Volume changes shown by some littoral anomuran crustacea

Abstract

P. platycheles was proved to be an osmoconformer, as expected. It is assumed that the other three species are conformers.Littoral specimens of E. bernhardus have a similar salinity tolerance to P. platycheles, surviving from between 17 and 20·4‰ salinity to between 40·8 and 51‰ salinity if a median lethal time of above 500 h is taken to indicate survival.The stenohaline species G. squamifera andP. longicornis swell rapidly and die in 60‰ s.w. (20·4‰ salinity). Their locomotion is rapidly impaired by swelling and the integument distorted.P. platycheles, a moderately euryhaline species, is capable of resisting swelling in 60‰ s.w., and eventually regains its original weight.Littoral E. bernhardus showed an unusual pattern of volume change in 60‰ xs.w. Initial swelling of 15·4‰ in the first hour was great compared with decapods like C. maenas or P. platycheles, yet did not cause much interference with movement, and was substantially reversed in a few hours.Increased urine production prevents swelling in P. platycheles. It is thought that increased antennary artery pressure and or a shift to a diuretic hormone balance cause increased nitration by the antennal gland.Increased urine production is delayed until substantial swelling has occurred in E. bernhardus.The abdomen of E. bernhardus makes up significantly more of the total animal weight in dilute media than in full sea water, confirming the idea that the abdomen is a ‘swelling reservoir’ protecting the rest of the animal from the mechanical effects of water inflow.Salt loss in the urine is more important than integumental loss in both E. bernhardus and P. platycheles when they are placed in 60 % s.w.