Cryptic Biodiversity and Speciation in Marine Populations:the Holoplankton Paradox

Cryptic species have been found in a wide range of marine organisms;with majority of them are benthic inverte-brates.In contrast,marine holoplanktons are thought to have lower diversity and slow speciation due to their strong dispersal po-tential.This paper reviewed studies on cryptic species and speciation in marine holoplankton.Based on findings in 38 studied tax-a,it was concluded that:1) cryptic species are pervasive in marine holoplankton,suggesting holoplankton speciation was more ac-tive than previously thought;2) Current morphospecies diversity is untenable to reflect true species diversity in marine holoplank-ton;3) Geographic isolation may facilitate cryptic speciation of marine holoplankton.However,contribution of allopatric speciationis still questionable;4) Ecological speciation may be the prevailing speciation mode in marine holoplankton.Cryptic speciation inmarine holoplankton is paradoxical,because rapid speciation under strong gene flowis countertuitive.Solution of this paradox willhelp us gain deep insights of marine speciation and biodivesity.