The Coscinodiscophyceae are a class of
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s.
They are similar to the Centrales, a traditional,
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
subdivision of the
heterokont algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
known as
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s.
The order is named for the shape of the
cell walls
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...
(or valves or frustules) of centric diatoms, which are circular or ellipsoid in valve view. The valves often bear
radially symmetrical ornamental patterns that can appear as dots when viewed with an
optical microscope. Some also bear spines on their valves, which may either increase cell surface area and reduce sinking, or act as a deterrent to
zooplankton grazers. Unlike pennate diatoms, centric diatoms never have a raphe.
In terms of
cell cycle,
vegetative
Vegetative describes vegetation. Vegetative may also refer to:
*Vegetative reproduction
Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in ...
cells are
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
and undergo
mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...
during normal
cell division. In sexual species,
oogamous meiosis produces
haploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
gametes, either
ova or
sperm cell
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...
s. These fuse to produce a
zygote which expands in size to develop into an
auxospore
In certain species of diatoms, auxospores are specialised cells that are produced at key stages in their cell cycle or life history. Auxospores typically play a role in growth processes, sexual reproduction or dormancy.Hoek, C. van den, Mann, D ...
from which full-sized vegetative cells are produced.
In some
taxonomy schemes,
[ the centric diatoms are known instead as order Coscinodiscophyceae, and in some schemes as order Biddulphiales.][
]
See also
* Pennales
The order Pennales is a traditional subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of pennate diatoms, which are elongated in valve view. The valves may be lin ...
References
Further reading
External links
{{Taxonbar, from=Q2698449
Heterokont classes