Trophogemma colantonii Ansari, Guidi, Dovgal, Balsamo & Semprucci, 2017, n. sp.

Trophogemma colantonii n. sp.

(Figs 2 a, 3a, 4, Table 1)

Diagnosis. Marine suctorian ciliate. Cell body weakly laterally flattened, gradually narrowing toward the upper end. Up to three longitudinal cuticular ribs along the body sides. Two short actinophores near the bottom of the cell body. Trophont with one apical fascicle bearing up to 25 rod-like tentacles and two fascicles on the tops of actinophores with 5–6 tentacles each. Stalk short and apically widening. Reproduction by vermigemmy.

Etymology. The species is named in honour of Professor Paolo Colantoni (University of Urbino, Italy), as a sign of gratitude for his essential contribution in the marine geology and biology of meiofauna, and in the success of the Scientific Cruises in Maldives planned by Albatros Top Boat.

Type material. Holotype and paratypes are deposited in the author’s collection at the Department of Biomolecular Sciences (DiSB), University of Urbino, Italy.

Type locality. Suvadiva Atoll of the Maldivian archipelago, 61 m depth (Station 1).

Type host. Harpacticoid copepod Stenhelia sp.

Morphological description. Marine. Cell body weakly laterally flattened and gradually narrowing toward the upper end. Trophont body size 58–64 µm × 25–30 µm. Ratio of length to width ca. 2:1 with the maximum width at the base of trophont (Fig. 4 a). Up to three longitudinal ribs of cuticle visible on both body sides. Two short actinophores located in the lateral part of the cell body and near its bottom. Trophont with rod-like tentacles (12–15 µm in length), not clavate and not contracted. Three fascicles of tentacles: one apical (19–25 tentacles) and two arising from the top of the two actinophores (5–6 tentacles each). Lateral tentacles absent. Macronucleus not visible. Stalk approximately 6–8 µm long, 3–4 µm, with apical widening and surface smooth (Figs. 2 a, 3a, 4a). Reproduction by vermigemmy (Figs. 4 b–c). Swarmer body length 25–49 µm, width 11–12 µm, stalk length 6–15 µm, thickness 1–2 µm.

Remarks. Trophogemma colantonii n. sp. (Fig. 4 a) is very similar to T. poljanskyi and T. wailesi for the gradual narrowing of the body cell toward the upper end, the presence of two actinophores near the bottom of the cell body and rod-like, not clavate, tentacles. Furthermore, tentacles were not contracted in the fixed specimens. However, the new species differs from the above cited species for the less flattened cell body, the absence of both lateral bundles of tentacles or separate lateral tentacles, and the very short stalk, long nearly one eighth of body length. Furthermore, a relevant differential character of T. colantonii n. sp. is the presence of longitudinal ribs along the body cuticle.

Host specificity and locality information. Trophogemma poljanskyi Jankowski, 1970 was recorded on the shrimps Spirontocaris arcuata Rathbun, 1902 from the Sea of Okhotsk (Kunashir Island) and Pandalus borealis Kröyer, 1838 from the Barents Sea (Murmansk) and Busse Lagoon (Sakhalin Island) (Fig. 3c). Another close species, Trophogemma wailesi (Kahl, 1934), has been recorded on the copepod Euchaeta japonica (Fig. 3b). Trophogemma colantonii n. sp. was found on a copepod of the genus Stenhelia Boeck, 1865 in the central area (St. 1) of the Suvadiva Atoll, and in particular in sandy sediments (sand: 93%, gravel: 5%, mud: 3%) at 61 m of depth.

NA—Not Available; NV—Not Visible; * - n = 3; ** —adopted from Jankowski, 1970; ***—adopted from Wailes, 1943