Abstract
Oligotrichids and choreotrichids are ciliate taxa contributing to the multi-step microbial food web and episodically dominating the marine microzooplankton. The global diversity and distribution of aloricate Oligotrichea are unknown. Here, the geographic ranges of the 141 accepted species and their synonyms in marine and brackish sea water are analyzed, using hundreds of taxonomical and ecological studies; the quality of the records is simultaneously evaluated. The aloricate Oligotrichea match the moderate endemicity model, i.e., the majority (94) of morphospecies has a wide, occasionally cosmopolitan distribution, while 47 morphospecies show biogeographic patterns: they are restricted to single geographic regions and probably include 12 endemic morphospecies. These endemics are found in the Antarctic, North Pacific, and Black Sea, whereas the “flagship” species Strombidinopsis cercionis is confined to the Caribbean Sea. Concerning genera, again several geographic patterns are recognizable. The species richness is distinctly lower in the southern hemisphere than in the northern, ranging from nine morphospecies in the South Pacific to 95 in the North Atlantic; however, this pattern is probably caused by undersampling. Since the loss of species might affect higher trophical levels substantially, the aloricate Oligotrichea should not any longer be ignored in conservation issues. The ecophysiological diversity is considerably larger than the morphological, and even tops the richness of SSrRNA and ITS haplotypes, indicating that probably more than 83–89% of the diversity in aloricate Oligotrichea are unknown. The huge challenge to discover all these species can only be managed by combining the expertises of morphological taxonomists, molecular biologists, ecologists, and physiologists.
Highlights
History of Discovery Based on morphologic and ontogenetic features, the Oligotrichea Butschli, 1887 unite the halteriids, oligotrichids, and choreotrichids
The majority of aloricate Oligotrichea (94 morphospecies) has a wide, occasionally cosmopolitan distribution, while 47 morphospecies are restricted to single geographic regions and include, conservatively estimated, 12 endemic morphospecies
The choreotrichid Leegaardiella elbraechteri and the oligotrichids Spirostrombidium echini, Strombidium glaciale, S. kryale, S. syowaense nom. corr., and Tontonia antarctica were only found in the Antarctic Sea
Summary
History of Discovery Based on morphologic and ontogenetic features, the Oligotrichea Butschli, 1887 unite the halteriids, oligotrichids, and choreotrichids (see ‘Classification and phylogeny’ and Table 1 for scientific and vernacular names). While the former two taxa contain exclusively aloricate (naked) species, the choreotrichids embrace naked species and the loricate (house-forming) tintinnids, which are not considered in the present compilation. In 1773, Muller described the first halteriid, viz., the freshwater species Trichoda grandinella [4], which was affiliated with the genus Halteria by Dujardin [5] In their revisions, Kent listed 21 species [6], Awerinzew 10 species [7], and Kahl 84 species [8,9], while the most recent monographs published in 1985 and 1986 [10,11] considered 127 species of aloricate Oligotrichea. Species descriptions do comprise information from live observation, silver impregnation, and scanning electron microscopy, but often sequence data of the small subunit ribosomal RNA gene (SSrRNA)
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