Isotype of this species is deposited in the Croatian National Diatom Collection as permanent slide under accession number HRNDC000009.
The specific epithet (“croatica”) refers to the name of the country Croatia from where this species is described.
CROATIA: Lake Vransko, diatom mats (43°52’54’ N, 15°35’49’ E), Coll. date: August 2012; (holotype MKNDC! slide 009624/A, isotype. HRNDC! Slide 000009, University of Zagreb, Croatia.
Light microscopy: Frustules elliptical to linear-elliptic with truncated ends. Valves strongly dorsiventral and semi-elliptical with dorsal margin arched and ventral margin biarcuate. Valve apices narrowly rounded and slightly ventrally deflected. Valve length 40–78 μm, valve width 6.5–12.0 μm, frustule width 16–27 μm. Axial area very narrow and biarcuate, central area not expressed from both valve sides. Raphe strongly biarcuate, proximal raphe ends seen at appropriate focus closely positioned and slightly dorsally deflected. Dorsal striae finely punctate, 18–22 in 10 μm, parallel in mid-valve becoming radiate to strongly radiate towards apices. Ventral striae radiate in the middle becoming weakly convergent towards apices, 19–24 in 10 μm.
Scanning electron microscopy: Transition from valve face and valve mantle is gradual. Valve face is flat, except in the central area where a large unornamented siliceous flap is present covering the proximal raphe ends. Externally, raphe is biarcuate with dorsally deflected distal raphe ends and proximal raphe ends covered with a large unornamented siliceous flap. Raphe is bordered with narrow axial rib, from both sides more expressed towards mid-valve. Distally, raphe is strongly dorsally curved. Internally, raphe slits are bordered with axial costae and terminating with simple ends located very close. Distally, raphe terminates with small helictoglossa. Near the central area, axial costa is strongly thickened from ventral side, while from dorsal side a strongly thickened projection is present. Both dorsal and ventral striae are uniseriate, composed of elongated, slit-like or irregularly-shaped areolae. The size of areolae is increasing towards apices. Slit like areola openings are oblique or transapically oriented. Dorsal striae parallel in the mid-valve, becoming strongly radiate towards the apices, ventral striae radiate in the mid-valve becoming convergent towards apices. Internally, areolae have transversally elongated openings, bordered by strongly thickened virgae and vimines. Girdle is composed of many narrow girdle bands bearing a single row of round areolae.
Caput Mihalić, Katarina; Gligora Udovič, Marija; Galović, Ines; Stanković, Igor; Šušnjara, Mirela; Žutinić, Petar; Kulaš, Antonija; Špoljarić, Igor & Levkov, Zlatko (2019): Tetramphora croatica sp. nov.—A new brackish-water species from Lake Vransko, Croatia // Phytotaxa, 401, 4; 276-286 DOI:10.11646/phytotaxa.401.4.5