A morphological study of subitaneous and diapause eggs in marine planktonic copepods

Many neritic, boreal and sub-temperate copepod species survive periods of environmental adversity by producing over wintering dormant eggs. To understand the nature of arrested development in these crustaceans, we recently studied resting and subitaneous eggs in Pontella mediterranea, a large neustonic copepod that occurs seasonally in Mediterranean surface waters. The species produces morphologically different eggs; smooth eggs that hatch with in 2 d at ca 21°C and spiny eggs that do not hatch under similar conditions. Eggs were fixed for EM immediately after deposition in the case of subitaneous and diapause eggs, and 2 wks and 6 mo later in diapause eggs. Females and eggs were fixed at 4°C in a mixture of 2.5% gluteraldehyde and 1% para formaldehyde buffered to pH 7.2 with 0.2. sodium cacodylate and 20% seawater, rinsed in the same solution with 0.55 M sucrose, and post-fixed and dehydrated in an alcohol series according to conventional procedures.