Didinium gargantua Meunier 1910

Mainly heterotrophic flagellates, dinoflagellates, cryptophytes, chlorophytes (cell diameter 510 µm); can ingest cells of equal size or larger

Cell broadly ellipsoidal, posterior widely rounded; Lugol?s fixed cells are occasionally globular, 70 (40-200) µm long and 50 (30-120) µm wide; anterior end truncated, with a distinct conical protrusion (= proboscis), occupying 15-25% of the body length (Fig 1,2,5); extrusomes scattered throughout cell, toxicysts are located between the nematodesmata (Fig 1).; Cytostome on the apical end of the proboscis; nematodesmata reach deep into the cell (Fig 1); cytostome flexible, ciliate can ingest prey larger than its own size.; 45 (50-75) equally spaced somatic kineties, only partly ciliated, forming anterior and posterior ciliary bands (ACB, PCB, wreath of pectinelles: about 15 kinetosomes per row; Fig 1,2,5) inclined to the body axis (Fig 1,5); cilia ~16 µm long; two dorsal brosses, one underneath each ciliary band (Fig 1), consist of 2-4 rows of dikinetids (characteristic for the different populations studied, however, not seen in Lugol?s fixed material).; One macronucleus, kidney-shaped to C-shaped, near the center of the body located (Fig 1,2).

Cell ellipsoidal, anterior end truncate with distinct conical protrusion (proboscis); two ciliary bands (anterior - ACB and posterior - PCB), two dorsal brosses, one underneath each ciliary band; one macronucleus, kidney-shaped to C-shaped

Temperature: 8-18 ºC (-2 ºC from sea ice) ; Salinity: 12-34 ? (41 ? from sea ice)

Didinium gargantua was originally described from the Arctic Sea (Meunier 1910) and recently redescribed from Antarctic sea ice (Petz, Song & Wilbert 1995). Most records from marine and brackish waters refer to this species. However, differences in the infraciliature between polar and North Sea populations suggest that at least three marine species of Didinium exist. Since protargol staining is neccessary to reveal the species specific features, we only refer to D. gargantua. A detail taxonomic study on Didinium from the Arctic type location is required, before further taxonomical steps are taken. These taxonomical problems should be recognised, when interpreting ecological data.

Rotates about main body axis.