HomeCAS Journal of Researchvol. 6 no. 1 (2012)

Cheliped Design and Mechanical Advantage of the Portunid Crabs, Scylla Serrata and S. olivacea*

Angelica Torio | Jimmy T. Masagca | Estrella T. Tribiana



Brachyuran crab chelipeds (= chelipeds) function in different ecological roles, including capturing the prey and processing, agonistic interactions, mate selection and handling. Cheliped morphology can explain the ability to crush hard prey, which in itself can be for force generation, transmission and distribution. This study determined the cheliped design and mechanical advantage of male and female chelipeds (pinchers) of two portunid crabs, Scylla serrata and S. olivacea from Panganiban, Viga and Virac, Catanduanes. Crab's carapace width and external cheliped dimensions were measured
using calipers. Different dimensions were defined in terms of 6 homologous landmarks found on all crab chelipeds and measurements between points were taken from external (lateral) and internal (medial) cheliped faces where possible, and all linear measurements were log10- transformed to compute for the mechanical advantage (MA). Results show that both S. serrata and S. olivacea have varied dimensions on the right and left chelipeds for both male and female samples. Computed MA in both portunid crabs are larger both in right and left chelipeds; and are higher in males compared to that of females indicating differences in force transmission for crushing food and antagonistic reaction. Cheliped designs and mechanical advantage of both S. serrata and S. olivacea differ in males from female samples confirming sexual dimorphic characters in chelipeds and possibly dimorphic force transmission forces in both sexes.