Isotype of this species is deposited in the Croatian National Diatom Collection as permanent slide under accession number HRNDC000002.
From Latin adjective “gracilis” (fine, narrow, slim, thin) referring to the general appearance and width of the cells.
Croatia: Adriatic Sea, south–eastern coast, open waters (N 42°20ʹ E 17°49ʹ). Plankton sample taken at 100 m depth, collected on March 10, 2016, by M. Mejdandžić. Holotype slide of the strain BIOTAII–60a deposited in The Friedrich Hustedt Diatom Study Centre, Bremerhaven, Germany as BRM ZU10/85. Isotype slides deposited at Macedonian diatom collection, Skopje, Macedonia under accession number 011650 MNDC and at Croatian National Diatom Collection under accession number HRNDC000002. GenBank accession numbers for BIOTAII-60 are: MF000607 (18S rRNA), MF000633 (rbcL) and MF000619 (psbC).
Cells of delicate appearance with lightly silicified frustules with one plate like plastid, twisted around apical axis: 13.2–36.0 μm long, 3.8–17.6 μm wide at constricted central part and 5.5–21.4 μm in widest part. Valves narrowly lanceolate with broad scalpeliform apices, 13.2–36.0 μm long, 2.2–10.2 μm wide. The transition from the elevated keel to the valve body creates an impression of a straight line. Virgae are straight, parallel and simple, extending through whole valve body, rarely bifurcated towards the valve margin. Valve striae 35–45 in 10 μm. Keel striae 40–52 in 10 μm. The striae are closed by a hymen with elongated rectangular perforations arranged in two parallel lines along the striae edges. Striae perforations 32–41 in 1 μm near the keel margin and 36–41 in 1 μm near the valve margin. Basal fibulae occasionally interconnected with adjacent fibulae with transverse connections in a H shape, 5–6 in 1 μm. The raphe canal is separated from the valve by raphe fibulae, 42–55 in 10 μm. Sigmoid raphe with simple and straight central and terminal endings. The cingulum is composed of one valvocopula and two to three copulae with smooth external surface. Valvocopulae and copulae straight, with transverse striae occluded by very lightly silicified hymenes with elongated elliptical to rectangular perforations, 6–8 and 31–42 in advalvar and abvalvar striae, respectively. Striae in copulae 60–70 in 10 μm, in valvocopulae 56–60 in 10 μm.
Mejdandžić, Maja; Bosak, Sunčica; Nakov, Teofil; Ruck, Elizabeth; Orlić, Sandi; Gligora Udovič, Marija; Peharec Štefanić, Petra; Špoljarić, Igor; Mršić, Gordan; Ljubešić, Zrinka (2018). Morphological diversity and phylogeny of the diatom genus Entomoneis (Bacillariophyta) in marine plankton: six new species from the Adriatic Sea // Journal of Phycology, 54, 2; 275-298. DOI:10.1111/jpy.12622.