Chromera
Alveolata: Chromerida (ref. ID; 7120)
- Chromera velia (ref. ID; 7120)
Descriptions
An autotrophic protist. Surface and flagella morphology of the motile form of Ch. velia revealed by field-emission scanning electron microscopy. (ref. ID; 7120)
Notes
The life cycle of Ch. velia consists of two main stages: flagellated cells and round, multiplying non-motile cells. Although Moore et al. (2008) noted that the flagellated cells were observed in senescent cultures and were very short lived, rapidly transforming back into the spherical non-motile form, we observed the flagellated stage to predominantly occur in freshly transferred cultures and to remain in that form for several hours before reverting to a spherical state. We have proved correct the hypothesis that Ch. velia is biflagellated and resembles a colpodellid (Moore et al. 2008; Obornik et al. 2009). The flagellated form of Ch. velia was found to be very similar in morphological appearance to the colpodellid Colpodella edax, formerly Alphamonas edax (Cavalier-Smith & Chao 2004; Leander et al. 2003). Both have a similar cell body shape with two flagella of approximately same thickness. They posses one short anterior and one long posterior flagellum. In common with colpodellids and perkinsids, Ch. velia flagella tapers to a narrow distal end and posses mastigonemes on their surface. However, there are also several notable differences between Ch. velia and Co. edax. First, the size of the motile form of Ch. velia is smaller than Co. edax (approximately 4 um vs 6 um, respectively). Second, the ventral side of the flagellated forms of Ch. velia possesses grooves for the flagella and an interiorly prominent rising ridge, while the motile form of Co. edax possesses a flattened ventral side. The flagellar grooves of Ch. velia are suggested to function in directing movement of both flagella. Third, the anterior flagellum of Ch. velia possesses a short vermiform appendage that is not seen on Co. edax flagella. This is similar to flagellar swellings seen on some heterokont zoospores, for example the zoospore of Vischeria stellata, which are suggested to play a role in photoreception (Santos & Leedale 1991). Finally, Ch. velia possesses a flap covering the anterior flagella insertion point and directed towards the anterior raised end of the ridge. This may work in a coordinated action with the appendage on the anterior flagellum to fulfil a sensory function or to limit the direction of flagellar movement.
It is not yet known if Ch. velia has photoreceptory equipment, however our study revealed the presence of a flagellar swelling, a curved anterior flagellar appendage and an anterior flap. These resemble surface features known to be present in heterokont algae where a photoreceptor is present (Anderson 1985, 2004; Kreimer 1994). The unique heterokont photoreceptor system consists of a flagellar swelling located at the base of the anterior-directed flagellum in association with an extraplastidal non-membrane bound eyespot or intraplastidial eyespot. Photoreception and phototaxis have major implications in the ecology and survival of phototrophic microbial eukaryotes and have evolved in several protist groups (Kreimer 1994). Within the alveolates, one group of marine dinoflagellates possesses the 'ocelloid' -one of the most remarkable photoreception apparatuses known, consisting of a cornea, iris, lens and retina (Gomez et al. 2009; Hoppenrath et al. 2009). (ref. ID; 7120)