A new species of porcelain crab, Megalobrachium lemaitrei n. sp., is described and illustrated from the Pacific coasts of Panama and Colombia. The new species is similar to its northern counterpart M. erosum (Glassell, 1936) in the general eroded appearance of the carapace and chelipeds, but is distinguished by the details of the carapace and cheliped ornamentation and pereopod setation. For comparison, Megalobrachium erosum is re-described on the basis of the type and other material.

Settlement is one of the critical points in the development of organisms with complex life cycles. Some marine invertebrates respond to specific cues such as substratum and conspecifics, and the larvae of species presenting gregarious settlement are characterized by a preference for settlement in patches with conspecifics over those without. An evaluation was made in the field of the effect of conspecifics density on the settlement of Petrolisthes laevigatus during two settlement seasons. The size-distribution and density were maintained constant throughout the first settlement season, while in the second year they were adjusted to match those presented in three previously identified periods during the season. The settlement rate of P. laevigatus was higher in the presence than the absence of conspecifics. There was evidence of saturation in the settlement of the higher densities, mainly at the beginning of the settlement season, when approximately 80% of the settlement occurred. We propose that gregarious settlement is an important factor in determining the distribution and abundance of P. laevigatus at different spatial scales, both within and among coastal areas, and could restrict the colonization of new areas and the recovery of populations reduced by disturbances.

The present paper reports the occurrence of Polyonyx gibbesi in Argentinean shelf waters and extends its distribution southwards in the western Atlantic. Forty-four specimens of P. gibbesi were found in stomach contents of the narrownose smoothhound shark Mustelus schmitti during November 2008.