Cell structure and asexual reproduction in Lagynion delicatulum (Stylococcaceae, Chrysophyceae)

Abstract

Lagynion delicatulum Skuja is a first record for New Zealand freshwaters. Individual vegetative cells in nature and culture were sessile, aflagellate, and surrounded by a hyaline lorica lacking mineral deposits. Cells were uninucleate, had one or two chloroplasts with girdle lamellae and ring nucleoids, several mitochondria, and two to four basal-body-like centrioles. Cell division was followed by the release of one or both progeny from the parent lorica as biflagellate zoospores without eyespots. The anterior flagellum bore a tomentum of fine fibrils and two balanced rows of tripartite tubular hairs. The posterior flagellum was short, scarcely visible with light microscopy. A paraflagellar rod and paraflagellar vanes were associated with its axoneme. The flagellar apparatus consisted of two basal bodies and three microtubular roots. The coplanar basal bodies diverged from each other at an angle of approximately 130°. Simple transitional helices were present. No root that could be identified with the R3 root of other stramenopiles was present. Settling zoospores produced a few long pseudopods, and lost flagella by abscission. Cells forming loricas had a circumferential array of numerous short pseudopodia. Similarities in morphology and reproduction suggest that at least those Stylococcaceae with apparently uniflagellate swarmers form a monophyletic group. Flagellar apparatus similarities between Lagynion and Hibberdia suggest a relationship, but this is not supported by previously-published phylogenies reconstructed from molecular sequences. Convergent evolution of flagellar apparatus architecture is a possibility.