The order Pennales is a traditional subdivision of the

heterokont The stramenopiles, also called heterokonts, are protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, an ...

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

known as

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

s. The order is named for the shape of the

cell walls A cell wall is a structural layer that surrounds some cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, and functi ...

(or valves or frustules) of pennate diatoms, which are elongated in valve view. The valves may be linear or oval in shape, and usually bear

bilaterally symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symme ...

ornamental patterns. These patterns are composed of a series of transverse lines (known as striae) that can appear as rows of dots when viewed with an

optical microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of micros ...

. Some pennate diatoms also exhibit a fissure along their longitudinal axis. This is known as a raphe, and is involved in gliding movements made by diatom cells; motile diatoms always possess a raphe. In terms of

cell cycle The cell cycle, or cell-division cycle, is the sequential series of events that take place in a cell (biology), cell that causes it to divide into two daughter cells. These events include the growth of the cell, duplication of its DNA (DNA re ...

, vegetative 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. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

and undergo

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

during normal

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

. Periodically,

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

produces morphologically identical

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s (isogametes), which fuse to produce a (sometimes

binucleate Binucleated cells are cells that contain two nuclei. This type of cell is most commonly found in cancer cells and may arise from a variety of causes. Binucleation can be easily visualized through staining and microscopy. In general, binucleati ...

)

zygote A zygote (; , ) is a eukaryote, eukaryotic cell (biology), cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individ ...

that develops into an

auxospore Auxospores are specialised cells in diatoms 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. G. and Jahns, H. M. ...

(from which full-sized vegetative cells are produced). In some

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

schemes, the pennate diatoms are divided into two groups: pennate diatoms without a

raphe Raphe ( ; from ;Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press. : raphae or raphes) has several differe ...

(a seam or ridge), known as araphids (order

Fragilariophyceae Fragilariales is a group of pennate diatoms lacking a raphe. Examples It includes the following genera: Fragilariales *'' Ardissonea'' *'' Asterionella'' *'' Asterionellopsis'' *'' Catacombas'' *'' Diatoma'' *'' Fragilaria'' *'' Fragilariforma ...

), and pennate diatoms with a raphe, known as raphids (order

Bacillariophyceae Bacillariophyceae is a class of diatoms. Previously, this class was equivalent to Diatomeae, the taxonomic name for all diatoms. However, due to both the known and estimated diversity of diatoms, since 2019 they have been expanded to several class ...

). File:Fragilariopsis kerguelensis.jpg, Pennate diatom without a raphe ''(

Fragilariopsis kerguelensis ''Fragilariopsis kerguelensis'', is a pennales, pennate diatom native to the Southern Ocean. It has been characterized as "the most abundant diatom in the Southern Ocean, Antarctic Seas". Description ''Fragilariopsis kerguelensis'' is a unicellu ...

)'' File:Lyrella hennedy 1600x contrast invertion.jpg, Pennate diatom with a raphe ''(Lyrella hennedy)''

References

{{Authority control Algae orders Biological oceanography Obsolete eukaryote taxa Planktology Diatoms

See also

References