Analysis of the mero-carpopodite joint of the American lobster and snow crab. II. Kinematics, morphometrics and moment arms

• Published in: Journal of the Marine Biological Association of the United Kingdom Vol. 83; no. 6; pp. 1249 - 1259
• Main Authors: Mitchell, S.C., DeMont, M.E.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.12.2003
• Subjects: Amphibia. Reptilia; Animals; Biological and medical sciences; Chionoecetes opilio; Crustacea; Crustaceans; Decapoda; Fitness equipment; Fundamental and applied biological sciences. Psychology; Homarus americanus; Invertebrates; Kinematics; Marine; Morphology. Histology. Cytology; Research Article; Shellfish; Snow; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; Walking; United Kingdom > UK; Motion; Interspecific comparison; Apodeme; Brachyura; Experimental device; Allometry; Appendix; Macrura; Crustacea; Marine environment; Chionoecetes opilio; Homarus americanus; Locomotion; Functional morphology; Arthropoda; Kinematics; Decapoda; Invertebrata; Morphometry
• ISSN: 0025-3154; 1469-7769
• DOI: 10.1017/S0025315403008609

This research reports on the kinematics of lobster and snow crab walking, documents changes in the moment arms of the mero-carpopodite joint during rotation, and examines scaling effects of morphological and mechanical variables in these crustacean species. Forward walking lobsters and lateral walking crabs were recorded and images analysed to describe the kinematics of these animals, and subsequently morphometric and moment arm measurements made. During forward walking the lobster maintains fixed mero-carpopodite joint angles during both the power and recovery strokes, though each of the walking legs maintains different joint angles. Legs 3 and 5 are maintained at angles which appear to equalize the flexor and extensor moment arms, and leg 4 joint angle appears to maximize the extensor moment arm. The snow crab has a joint excursion angle of between approximately 50° to 150° and, during flat bed walking, the leading and trailing legs move through similar excursion angles. The length of the meropodite for both species are longer for the anterior two leg pairs relative to the posterior two pairs and the rate of growth of the meropodite is largely isometric for the lobster while consistently increases with positive allometry in the crab. The flexor and extensor moment arms generated as the joint undergoes flexion/extension show two distinct patterns with the extensor moment arm being maximized at relatively low joint angles (55°–115°) and the flexor moment arm reaching a plateau at joint extension with angles between 95° and 155°. The flexor apodeme possesses the largest moment arms in all legs for both species, suggesting the flexors are able to generate greater torques. It appears that, mechanically, these laterally moving animals may be ‘pulling’ with the leading legs to a greater extent than ‘pushing’ with the trailing legs.