the giant squid Architeuthis dux Steenstrup Decapoda, Architeuthidae. Ultrastructural study of muscle cells and their connections in the digestive tract of Sepia officinalis.

Role of aerobic and anaerobic circular mantle muscle fibers in swimming squid: Hectocotylus regeneration in wild-caught squids. Cephalopoda , in Microscopic Anatomy of Invertebrates. Mollusca II , Vol. Insights from diploblasts; the evolution of mesoderm and muscle. An octopus-bioinspired solution to movement and manipulation for soft robots. Biochemical and structural aspects of molluscan muscle , in The Mollusca, Vol. Academic Press; , 77— Of the movement of worms.

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The Musculature of Coleoid Cephalopod Arms and Tentacles

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