a1 Port Erin Marine Laboratory (University of Liverpool), Port Erin, Isle of Man
a2 Present address: National Rivers Authority, Thames Region, Aspen House, The Grange, Crossbrook Street, Waltham Cross, Herts, EN LX
a3 Institute of Oceanographic Sciences, Deacon Laboratory, Wormley, Surrey, GU UB
A study was made ofGeryon trispinosus (Herbst) from the Porcupine Seabight in the north-east Atlantic, based on detailed examination of 687 specimens, and carapace length data for a further 2000. Evidence indicates that males become sexually mature at 30–35 mm carapace length, and females between 12 and 15 mm. There is probably a terminal anecdysis, in males at 55–65 mm and in females at 45–50 mm. The chelae show limited heterochely and marked right-handedness in both sexes. Relative growth in chelae and abdomen followed expected patterns, except that the right chelae of males decreased in relative size at the puberty moult. Seasonal reproduction is indicated: laying in September/October, hatching the following May, and settlement from the plankton in August/September.