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Title: Pennales  
Author: World Heritage Encyclopedia
Language: English
Subject: Coscinodiscophyceae, Plankton, Diatom, Diatoms, Lake Mashū
Collection: Algae Orders, Biological Oceanography, Diatoms, Planktology
Publisher: World Heritage Encyclopedia


Marine diatoms
Scientific classification
Domain: Eukaryota
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Bacillariophyceae
Order: Pennales

Order Pennales is a traditional subdivision of the heterokont algae known as diatoms.[1][2] 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 linear or oval in shape, and usually bear bilaterally symmetrical 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. 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, vegetative cells are diploid and undergo mitosis during normal cell division. Periodically, meiosis produces morphologically identical haploid gametes (isogametes), which fuse to produce a (sometimes binucleate) zygote that develops into an auxospore (from which full-size vegetative cells are produced).

In some taxonomic schemes,[2] the pennate diatoms are divided into two groups: pennate diatoms without a raphe, known as araphids (Order Fragilariophyceae), and pennate diatoms with a raphe, known as raphids (Order Bacillariophyceae).

See also


  1. ^ Hoek, C. van den, Mann, D. G. and Jahns, H. M. (1995). Algae : An introduction to phycology, Cambridge University Press, UK.
  2. ^ a b Round, F. E. and Crawford, R. M. (1990). The Diatoms. Biology and Morphology of the Genera, Cambridge University Press, UK.
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