| Summary: | 博士 === 國立臺灣海洋大學 === 海洋生物研究所 === 101 === Keelungia pulex nov. gen. et nov. sp. is described from coastal waters of NE Taiwan. The new species is heterotrophic and feeds on bacteria. Cells are oblong-ovoid, biflagellate and glide along the sides of the flask. Each cell is approximately 8-11 μm long, and one of the smallest euglenid flagellates presently known. Keelungia lacks pellicular plate and in this respect resembles diplomonads and Symbiontida, which are thought to be among the basal groups of Euglenozoa. SEM showed the presence of 10 evenly spaced longitudinal striae in the cell surface, but the striae are difficult to see in the light microscope. TEM showed each stria to comprise a double set of very low longitudinal ridges separated by a shallow furrow, and supported by ca 5 microtubules beneath the plasmalemma, unlike the situation in diplomonads and Symbiontida. The cell surface was further subtended by an extensive system of rough cisternae of endoplasmic reticulum. Keelungia pulex is phylogenetically related to species of Ploeotia and to Lentomonas applanata, but differs in details of the feeding apparatus and in the absence of pellicular plate. Sequencing of SSU rDNA indicates that Ploeotia, Keelungia and Entosiphon form a clade near the base of the euglenid phylogenetic tree.
Two phagotrophic euglenid strains (Strains Pac/Tam) were isolated from coastal locations in Taiwan. Ultrastructure characteristics of these two strains included five pellicle strips joined at posterior end and these strips were formed by major grooves with bifurcated edges. The feeding structure started at the anterior end with a lip. Underneath the lip was a comb composed of layers of microtubules. Following the comb, there were 2 supporting rods that tapered towered the posterior end, and a number of vanes with attached microtubules occurred between the rods. These morphological characteristics were similar to Ploeotia costata Strain CCAP1265/1. However, the 18S rRNA sequences of Strains Pac/Tam lacked a group I intron, but possessed three extra insertions with lengths of 116 bp, 67 bp, and 53 bp, respectively. Phylogenetic analysis indicated low sequence similarities Strains Pac/Tam and CCAP 1265/1. Strains Pac/Tam are thus regarded as a cryptic species within P. costata. Giographic separation was proposed as the mechanism that created the observed genetic divergence.
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