The individuals are uni- or multicellular, free-swimming or motionless.
The cells (which in the multicellular forms are loosely connected
together, often only by mucilaginous envelopes) are naked or surrounded
by a mucilaginous cell-wall, in which silica is never embedded. They
contain one cell-nucleus, one or more pulsating vacuoles, and one to
two band- or plate-like chromatophores with a brown or yellow colour,
and sometimes a pyrenoid.
Reproduction takes place by vegetative division, or asexually by
zoospores, akinetes (or aplanospores?). Sexual reproduction is unknown.
They are all fresh water forms.
To this class may perhaps be assigned the recently arranged and
very little known orders of _Calcocytaceæ_, _Murracytaceæ_,
_Xanthellaceæ_, and _Dictyochaceæ_, which partly occur in the
free condition in the sea, in the so-called “Plankton,” and
partly symbiotic in various lower marine animals.
The _Syngeneticæ_ are closely related to certain forms in the
animal kingdom, as the Flagellatæ.
Order 1. =Chrysomonadinaceæ.= Individuals, uni- or multicellular,
swimming in free condition, naked or surrounded by a mucilaginous
covering. The cells are generally oval or elongated, with 2 (rarely
only 1) cilia, almost of the same length, and generally with a red
“eye-spot” at their base, and with 2 (rarely 1 only) band-shaped
chromatophores. Reproduction by the longitudinal division of the
individual cells either during the swarming, or during a resting stage;
in the multicellular forms also by the liberation of one or more cells,
which in the latter case are connected together.
A. Unicellular: _Chromulina_, _Cryptoglena_, _Microglena_,
_Nephroselmis_.
B. Multicellular: _Uroglena_, _Syncrypta_ (Fig. 11), _Synura_.
[Illustration: FIG. 11.--_Syncrypta volvox_: the multicellular
individual is surrounded by a mucilaginous granular envelope.]
Among the unicellular Chrysomonadinaceæ are probably classed
some forms which are only stages in the development of the
multicellular, or of other _Syngeneticæ_.
Order 2. =Chrysopyxaceæ= are unicellular, and differ mainly
from the preceding in being attached either on a slime-thread
(_Stylochrysalis_), or enclosed in an envelope (_Chrysopyxis_,
Fig. 12). They have two cilia, and multiply by longitudinal
(_Chrysopyxis_) or transverse division, and the swarming of one of the
daughter-individuals (zoospore). Division may also take place in a
motionless stage (_palmella-stage_).
[Illustration: FIG. 12.--_Chrsopyxis bipes_: _m_ envelope, _Ec_
chromatophore, _cv_ contractile vacuole.]
Order 3. =Dinobryinaceæ.= The individuals are originally attached,
uni- or multicellular; each individual cell is distinctly contractile,
and fixed at the bottom of a cup-shaped, open envelope. Cilia 2, but
of unequal length. Asexual reproduction by zoospores, which are formed
by straight or oblique longitudinal division of the mother-cell,
during a palmella-stage which is produced in the winter aplanospores.
_Epipyxis_, _Dinobryon_.
Order 4. =Hydruraceæ.= The individuals are attached, without cilia,
multicellular, branched, and with apical growth. The cells are
spherical, but in the final stage almost spindle-shaped, and embedded
in large masses of mucilage. Asexual reproduction by zoospores which
are tetrahedric, with 1 cilia, and by resting akinetes. _Hydrurus_ is
most common in mountain brooks.