The Occurrence and Distribution of Stalked Barnacles of the Genus Octolasmis on the Gills of Mud or Mangrove Crab, Genus Scylla

摘要

Several specimens of the mud crab, Scylla cf. tranquebarica (Fabricius, 1798), were examined for the presence of stalked barnacles on the gills. Eighty-five percent of the crabs, for the size group 50 to 108 mm carapace width, were found infested with stalked barnacles. In all crabs, the barnacles were found attached to the inner (hypobranchial) surface of the gill with the exception of a single crab in which the barnacles were also found attached to the outer (epibranchial) surface of the gill. The stalked barnacles were identified as Octolasmis cor (Aurivillius, 1892) and O. angulata (Aurivillius, 1894), and our size-frequency data support the view that they are indeed distinct species. Their distribution on various parts of the gills, i.e., proximal, medial, or distal, was noted. Most of the barnacles were found attached to the medial part of the gill (O. cor 55%; O. angulata 57%), followed by the proximal part (O. cor 31%; O. angulata 38%), and the distal part (O. cor 14%; O. angulata 5%). Gill number 7 bore the maximum number of O. cor (33%) found, whereas gill number 4 harboured the maximum number of O. angulata (30.2%). Spanish Divers specimens du crabe Scylla cf. tranquebarica (Fabricius, 1798), ont ete examines pour rechercher la presence de bernacles pedoncules sur les branchies. Un total de 85% des crabes, pour le groupe de taille de 50 a 108 mm de largeur de carapace, ont ete trouves infestes par des bernacles pedoncules. Dans tous les crabes, les bernacles ont ete trouves accroches a la face interne de la branchie (hypobranchie) a l'exception d'un seul crabe chez lequel les bernacles ont ete trouves sur la surface externe (epibranchie) de la branchie. Les bernacles ont ete identifies comme Octolasmis cor (Aurivillius, 1892) et O. angulata (Aurivillius, 1894) et nos observations sur la distribution des tailles soutiennent l'hypothese qu'elles sont vraiment des especes separees. Leur distribution sur les differentes parties des branchies, i. e., proximal, median ou distal ont ete notees. La plus part des bernacles ont ete trouves accroches dans la partie mediane de la branchie (O. cor 55%; O. angulata 57%), suivie par la partie proximale (O. cor 31%; O. angulata 38%), et la partie distale (O. cor 14%; O. angulata 5%). La branchie 7 porte le nombre maximum de O. cor (33%) trouves, alors que la branchie 4 accueille un maximum de O. angulata (30.2%).