PHYCOLOGICAL SOCIETY OF AMERICA
Antithamnion defectum has a typical three
stage red-algal life history. The three stages are the tetrasporophyte
which is diploid, the dioecious gametophyte
stage which is haploid, and the carposporophyte stage which is
diploid and grows on the female gametophyte as can be seen in the
cartoon above. Therefore, the sporophyte and gametophyte are isomorphic,
meaning they appear identical except for their reproductive structures.
diploid tetrasporophyte undergoes meiosis creating tetraspores,
which are oval shaped, red, cruciately divided and pedicellate,
which can be seen in the picture to the right. Released spores
settle and grow into haploid male and female gametophytes. Male
gametophytes have unpigmented spermatangia which grow from the
adaxial side of the inner cells of branchlets as seen in the picture.
The three pictures below are actually of spermatia on A. dendroidem,
but they would look similar in A. defectum. One study
investigating the spermatangial development in Antithamnion found
that spermatangial vesicles within the spermatia (something common
in red algae) may be responsible for making spermatial attachments.
Spermatial attachments are long, thin filaments which aid in the
binding of the spermatia to the trichogyne by extending the surface
area of the spermatia and by having ligands which preferentially
bind to particular carbohydrate receptors on the trichogyne. 
female gametophyte has 4-celled carpogonial branches which grow from
the basal cells of apical branches. The picture shows a typical apical
section of A. defectum, although no carpogonial branches
are present. Syngamy is oogamous,
as the non-swimming (flagella-lacking) spermatia attaches to the trichogyne of
the procarp. Only one carposporophyte develops
per carpogonial branch. After fertilization, the auxiliary
cell is cut off from the supporting cell.
The auxiliary cell divides to form a lower foot cell and an upper gonimoblast
cell which eventually forms the carposporophyte. The carposporophyte
is diploid, and develops on the female gametophyte until the diploid
spores are released. These spores grow into tetrasporophytes, and
the cycle begins again!  The
two drawings below show a carpogonial branch pre-fertilization and
a carposporophyte growing on the female gametophyte.
- This cycle can happen relatively quickly in laboratory conditions,
on the order of a few months, but could take longer in
to wave conditions, availability of space to settle, and difficulty
for the male spermatia to find the trichogyne of the female procarps.
Read more about the timing of the life-cycle on the growth-experiment page.
From my findings and looking through the Gilbert M. Smith Herbarium,
it seems that all life stages of Antithamnion could be found at any
time of year.
Antithamnion Home | Taxonomy | Distribution/Ecology | Morphology | Life
Growth Experiment |Photo
Gallery | Terms
References and Acknowledgements
© 2005 Charlotte Stevenson