The structure and function of the labrum in the lobster Homarus gammarus (L.)

Abstract

The labrum of decapod crustaceans is a soft lobe overhanging the mouth. The labral skeleton, musculature and innervation of Homarus gammarus are described. There are three bilateral groups of sensory neurons innervating the floor, lobe and lateral walls of the labrum. These are probably responsible for the phasic afferent activity that can be recorded from the inner labral nerve on mechanical deformation of the labrum. The labrum undergoes rhythmical retraction-protraction move­ments during ingestion and is shown to be active during both mandibular activity and oesophageal peristalsis. Studies were made on the duration and frequency of labral ‘swallowing’ activity. The role of the labrum in feeding is discussed.

Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food

“…All sets of mouthparts are involved in food handling and contain chemoreceptor neurons (Garm, 2004;Garm, 2005;Garm and Høeg, 2006), with the outer ones being much bigger and playing a more important role in handling bigger pieces of food than the inner ones. Although it is not possible to ablate the entire mandibles, it has been shown in another species of portunid crab (Salindeho and Johnston, 2003) and a wide array of other decapods (Garm, 2004) that only their palps, which can be ablated, bear setae and, in Homarus, that the labrum does not respond to chemical stimulation (Robertson and Laverack, 1979a). Taken together, this suggests that no chemoreceptors were left in the outmost portion of the oesophagus (mandibular processes + labrum).…”

Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food

“…All sets of mouthparts are involved in food handling and contain chemoreceptor neurons (Garm, 2004;Garm, 2005;Garm and Høeg, 2006), with the outer ones being much bigger and playing a more important role in handling bigger pieces of food than the inner ones. Although it is not possible to ablate the entire mandibles, it has been shown in another species of portunid crab (Salindeho and Johnston, 2003) and a wide array of other decapods (Garm, 2004) that only their palps, which can be ablated, bear setae and, in Homarus, that the labrum does not respond to chemical stimulation (Robertson and Laverack, 1979a). Taken together, this suggests that no chemoreceptors were left in the outmost portion of the oesophagus (mandibular processes + labrum).…”

Embryonic Development of Appasus japonicus Vuillefroy, With Special Reference to Mouthparts Formation (Insecta: Heteroptera, Belostomatidae)

“…The labrum is a structure located anterior to the mouthparts in most extant arthropods (Budd 2021 ). In arthropods with biting‐type mouthparts, the labrum is thought to function as an organ that prevents food from falling forward during feeding (e.g., Robertson and Laverack 1979 ; De Jong et al 2002 ). In contrast, in Hemiptera, the labrum forms a tubular structure that cover the proximal part of the mandibular and maxillary stylets.…”

A New Family for a New Genus and New Species of Hermit Crab of the Superfamily Paguroidea (Decapoda: Anomura) and Its Phylogenetic Implications

“…Among other reptant decapods, a toothed incisor process is not uncommon (e.g., Huxley, 1880;Patwardhan, 1935b;Snodgrass, 1950;Poore, 1975Poore, . 1994Wales et ai, 1976;Robertson and Laverack, 1979;Suthers and Anderson, 1981;Factor, 1989;Scholtz and Richter, 1995). While Poore (1994) considered the anterior truncated, blade-like portion and posterior toothed margin of the mandible of thalassinideans as representing the plesiomorphic condition, a toothed cutting edge was regarded as apomorphic.…”

Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food

“…All sets of mouthparts are involved in food handling and contain chemoreceptor neurons (Garm, 2004;Garm, 2005;Garm and Høeg, 2006), with the outer ones being much bigger and playing a more important role in handling bigger pieces of food than the inner ones. Although it is not possible to ablate the entire mandibles, it has been shown in another species of portunid crab (Salindeho and Johnston, 2003) and a wide array of other decapods (Garm, 2004) that only their palps, which can be ablated, bear setae and, in Homarus, that the labrum does not respond to chemical stimulation (Robertson and Laverack, 1979a). Taken together, this suggests that no chemoreceptors were left in the outmost portion of the oesophagus (mandibular processes + labrum).…”

Embryonic Development of Appasus japonicus Vuillefroy, With Special Reference to Mouthparts Formation (Insecta: Heteroptera, Belostomatidae)

“…The labrum is a structure located anterior to the mouthparts in most extant arthropods (Budd 2021 ). In arthropods with biting‐type mouthparts, the labrum is thought to function as an organ that prevents food from falling forward during feeding (e.g., Robertson and Laverack 1979 ; De Jong et al 2002 ). In contrast, in Hemiptera, the labrum forms a tubular structure that cover the proximal part of the mandibular and maxillary stylets.…”

A New Family for a New Genus and New Species of Hermit Crab of the Superfamily Paguroidea (Decapoda: Anomura) and Its Phylogenetic Implications

“…Among other reptant decapods, a toothed incisor process is not uncommon (e.g., Huxley, 1880;Patwardhan, 1935b;Snodgrass, 1950;Poore, 1975Poore, . 1994Wales et ai, 1976;Robertson and Laverack, 1979;Suthers and Anderson, 1981;Factor, 1989;Scholtz and Richter, 1995). While Poore (1994) considered the anterior truncated, blade-like portion and posterior toothed margin of the mandible of thalassinideans as representing the plesiomorphic condition, a toothed cutting edge was regarded as apomorphic.…”

Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food

“…All sets of mouthparts are involved in food handling and contain chemoreceptor neurons (Garm, 2004;Garm, 2005;Garm and Høeg, 2006), with the outer ones being much bigger and playing a more important role in handling bigger pieces of food than the inner ones. Although it is not possible to ablate the entire mandibles, it has been shown in another species of portunid crab (Salindeho and Johnston, 2003) and a wide array of other decapods (Garm, 2004) that only their palps, which can be ablated, bear setae and, in Homarus, that the labrum does not respond to chemical stimulation (Robertson and Laverack, 1979a). Taken together, this suggests that no chemoreceptors were left in the outmost portion of the oesophagus (mandibular processes + labrum).…”

Embryonic Development of Appasus japonicus Vuillefroy, With Special Reference to Mouthparts Formation (Insecta: Heteroptera, Belostomatidae)

“…The labrum is a structure located anterior to the mouthparts in most extant arthropods (Budd 2021 ). In arthropods with biting‐type mouthparts, the labrum is thought to function as an organ that prevents food from falling forward during feeding (e.g., Robertson and Laverack 1979 ; De Jong et al 2002 ). In contrast, in Hemiptera, the labrum forms a tubular structure that cover the proximal part of the mandibular and maxillary stylets.…”

A New Family for a New Genus and New Species of Hermit Crab of the Superfamily Paguroidea (Decapoda: Anomura) and Its Phylogenetic Implications

“…Among other reptant decapods, a toothed incisor process is not uncommon (e.g., Huxley, 1880;Patwardhan, 1935b;Snodgrass, 1950;Poore, 1975Poore, . 1994Wales et ai, 1976;Robertson and Laverack, 1979;Suthers and Anderson, 1981;Factor, 1989;Scholtz and Richter, 1995). While Poore (1994) considered the anterior truncated, blade-like portion and posterior toothed margin of the mandible of thalassinideans as representing the plesiomorphic condition, a toothed cutting edge was regarded as apomorphic.…”