The Importance of Flagellar Arrangement and Insertion in the Interpretation of the Theca of Prorocentrum (Dinophyceae)

Abstract

The theca and the flagella of the marine dinoflagellate Prorocentrum minimum were studied by means of scanning and transmission electron microscopy. The relative positions of emergence of the flagella, the spatial conformation of the "transverse" flagellum and its characteristic arrangement in an anti-clockwise circle suggest new considerations on the construction of the theca of this species. A new interpretation of the theca is proposed and discussed in relation to the previous ones, considering evolutionary implications.

High-speed video observation of swimming behavior and flagellar motility ofProrocentrum minimum (Dinophyceae)

“…However, we do not consider that the possible effect in swimming behavior affects the following discussion, because the swimming speed in the present study does not differ from those of previous studies, as discussed below. The mastigonemes on the transverse flagellum of P. minimum observed by electron microscopy (Honsell and Talarico 1985) are too small to be observed by light microscopy. Hence, absence of flagellar membrane or mastigonemes on both flagella in our study must not lead to the interpretation that these flagella would not have such ultrastructures.…”

“…Then, how does each flagellum function in swimming? As reviewed by Levandowsky and Kaneta (1987) and Goldstein (1992), several studies examined the dinoflagellates' flagellar waveforms and water streaming around the cell and the flagella (Metzner 1929, Peters 1929, Brokaw and Wright 1963, Jahn et al 1963, Gaines and Taylor 1985, Honsell and Talarico 1985, Cachon et al 1992. We can assume the function of the longitudinal flagellum is the same as that in spermatozoa (Peters 1929, Maruyama 1981.…”

Functional roles of the transverse and longitudinal flagella in the swimming motility ofProrocentrum minimum(Dinophyceae)

“…Holwill and Sleigh (1967) In the present model, CN and CT are obtained from Lighthill (1976) and Holwill and Sleigh (1967), and the wavelength for each flagellum is calculated from Equations·15-20. The dimensions of the flagella and flagellar hairs were measured from electron micrographs of P. minimum in Honsell and Talarico (1985), which shows a smooth-surfaced longitudinal flagellum and a transverse flagellum with flagellar hairs. The longitudinal flagellum (LF) is regarded as smooth-surfaced with a diameter of 0.4·µm.…”

“…The diameter of the transverse flagellum and the length and diameter of a flagellar hair are assumed to be 0.2·µm, 0.8·µm and 0.06·µm, respectively. The density of the flagellar hairs on the transverse flagellum is assumed to be eight hairs per micrometer, based on the electron micrographs in Honsell and Talarico (1985). The flagellar hairs on the transverse flagellum are assumed to be arranged at even angle intervals, and one of the flagellar hairs is assumed to be oriented in the direction of the movement relative to the cell frame.…”

“…These suggestions are confirmed by observations of water movement around the organism (Jahn et al, 1963;Peters, 1929). Further electron microscopic studies (Honsell and Talarico, 1985) gave rise to hypothesizes of mechanisms how a transverse flagellum generates thrust (Gaines and Taylor, 1985;LeBlond and Taylor, 1976; for reviews, see Levandowsky and Kaneta, 1987;Sleigh, 1991;Goldstein, 1992). However, a quantitative examination of how the swimming motion and flagellar motion are linked is lacking, which makes it difficult to decide which flagellum is responsible for thrust generation during swimming.…”