Constructional morphology of the shell/ligament system in opisthogyrate rostrate bivalves

ABSTRACTThe bivalve ligament provides the thrust for shell opening, acting as the resistance in a lever system against which adductor muscle effort is applied. Usually, its outer lamellar layer is subjected to tensile stress, while the inner fibrous layer is compressed, with the pivotal axis located between them. However, opisthogyrate rostrate bivalves display a concave dorsal margin, and both the umbo and the postero-dorsal angle of the shell project dorsally to the ligament, which then fails to act as pivotal axis. Three opisthogyrate rostrate genera of unrelated lineages show somewhat different solutions to this morpho-functional challenge. In Cuspidaria (Anomalodesmata), the ligament is internal, subjected only to compression and ventral to the pivotal axis, a thickened periostracum develops, forcing the dorsal margins of the valves to act as pivotal axis, and the posterior parts of the shell's dorsal margins gape dorsally. In Nuculana (Palaeotaxodonta), the inner layer of the ligament is internal, the outer layer is external but reduced, and some species develop a dorsal ridge parallel to the commissural plane, on a level with the rostrum and acting as pivotal axis. In Pterotrigonia (Palaeoheterodonta) and other rostrate trigoniides, the ligament is external opisthodetic, but is allometrically reduced. Trigoniides may also develop a dorsal ridge.

Download Full-text

Observations on Certain Mechanical Properties of the Ligament of Pecten

Journal of Experimental Biology ◽

10.1242/jeb.30.4.453 ◽

1953 ◽

Vol 30 (4) ◽

pp. 453-467 ◽

Cited By ~ 1

Author(s):

E. R. TRUEMAN

Keyword(s):

Mechanical Properties ◽

Tensile Stress ◽

Central Region ◽

Outer Layer ◽

Dorsal Margin ◽

Pecten Maximus ◽

Lower Efficiency ◽

Loading And Unloading ◽

Opening And Closing ◽

Associated Species

The ligament of Pecten maximus consists of two layers, the outer extending along the dorsal margin of the valves, and the inner situated between the valves in the region of the umbo. The former appears fibrous and is somewhat similar to the outer layer of other ligaments. The inner layer consists of three parts, a large central non-calcified structure and two lateral calcified regions attaching the former to the valves. The central region is characteristic of the ligament of P. maximus and associated species, this layer being uniformly calcified in the ligament of most bivalves. When the valves are closed the outer layer is subjected to tensile stress and the inner to compression, and the force so derived tends to open the valves. This force and that required just to close the shell are expressed as the opening and closing moments of the ligament respectively, and these have been determined for various lamellibranchs. The exact conditions of the opening and closing of the valves have been observed by drawing the stress-strain curves for the intact ligament, plotting the applied moment against the angle of gape. The loading and unloading curves so produced describe a hysteresis loop. The area enclosed in that of Pecten (or Chlamys) is markedly less than that of other lamellibranchs and indicates the greater efficiency of the ligament of the former. The mechanical properties of the isolated central region of the inner layer of the ligament of Pecten were investigated and showed similar properties to those of the intact ligament. The modulus of elasticity in compression of this region of the ligament of Pecten is approximately one-seventh of that of the inner layer of Ostrea or Lutraria, which are calcified structures. The ligament of the latter two bivalves has a greater opening moment but lower efficiency than that of Pecten. The characteristics of the ligament of Pecten are probably due to the central non-calcified region of the inner layer. The significance of these properties in regard to the swimming habit of Pecten is briefly discussed.

Download Full-text

The Ligament of Mya Arenaria (Myoidea) Revisited

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315400038753 ◽

1997 ◽

Vol 77 (4) ◽

pp. 1231-1233

Author(s):

Antonio G. Checa ◽

Gerhard C. Cadée

Keyword(s):

Three Dimensional ◽

Adductor Muscle ◽

Mantle Cavity ◽

Mya Arenaria ◽

Fibrous Layer ◽

Dorsoventral Axis ◽

Lamellar Layer ◽

Posterior Extension ◽

Mode Of Attachment

The ligament of the bivalve Mya arenaria was previously described as being composed of two layers: a fibrous and a lamellar one, the fibrous layer being more extensive. Other features described, such as the three-dimensional extent of the layers and their mode of attachment to the chondrophores, have been found to be inaccurate to a certain extent. The ligament is therefore redescribed here. It is conical in appearance and attached to the left chondrophore only at its margin, its interior being occupied by an epithelium, which is an extension of the mantle isthmus. The lamellar layer is a pyramidal body which merges into and constitutes the posterior extension of the fibrous layer. The whole structure is internal and may rotate around the dorsoventral axis, thus being suited to allow rocking of the valves. This kind of movement is used when Mya contracts the anterior adductor muscle to eject water from the mantle cavity during burrowing. In this respect the ligament is unique among those known in bivalves.

Download Full-text

Stress Analysis and Microstructure Evolution of Titanium Alloy Pipe during Flattening Processing

Materials Science Forum ◽

10.4028/www.scientific.net/msf.944.1088 ◽

2019 ◽

Vol 944 ◽

pp. 1088-1093

Author(s):

Jun Chen ◽

She Wei Xin ◽

Wei Zhou ◽

Qian Li ◽

Si Yuan Zhang ◽

...

Keyword(s):

Titanium Alloy ◽

Tensile Stress ◽

Compressive Stress ◽

Outer Layer ◽

Contact Stage ◽

Straight Wall ◽

Vertical Part ◽

Left And Right ◽

Titanium Alloy Tube ◽

Flattening Process

TA24 titanium alloy pipe with 638mm diameter and 19mm wall thickness is carried out continuous load flatten test, and the stress of internal and external pipe wall during flatten process is studied in this paper. The results show that the TA24 titanium alloy tube has good flattening performance, and the flattening process has experienced original stage, flattened oblate stage, flattened straight wall stage, flattened depressed stage, flattened concave contact stage. During the flattening process, the outer layer of the upper and lower wall of the tube is subjected to compressive stress, and the inner layer material is subjected to tensile stress. The tensile and compressive forces cause the vertical part of the upper and lower walls to be concave. The outer layer of the left and right circular arc parts is subjected to tensile stress and the inner layer is subjected to tensile stress. The compressive stress also causes the radius of the arc to decrease due to the combined force of the tensile and compressive forces, that is, the flattening occurs. With the decrease of and pressing distance under continuous loading condition, the metal on the left and right sides of the pipe gathers toward the middle depression, which aggravates the deformation of the upper and lower walls until the upper and lower walls contact, and the arc radius of the left and right walls decreases until the outer surface cracks. The pipe microstructure changes significantly into elongated deformation structure during the flattening process. The most severe part of the deformation is the left and right end arc of the pipe, followed by the upper and lower end depression.

Download Full-text

The Ligament of Pecten

Journal of Cell Science ◽

10.1242/jcs.s3-94.26.193 ◽

1953 ◽

Vol s3-94 (26) ◽

pp. 193-202

Author(s):

E. R. TRUEMAN

Keyword(s):

Central Region ◽

Outer Layer ◽

Protein Complex ◽

High Efficiency ◽

Dorsal Margin ◽

Pecten Maximus ◽

Associated Species

The ligament of Pecten maximus consists of two layers, the outermost situated along the extensive dorsal margin of the valves, the inner between them at the umbo. The former, composed largely of tanned proteins, is laminated and is somewhat similar to the outer layer of other ligaments. The inner layer is divided into three parts, a large central non-calcified structure and two lateral calcified regions attaching the former to the valves. The lateral parts resemble the entire inner layer of the ligament of most other lamellibranchs, which is generally uniformly calcified. The central region, consisting mainly of a tanned protein complex, is gelatinous in appearance and is characteristic of P. maximus and associated species. This type of structure is particularly suitable for the rapid and frequent opening of the valves, and its relatively high efficiency may be largely attributed to the non-calcified region of the inner layer.

Download Full-text

The Ligament of the Lucinacea (Eulamellibranchia)

Journal of Cell Science ◽

10.1242/jcs.s3-101.53.25 ◽

1960 ◽

Vol s3-101 (53) ◽

pp. 25-36

Author(s):

J. A. ALLEN

Keyword(s):

Outer Surface ◽

Outer Layer ◽

Intermediate Stage ◽

Basic Structure ◽

Adductor Muscle

The basic structure of the opisthodetic ligament of the Lucinacea consists primarily of inner layer, anterior and posterior outer layers, and periostracum. This is secondarily extended by fused periostracum and fusion layer. Fused periostracum extends as far as the posterior adductor muscle and, except in the Ungulinidae, to the anterior adductor. The fusion layer covers the posterior outer layer and a little beyond. Only in Loripes lucinalis is the fusion layer to be found anteriorly. Below the umbos the inner layer, posterior outer layer, and overlying fusion layer are split. This split can be explained in terms of the growth and form of the shell. The anterior outer layer fills the split and extends to the anterior limit of the lunule. The ligament, external in the Ungulinidae, becomes progressively more internal. At the same time the posterior limit of the outer layer becomes modified as a result of the elongation of the outer surface of the outer mantle fold between the pallial lobes in the depth of the posterior mantle embayment. The Lucinidae are most specialized in this respect where, in L. lucinalis, a tongue of tissue divides much of the ligament horizontally. The Thyasiridae, the remaining family of the group, occupies an intermediate stage in this specialization.

Download Full-text

Observations on the Ligament of Mytilus edulis

Journal of Cell Science ◽

10.1242/jcs.s3-91.15.225 ◽

1950 ◽

Vol s3-91 (15) ◽

pp. 225-235

Author(s):

E. R. TRUEMAN

Keyword(s):

Mytilus Edulis ◽

Outer Layer ◽

Tensile Strain ◽

Normal Adult ◽

Dorsal Margin ◽

Longitudinal Plane

1. The ligament of Mytilus edulis is situated between the valves of the shell immediately below the dorsal margin and may be divided into two main layers, the inner and the outer, the principal features of which appear to correspond with those of other bivalves. 2. The outer layer is subjected to a tensile strain transverse to the longitudinal plane of the shell, which is imposed by the addition of the inner layer. This strain is increased when the valves are closed. At the same time the inner layer is compressed. It is significant, however, that the birefringence of the main outer layer is much smaller than-in Tellina. 3. The prodissoconch has a small internal ligament which is replaced by the normal adult structure as the posterior dorsal margin of the young mussel is extended. 4. The axis about which the valves open is situated along a line drawn between the two main layers. Anteriorly the adult ligament becomes split and ceases to function. Possible explanations are suggested.

Download Full-text

Extraverts Have Larger Social Network Layers

Journal of Individual Differences ◽

10.1027/1614-0001/a000048 ◽

2011 ◽

Vol 32 (3) ◽

pp. 161-169 ◽

Cited By ~ 74

Author(s):

Thomas V. Pollet ◽

Sam G. B. Roberts ◽

Robin I. M. Dunbar

Keyword(s):

Social Network ◽

Social Relationships ◽

Outer Layer ◽

Network Size ◽

Emotional Intensity ◽

Emotional Closeness ◽

Network Layer ◽

Network Layers ◽

Social Network Size

Previous studies showed that extraversion influences social network size. However, it is unclear how extraversion affects the size of different layers of the network, and how extraversion relates to the emotional intensity of social relationships. We examined the relationships between extraversion, network size, and emotional closeness for 117 individuals. The results demonstrated that extraverts had larger networks at every layer (support clique, sympathy group, outer layer). The results were robust and were not attributable to potential confounds such as sex, though they were modest in size (raw correlations between extraversion and size of network layer, .20 < r < .23). However, extraverts were not emotionally closer to individuals in their network, even after controlling for network size. These results highlight the importance of considering not just social network size in relation to personality, but also the quality of relationships with network members.

Download Full-text