Tintinnoinea
Classification scheme based on morphologically similar groups of species

South Atlantic species are arranged below in 4 groups according to characteristics that can be easily distinguished by standard microscope observation. However, some genera and species (Helicostomella, Metacylis and a few species of Dictyocysta and Eutintinnus) are included in groups whose diagnostic features may only occasionally (or never) coincide with those of the taxa. For instance, Helicostomella has never been reported as having an agglutinated lorica, but since all other genera with a well-differentiated spiralled collar and a bowl fall smoothly into the "agglutinated lorica group", it was found reasonable to include it there as well. Moreover, such exceptions are applicable at infraspecific levels as well: Laackmanniella naviculaefera includes 3 different morphotypes (or formae): forma coxliella and forma prolongata have a hyaline lorica, while forma naviculaefera can be densely covered by biogenic particles (Alder, 1995). The "genus" Coxliella furnishes another vivid example of difficulties with tintinnid systematics: several culture- and plankton sample-based studies (Laval-Peuto, 1981; Williams et al., 1994; Alder, 1995) have demonstrated that at least some of the species described in this genus are but transitional forms of various species belonging to several genera.

Group 1. Species with agglutinated biogenic or arenaceous particles on their lorica

—Subgroup 1A.
Features of lorica obscured by densely agglutinated, evenly distributed particles:
Genus Codonella
Genus Codonaria
Genus Tintinnidium
Genus Poroecus
Genus Stylicauda
Genus Tintinnopsis (Tintinnopsis complex)

—Subgroup 1B.
Lorica with clearly differentiated bowl and collar. Usually with agglutinated (biogenic and/or arenaceous) particles, located almost exclusively on bowl:
Genus Laackmanniella
Genus Codonellopsis
Genus Stenosemella
Genus Helicostomella
Genus Metacylis (never with agglutinated particles)

Group 2. Lorica fenestrated

—Subgroup 2A.
Conspicuous fenestrae on bowl and collar; very exceptionally with agglutinated (biogenic) particles:
Genus Dictyocysta

—Subgroup 2B.
One or two rows of small, inconspicuous fenestrae located on precollar and in middle of bowl; lorica without agglutinated particles:
Genus Petalotricha

Group 3. Lorica covered by an atypical gelatinous external coating

Genus Brandtiella

Group 4. Hyaline lorica

—Subgroup 4A.
Lorica wall usually with few longitudinal fins:
Genus Stelidiella
Genus Amphorellopsis
Genus Ormosella
Genus Amphorides
Genus Steenstrupiella

—Subgroup 4B.
Lorica open at both ends:
Genus Salpingella
Genus Eutintinnus (very rarely with few scattered particles on lorica)
Genus Clevea?
Genus Daturella

—Subgroup 4C.
Species with differentiations at oral end (inner and outer collar, oral band or denticles):
Genus Acanthostomella
Genus Ascampbelliella
Genus Favella
Genus Cymatocylis

—Subgroup 4D.
Lorica wall translucid, generally with two conspicuous laminae:
Genus Undella
Genus Amplectella
Genus Undellopsis
Genus Parundella
Genus Albatrossiella?

—Subgroup 4E.
Lorica wall conspicuous, few to many vertical, simple (dextrogyrous, levogyrous or both), branched, or anastomosed ribs:
Genus Rhabdonella
Genus Protorhabdonella?

—Subgroup 4F.
Lorica wall usually with conspicuous, anastomosed reticulum on posterior half:
Genus Epiplocylis
Genus Epiplocyloides
Genus Epicancella
Genus Cyttarocylis

—Subgroup 4G.
Lorica wall with regular, hexagonal prismatic alveoli:
Genus Climacocylis
Genus Xystonella
Genus Xystonellopsis

Miscellaneous (ungrouped)

Genus Dadayiella.