The structure and function of thoracic exopodites in the larvae of the lobster
            <i>Homarus gammarus</i>
            (L.)

Neil, Douglas M.; Macmillan, David L.; Robertson, Robert; Laverack, M. S.

doi:10.1098/rstb.1976.0038

Cited by 30 publications

(3 citation statements)

References 25 publications

(23 reference statements)

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“…Accordingly, the experimental light must have been well discernible by the lobster larvae. Under laboratory conditions newly hatched larvae always stayed at the surface and swam directly towards any light source in accordance with observations of Neil et al (1976), Dunn & Shelton (1983) and Watt & Arthur (1996), who reported that larvae after hatching always swim towards the sea surface. In our experiments, the newly hatched lobster larvae reacted immediately to light Á irrespective of the direction Á even if it came from the bottom and responded with a downward vertical swimming speed of about 4Á5 cm s (1 (including the sinking rate of 1.7 cm s (1 ).…”

Section: Phototaxis and Vertical Distributionsupporting

confidence: 89%

“…The locomotion ability of larvae changes during their larval development (Ennis 1995) and the major swimming appendages of the pelagic larvae are the exopodite branches of the third maxillipeds, the chelipeds and the four pairs of pereipods (Neil et al 1976). By beating of the exopodites, the larvae carry forward, backwards or upwards; when their motion ceases, however, the larvae sink towards the bottom (Hadley 1908).…”

Section: Stocks Of European Lobsters (Homarus Gammarusmentioning

confidence: 99%

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Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

Schmalenbach

Búchholz

2010

Marine Biology Research

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Section: Phototaxis and Vertical Distributionsupporting

confidence: 89%

Section: Stocks Of European Lobsters (Homarus Gammarusmentioning

confidence: 99%

Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

Schmalenbach

Búchholz

2010

Marine Biology Research

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“…Before going on to discuss the determinative influences, it is interesting to note that the critical period is also the time when the lobster changes its habitat. The larval stages are all pelagic and live in the plankton, staying afloat by accessory swimming appendages ( Neil, Macmillan, and Laverack, 1976). These accessory appendages degenerate at the molt to the fourth stage (Govind, Kirk, and Pearce, 1988a).…”

Section: Critical Period For Determining Asymmetrymentioning

confidence: 99%

Claw asymmetry in lobsters: Case study in developmental neuroethology

Govind

1992

J. Neurobiol.

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An enduring debate in the study of development is the relative contribution of genetic and epigenetic factors in the genesis of an organism, that is, the nature vs. nurture debate. The behavior of the paired claws in the lobster offers promising material for pursuing this debate because of the way they develop. The paired claws and their closer muscles are initially symmetrical; both are slender in appearance and have a mixture of fast and slow fibers in their closer muscles. During a critical period of development, they become determined into a major (crusher) and minor (cutter) claw and during subsequent development acquire their final form and behavior: The crusher becomes a stout, molar-toothed claw capable of closing only slowly because its closer muscle has 100% slow fibers while the cutter becomes a slender, incisor-toothed claw capable of closing rapidly because its closer muscle has 90% fast fibers. Our initial hypothesis was that the more active claw became the crusher and its less active counterpart the cutter. Presumably, nerve activity would influence muscle transformation, which in turn would influence the exoskeleton to which they attach and hence claw morphology. Curtailing nerve activity to the claw prevented crusher development, while reflex activation of a claw promoted its development; both results support the notion that nerve activity directly regulates claw form and function. This is not, however, the case, for when both claws were reflexly exercised neither formed a crusher, signifying rather that bilateral differences in predominantly mechanoreceptive input to the paired claws somehow lateralized the claw ganglion [central nervous system (CNS)] into a crusher and cutter side. The side experiencing the greater activity becomes the crusher side while the contralateral side becomes the cutter and is also inhibited from ever becoming a crusher. This initial lateralization in the CNS is expressed, via as yet unknown pathways, at the periphery in claw morphology, muscle composition, and behavior. The critical period defines a time when the CNS is susceptible to being lateralized into a crusher and cutter side. Such lateralization is dependent upon experience of the environment in the form of mechanoreceptive input. In the absence of such experience, the CNS is not lateralized and paired cutter claws develop. Thus, while the critical period for crusher determination is genetically determined the actual trigger is influenced by experience.

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Highly active neuromuscular system in developing lobsters with programmed obsolescence

Govind

Kirk

Pearce

1988

J of Comparative Neurology

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The primary locomotory apparatus in the three larval stages of the lobster, Homarus americanus, are paddlelike structures on the thoracic appendages called exopodites, which beat almost continuously. Consequently their power and return-stroke muscles are examples of highly active but short-lived neuromuscular systems. The muscles, which are well vascularized, are of the fast type with 2-3-micron sarcomere lengths and 6 thin filaments surrounding a thick one. The most striking feature, however, is the large volume of mitochondria making up 40-50% of the fiber. They appear as simple cylinders packed several layers deep along the periphery of the fiber and as large, multibranched forms distributed throughout the fiber and subdividing it into smaller units. The motor innervation to the return-stroke muscle is via 3 excitatory axons, which generate large junctional potentials and twitch contractions. The muscle is densely populated with large neuromuscular synapses, most of which have a well-defined active site or dense bar denoting the site of transmitter release. Altogether this motor system is specialized for prolonged activity. Atrophy of the neuromuscular system occurs by the late larval third stage. The muscle fibers lose their identity, fuse, and become vacuolated. The myofibrils condense and erode and the mitochondria are lost. Atrophy of motor innervation is gradual with individual axons dropping out. The largest axon providing most of the innervation is the first to degenerate. Early degenerative changes affect the axon and neuromuscular terminals but not the synaptic contacts, dense bars, and vesicles, which appear intact. Continued atrophy in the postlarval fourth stage reduces the exopodites to vestiges. Thus the return-stroke muscle of the larval exopodites in which muscle fiber and motoneurons are identifiable permits study of the interaction between a neuron and its target muscle undergoing programmed obsolescence.

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The structure and function of thoracic exopodites in the larvae of the lobster Homarus gammarus (L.)

Cited by 30 publications

References 25 publications

Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

Claw asymmetry in lobsters: Case study in developmental neuroethology

Highly active neuromuscular system in developing lobsters with programmed obsolescence

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