Phylogeny, evolution and biogeography of the marine isopod subfamily Idoteinae (Crustacea: Isopoda: Idoteidae)

The patterns of spatial distribution attained by the genera of Idoteinae are discussed in hght of a cladistic analysis of the suborder Valvifera and the subfamily Idoteinae.A schematic pattern analysis technique is demonstrated and reveals the probability of multiple origins of similar pleonal morphologies among various genera of Idoteinae.Reduction in the maxillipedal palp has occurred numerous times within the Idoteinae.while loss of the biramous uropodal condition has probably occurred twice.A geographic cladogram of temperate Gondwanan shores is proposed.An evolutionarybiogeographic narrative is presented, in which a set of hypotheses is developed to describe the history of the Idoteinae in time and space.The subfamily Idoteinae appears to form two principal lines of descent, both arising in the Triassic or Jurassic.One of these lines remained closely tied to the Southern Hemisphere (primarily Old World) temperate marine shores from which the Idoteinae is derived.The other line invaded the Northern Hemisphere and various New World environments, and more recently (Cenozoic) underwent a radiation in the American tropics.The success of this latter lineage (e.g., Erichsonella.Eusymmerus, Parasymmerus.Cleantioides) may be due to certain morphological and life history adaptations not found in New World species of the former line (e.g., Idotea.Synidotea).The Valvifera probably originated in the temperate Southern Hemisphere, at least by Permean/Triassic times.Global distribution patterns of some genera can be ascribed most parsimoniously to vicariance processes, and in others to dispersal, ecological phenomena, or a combination of processes.Other factors have apparently also affected modern distributional patterns of idoteine genera, for example, extinctions.Biogeographical data can be used to elucidate viable alternative cladistic hypotheses to those generated solely on parsimonious patterns of synapomorphy.Biogeographic data can also be used, in conjunction with the cladogram, to identify probable ancestral taxa.