Further observations on the fine structure of marine collared flagellates (Choanoflagellata) from arctic Canada and west Greenland: species ofParvicorbiculaandPleurasiga

摘要

New observations amplifying and sometimes correcting existing descriptions have been compiled forParvicorbicula socialis(Meunier) Deflandre,Parvicorbicula quadricostataThrondsen,Pleurasiga minimaThrondsen, andP. reynoldsiiThrondsen from arctic material prepared as whole mounts at the time of gathering. Introductory details on localities, techniques, terminology, etc. relevant to these and other organisms to be considered later are recorded here. Special attention has been paid in each case to previously unrecorded details of lorica construction and, where material has been abundant (P. socialisandP. quadricostata), also to the range of variability in wild populations which, in these two taxa, is shown to be greater at the hind end of the lorica than elsewhere. Some differences from the type descriptions, notably up to 50 larger lorica size in three species and other differences which are interpreted as seasonal in one species (P. socialis), are thought to be ecologically but not taxonomically significant. Other details such as the shapes of costal tips, the nature of the junctions, and the mode of suspension of the protoplast within the lorica, most fully explored inP. quadricostata, are thought to be of possible phyletic significance though full discussion is deferred pending availability of additional taxa. The only nomenclatural recommendation given here is to confer specific rank onPleurasiga minimavar.minutaLeadbeater (asP. minutaLeadbeater) to separate it fromP. minimaThrondsen itself, which is recorded electron microscopically here for the first time and is shown to be a clearly defined and different taxon. This work is continuing.