Bütschli, 1887
Body ovoid to elongate, sometimes tailed, with thickened pellicle. Somatic ciliature commonly reduced. Adoral membranelles extensive and conspicuous, in two sections: one inside oral cavity (internal adoral membranelles), other (external adoral membranelles) on body surface encircling anterior cell pole. Stomatogenesis in pouch below surface. Mainly marine pelagic organisms, free-swimming (even when loricate); usually free-living, rarely associated with echinoids.
Suborder Strobilidiina
Family Strobilidiidae
Key to oligotrichid genera
This key covers all the well-known aloricate genera, including those so far only recorded from fresh waters. However, many of these were established as a result of splitting the genus Strombidium, which is widespread in marine habitats, suggesting that they may be recorded in marine environments in the future.
1a Adoral zone of membranelles forming closed circle in top view (Strobilidiids, Tintinnids) -> 11
1bAdoral zone of membranelles forming open circle in top view (Halteriids, Strombidiids) -> 2
2a Several rows of longitudinal somatic kineties (Halteriids) -> 3
2bSomatic kineties transversely or spirally arranged (Strombidiids) -> 5
3Somatic kineties very short, cilia very long and stiff, fused to cirri-like bristles -> 4
3bSomatic kineties distinctly longer, cilia soft, not fused to bristles: Genus Meseres (Meseres).
4aSomatic kineties without horizontal row close below each bristle complex: Halteria (Halteria).
4bSomatic kineties with additional horizontal row close below each bristle complex: Pelagohalteria (Pelagohalteria).
5aBody with elongate tail: Genus Tontonia (Tontonia).
5bBody without tail -> 6
6aCytopharynx lined with thick fibres, forming basket: Genus Cyrtostrombidium (Cyrtostrombidium).
6bCytopharynx without basket -> 7
7aWith permanent neoformation organelle -> 8
7bWithout permanent neoformation organelle -> 9
8aWith ventral kinety: Genus Limnostrombidium (Limnostrombidium).
8bWithout ventral kinety: Genus Pelagostrombidium (Pelagostrobilidium).
9a Equatorial kinety transversely arranged, not extending to posterior body pole, ventral kinety at about right angle to equatorial kinety: Genus Strombidium (Strobilidium).
9bEquatorial kinety distinctly spiralling, extending to posterior pole, ventral kinety parallel to equatorial kinety -> 10
10aEquatorial kinety with about 1 turn around body: Genus Spirostrombidium (Spirostrombidium).
10bEquatorial kinety with several turns around body: Genus Laboea (Laboea).
11aWith distinct lorica: Suborder Tintinnoinea (Tintinnids treated in separate chapter).
11bLorica lacking or indistinct -> 12
12aExternal adoral membranelles separated into outer and inner portions (sometimes with indistinct hyaline lorica): Genus Leegaardiella (Leegaardiella) (Leegaardiella 2).
12bExternal adoral membranelles not as above -> 13
13aSome somatic kineties form spiral at posterior end of body: Genus Strobilidium (Strobilidium).
13abSomatic kineties not as above -> 14
14aSomatic kineties longitudinal and transversely arched: Genus Pelagostrobilidium (Pelagostrombidium) (Pelagostrobilidium 2).
14bAll somatic kineties more or less longitudinal -> 15
15aMany (usually >10) somatic kineties extending over entire length of body: Strombidinopsis (Strombidinopsis).
15bFew short somatic kineties -> 16
16aSomatic kineties ciliated: Genus Rimostrombidium (Rimostrombidium).
16bSomatic kineties nonciliated: Genus Lohmanniella (Lohmanniella).
Note
A phylogenetic approach using morphologic and morphogenetic characters resulted in a considerably different system for aloricate oligotrichs (Petz and Foissner, 1992). As this group dominates the ciliate fraction in the marine plankton, this improved scheme is given below. Apomorphies showed that strombidiids are more closely related to tintinnids and strobilidiids than to halteriids, which makes the recently proposed order Choreotrichida Small and Lynn, 1985 superfluous. It also followed from that study that the hypotrichs should be elevated to class rank as later proposed by Tuffrau and Fleury (1994).
Outline classification
Class Oligotrichea Bütschli, 1887
Subclass Halteriia Petz and Foissner, 1992
Order Halteriida Petz and Foissner, 1992
Family Halteriidae Claparède and Lachmann, 1858
Subclass Oligotrichia Bütschli, 1887
Order Strombidiida Jankowski, 1980
Family Strombidiidae Fauré-Fremiet, 1970
Order Oligotrichida Bütschli, 1887
Suborder Strobilidiina Jankowski, 1980
Family Strobilidiidae Kahl in Doflein and Reichenow, 1929
Suborder Strombidinopsina Small and Lynn, 1985
Family Strombidinopsidae Small and Lynn, 1985
Suborder Tintinnoinea Kofoid and Campbell, 1929 (see separate chapter)