- A small and hard to find group.
- Originally discovered in cultures of tropical green algae
- Also probably live among grains of sand
- Net like mass of amoeboid cells form a reticulate plasmodium
- Have green secondary plastids, with a nucleomorph and CER
- Structure & metabolism
- Amoeboid cells, interconnected by filopodia
- Can produce ovoid zoospores
- Single subapical flagellum, with very delicate hairs
- Spirals backward around cell
- No eyespot
- Trichocysts are present
- Chloroplast is secondary, with a CER and nucleomorph
- Green algal origin of plastid was inferred from pigmentation
- Chlrophylls a and b, and probably carotenoids
- This has been confirmed by molecular systematic studies of both chloroplast
and nuclear genome
- A prominent stalked pyrenoid, reserve polysaccharide (located outside
of the entire chloroplast), and nucleomorph all lie in a very close
- Ultrastructural studies by Sarah Gibbs et al. demonstrated plastid
ultrastructure, identified nucleomorph, and suggested secondary origin
- Recently, Geoff McFadden has been studying the nucleomorph genome
- Very small, highly compacted eukaryotic genome
- Even the introns have been reduced in size (but not eliminated)
- A sexual cycle has been reported, but has not been studied in detail.
- Four genera and six species, with several undescribed species known
- Chlorarachnion reptans has been best studied
- Cryptochlora perforans invades dead algal filaments
- Found in warmer marine waters worldwide
- Mixotrophic, capturing bacteria, flagellates, and eukaryotic algae.
- Economic Importance
- Of great evolutionary and biological importance, but of no direct economic
Required Reading: VdH: Chapter 18
Gilson, P.R., and G.I. McFadden. 1996. The miniaturized nuclear genome of a
eukaryotic endosymbiont contains genes that overlap, genes that are cotranscribed,
and the smallest known spiceosomal introns. Proc. Natl. Acad. Sci. USA
Ludwig, M., and S.P. Gibbs. 1989. Evidence that the nucleomorphs of Chlorarachnion
reptans (Chlorarachniophyceae) are vestigial nuclei: morphology, division,
and DNA-DAPI fluorescence. J. Phycol. 25:385-394.
McFadden, G.I., P.R. Gilson, and C.J.B. Hoffmann. 1997. Division Chlorarchniophyta.
Pl. Syst. Evol. [Suppl.] 11:175-185.
Van de Peer, Y., S.A. Rensing, U.-G. Maier, and R. De Wachter. 1996. Substitution
rate calibration of small subunit RNA identifies chlorarachniophyte endosymbionts
as remnants of green algae. Proc. Natl. Acad. Sci. USA 93:4467- .