Observations on Lorica Structure and Aspects of Replication in the Pleurasiga sphyrelata Thomsen Complex ( =Polyfibula spp. gen.n.) (Choanoflagellata)

Members of all previously known forms of the Pleurasiga sphyrelutu Thomsen, 1973 complex, with some additions, have been studied as dry whole mounts of wild material collected in six different climatic regions extending from the arctic to the equator and further south. Light microscopy has been used throughout to standardise sizes and to record gross shapes. Transmission electron microscopy has added details of the protoplast, lorica structure and development, while scanning electron microscopy of selected cells has indicated clearly the nature of the outermost lorica components. New findings include a demonstration that the three transverse costae characteristic of all members of the group are within the circle of longitudinal costae and not outside them. The posterior transverse costa is further shown to be intimately involved with attachment of the lorica to the protoplast and it is also that for which costal strips are formed first in a new replication cycle. Recommendations on terminology, nomenclature, and a revised taxonomic scheme are summarized. Formal descriptions are provided for Polyfibula gen.n. with five component taxa treated as of equal weight for the time being. Three draw on existing names ( P. sphyrelata, P. caudata and P. elatensis ) while two are new ( P. stipitata sp.n. and P. hexacostata sp.n.).