Influence of diel behaviour in the morphology of decapod natantia

Natantia is a group of decapod species showing morphologically convergent adaptations for swimming behaviour (i.e. the shrimps and prawns morphotype). Different categories are identified in relation to water column or seabed zones where the diel behaviour takes place (i.e. pelagic and nektobenthic submorphotypes). In the present study, we hypothesized a morphological convergence in different pelagic and nektobenthic species based on common nocturnal or diurnal behaviour. We analysed the pattern of morphological variation in 56 Atlanto-Mediterranean species by measuring biometric and morphometric (i.e. landmarks) characters. We also extensively reviewed the literature, recompiling information on species diel behaviour and type of displacement. That information was organized in different grouping variables and their categories: Diel-Behaviour (categories: Diurnal and Nocturnal); Sub-Morphotype (categories: Nektobenthic and Pelagic); and Classification-Status (categories: Penaeidea or Caridea). Soft independent modelling of class analogy analysis was performed per each variable to group species in each category and consequently obtain a morphological model of reference. The results obtained indicate that species sharing the same type of diel behaviour present morphological convergence in characters located in the cephalothorax and rostrum areas. Differences in the size of eyes were not related to nocturnal or diurnal rhythms but to the type of displacement (i.e. pelagic and nektobenthic). The results were interpreted assuming that visual predators exert a morphological selection on natantia depending on the presence o absence of environmental light when animals are active.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 517–532.