Chromosome numbers of gammarids

Abstract
The chromosomes of nine species of gammarids have been studied in oocytes and embryos. There is no evidence that polyploidy has played a part in gammarid evolution. Three of the species which we have studied,Gammarus pulex(L.),Marinogammarus marinus(Leach) andM. pirloti(Sexton & Spooner) show chromosomal polymorphism. There is no evidence that this polymorphism depends on the existence of a Robertsonian ‘fragmentationfusion’ system; rather it appears to be due to the presence of supernumerary chromosomes.