Holotrich
Encyclopedia
Holotricha is an order of ciliate
protists. The classification has fallen from use as a formal taxon
, but the terms "holotrich" and "holotrichous" are still applied descriptively to organisms with cilia of uniform length distributed evenly over the surface of the body.
The order Holotricha was erected in 1859 by Friedrich Stein
, who developed a system of classification in which ciliates were categorized according to the type and distribution of their cilia. The four major subdivisions of Stein's Ciliata were: Heterotricha, Peritricha, Hypotricha and Holotricha. The latter was reserved for organisms with cilia covering the entire surface of the body. The order included five families, within which a very diverse collection of genera
were grouped. Among the better-known ciliates in Stein's Holotricha were Coleps
, Nassula
, Lacrymaria
, Loxodes, Colpoda
, Glaucoma
and Paramecium
.
Stein's scheme was amended in 1889 by Otto Bütschli
, who divided the Ciliata into two orders: Holotricha and Spirotrich
a. Bütschli's Holotricha were described much as Stein's had been, as ciliates with relatively uniform somatic cilia. The other three orders of Stein's Ciliata were placed in a lower rank under the new order Spirotricha: ciliates possessing a well-developed structure of spiralling membranelle
s around the oral cavity.
Versions of Bütschli's two-order scheme were used by taxonomists throughout the first half of the twentieth century, although many adjustments were made to the arrangement of families and genera within those groups. Meanwhile, improved laboratory methods and the advent of the electron microscope began to reveal inadequacies in the old scheme; and, as inconsistencies accumulated, dissatisfaction with the system grew. Nonetheless, Holotricha remained in use as a high-level taxon until 1974, when John Corliss proposed a complete revision of the phylum Ciliophora. In his system, Spirotricha is retained as an order, under the class Polyhymenophora, but Holotricha does not appear at any rank. Recent systems of classification, including an influential scheme proposed by Pierre de Puytorac in 1994, and Denis Lynn's revision of 2002, make no mention of Holotricha.
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...
protists. The classification has fallen from use as a formal taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
, but the terms "holotrich" and "holotrichous" are still applied descriptively to organisms with cilia of uniform length distributed evenly over the surface of the body.
The order Holotricha was erected in 1859 by Friedrich Stein
Samuel Friedrich Stein
Samuel Friedrich Nathaniel Ritter von Stein was a German entomologist chiefly interested in Diptera.Born in Niemegk near Potsdam, Brandenburg, in 1850, Stein became a Professor at the Forest and Agriculture Institute in Tharandt in Sachsen , 20 km south-west of Dresden. This was one of the...
, who developed a system of classification in which ciliates were categorized according to the type and distribution of their cilia. The four major subdivisions of Stein's Ciliata were: Heterotricha, Peritricha, Hypotricha and Holotricha. The latter was reserved for organisms with cilia covering the entire surface of the body. The order included five families, within which a very diverse collection of genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
were grouped. Among the better-known ciliates in Stein's Holotricha were Coleps
Coleps
It is a cell.Coleps is a genus of ciliated Prostomatea with barrel-shaped bodies. The can grow up to 250 micrometers in length, but are usually under 100 micrometers in their longest axis. Coleps can be taxonomically distinguished by the ornamentation of their ectoplasmic calcium carbonate...
, Nassula
Nassula
Nassula is a genus of unicellular ciliate protists, belonging to the class Nassophorea. Like other members of the class, Nassula possesses a basket-like feeding apparatus made up of cytopharyngeal rods , which are themselves composed of closely packed microtubules...
, Lacrymaria
Lacrymaria
Lacrymaria is a genus of fungi in the family Psathyrellaceae. There are 14 species in the genus, with a widespread distribution.-Species:*Lacrymaria asperospora Watling *Lacrymaria atricha Kits van Wav....
, Loxodes, Colpoda
Colpoda
right|thumb|250px|Typical large colpoda @ 400Xright|thumb|250px|Measurements of large colpoda in micrometresColpoda is a genus of ciliate in the class Colpodea Order Colpodida Family Colpodidae.- Description :...
, Glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...
and Paramecium
Paramecium
Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 0.05 to 0.35 mm in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion at speeds of approximately 12 body...
.
Stein's scheme was amended in 1889 by Otto Bütschli
Otto Bütschli
Johann Adam Otto Bütschli was a German zoologist and professor at the University of Heidelberg. He specialized in invertebrates and insect development...
, who divided the Ciliata into two orders: Holotricha and Spirotrich
Spirotrich
The spirotrichs are a large and distinctive group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down to the left side of the mouth. There may also be...
a. Bütschli's Holotricha were described much as Stein's had been, as ciliates with relatively uniform somatic cilia. The other three orders of Stein's Ciliata were placed in a lower rank under the new order Spirotricha: ciliates possessing a well-developed structure of spiralling membranelle
Membranelle
Membranelles are structures found around the mouth, or cytostome, in ciliate protists. They are typically arranged in series, to form an "adoral zone of membranelles," or AZM, on the left side of the buccal cavity . The membranelles are made up of kinetosomes arranged in groups to make up...
s around the oral cavity.
Versions of Bütschli's two-order scheme were used by taxonomists throughout the first half of the twentieth century, although many adjustments were made to the arrangement of families and genera within those groups. Meanwhile, improved laboratory methods and the advent of the electron microscope began to reveal inadequacies in the old scheme; and, as inconsistencies accumulated, dissatisfaction with the system grew. Nonetheless, Holotricha remained in use as a high-level taxon until 1974, when John Corliss proposed a complete revision of the phylum Ciliophora. In his system, Spirotricha is retained as an order, under the class Polyhymenophora, but Holotricha does not appear at any rank. Recent systems of classification, including an influential scheme proposed by Pierre de Puytorac in 1994, and Denis Lynn's revision of 2002, make no mention of Holotricha.