| Summary: | Starch gel electrophoresis was employed to discern the genetic population structure in four principal species of deep-sea Crustacea from the North Atlantic and Indian Oceans. The number of loci screened in each species varied from 8 to 20. Observed heterozygosity ( H o ) was typically lower than expected. Values of H o varied from 0.000 to 0.172, which are in the normal range of invertebrates and deep-sea Crustacea. Allelic frequency data of the vent-endemic caridean shrimp Rimicaris exoculata indicate that all morphotypes of R. exoculata examined, from two hydrothermal vent fields (located along the Mid-Atlantic Ridge), including those previously interpreted as representing separate species, are conspecific. Conversely, genetic identity between a single putative specimen of Chorocaris fortunata and R. exoculata was high for intergeneric comparisons. Estimates of variance of allele frequencies among populations ( F ST ) between sites were very low (mean F ST = 0.001) indicating no significant genetic differentiation between populations separated by approximately 370 km. The biology and genetics of populations of the majid crab Encephaloides armstrongi separated by depth were studied. The overall sex ratio was male-biased ( p < 0.01 ). In both male and female E. armstrongi , individuals from a single population located at 150 m depth were significantly smaller than individuals at all other stations and were considered to represent a juvenile cohort. Additional, significant differences in length frequency were detected between male crabs from populations between 300 to 650 m depth. Six enzyme systems coding for eight loci for individuals were sampled from each population of E. armstrongi . Genetic identity ( I ) values between populations of E. armstrongi ( I = 0.98-1.00) were typical of conspecific populations. For both male and female E. armstrongi significant genetic differentiation was detected between the population located at 150 m depth and all other populations. Analyses of F IS (The correlation between ...
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