Global diversity of aloricate Oligotrichea (Protista, Ciliophora, Spirotricha) in marine and brackish sea water

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.

Figure 1. Rate of discovery.

The published descriptions of new halteriid, oligotrichid, and aloricate choreotrichid species (including synonyms, nomina dubia, and nomina oblita) per year.

Figure 2. Morphology of main groups.

Generalized ventral (a–c, f), dorsal (d, e), top (g), and posterior polar (h) views after protargol impregnation (a, after ; b, d, f, originals; c, e, after ; g, h, after [192]). a, b: The halteriid genera Meseres and Pelagohalteria. c: The oligotrichid genus Strombidium. d–h: The choreotrichid genera Strombidinopsis (d), Rimostrombidium (e), Lohmanniella (f), and Leegaardiella (g, h). B – bristle kineties, BM – buccal membranelles, CM – collar membranelles, E – endoral membrane, GK – girdle kinety, ICM – inner portion of collar membranelles, OCM – outer portion of collar membranelles, P – paroral membrane, SK – somatic kineties, VK – ventral kinety.

Figure 3. Global distribution of genera.

Red colour marks the presumptive range in marine and brackish sea water (Table S1). Note that the distribution in freshwater and saline inland waters is not considered. a: Apostrombidium, Lynnella, Opisthostrombidium, and Parastrombidinopsis. b: Cyrtostrombidium. c: Foissneridium. d: Laboea. e: Leegaardiella. f: Lohmanniella and Rimostrombidium.

Figure 4. Global distribution of genera.

Red colour marks the presumptive range in marine and brackish sea water (Table S1). Note that the distribution in freshwater and saline inland waters is not considered. a: Meseres. b: Novistrombidium. c: Omegastrombidium. d: Parallelostrombidium. e: Parastrombidium. f: Paratontonia and Strombidium.

Figure 5. Global distribution of genera.

Red colour marks the presumptive range in marine and brackish sea water (Table S1). Note that the distribution in freshwater and saline inland waters is not considered. a: Pelagohalteria. b: Pelagostrobilidium. c: Pseudotontonia. d: Spirostrombidium. e: Spirotontonia. f: Strombidinopsis. g: Tontonia. h: Varistrombidium.