Talk:Conceptacle/sandbox

Conceptacles are specialised cavities of marine and freshwater algae that contain the reproductive organs. They are situated in the receptacles and open by a small ostiole. Conceptacles are present in Corallinaceae, and hildenbrandiales, as well as the brown fucales. In the Fucales there is no haploid phase in the reproductive cycle and therefore no alternation of generations. The thallus is a sporophyte. The diploid plants produce male (antheridia) and female (oogonia) gametangia by meiosis. The gametes are released into the sea, after fusion the zygote settles and begins growth.

Two taxa, the corallines and Hildenbrandiaceae, bear conceptacles, although the striking difference between their formation indicates that the conceptacles are not homologous. Similar structures also exist: cryptostomata are similar to conceptacles but differ having only hairs and are sterile. Caecostomata, are found only in Fucus distichus, in these the ostiole becomes blocked during development.

Morphology
Conceptacles can measure from 40–150 &mu;m in diameter in some Hildenbrandiales. Some conceptacles are pits within the thallus, whereas others form raised domes protruding above it. Conceptacles open to the environment via one or many pores, depending on the species and the type of conceptacle.

Components
This is a central pillar constituting central calcified cells covered by cellular debris.
 * Columella.


 * Roof filaments.

In asexual conceptacles, the spores tend to be large, and so are squeezed in, filling the conceptacle chamber "like orange segments".
 * Spores.

Types of conceptacle
There are a range of different conceptacles, classified according to the nature of the spores that they contain; some species may possess as many as four distinct types. For example, Lithophyllum incrustans bears asexual, male, female and cystocarpic (strictly, a type of female) conceptacles, discussed below.

These develop where weakly-calcified cells break down to produce a cavity. In L. incrustans, Their columella is central and obvious (see above); it is accentuated by the spores (which may be bispores, tetraspores, etc), which squeeze against the columella and conceptacle walls. Asexual conceptacles may be uniporate or multiporate.
 * Asexual conceptacles.

These lack a columella. L. incrustans has distinct male and female plants; the two conceptacle types never co-occur on the same thallus. Male conceptacles tend not to sit as deep within the thallus as female conceptacles.
 * Sexual (male / female) conceptacles.

These are not associated with tissue demineralization; rather, they start to form at the centre and develop radially.
 * Cystocarpic conceptacles.

Development
In most coralline algae, a cluster of reproductive cells forms in the middle layer of the alga, and is engulfed by the surrounding tissue, which grows up and over the reproductive cells to form a roof and a uniporate conceptacle. Caps may subsequently develop to protect the opening.

Different modes of conceptacle formation exist. In the coralline Bossiella, the conceptacle instead forms in the outer layer. A thickening forms, which separates the outer epithallium from the underlying cortex; this thickening and the overlying epithallium will end up being the cap of the conceptacle, and the underlying cells will develop to become reproductive initials. Once the cap is formed, the filamentous cells underneath begin to degrade. The tissue around the edge of the cap grows more quickly. This combination produces a chamber beneath the cap.

Evolutionary history
Conceptacles appear in the fossil record at least as early as the Silurian. Similar structures have been noted in Prototaxites, which would imply that this giant land organism was not a simple fungus (as most paleontologists assume today) but a lichen.

Further references
http://www.mbari.org/staff/conn/botany/browns/Cystoseira/lifehistory.htm