ciliate
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...
s. They typically have a prominent adoral zone of
membranelle Membranelles (also membranellae) are structures found around the mouth, or cytostome, in ciliates. They are typically arranged in series, to form an "adoral zone of membranelles," or AZM, on the left side of the buccal cavity (peristome). The membra ...
s circling the mouth, used in locomotion and feeding, and shorter cilia on the rest of the body. Many species are highly contractile, and are typically compressed or conical in form. These include some of the largest
protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
, such as ''
Stentor
In Greek mythology, Stentor (Ancient Greek: Στέντωρ; ''gen''.: Στέντορος) was a herald of the Greek forces during the Trojan War.
Mythology
Stentor is mentioned briefly in Homer's ''Iliad'' in which Hera in the guise of Stent ...
'' and ''
Spirostomum
''Spirostomum'' is a genus of ciliated protists that belongs to the class Heterotrichea. It is known for being very contractile.Fernandes, N.M.; da Silva Neto, I.D. (2013). “Morphology and 18S rDNA gene sequence of ''Spirostomum minus'' and ''S ...
'', as well as many brightly pigmented forms, such as certain ''
Blepharisma
''Blepharisma'' is a genus of unicellular ciliate protists found in fresh and salt water. The group includes about 40 accepted species, and many sub-varieties and strains. While species vary considerably in size and shape, most are easily iden ...
''.
Etymology
The term ''heterotrich'' derives from the
ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
(), meaning "another, different", and , (), meaning 'hair', because of the contrast between the regular somatic ciliation and the one of the oral zone.
Ultrastructure
A number of ultrastructural details characterize the group. The cilia on the body are in