Cochliopodium, Van Wichelen & D’Hondt & Claeys & Vyverman & Berney & Bass & Vanormelingen, 2016

Van Wichelen, Jeroen, D’Hondt, Sofie, Claeys, Myriam, Vyverman, Wim, Berney, Cédric, Bass, David & Vanormelingen, Pieter, 2016, A Hotspot of Amoebae Diversity: 8 New Naked Amoebae Associated with the Planktonic Bloom-forming Cyanobacterium Microcystis, Acta Protozoologica 55 (2), pp. 61-87 : 74-76

Cochliopodium

The lens-shaped strain A1 HEB was placed in the monophyletic genus Cochliopodium ( Fig. 7A), but the 18S rDNA sequence differed from other representatives of the genus by no less than 19.7–23.5% (143–301 bp).

Locomotive amoebae of strain A1 HEB were round, oval or triangular (with the base directed anteriorly), had a length of 15–40 µm (mean 26 µm), a width of 15–54 µm (30) and a L/W ratio 0.7–1.2 (0.9) ( Fig. 7B). The central mass of granuloplasm was always entirely surrounded by a hyaline sheet that covered 12–40% (23) of the body length and was often much narrower posteriorly (e.g. Figs 7B 3, 5). Locomotive amoebae contained 1–14 pointed subpseudopodia of maximally 10 µm long, that were never furcated and mostly situat- ed at the lateral and anterior hyaloplasmic margin ( Figs 7B 1–4). Uroidal structures were rarely visible posteriorly, either consisting of one to a few trailing adhesive filaments of maximally 10 µm long ( Figs 7B 4, 5) or rarely plicate with a length of maximal 13 µm ( Figs 7B 8, 9). The slightly ovoid vesicular nucleus was 3–5 µm in diameter and contained one globular nucleolus of 1–2 µm. Only one, centrally located contractile vacu- ole was visible in each trophozoite. The granuloplasm contained many, 1–2 µm long, opaque granules and up to 20 irregular, sometimes plate-like shaped crystals of 1–6 µm long. With bright field illumination easily visible micro-scales were about 0.9 µm long and 0.6 µm wide. These entirely covered the tectum, forming a regular punctuation of the hyaloplasm up to the cell’s margin ( Fig.7B 8). The trophozoites could also adopt a globular to ovoid bell-shaped form that had a length of 8–30 µm (13) and a width of 8–22 µm (11). These were predominantly seen attached when feeding on Microcystis colonies ( Fig. 7B 11). The clear peripheral hyaloplasmic sheet around the cell was then completely retracted with the exception of a small zone posteriorly where the hyaloplasm was clearly folded towards the substratum (for instance a Microcystis cell). When a potential food item was detected, this fringe of folded hyaloplasm did produce some small hyaline subpseudopodia that started surrounding the object of interest ( Figs 7B 6, 7). Under a coverslip, this bell-shaped form could swiftly transform into a locomotive form with the re-formation of the peripheral hyaloplasmic sheet. The posterior fringe of folded hyaloplasm was then still visible for a while when it slowly retracted ( Figs 7B 8, 9). Floating amoebae were globular to ovoid with a diameter of 8–20 µm (13), containing 2–8 long thin pseu- dopodia of maximal 36 µm long ( Fig. 7B 12, 13). No cyst stage was observed. Although this strain initially grew well with Microcystis offered as food it suddenly died after several weeks. Due to this early loss, no TEM analysis could be carried out to retrieve detailed information on the scale structure.

Around 20 mainly morphologically defined Cochliopodium species currently exist ( Geisen et al. 2014), 8 isolated from freshwater, 2 from fresh to brackish water, 3 from brackish, 4 from marine and 3 from terrestrial habitats. Of the 3 freshwater strains without molecular data, C. minutum was assigned a nomen dubium ( Kudryavtsev 2006), C. vestitum is more than twice as large (L: 39–70 µm, mean 59; W: 48–74, mean 65) and has with LM clearly visible spines on the scales ( Kudryavtsev 2005) and C. granulatum ( Penard 1902) , apart from also being much larger (generally> 50 µm), has many large subpseudopodia during locomotion and seems to preferably graze on diatoms. C. minutoidum , isolated from terrestrial habitats ( Kudryavtsev 2006), is only half as large (L: 8–20 µm (mean 14), W: 9–24 (17)). Given the molecular difference, the absence of the above-mentioned morphological features ( Fig. 7B) and its specific ecology, our Microcystis -associated strain is undoubtedly a new species of Cochliopodium . However, since we lacked detailed information on the scale structure, we opted not to give this taxon an official name.