The broader pole, or apex, of the valve in genera having the shape of a club. Example genera include Didymosphenia, Gomphoneis, and Gomphonema.
The internal, distal termination of the raphe in the shape of a pair of lips or a rolled tongue. The helictoglossa occurs in many raphid diatoms. If present, it can be distinguished in the light microscope in valve view by optical dissection (focusing through many narrow, optical planes). It may also be visible in girdle view as a thickened lip of silica. Plural form is helictoglossae. From Greek for rolled tongue.
A valve with poles, or apices, of the apical axis having different shapes. Heteropolar valves are asymmetrical to the transapical axis. Example genera include Gomphoneis and Gomphonema.
Frustules in which one valve differs from the other morphologically. Frustules may be heterovalvar in their valve ornamentation or their raphe system. The term is often applied to the monoraphid diatoms, in which one valve has a normal raphe valve and the other has a rapheless valve.
The single specimen used by an author to name a taxon; the type specimen; a type material recognized by the International Code of Nomenclature for algae, fungi, and plants (ICN).
The author of the taxon designates this specimen as a type according to the ICN.
The ICN uses a system called typification that makes objective identification possible by linking a name with an actual specimen. Typification is intended to create a stable system of nomenclature by tying the published name to a specimen or a suite of specimens. Note that, for diatoms, a slide may be designated as a holotype, rather than a single specimen. Although this practice is permitted within the ICN, it is not encouraged because confusion could arise later regarding the intent of the author.
Several other kinds of type material are recognized by the ICN, including isotype, lectotype, neotype and paratype. Types are not expected to be “typical” or “idealized” specimens, although workers may find such use of the terms.
A silica extension with the shape of a hood on the inside of a valve. It occurs only in some species of Planothidium where it partly covers the inside of the asymmetrical central area of the rapheless valve. See also rimmed depression.
Any area of a diatom valve that is unornamented (lacking pores or other structures).
A very delicate silica membrane covering a pore and itself perforated by smaller round or elongate pores. Found in many raphid diatoms such as the genus Cocconeis. Plural form is hymenes.